Classic 2CV Racing Club Ltd

Classic 2CV Racing Club Ltd Forum => 24h-Race => Topic started by: Trevor Williams on August 26, 2008, 07:14:09



Title: Valve question
Post by: Trevor Williams on August 26, 2008, 07:14:09
Just interested in whether anyone else has had either the heads of the valves coming off, or little nicks out of the valve head surface? One head and piston destroyed in my race engine this year by the latter, as well as the same happening in an engine I leant out last year. Both had the waisted stem valves
Trevor


Title: Re: Valve question
Post by: Paul Robertson on August 26, 2008, 08:42:28
Inlet or exhaust trev?
We could send it to mike and see what the metallurgy boffins come up with.


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on August 26, 2008, 11:28:49
We have had to replace both inlet and exhaust valves after just two hours of running all this season!
We have had problems with both the standard stem and the waisted stem valves each with different
faults. ???


Title: Re: Valve question
Post by: Martin Harrold on August 26, 2008, 18:13:39
We are not quite sure why, possibly over-revving by a newbie, but in testing at Snet, the head of one valve, standard I guess but Dicky knows exactly, came off and ended up coming 99% out of the crankcase on the other side. Pity it is not just a new valve that's needed.


Title: Re: Valve question
Post by: Pete Sparrow on August 26, 2008, 20:36:16
We had an exhaust valve head fall off, wasted stem.
Car 29 and 64 also had the same problem with wasted valves.
It does seem like a rerun of 2004 the difference being that there are failures of both wasted and standard valve, the former being more prone to this having a flatter back face and thinner stem. Valve spring rate???


Title: Re: Valve question
Post by: Mary Lindsay on August 26, 2008, 21:13:46
Last year we had the same problem with the head coming off a valve and shot blasting the inside of the engine.
Mary Lindsay
Car no 42.


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on August 27, 2008, 00:25:24
Sorry about the spelling mistake :o
All season we have been trying different valve spring rates and still suffer with the same problems.
Make the springs too strong and the valve heads fall off or distort, make them too soft and the valves
bounce at high-ish revs and you end up with the same results! DEAD ENGINES
Is it not about time this problem was sorted out properly, or do we all go and have valves made from
stainless steel.
Most people know what the fault is!! :-X Let's get it sorted out now so that everyone can have some
reliability(for a change).


Title: Re: Valve question
Post by: Andrew Bull on August 27, 2008, 07:51:47
Tell me mark, what is the problem, because i dont know? your post infers that you know someone who knows or you know yourself!

PS how did you get on with the chopper?

Cheers Bully


Title: Re: Valve question (lets gather some real info)
Post by: Andrew Bull on August 27, 2008, 08:04:07
Do we actually know the problem?  or are we just extrapolating from talk that occurrs.  Is the Technical committee involved in trying to sort out whether there is a problem. (I know Paul Has replied)

Is it just non regular drivers putting 9000 rpm on them!

Lets gather the info correctly and do some proper diagnosis work. Draw up matrix of what failed and how its installed. 5 Why's!!  root cause analysis, fish bone.... whichever technique you choose.

More information should be provided to try to obtain the best possible picture for analysis.
New or old valve?
Which valve? NS / OS inlet/ex
Manufacturer of valve?
What type of valve?
Standard / modified valve guide?
With which driver did it fail? (could have been buzzed as martin suggests?)
Springs when installed? New/ 2nd hand/ double?
Normal rev limit for your setups? 
Valve Clearances?
Normal operating temperature of your engine?
Cam Number? (Could be a dodgy batch)
New cam or 2nd hand before grinding?
etc etc.


Mark, have you had problems with one particular pair of heads or have all your engines required this level of maintenance?

Of course, if somebody else actually knows what the cause of the problems is, then please shut me up.

For further info, i ran a full blown race engine on the road (was actually 10thou under barrel-barrel size) with race cam, rim flow & wasted stem valves (machined by Bas) 2nd hand springs and double springs with standard, full length valve guides in ported heads. This engine did over 10,000 miles at pretty much full chat. I never drove it slow and my gear changes usually occurred when the engine wouldnt rev any more.  The cam has since been removed and is now in one of our race engines as it was deemed good for use.  The valves are fine and have been ground in with minimal effort and a standard cam has been installed.  I cant stand the noise the cam makes with no backlash gear. 

If we want to do then lets do it right.  If you want to jump to conclusions on heresay and talk then ignore me. 

Best regards and see you at Mallory

Andrew Bull


Title: Re: Valve question
Post by: Paul Robertson on August 27, 2008, 08:16:15
Some might say it's the c word.











must wash my mouth out


Title: Re: Valve question
Post by: Andrew Bull on August 27, 2008, 08:42:48
I'll bring the soap


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on August 27, 2008, 10:04:55
Unfortunately all of our engines have suffered in varying degrees.All the valves we fit are new with new
valve springs (inners and outers). After only two hours of track time we are seeing upto 30% leakage
through valve distortion.It is now getting very tedious and expensive.Ramp speed on closing is probably
a major cause!


Title: Re: Valve question
Post by: Paul Robertson on August 27, 2008, 10:17:14
Or valves not up to the job of racing!!


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on August 27, 2008, 10:42:06
I had a conversation with another club member last weekend who is running stainless steel valves and has
done so for several seasons and claims to have had no problems since fitting them!Could this be the answer
or do we investigate further?
Bully, i have sent the file to my engineering works, just waiting for price and time scale.


Title: Re: Valve question
Post by: Mary Lindsay on August 27, 2008, 15:26:31
Quote
Is it just non regular drivers putting 9000 rpm on them!
You are joking of course!
We are very careful not to over rev the engine especially as it is a 24 hour race. Anyway I don't think ours would have been capable of those sort of revs!


Title: Re: Valve question
Post by: Derek Coghill on August 27, 2008, 16:19:18
I've had no valve problems so far; haven't had the heads off since the 24hr but can do so and have a look easily enough. Modified standard valves in mine as far as I remember.

Where are the little nicks from, Trev? The edge of the valve, the sealing face or elsewhere?


Title: Re: Valve question
Post by: Paul Robertson on August 27, 2008, 16:25:23
I had a conversation with another club member last weekend who is running stainless steel valves and has
done so for several seasons and claims to have had no problems since fitting them!Could this be the answer
or do we investigate further?
Bully, i have sent the file to my engineering works, just waiting for price and time scale.
I would think this would be the best idea.


Title: Re: Valve question
Post by: Trevor Williams on August 27, 2008, 17:21:46
Derek
Edge of the valve around the circumference. One valve has minute cracks starting to move away from the nicks


Title: Re: Valve question
Post by: Marc Fenner on August 27, 2008, 19:03:57
Im talking to a guy at the moment who has titanium valves made for his 2cv projects. Trying to find out the price of  them as a set for me and also as a bulk buy. They may be able to do stainless ones too.


Title: Re: Valve question
Post by: Derek Coghill on August 27, 2008, 20:26:22
Trev, next question; has it been touching the piston?


Title: Re: Valve question
Post by: Trevor Williams on August 27, 2008, 22:22:34
Derek
Absolutely not, only damage is from the bits of valve that went round the combustion chamber


Title: Re: Valve question
Post by: Francis Rottenburg on August 28, 2008, 14:32:28
Any correlation to the weather conditions?  Most of the recent 24 hours have been either wet or bloody monsoon so engines would have been running very cool.  I understand you had a good deal of dry weather in which case temperatures might have been similar to 2004.  What fans were people running on the failed engines?  Seems odd that the problem disappeared and suddenly came back again.


Title: Re: Valve question
Post by: Marc Fenner on August 28, 2008, 16:34:57
The other thing is fuel at the circuit ???


Title: Re: Valve question
Post by: Andrew Bull on August 29, 2008, 13:06:49
We have been fortunate enough to have a valve that has finally revealed its failure on the bench rather than in the engine.  Sammie rebuilt Mark Fenners engine and found one broke in her hand as she was grinding it in.  Therefore we can actually look at something that doesnt resemble Kryton's chewing gum.

The failure faces clearly show striations (clamshell lines) propogating from Two points approximatley 180 degrees apart, on the outside edge. This is the classic sign of Fatigue Failure.   Then in the centre there is a clear brittle fracture, obviously at the point when it could not cope.  This valve must have been on the point of separation, with just enough left to hold it together when it was removed from the engine.

Fatigue failure occurs with initial crack initaition.  The origin of the crack can be any microscopic surface flaw, mark, scratch, defect or stress raiser.  In our case i beleive the surface finish on the 'Machined' wasted stem valve is the major contributor as it is turned, thus creating hundreds of annular rings around the stem.  Perfect stress raisers, when combined with flexural (Bending) loading on the stem, and thus giving an indication as to why we have two origins.

Then propogation, where the crack has repeated breaks during each loading cycle.  This creates the tell tale striations formed from this failure mode.

Then Brittle fracture which essentailly is the final 'give up' when there is no longer enough material left to be strong enough to withstand the normal axial loading through the centre axis of the stem.

In a nutshell, the valves are machined to create wasted stem, This leaves marks which are stress raisers.  the valve has pull forces and bending forces acting upon it.  As it bends time and again it creates a crack where a machining mark is (or scratch / mark). This crack grows with each bending cycle, and then it fails completely. 

I hope this may provide some more direction. 

A couple of ways to reduce potential crack initiation would be to shot peen the machined surfaces.  This reduces stress raisers and work hardens the surface where cracks occur.  Or, if the wasted area was ground this would create a much smoother surface again reducing stress raisers on the stem.


Any comments? 



Title: Nothing to do with racing
Post by: Martin Harrold on August 29, 2008, 21:17:27
I can confirm the concept of what Andrew is talking about. A distant relative who was a top boffin at Farnborough led the team that fished all the failed Comets out of the Irish Sea and elsewhere many, many, years ago. He built a pressure tank and eventually worked out that the reason for failure was cracks caused by flexing of the structure which emanated from the corner point of the then square corners of the window apertures. That's why all planes now have rounded window apertures.
  Smooth metal surfaces and openings are much less prone to stress and fatigue failure.
  He wrote the official history of Farnborough - and if anyone is interested I will be happy to lend them a copy.


Title: Re: Valve question
Post by: Steve Cowell on August 29, 2008, 21:47:14
as Pete said,we in car 29 had 1 valve head drop off, and 2 others nick the edges  ???


Title: Re: Valve question
Post by: Derek Coghill on August 29, 2008, 23:08:40
<Any comments?>

Wouldn't it be a bit difficult to grind the waisted-stem valves? How about sanding/polishing once they've been made? As regards shot-peening hardening the surface, if it's already prone to cracking won't that make it more so?

No comments, just more questions!


Title: Re: Valve question
Post by: Andrew Bull on August 30, 2008, 11:13:37
Work Hardening the surface would help to reduce the chance of Crack initiation.  As for grinding the area there should be no problems as there would not be any undercuts so a shaped wheel could be quite adequate.  Obviously i'm not talking about doing the grinding ourselves, but it could be an alternative manufacturing method. 


Title: Re: Valve question
Post by: Derek Coghill on August 30, 2008, 12:29:29
What about valves that people already have? The obvious thing would be not to use them, but then they'd have to buy (or make) more.


Title: Re: Valve question
Post by: Paul Robertson on August 30, 2008, 16:18:15
Following discussions with the committee we have asked mark to organise enough stainless valves for 100 engines.This has reduced the cost per valve considerably and they should be no more than 15 per valve.
As for delivery time we don't know at the moment,we may all have to play a bit of russian roulette at mallory.
Paul


Title: Re: Valve question
Post by: Trevor Williams on August 30, 2008, 16:24:55
Paul
If the club are getting the valves made, can the be made to the exact specification in the regulations? That way it would then be pointless trying to do anything else to them and they almost become a standard item
I'll take enough for 5 engines!
Trevor


Title: Re: Valve question
Post by: Martin Harrold on August 31, 2008, 11:32:37
We'll have enough for three engines


Title: Re: Valve question
Post by: Martin Sadler on August 31, 2008, 22:53:10
I'm new to these 2cv things and are severely dismayed at what seems to be an onging problem with these engines. I've just dismantled one of Keith Shoebridges engines - race engine no 3 (one that didnt totally distroy its self) to find the widely reported inlet valve nicks/chips distroyed head, piston, barrel etc. Our no 1 race engine totally distroyed its self and wont even make an interesting coffee table. What concernes me is that these problems go back so long - 2004. I've read all the reports in the historic forums and what we are experiancing is exactly the same. With out a doubt there is still something fundermentally wrong inside these engines and no fix has been found - or given out to all competetors.
I have given whats salvageable to my cylinderhead company to see if they can come up with ideas/remidies. Here are a few of the things they and I have come up with.-
1. the valve material is S**t - his words not mine and has no place in a racing engine. Waisted or standard. The valves in this engine were NOT waisted
2. the valve seat angles are wrong and will promote valve pounce
3. the valves are of a 2 piece construction - see 1 above.
4. the valve springs are almost coil bound on full lift and show referance marks where they have actually touched.
5. there is evidence that the inlet valve on the off side bank has hit the piston
6. on full lift at high reves with valve bounce a posibility, have the valves touched?

Many of these points have been made recently and in also in 2004, and I cant see why the technical commitee hasnt investigated this in depth and made parts available to all that will stop it happening. They have stipulated a control cam why not go further so that if there is a fix, make it available to all via the club - they do it in NASCAR in the states and it keeps the racing fast, reliable and cuts out any cheating/advantage by one team over another.

I plan over the next few days to measure the cam lift , duration, and check timing. This engine does not run a vernier so the siming should be standard. I will be looking specifically to see if the off side inlet lobe is ground slightly advanced over the near side, if it is the club needs to talk to Kent at depth about a redesign. Before any body asks yes I did check the valve cleanance before strip down and they were all ok.

Martin
07867.798680



Title: Re: Valve question
Post by: Mary Lindsay on September 01, 2008, 09:13:23
We did wonder if it was because the valve appears to be made of two different metals. We found that part of the valve that broke on our engine last year was magnetic and part was not.


Title: Re: Valve question
Post by: Paul Robertson on September 01, 2008, 10:13:29
We have had valve problems for over 15 years now ,the move to the waisted valves was made as they were the only thing available as a replacement for the standard two piece valve .This appeared to have stopped the problem until this season,when for whatever reason we appear to be back to square one.
 The one piece stainless valves will not be ready until after mallory and will be made to original seat angles as per our regs.
 I have timed more camshafts than most in the club and can say i have yet to find a cam ground outside of kent's tolerances and most to be spot on.
 If you are a club member and wish the technical committee to investigate something with a view to a rule change please contact them and request they do so.


Title: Re: Valve question
Post by: Martin Sadler on September 01, 2008, 12:23:32
HI Paul,
I'm not a member yet but I will be next year.
Now back to valves. Have you found a reason or have any thoughts why the off side cylinder seems to be the one that fails / has the valve marks in the piston - not the nearside. All 3 of Keiths race engines failed on the off side? I can find nothing wrong in the crank area, rods etc
Martin
07867.798680


Title: Re: Valve question
Post by: Andrew Bull on September 01, 2008, 13:21:49
Valve material may well be sh1t, but should the tech committee could have one analysed? Many Test Labs can perform material composition analysis if required.  Also Universities have a vast engineering resource. 

Offside of the engine has that large heat sink bolted on.  (AKNA The alternator).

If you have evidence of Coil Binding on the springs then that points to one of three things.  Rocker Ratio / modified rocker foot.  Valve float off the peak of the lobe.  Knackered springs. Given Paul's comments about Cams I havent included the grind as a possible cause.  Timing could be, if the engines dont have verniers then the standard Citroen manufacturing tolerances are still applicable to the Timing of the cam, and you cant dial it in to the perfect timing.  One of the reasons for the control cam.

The Cam itself may also show signs of an impact wear area after the peak where the follower comes back into contact after float.

If you have coil bound the springs then i should check the rocker arms, pushrods, and cam followers. 

The other consideration is the springs.  Were they new.  Were they Tested?  double? 

Your Points 4,5,and 6 all point to high rev damage though.  If you are seeing evidence of touching on other valves in the engine then there is a strong possibility that high revs has caused the initial tweak to the valve, thus weakening it.  Have you calibrated the rev counter?

Points to note for the Tech committee. 
1) Stainless Valves -      on order PR
2) Investigate material properties of current valves
3) Publish / obtain / calculate, recomended Valve spring pressures.  Kent Cams may help?
4) Investigate progressive springs and rates.   


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on September 02, 2008, 00:51:33
Replying to the many questions/comments on this seemingly frustrating subject!
An order was placed yesterday for 400 one piece stainless steel valves which will not be available untill
after the final 2x rounds at Mallory park.
Going onto some of the points raised by Andy regarding the tech comittee,
current valve materials:-
I am speaking to York university as to having currently available valves tested,i will keep everybody informed as progress is made.
Progressive valve springs:-
I have tested with progressive valve springs and have found no difference in performance or reliability
over standard double springs.
Valve spring rates:-
Valve spring rates are different from valve to valve, mainly due to valve weight but cam profile and rocker
ratio and max rpm come into the equation.I will post some recomendations in the next few days for the
current valves.
Valve springs going coil bound:-
If your valves are installed to standard citroen spec, the valve spring cannot become coil bound!
Valve bounce/too many revs shows the same markings on the valve springs as going coilbound.
Suggestions:-Check insalled heights/fit a rev limiter!
I am currently testing the effects of heat build-up on all types of valves available because i am convinced
that most people are running their engines too hot, the car that won the 24hr this year ran a 9 blade fan
and suffered no engine damage whatsoever.We ran a 6 blade fan and still over heated the engine on one
side.
I will post my results in due coarse.
Mark. Whitwell Motorsport.
                 



Title: Re: Valve question
Post by: Andrew Bull on September 02, 2008, 07:51:47
Thanks for the Info Mark.  I look forward to seeing some of the results. 

The heat thing is a bit odd.  We have run 3 blade for a good few years now including all this year, but did a cam follower not a valve in the 24hr.  Although if a valve got sticky due to heat then this could have the result of knocking the bottom out of a follower. 

For all intersted parties there is a very useful explanatory guide on http://www.aa1car.com/library/ar1192.htm (http://www.aa1car.com/library/ar1192.htm)

I know its talking about yank tanks but the thoeries are the same and we are running a hemi head anyway. It's an interesting lunch time read and talks frequently about valve float, seat bounce, and bending of stems causing fatigue failures when attention is not paid to the alignments and seat cutting, and valve guide wear and alignments.

Cheers


Title: Re: Valve question
Post by: Geoff Archer on September 02, 2008, 14:19:04
My engine from pete was the exhaust valve, found the head in the sump


Title: Re: Valve question
Post by: Martin Sadler on September 03, 2008, 12:33:06
Andrew
aa1car.com excellent site with a lot of very relavent facts and tips
Martin


Title: Re: Valve question
Post by: Andrew Bull on September 03, 2008, 15:59:55
Martin, I think ive just given my secret away.  I know feck all really, just read alot. 

Mark, Do you know what grade of stainless material they will be made from.  You know the DIN / EN spec or designation.

Cheers 


Title: Re: Valve question
Post by: mark turner Whitwell Motorsport on September 03, 2008, 23:08:04
We (as a club/tech comittee/management comittee) are having discussions with the manufacturers as to
what is the correct material shape and profile for our needs. We are not going to rush into a product that is not what we want! I believe experiance and research count for an awfull lot. Time and testing will tell us
everything,so stay tuned! We will keep you all informed on progress ;D


Title: Re: Valve question
Post by: Bas on September 04, 2008, 15:09:56
Martin, I think ive just given my secret away.  I know feck all really, just read alot. 

Mark, Do you know what grade of stainless material they will be made from.  You know the DIN / EN spec or designation.

Cheers 
                                                                                                                                                                                        bully think the grade should be 21 4n austenitic stainless thats 21% chrome  4%nickel         very tough stuff


Title: Re: Valve question
Post by: Bas on September 04, 2008, 15:15:29
dont know about the valves being waisted but i certainly was! how about watching the sun come up again pete?also thought gadget needed rear view mirrors in our garage sunday night!  laugh i nearly bust a gut!


Title: Re: Valve question
Post by: Pete Sparrow on September 08, 2008, 06:31:21
Bas, now you're giving my secrets away, people will talk if they thought we spent the night together  :o


Title: Re: Valve question
Post by: Nigel Hollis on September 08, 2008, 19:56:36
By changing to very hard valve material could this mean shifting the problem somewhere else i.e. valve seats?


Title: Re: Valve question
Post by: Paul Robertson on September 15, 2008, 07:54:03
From my talks with the valve company nigel ,no .


Title: Re: Valve question
Post by: Roy Eastwood on September 19, 2008, 09:16:03
Just interested in whether anyone else has had either the heads of the valves coming off, or little nicks out of the valve head surface? One head and piston destroyed in my race engine this year by the latter, as well as the same happening in an engine I leant out last year. Both had the waisted stem valves
Trevor

Myself & Richard Dalton, got precisely that problem (little nicks out of the valve head surface) when we started racing in Belgium, can't remember which year but we used a 'standard' Piper 285 or possibly a Newman cam, we never had the problem using a standard Citroen cam during all the time we raced up until 2003.

Having done most of the UK 24 hour races until 2003, more than one even with the same engine used to win the previous year's event, I can say that we never had valve problems with that original camshaft. As far as team driving restrictions on the engine - we did set rev. limits but I would admit to always being an abuser of the rev. limit - I would keep the pedal to the floor almost until the valves bounced - hardly the best way perhaps, my lap times never the best - but we never wrecked a single engine in all those years.

The only problems we found in engines built by ourselves for the UK series (up to 2003) were down to poor component selection, the use of non original valves (we got burrs on the collet grooves), if we were too ambitious at bringing the piston closer to the head we then had problems with the piston 'kissing' the cylinder head land.

One really useful exercise would be to remove a quantity of the club cam from well used engines and check what the profile has become, you may well find a totally unsuitable profile has developed simply because of wear on the ramp. The Citroen camshaft is chilled cast iron and the racing club profile is a very vigorous grind from the original, taking the surface way below the hardening induced by the effect of chilling.

The waisted valves commonly available in UK are widely used in French 2cv cross racing with (standard Citroen cam) no problems.




Title: Re: Valve question
Post by: Roy Eastwood on September 19, 2008, 09:48:45
We did wonder if it was because the valve appears to be made of two different metals. We found that part of the valve that broke on our engine last year was magnetic and part was not.

This is normal and is the principle reason why valves are NOT made one piece, the head needs to perform in quite a different function to the stem, the valve has a noncorrosive steel head welded to a wear-resisting steel stem.

Please note that when I wrote the above I did not know that Paul was looking into the production of one piece valves - so this is not intended as criticism - simply an explanation of why valves are usually bimetal.



Title: Re: Valve question
Post by: Paul Robertson on September 19, 2008, 10:54:43
I remember the first 24hr race we ever did seeing graham harpers engine with a hole in the piston where the valve head fell off ,and that was way back in 1994, i have also seen the inlet valve chipping on numerous standard engines over the years ,as well as the cam lobe wear that is always blamed on the club cam regrind.
 Andy Bull has just finished plotting the standard profile against the club profile so we can scrutineer the cam without an engine strip and it looks almost identical, other than a flatter peak on the club cam giving longer full lift.


Title: Re: Valve question
Post by: Sean on September 20, 2008, 17:34:38
Hi Sean here (looks after Mr Coghill, and helps out with Harper ;) )been trying to join in for ages...anyhow

Intresing stuff on cams & valves

http://www.gsvalves.co.uk/general_faults.htm (http://www.gsvalves.co.uk/general_faults.htm) any look familiar? nice simple expalnations for failures.


Title: Re: Valve question
Post by: Sean on September 20, 2008, 17:45:31
We did wonder if it was because the valve appears to be made of two different metals. We found that part of the valve that broke on our engine last year was magnetic and part was not.

They dont brake at the join they seem to go at the start of the flare on the stem so that would suggest there is proplems with either the machining causing a stress or metallurgy during the forging process

The join is about 1/3 of the way up the stem and is roughly at the point where the stem emerges from the guide easy to find with a small magnet and if you polish the valve you can see the change in colour too.

Trouble is a dropped head mashes whats left so badly its impossible to get a clear picture of the original fracture

Sean


Title: Re: Valve question
Post by: Roy Eastwood on September 22, 2008, 07:46:44
We did wonder if it was because the valve appears to be made of two different metals. We found that part of the valve that broke on our engine last year was magnetic and part was not.

They dont brake at the join they seem to go at the start of the flare on the stem so that would suggest there is proplems with either the machining causing a stress or metallurgy during the forging process

The join is about 1/3 of the way up the stem and is roughly at the point where the stem emerges from the guide easy to find with a small magnet and if you polish the valve you can see the change in colour too.

Trouble is a dropped head mashes whats left so badly its impossible to get a clear picture of the original fracture

Sean

Breaking or bending of inlet valves has been a problem only since the introduction of the club controlled cam, before that the only breakages were of exhaust valves which got 'buzzed' on a changedown from 4th to 2nd.

The problem that needs curing is how the valve relates to the camshaft/piston/head, which might involve getting valve spring rates absolutely matched to the cam with a self-imposed rev. limit.



Title: Re: Valve question
Post by: Sean on September 23, 2008, 06:42:19
Breaking or bending of inlet valves has been a problem only since the introduction of the club controlled cam, before that the only breakages were of exhaust valves which got 'buzzed' on a changedown from 4th to 2nd.

The problem that needs curing is how the valve relates to the camshaft/piston/head, which might involve getting valve spring rates absolutely matched to the cam with a self-imposed rev. limit.


Agree with you Roy something about that cam means the cam, valve train and valves dont seem suited to each other. whether its profile, springs or what...
 How does the re grind affect the angles at the rockers, has this an effect on the rates the valves move at?
Sean


Title: Re: Valve question
Post by: Derek Coghill on September 23, 2008, 12:12:42
It doesn't, you take that up with the adjusters....but if there's more lift over the same duration (see Bully's post elsewhere), valve speed will be greater and there'll be a difference of rocker-to-valve angles at maximum lift.


Title: Re: Valve question
Post by: David Bain on September 25, 2008, 21:16:10
Assuming it's not a trade secret, how is the greater dwell obtained? Remetalling the ramps to increase dwell while maintaining the standard lobe height or cutting down the lobe and rehardening? There seems to be a geometry aspect to this drama and knowing this might bring more understanding - or simply increase the number of back-of-envelope sketches.


Title: Re: Valve question
Post by: Francis Rottenburg on September 26, 2008, 09:33:37
The problem went away to some extent and has reemerged at this year's event.  It would be interesting to know how many of the cratered engines were using new valve springs?  Were people rebuilding engines with springs that were new two or three years ago?  Did anyone take the springs out of the remains and check the rates?  I remember Paul did some very revealing work on old vs. new spring rates that showed a marked degradation of some springs.  How many were using double springs?  At the least it would indicate whether new or checked springs have to be fitted before every season/24 hour.


Title: Re: Valve question
Post by: Paul Robertson on September 26, 2008, 12:59:17
One of mine let go and has good double valve springs francis.


Title: Re: Valve question
Post by: Marc Fenner on September 30, 2008, 17:43:36
As many of you know i am doing a degree in motorsport technology. I have been asking about different ideas as to why we are lossing valves.

A few things have been suggested.

1. The cam is too steep on closing causing more strain on the valve itself.


Title: Re: Valve question
Post by: Marc Fenner on September 30, 2008, 17:49:27
2. The valve is getting to hot. One idea was to drill the fins on the head which increases the surface area.
3. We need to think about changing the valve retainers and make them lighter. Maybe titanium???

There where a few other things too that they said to look into. All the above stuff is stuff they mentioned to me and i may have cut corners. The old chinese wispers things.

They are happy to look at the info we have. I have printed of Andys cam profile info and club rules for them to look at.
These guys are known for being the best in the uk even europe. Who knows they may be able to help!
Any other info i can pass onto them would be useful.


Title: Re: Valve question
Post by: Sean on October 05, 2008, 15:34:29
Andy Bull has just finished plotting the standard profile against the club profile so we can scrutineer the cam without an engine strip and it looks almost identical, other than a flatter peak on the club cam giving longer full lift.

just spotted the plotting post over in tech.
Surley the top of the graph isnt going to be the problem bit is it? ,the much steeper opening and more importantly closing profiles... the area in the last 1mm of closing on the inlet looks "intresting". Assuming there is still a bit of work to do with plotting accuracy innitially there appears to be a much softer close on the Std cam with that extended curve :-\

Sean


Title: Re: Valve question
Post by: Rambo on October 26, 2008, 12:12:17
Many years ago I overhauled a few Citroen SM engines, and they had sodium-cooled exhaust valves, which are hollow stemmed with welded heads. One of them had a head come off while being ground, and non cooled one piece stainless valves are the replacements. The problem there was due to corosion at the weld, and as these engines were also fitted to the Maserati Merak a lot of engines were badly damaged when they were started after a few years hybernation. NEVER try to start one of these cars if it has been dormant without knowing if it has the stainless valves. Could our recent problems be that everyone fitted new valves as a precaution after 2004, and those valves are now coming to the end of their lives with the current cam?


Title: Re: Valve question
Post by: Trevor Williams on December 20, 2008, 13:41:32
I have just finished measuring a load of valve springs and discovered that three of the new ones that I have are very low.
They didn't even get to 100psi.
So, bit of free advice - check your valve spring rates!


Title: Re: Valve question
Post by: Paul Robertson on December 23, 2008, 11:37:29
 I have just tested over 120 second hand and previously raced valve springs ,there were less than 10% that were within 5psi of the recommended pressure to be used singly.
 I would suggest that if you are running single valve springs you are at great risk of damaging your engine and that valve springs should be checked / changed after they have done a couple of seasons racing,especially if the engine has been used for the 24hr race .I would also suggest that all valves should have inner and outer valve springs fitted.

Paul

these are my suggestions not those of the classic 2cv racing club


Title: Re: Valve question
Post by: Derek Coghill on December 23, 2008, 14:33:16
Paul, Norry also recommmends double springs but suggests that they be changed even more frequently.


Title: Valve spring pressures
Post by: Martin Harrold on January 14, 2009, 22:20:56
Paul, Trev:

I've found that a local firm which makes springs for one of the products we manufacture can also test (and make) valve springs. So, we are getting them to test some we have. I read that 100lb is a minimum target figure. Do you know what the spec figures / range are for the main valve spring and for an inner valve spring ?

Out of interest, I asked them to check test some suspension springs we've had from their friends at SpringCoil. Those springs have the rating written on them. They tell me that they cannot test them but they can do a calculation. They say (and I can't believe that they are correct) that there is only one machine in the UK big enough to actually test those springs, which is at some kind of institute in Sheffield.


Title: Re: Valve question
Post by: Paul Robertson on January 15, 2009, 09:33:40
Martin,you need to be looking at 150psi for the main spring at installed height +full lift or by my calculation when the spring is 27mm long.The inner when fitted inside the outer should give an increase of 20-30 psi.So combined pressure should be 170/180psi.
Springcoil have their two test rigs (one computerised, one manual)which i have seen them use, they have one employee that all he does is measure spring pressures.
HTH Paul


Title: Re: Valve question
Post by: Martin Harrold on January 18, 2009, 22:02:18
Paul - thanks. I'll keep you posted. Out of interest, have SpringCoil ever been asked to make valve springs?


Title: Re: Valve question
Post by: Paul Robertson on January 19, 2009, 11:40:32
Not by me martin.