Piston to head (not valves) contact

[Jose M Oliva]

Hello everybody and happy new year.

I have just finished my engine and have found pistons "kissing" heads (not valves) at TDC. The story is as follows:

I rebuilt the engine fitting new pistons and barrels. Pistons are 9:1 compression ratio ones made in Argentina (Kereben) and so are barrels. These have been machined to the Tech Regs minimum allowed distance (395,50 mm top of barrel to top of barrel).

Engine turned normally by hand and you could notice nothing. Once the car started, the noise was a bit of a diesel, with a slight clack-clack-clack coming from both head covers. I was afraid of valve to piston contact, because I have fitted a new Club camshaft too.

Then I dismantled both cylinder heads and found signs of slight contact between pistons and heads on both cylinders at the area opposite to the spark plug. I removed these traces with just emery cloth and refitted everything.

After doing that the noise has totally dissapeared on one side, remaining at the other. After some time at fast idle and a brief drive (max. 4000 rpm) through the neighbourhood this has nearly completely dissapeared too.

After this explanation my question is: has anybody experienced this issue before? What amazes me is the incredibly close tolerance between pistons and heads that you can get them in contact by removing such a little amount of material from the barrels (with 9:1 and not 8,5:1 pistons, I know). Perhaps not a very accurate machining job with the barrels?

Thanks for your comments and best regards,

José M. Oliva
Madrid (Spain)

[Paul Robertson]

This is very common with the argentinian pistons jose,you have done the correct thing by removing a small amount of material from the pistons.Have you had the barrels honed? (my recommmendation is at least 0.075mm piston clearance) as the argentinian barrels are not the straightest thing in the world.

[Dennis List]

I'm also hearing a strange clacking noise with my newly rebuilt engine with a cam shaft similar to the club one, and 9.0:1 barrels and pistons. Could you confirm the sound after watching the short video i made?

Vid here:
http://www.youtube.com/watch?v=Tq7tw-eJxfY

[Paul Robertson]

that's very rough dennis,sounds more like the crank to me.

[Dennis List]

I hear loose rocker arms (those lower bolts being loose) could also be the cause of this problem. Will check tomorrow.

[Jose M Oliva]

Yours is a real NOISE, mine was much more subtle.

Finally I had to dismantle again the rebel cylinder as noise was reluctant to dissappear totally. Once again I found traces of piston to head contact, so I removed with emery and now everything goes fine.

Paul, I didn't have barrels honed but now I think it could have been a wise decission. After 250 km run-in the engine has burned a little oil, so I will keep an eye on it. Good news is that after this process now I am an expert in dismantling barrels with engine in car...

Regards,

José

[Roy Eastwood]

Could be pistons fitted back to front, i.e. with the arrows facing to the rear.......

I'm also hearing a strange clacking noise with my newly rebuilt engine with a cam shaft similar to the club one, and 9.0:1 barrels and pistons. Could you confirm the sound after watching the short video i made?

Vid here:
http://www.youtube.com/watch?v=Tq7tw-eJxfY