At what head thickness will valves contact pistons?

[Beaubo]

My head has been milled to 5.165 I have searched and found the minimum head thickness recommendation is 5.185.

My question is at what point will the valves and pistons make contact?

Will the composite Felpro gasket I have be sufficiant enough to add more thickness?

I really don't want to have to pull the block to have it milled for an mls gasket. I know Cometic can make a thicker gasket but really dont want to go that route.
Thanks dsm community for the advise.

 

[BogusSVO]

With stock cams you will be fine.

 

[Diamond Star Werks]

Get some play-do and check your clearences to see how much you have left.

 

[Beaubo]

Thanks Bogus! I knew you would be the guy to chime in for this question.
Do you know at what thickness will it not be fine?

And I hope this isn't a totally stupid question but I have searched and have had no luck have you or anyone you know used two composite head gaskets stacked with any luck?

Would the failure happen in-between the two gaskets if it were to fail?

MJ I have heard of doing this but how exactly is it done?

 

[Breezio69]

You take playdoh and a dough roller, make a nice flat sheet a few mm's thick, cut out circles about the size of your pistons and slap em on there. Put the head on, timing belt, timed correctly as if you were to start the motor, then turn it by hand a few full rotations and disassemble, check playdoh. If you see the piston through the playdoh you have no clearance.

Had to do this on a quad I built with oversized valves. Its time consuming but I ended up having to mill the reliefs in the piston, so I'm glad I did it.

As far as two head gaskets, that's just asking for premature failure.

 

[BogusSVO]

^^^^^ Thats close.

No need to cover the piston with clay, just some on the valve relief.

You want about .060 on the intake, and .080 on the exhaust side.

With the way some shops mill heads, I would bet there are more than a few DSM with heads thinner than that running the roads.

 

[Beaubo]

Thanks guys I am greatful for the quick responses. I am going to just put it together I trust Bogus' advice that I will be ok at 5.165. Thanks again!

 

[black97spyder]

The play-do trick works!! When i was building a high compression small block Chevy with small combustion chambers I had 0 clearance. My valves all touched the pistons, sooo instead of messing with the bottom end I got the valves sunk to the proper depth and then made sure the spring height and tension was correct before I installed the head.

You should be able to sink the valves in your 4g63 head some to help clearance but only have a HIGHLY trusted machine shop do the work as it has to be VERY precise!

Hope this helps!!

 

[Beaubo]

Thanks Black97! I migiht try the Play Doh thing just to see what my clearances are and to find out if next time around I will need to pull the motor for resurfacing and get a thicker MLS gasket, or shop around and get a new head.
I would have already bought a new head but the one I have has been ported and flow benched and flows gobs and gobs of air. It would be nice to keep it for another go around. Thanks again DSMTuner community.

 

[Diamond Star Werks]

^^^^^ Thats close.

No need to cover the piston with clay, just some on the valve relief.

You want about .060 on the intake, and .080 on the exhaust side.

With the way some shops mill heads, I would bet there are more than a few DSM with heads thinner than that running the roads.

Yeah I just sent in a head only to find out it was cut 5thou too deep already. Knew there was something wrong with it when I seen all valves had flat spots on the, edges.

 

[delta448]

You should be able to sink the valves in your 4g63 head some to help clearance

A much better solution is to cut the piston's valve reliefs deeper, assuming you are able. "Sinking" the valves will neuter the airflow much the same way as reducing the camshaft duration, since the valve has to lift further before it clears the combustion chamber and begins flowing reasonable amounts of air.

 

[Breezio69]

^^^^^ Thats close.

No need to cover the piston with clay, just some on the valve relief.

You want about .060 on the intake, and .080 on the exhaust side.

With the way some shops mill heads, I would bet there are more than a few DSM with heads thinner than that running the roads.

Yeah, when I did it to the dohc one banger I did the entire piston with a thin layer, I'm sure that's a bit overkill on a 4cyl though. That motor threw down 59 ponies on the kbr dyno here, stock was 27 haha

Sorry back on topic.

I think you'll be fine

Also, I don't know if your thinking of using a factory gasket? But there are gaskets a tad thicker to make up for a decked head. I forgot who makes em.