I finally got around to checking my piston to valve clearance. It was spectacular and never got close to spec(.08 I believe is minimum). Problem I have is that the piston is just barely hitting the hump for he spark plug. Luckily I noticed it as I was starting to clean the heads one final time before installing them. I saw this nick in all 4 cylinders .


I went ahead and confirmed with clay that they were new and fresh marks. Sure enough they are. There is a large knot for the spark plug threads and I think I should be OK to grind some away but wanted to see what others had for ideas. Biggest thing is will be I OK to use these heads.

Here is where it is contacting on the piston.




I didn't have a head gasket so that is another .051 of clearance but if I am lucky that currently gets the piston to not touch the head I still need some clearance for safety!

Here is the head with clay on it.

 

No help?

If matters these are 317 heads and it is a 408 built from a LQ9 block. The pistons are Dimond nitrous pistons.

 

File it off or dremel the spot on the head.

 

I think I would rather have material taken off the piston. I don't think I would want that spark plug boss any thinner as it may crack easier upon removal of the plugs.

 

Off of the piston? Seems much safer and I would feel better taking a few thousands off the head. A replacement pair of 317s only cost around $250 and are easily changed if something does happen, vs. cutting into the pistons. What do others think?

I think the gasket should get me so they don't touch so that means I would need to take .03-.05 off the spark plug boss. Seems insignifigant enough but maybe I am wrong.

 

Grind away the dome on the piston.

 

I was really hoping to not hear that any more. I surely don't want to cut the piston but if that seems to be the best idea then that just might have to happen.

 

Put the gasket on, snug it down, and re-check it........

 

It's really not that big of a deal, all you would have to do is lay over that sharp edge into an angle or a gradual radius. You won't even take off enough to throw off the balance of the crank or anything like that.

 

I'd vote towards taking some off the piston as well..

 

Ok. I'll throw a vote in to take some off the head people rework chambers every day....

 

Just throwing it out there..but what about adding a 2nd spark plug washer? Fully compressed it has to be about as thick as the head gasket.

 

these are tapered seat plugs, no washers.

 

It isn't hitting the plug. It is hitting the head only.

 

I am getting almost a 50/50 of head vs. piston recomendations. I think I am going to take a touch off the head and see what happens. If a few hits of the file get me enough room great! If a few hits still isn't enough I might take a touch off the piston.

These heads will be on the engine no more then a year. I have another set of 317s that are going to get ported and polished of possibly look into a better set of heads. Not sure but regarless these heads are temperary. The only down side of not taking it off the piston I will need to do the same to my other set of 317s. I will address the issue then and possibly look deeper into cutting the pistons.

Thanks for the ideas and help.

 

This was my thinking as well. As a matter of fact my CNC heads have this area smoothed over real well. Wont hurt the head a bit or they wouldn't be doing it.