custm2500

iTrader: (11)

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.

custm2500

iTrader: (11)

No help?

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

01ssreda4

iTrader: (96)

File it off or dremel the spot on the head.

bww3588

iTrader: (49)

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.

custm2500

iTrader: (11)

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.

KCS

iTrader: (20)

Grind away the dome on the piston.

custm2500

iTrader: (11)

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.

Old Geezer

iTrader: (3)

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

KCS

iTrader: (20)

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.

Fade2blk500

iTrader: (18)

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

mark21742

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

MX6.0

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.

bww3588

iTrader: (49)

these are tapered seat plugs, no washers.

custm2500

iTrader: (11)

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

custm2500

iTrader: (11)

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.

01ssreda4

iTrader: (96)

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.