Head To Piston Clearance

[icanfixall]

Where can I find the clearance on the piston to head? Also what is the distance the pistons stand up above the block? I have some demensions on my first rebuild but I'm now looking for the factual numbers on this. So far my demensions on my second motor are 19 thousands clearance between the head and the pistons. I read it here or "over there" that we needed 30 thousands clearance from the head and pistons. At least thats what I have been posting. Now I just want to hear it or see it written somewhere. Thanks guys and all....

 

[pafixitman]

According to my '93 powertrain manual, page 03-01D-85:
Piston height above crankcase is 0.010-0.031. Headgasket surface flatness is 0.003 in any 6" / 0.006 overall.

Not sure if that answers your question or not. It apeears that you are almost in the dead middle at 19.

 

[pafixitman]

Based on pete's comment over there
Valve head recession relative to deck surface is:
Intake 0.042-0.054 and exhaust 0.051-0.063

 

[icanfixall]

Thanks guys. I have all that information. What I need is the actuall clearance the piston has from the head with the head gasket compressed. My pistons are between 47 and 52 thousands above the deck.

 

[highest_vision]

Bazooka bubble gum and two extra head gaskets. Mike the gum
James

 

[icanfixall]

James... Just 1 head gasket is all you need to use and instead of bubble gum using clay (the kind we played with as kids) will do a better job. If as posted here and there that the pistons stick out of the block deck 10 to 31 thousands then I'm really tighter than that. My pistons in the first rebuild were between 47 and 52 thousands up out of the block. Now take a Felpro head gasket at about 72 thousands and deduct 52 from that and we have a clearance of 20 thousands from the piston and head. As you can see anything from 25 to 60 thousands would be factory acceptable clearance using the Felpro head gaskets. They are supposed to be 10 thousands thicker than the OEM head gaskets. I really need to look at this when I get my pistons back from Florida. Life goes on.....

 

[highest_vision]

Just telling you some stuff I knew worked. Not supposed to chew the gum that way it won't stick. 2 gaskets so you can do all eight cyls. Didn't know how picky you were getting
Unless you are going for a cam grind or something that affects valve-to-piston clearance, I think you will have nothing to worry about.
James

 

[highest_vision]

I'm thinking I like clay better. Washes off pretty easy, could be reused. Couldn't chew it when you were done but maybe I will use it next time.
James

 

[icanfixall]

It appears the factory specs are 10 to 31 thousands for piston above the deck. I'm already at 47 to 52 thousands above the deck. That makes me 21 thousands out of specs. I don't know what that will cause. I know what the cam is doing with the valves open when the piston is near them and just can't afford contact. The valves will have a lift of 0.2535 for the intake and 0.25308. Thats just a little more than 1/4 inch lift. Now deduct the recession in the heads of intake 0.042 to 0.054 and exhaust at 0.051 to 0.063 and you can see where "things" get really close. The intake valve opens 17.2 degrees before BTDC and closes 42.8 degrees ABDC. Now the exhaust opens 51,2 degrees BBDC and closes 20.8 degrees ATDC.

 

[highest_vision]

Maybe you need to degree the time your pistons are level with the deck, at 50% above deck and 50% returning to level. This should give you a better idea of what you have to work with.
Also you could fab a couple deckplates. Common on larger engines, see no reason why you couldn't make it work on this application. Beware of top end geometry though.
James

 

[typ4]

That is a lot of protrusion, I bet when the rods heat up there will be problems. I cant find any clearance specs, but I will check on it monday.

 

[bikepilot]

Just keep in mind that con rods to stretch at rpm so your static clearance will be a tad bit more than your dynamic clearance. My experience comes mostly from race bikes, but on say a TL1000 (90 deg V-twin suzuki superbike) you've got to go with Ti Con rods to safely reduce the squish much below 0.9mm. Of course those rev to 11k rpm and have huge (for a bike) pistons.....

have fun