piston clearence

alan · tinkerer Joined: 07 Apr 2002 Posts: 429

Yes, it will, if using a big valve, and probably a small valve too. You need to cut reliefs into the piston crowns for the valves.

Build it properly, and it will not blow head gaskets.

Racegem · backyard mechanic Joined: 30 Jan 2002 Posts: 987

1), It can, depending on the size of the camshaft and whether the head's been shaved or the block decked or both.
2), And your gasket question, there are so many variables it's hard to give a straight answer. Upping the compression too much will cause detonation unless you're running with racing type/high octane fuels. When you do run these fuels to stop detonation, you can then have problems with rings or blowing gaskets. That said, I know of guys who have had 1600 heads on G200Z blocks without any dramas, but fuel quality was a bit better back then. You could kill two birds with one stone and put dished pistons in. They lower compression a bit and could give you the clearance you need for the valves.
And if your head or block aren't dead straight, you'll blow head gaskets on any motor with any sort of compression.

Hope this helps you Tom, without the slagging match, although it has been entertaining... lol

Yonnee.

Momo · backyard mechanic Joined: 08 Feb 2002 Posts: 561

So - if my valves are hitting the tops of my pistons, (I know we're talking about different bottom ends) would an adjustable cam gear overcome the problem or not?? and would an adjustable cam gear be appropriate for Tom's setup???

Racegem · backyard mechanic Joined: 30 Jan 2002 Posts: 987

Nope, If you've got a camshaft that's big enough to make the valves touch the pistons, no amount of changing the cam timing will get them to clear while still allowing the motor to run.

Yonnee.

tommop · rice boy Joined: 05 Apr 2002 Posts: 23

Gene FJ20DET · Posted: Wed Apr 10, 2002 11:51 pm Post subject: easy fix!

get an old valve, cut groovs into the edges, then stick it in a drill ( it should look like a drill powered milk shake maker, if u know what i mean) have the valve in the head and the head bolted down to the block. fix the drill to the "drill bit valve" where the valve spring would usually sit. then drill into each piston at the inlet and exhorst manifolds. thenu can deck the block, shave the dead and put the biggest fucking cam u want in it. the valvs would usually hit but cause the pistons have been cut to the shape of the valvs where the valves would hit it dont!
happy burnouts!
gene
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Gene FJ20DET · Posted: Wed Apr 10, 2002 11:52 pm Post subject: Re: piston clearence

no. and look at "easy fix" u can do it yaself
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alan · tinkerer Joined: 07 Apr 2002 Posts: 429

Although Yonnee's advice is spot on, I dont think there much point of using a 1600 head if you put in dished pistons to drop compression. Might as well stay with the original head. They will flow adequately for a cam upgrade for a NORMALLY aspirated engine.

The machine shop will use a flycutter to cut reliefs into the piston crowns. The issue here is how far can they go? There is a limit. You will need to determine this, before taking the head, block, and connected pistons to the machine shop for the work to be done. IF you need to know how, post again.

It cost me, about 6 years ago, $80 to have 8 reliefs done. However, I only gave them the pistons, and I told them where to cut. Probably cost you $150 now, at a guess.

tommop · rice boy Joined: 05 Apr 2002 Posts: 23

tommop · rice boy Joined: 05 Apr 2002 Posts: 23

Gene FJ20DET · Posted: Thu Apr 11, 2002 10:09 pm Post subject: HAHAH

u strip the motor in the procces!! lol do it in the middle of a rebuild. thats what my bro did. worked wonders. the guy at head tourque showed him how to do it
gene
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Racegem · backyard mechanic Joined: 30 Jan 2002 Posts: 987

No, what Alan meant was if you put a 1600 head on a G200 to up the compression, and then put in dished pistons, you will bring the compression down again. You may as well run the standard G200 head that came with the motor. However... regardless of motor/head combo, if you go too large with camshaft lift, you'll kiss the pistons.

Quick build?
-Have the entire rotating mass balanced. (crank and flywheel)
-Fresh rings and bearings.
-Quality pistons. (if your buget can stretch)
-Have the head checked and shaved. (and ported if you can stretch again)
-Choose a mild to medium camshaft. That way you wont need to modify the pistons. Big cams can also be a bitch to drive gently.
-Adjustable cam gear. (to make the most of your new camshaft)

That should give you a good reliable motor that should be within your budget, and, with a decent carby, exhaust and dissy recurve, should give even a few V8's a fright.

Hope this helps,

Yonnee.

alan · tinkerer Joined: 07 Apr 2002 Posts: 429

You mentioned the dished pistons earlier in this thread. Does that mean you know of any 87mm dished pistons suitable for installing into a G200 turbo biuld? By suitable, I mean dished enough, or lower in height, that the compression comes way down , thus not requiring a decompression plate?

Fastgem · tinkerer Joined: 04 Oct 2001 Posts: 166

Im pretty sure you can get the piazza 4zc1 pistons in there