Help me determine my piston-to-head clearance!

[GhostAccord]

I'm just curious as to how much they are going to charge you to get your pistons machined and have a custom head gasket made?

[Youngill726]

I am in the same boat with my pistons sticking up 18 thousandths. Things is I'm running h23 with mahle h23 dish pistons and Bisi F22 . I spoke with cometic about gasket about .086. Piston compression was 9:0:1. I'm scared to think about the compression now. Hard to think why F22 are not supported by them. I think cutting the pistons would be my last resort but my block isn't sleeved.

[Jarrett]

You're not being clear at all about what your problems stem from because you just listed engines and were not specific to which components you had from those engines. At the very least it seems that you're running forged non-FRM pistons (if they truly are for an H23A) in an FRM block. You have problems whether or not you have clearance issues or not.

[GhostAccord]

@ only 0.018" out of the hole...are you sure your not running H22 pistons? H23 pistons are the same compression height as F22 pistons and on H23 rods (same as F22) you should only be 0.002 out of the hole on a stock H23/F22 block deck height.

[Youngill726]

Sorry man I don't mean to thread jack. @ Jarret sorry bout other posts for not being specific. I'm running mahle h22 pistons and F22 rods.

[ON_N20]

I'm just curious as to how much they are going to charge you to get your pistons machined and have a custom head gasket made?

So to update on my progress here, I went to my local machinest. He has a real nice shop and will be milling my pistons with a vertical CNC mill. His estimated time to complete will be about 2-3 hours, and cost me around $210 (hopefully even a little less ).

He also brought up a good point when determining the piston to head clearance, is that you NEED to know what your piston rock is in the cylinder. In other words if your looking at your piston down in the hole, rock it from side to side parallel to the wrist pin axis, and measure the rock. To do this I set up a dial indicator on the top edge of the piston, with the piston at TDC. My aftermarket pistons have .020" of rock - quite alot actually, but not unusual since they are forged low compression pistons with the intent to be a turbo application, so they naturally have alot of piston to cylinder wall clearance.

Now knowing this information does change my original number a bit. With the piston at absolute TDC with the dial indicator on the edge of the piston, if I rock the piston so that it is at the minimum at TDC, I am currently .022" out the block, and with the piston rocked to the maximum at TDC, I am .042" out the block. That .005" more than my original averaged measurement I had before at .037". You will also notice the difference between max and min piston height is .020", exactly what I seperatly measured for the rock earlier.

So, if you know the rock of the piston and you have your TDC measurements, then you know for sure that no matter the operating condition, you will know the maximum static height that the pistons will ever reach in relation to the cylinder head. You WILL still have to factor in the variables of rod stretch and heat expansion and add that to your calculations.

Whether your planning on a certain thickness head gasket, or like me and having to mill the top of the pistons, this is info you need to know, to be able to calculate the optimum piston to head clearance, also known as squish or quench. I hope this helps others!

I will chime in again tonight when I get my pistons back, and hopefully by then I'll have the engine mostly build by the end of the day (pistons should be done by noon).

[prNonVtec4u]

This is an issue i've been dealing with since my last build...

My setup's pistons come out of the hole .032" WITHOUT rock being in the equation! Not to mention my head's been hella cut, lol. Running an OEM head gasket (GE modified for bore), we've always measured it at .048", only leaving me with ±.016" (minus "rock)....

I've had NOTHING but head gasket issues with this up to this day (8 so far)... I just took it apart again 2 days ago since it blew on the dyno and after inspection, the pistons WERE making contact with the head at high rpms. Cometic = FAILED at helping with the situation and will not bother with an F series gasket whatsoever even though they manufacture the LESS popular, ALMOST identical H23 one. Even was asked to send a spare gasket and they would see if they had the "tooling" for it. I had a spare OEM head gasket laying around that i couldn't use due to being stock bore, and shipped it over and crossed my fingers... Led to nothing.

I personally didn't have it in me to take the block apart AGAIN so milling the pistons was not the option for me... So what am i doing now? I found a company out of Lubbock, TX called Lubbock Gaskets. They specialize in making custom, solid copper headgaskets. I contacted Cometic once more and had them overnight my gasket over to this place. They're currently using my OEM gasket as a template for their machine and am having a .090" thick, 88mm bore, solid copper gasket made . I'm aware of how "finicky" they are at sealing coolant/oil, but willing to take the chance if it'll at least hold my compression, lol

[GhostAccord]

$210 is a hefty price to pay to have a set of brand new pistons machined. To be honest, I would have sold them and bought new ones.... Probably would have saved yourself $150-$200.

As for piston rock, I mentioned that already and no one seemed to take any interest in it. Guess all it takes is having to spend extra money to fix an issue for people to realize what it takes to build an engine.

Hopefully everything will work out for you now.

[Jarrett]

Like GhostAccord said, sell your pistons if you can. If he got custom pistons for $500 then I'd go that route.

[wed3k]

500 bucks is a little too cheap to be true. my custom pistons with different wrist pins and comp height with coating came out to 850.

[Jarrett]

In the interest of full disclosure I've never bought custom pistons. I was simply relying on what GhostAccord said he got his for. I can imagine if it's a modified design of a shelf item then it might be cheaper than something totally custom. But that's just me blurting out stuff in which I have no experience.

[GhostAccord]

500 bucks is a little too cheap to be true. my custom pistons with different wrist pins and comp height with coating came out to 850.

What did they charge you for coating your pistons? I got my custom Wiseco slipper skirts with an 89mm bore, 92.08mm compression height, 0.06mm dome for $550, back in 09. They tried to sell me on the coatings. I didn't bother with it on an N/A build w/iron sleeves.

I paid $1373 shipped for Carrillo H22 A beam rods and Custom Wiseco pistons. Rods were $750 Pistons were $550 + shipping...... John and Rob down at Race Engineering set me up with the set. I think the rods were on sale. regular $850 -$875 IIRC.

[Jarrett]

92mm compression height!!!! Holy crap. Forget valve reliefs. When you turned the key to start that engine you made your own piston reliefs!

Kidding, I know you meant 29mm.

[wed3k]

idk, it was all included with a package with hastings rings. (Ross pistons for my VW)

coatings are proven...im going to send out my head and valves to have it all coated and maybe the skirts of my arias pistons. (12:1 f22 build)

id honestly wouldn't buy anything higher than a chinese rod aka bisimoto, scat, eagle, CAT. those are proven to handle 600hp.

i don't like wiseco's because i find them heavy but thats just my opinion.

[GhostAccord]

92mm compression height!!!! Holy crap. Forget valve reliefs. When you turned the key to start that engine you made your own piston reliefs!

Kidding, I know you meant 29mm.

Thanks
The piston dome volume is actually .6 not .06...lol

idk, it was all included with a package with hastings rings. (Ross pistons for my VW)

coatings are proven...im going to send out my head and valves to have it all coated and maybe the skirts of my arias pistons. (12:1 f22 build)

id honestly wouldn't buy anything higher than a chinese rod aka bisimoto, scat, eagle, CAT. those are proven to handle 600hp.

i don't like wiseco's because i find them heavy but thats just my opinion.

Coatings definitely work on the piston top and combustion chambers. I'm going with the cheaper route and using the high polish approach.

Weight was a big concern with my N/A build. Lightest combo I could find;
Wiseco Custom Piston - 328 grams
Carrillo H22 Pro A Rod - 496 grams
Total = 824 grams
(actual weights)