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Old 08-08-2018, 08:11 PM   #21
Yoyodyne
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Default Re: Piston to head clearancing

Has anyone here ever set the clearance close enough that they hit the heads? .045 seems real conservative on a low rpm engine with a close piston to wall clearance that keeps the pistons from rocking. I've seen .030 and less on OHV engines, and it seems that less is better, right?
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Old 08-08-2018, 08:20 PM   #22
3739ford
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Default Re: Piston to head clearancing

What can be used if you don't have any used head gaskets?
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Old 08-08-2018, 10:34 PM   #23
Ol' Ron
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Default Re: Piston to head clearancing

Yes, you can use a tighter piston to head clearance, if you use a lighter piston. The heavy 4 ring pistons have a tendency to stretch the rods a little. Especially is you running a good cam at run over 5000 RPM;s Just remember ONE thing: There;s always a reason for making a modification. Some work, some don't.
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Old 08-08-2018, 10:35 PM   #24
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Default Re: Piston to head clearancing

lower compression when using a blower also.
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Old 08-09-2018, 06:41 AM   #25
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Default Re: Piston to head clearancing

Quote:
Originally Posted by 3739ford View Post
What can be used if you don't have any used head gaskets?
A new one? Can't see why not.

Mart.
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Old 08-09-2018, 07:42 AM   #26
Jack E/NJ
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Default Re: Piston to head clearancing

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3739ford>>>What can be used if you don't have any used head gaskets? >>>
Mart>>>A new one? Can't see why not.>>>

Nope. Can't do that. Cuz the new one will then be a used one. 8^) Jack E/nJ
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Old 08-09-2018, 10:13 AM   #27
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Default Re: Piston to head clearancing

Nah, if it's a coper gasket, installing it and toqueing it down for measurement purpose, won't make it a used gasket. Just refit to the same side, it'll be as good as new.
You can also grease the felpro type ones and use them as above.
With the coper gaskets you can use um a good few times without a worry.
I believe ol Ron does this as well.
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Old 08-09-2018, 10:14 AM   #28
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Default Re: Piston to head clearancing

Double post.

Last edited by scooder; 08-09-2018 at 10:23 AM.
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Old 08-09-2018, 11:13 AM   #29
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Default Re: Piston to head clearancing

Using head gaskets over, has been a practice since the stockcar days. I have a stack of old copper gaskets and I can't remember buying a new one. Same with bearings. I use Hi tac or copper coat. In the future I'll use Latex paint on the aluminum side. For the new builders, better check the cam bearing clearance, Some of these are way out. Now I measure them before i remove them. Gota admit, they're well lubricated.
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Old 08-11-2018, 01:33 PM   #30
flathead47
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Default Re: Piston to head clearancing

Does anyone have a picture of a head before and then a picture after the head has been milled .... thanks
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Old 08-11-2018, 04:50 PM   #31
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Default Re: Piston to head clearancing

Won't be much to see.
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Old 08-12-2018, 05:06 AM   #32
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Default Re: Piston to head clearancing

Well, my 1 millimeter milled 8BA head here.

Got 8,5 bar = 123 psi compression with these (with FelPro gaskets)
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Old 08-12-2018, 05:23 AM   #33
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Default Re: Piston to head clearancing

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Originally Posted by 39voorti View Post
Well, my 1 millimeter milled 8BA head here.

Got 8,5 bar = 123 psi compression with these (with FelPro gaskets)
Lemme see, 1 MM is about .040", right? Have you checked the resulting piston clearance? It would be interesting to know. As I said in an earlier post, .050 clearance with Edmunds heads on my 8BA gives 160 lbs. (Fel-Pro gaskets as well).
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Old 08-12-2018, 02:59 PM   #34
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Default Re: Piston to head clearancing

The other thing you need to think about if you're running a tighter squish than about .035 to .040 is piston to cylinder wall clearance and piston rock. When running larger clearances (with forged pistons for example), you will have more potential piston rock (especially when cold). This means that the static dimension of .040 might get to .020 on the 'high side" if the piston rocks (just for discussion sake). There is always a certain amount of rock - though it will vary by piston material, bore clearances, application, ring packs, etc..

To see for yourself, when building a new engine push on the sides of the pistons and put a dial indicator on the edge - you'll get an idea as to how much rock is possible with just hand force.
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Old 08-12-2018, 11:19 PM   #35
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Default Re: Piston to head clearancing

Dale, excellent point!!
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Old 08-13-2018, 02:38 AM   #36
39voorti
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Default Re: Piston to head clearancing

Quote:
Originally Posted by tubman View Post
Lemme see, 1 MM is about .040", right? Have you checked the resulting piston clearance? It would be interesting to know. As I said in an earlier post, .050 clearance with Edmunds heads on my 8BA gives 160 lbs. (Fel-Pro gaskets as well).
Yes 1mm is around 0.040.

I have not done any other measuring, not anything else than enjoyed the better performance of my flathead
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Old 08-16-2018, 05:07 PM   #37
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Default Re: Piston to head clearancing

Couldn't you measure the squish through the spark plug hole, with the foil ball on the enf of a piece of tie wire. This could be done without pulling the heads, what you say ol' Ron. Al
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Old 08-16-2018, 05:17 PM   #38
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Default Re: Piston to head clearancing

You could, but it would be difficult to know where you were on the piston dome. The clearance will vary around by location. When you do this check, you do it in several positions for each piston. You can attemp to modify the head for more uniform measurements or use the tightest measurement for your reference.
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Old 08-16-2018, 05:40 PM   #39
Ol' Ron
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Default Re: Piston to head clearancing

Yes, this can be done with rosin core solder. However, it takes practice getting the solder in the right locations. But it does give a very accurate measurement.

I've never had to take more than 25 or 30 tho off, I like to get the clearance down to around 30 tho around the edge of the Distion, then shape the edge down with a Dremel, to 45.

It's importan to realize we're talking street engines here and forged pistons with large wall clearances are a different story. I build my engines with Egge 3 ring and fir the pistons to .002 wall clearance. Seems to work quite well
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Old 08-16-2018, 05:46 PM   #40
Ol' Ron
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Default Re: Piston to head clearancing

Yes, this can be done with rosin core solder. However, it takes practice getting the solder in the right locations. But it does give a very accurate measurement.

I've never had to take more than 25 or 30 tho off, I like to get the clearance down to around 30 tho around the edge of the Distion, then shape the edge down with a Dremel, to 45.

It's importan to realize we're talking street engines here and forged pistons with large wall clearances are a different story. I build my engines with Egge 3 ring and fir the pistons to .002 wall clearance. Seems to work quite well
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