Piston to Head Clearance?

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Model T Ford Forum: Forum 2011: Piston to Head Clearance?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Gene Carrothers Huntington Beach on Friday, December 09, 2011 - 10:30 pm:

I was chasing a small noise and found my #1 and 2 pistons kissing the Z head with the gasket off. Hope that solves my ticking.

My question is, How much clearance would be acceptable without the gasket between the top of the pistons and the head? I have alum pistons and wondered if I need to be concerned with any expansion when they heat up or at high RPM.

I blued the piston tops and sanded down the high spots. Looks like I now have some clearance without the gasket.

It also looked like my #4 piston had been hitting the edge of the gasket that had squeezed out slightly in the narrow area beteen the two cylinders. Would be nice if there was some kind of indexing to mate the head to the block so perfect alighment could be acheived. There's quite a bit of play especially until nearly all the bolts are put in.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Shirley on Saturday, December 10, 2011 - 04:44 am:

Use Playdough, put a roll a little smaller than a pencil around the crown of each piston. Cut a circle of kitchen plastic rap and lay it over the Playdough, bolt the head and gasket on with a few bolts. Remove the spark pugs and crank the engine over by hand. Take the head off and cut V shaped notches in the Playdough and measure the thickness.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Shirley on Saturday, December 10, 2011 - 04:52 am:

Playdough should measure minimun of 1/8 inch at it's thinnest.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gene Carrothers Huntington Beach on Saturday, December 10, 2011 - 11:12 am:

Bob Thanks for the advice,

Did you mean there must be at least .125" clearance? I used some modeling clay and now have about .065" clearance at all cylinders without the gasket and the head tightened down.

If that is true I'll have to remove quite a bit.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Shirley on Saturday, December 10, 2011 - 02:38 pm:

I'm betting on a flat head engine, .065 will be just fine. Was the head (marked), by contact with the piston, from where it ran before? If not, I would not worry about it.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Saturday, December 10, 2011 - 02:49 pm:

Gene; He said WITH the gasket. I have a Z head on the truck and I started with .030" without the gasket and have no piston noise.

The .030 and .060 crushed copper gasket thickness gives about 3/32" clearance, which is ample. The larger the clearance, the less squish and the less efficient combustion.

Sincerely

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare on Saturday, December 10, 2011 - 04:40 pm:

Just watch the sides of the piston and head placement, sometimes ( especially on high domed pistons ) you have to wiggle the head to get a clear placement/movement.

David.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ricks_-_Surf_City on Saturday, December 10, 2011 - 05:07 pm:

Has anybody installed indexing tubes like later engines have? The gasket bolt holes are especially sloppy.

rdr


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