model B piston clearance in the block

[Steve in Tampa]

when you bore a new cylinder, what should the clearance be for the piston? Thanks, steve

[Pete]

Originally Posted by Steve in Tampa

when you bore a new cylinder, what should the clearance be for the piston? Thanks, steve

Use the piston manufacturer recomendation.

[Steve in Tampa]

clearance between piston and cylinder wall on a new bore steve

[Russ/40]

Pete gave you the proper answer.

[Steve in Tampa]

.o30 pistons nos , no info

[johnneilson]

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post a couple pictures of the NOS pistons, we might be able to determine starting point.

Depending on the design, the proper clearance can be .003-.010

J

[nkaminar]

The clearance is measured at the points cross wise in the engine (side to side not fore and aft). The pistons are ground eccentric so that the clearance fore and aft is greater. This allows for expansion of the piston. That applies to a piston with a full skirt. The clearance in the side to side direction will be about 0.004.

For pistons that are ground round (don't use these) the clearance is greater, perhaps 0.010. For pistons that have only a partial skirt (slipper pistons), like Egge pistons, the clearance can be less, and I don't know what it should be.

As Pete said, use the recommendation of the piston manufacturer. If not supplied with the pistons, contact them to get their recommendation.

[Patrick L.]

Yep, what Pete said.

A general rule of thumb is .001" per inch of bore. And I think loose is better than tight.

[Bob Bidonde]

The November 1932 Service Bulletin, Page 66, indicates the fit for aluminum alloy split skirt pistons is 0.0005" to 0.0025".

[Bob C]

Originally Posted by Bob Bidonde

The November 1932 Service Bulletin, Page 66, indicates the fit for aluminum alloy split skirt pistons is 0.0005" to 0.0025".

I saw that also and thought it must be a miss print, seems way to tight.

[Jim Brierley]

Originally Posted by Bob Bidonde

The November 1932 Service Bulletin, Page 66, indicates the fit for aluminum alloy split skirt pistons is 0.0005" to 0.0025".

Don't use the info above! This was for pistons with a full split skirt, not like todays pistons. I usually bore to .003" and hone another .0005" looser is better than too tight! Racing pistons are a different story, and require much more clearance. Too tight will result in scouring of the pistons and walls, you don't want this.

[ursus]

Regarding the quote from nkaminar in Post #7: "For pistons that are ground round (don't use these) the clearance is greater, perhaps 0.010"

I wonder what is wrong with concentric ground pistons? I know it is old technology but I have pulled this type of piston from old engines that had an apparently long and useful life. These were also split skirt pistons which were set up much tighter than the 0.010 inches cited.

[BRENT in 10-uh-C]

Originally Posted by Steve in Tampa

when you bore a new cylinder, what should the clearance be for the piston? Thanks, steve

Steve, have you actually measured the pistons? Often times, I find that pistons are generally manufactured in a (under)size so when the cylinder is bored (-and then honed) to the nominal oversize, the correct amount of clearance the manufacturer desires is there.