maximum cylinder bore

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Tmodelt
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maximum cylinder bore

Post by Tmodelt » Sat Mar 09, 2019 12:03 pm

Attempting to acquire all parts and pieces to build my next speedster engine. What is the maximum SAFE cylinder bore for a 26 / 27 Model T engine? I will be using a pressurized oil system and Chevrolet OHV conversion.

The reason that I ask is that I inherited a set of Model A aluminum standard bore pistons (new) when my grandfather passed away several years ago.

From my research, that would require a .125" overbore.

Any and all responses will be greatly appreciated.


Kevin Pharis
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Re: maximum cylinder bore

Post by Kevin Pharis » Sat Mar 09, 2019 12:31 pm

There are plenty of .125” overbore motors out there. And some of them even use stock A pistons too. Not worth the effort in my opinion, after all the time you spend making special length rods you will find that your compression was actually lowered due to the flat top A piston.

It’s certainly possible... you will have to weigh the pros and cons against what works best for you


Topic author
Tmodelt
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Re: maximum cylinder bore

Post by Tmodelt » Sat Mar 09, 2019 12:49 pm

Thanks Kevin.

The pistons that I possess have a chamfer at the top (about 3/8") then transition to a flat top. Does this make them high compression? I wouldn't consider them "domed".

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Mark Gregush
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Re: maximum cylinder bore

Post by Mark Gregush » Sat Mar 09, 2019 1:19 pm

They might not be A pistons. Could have been the pistons to use with Chevrolet crank and rods. What is the wrist pin size? A would be around 1 inch.
I know the voices aren't real but damn they have some good ideas! :shock:

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Erik Barrett
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Re: maximum cylinder bore

Post by Erik Barrett » Sat Mar 09, 2019 1:29 pm

We run a 3.880" bore on the Wild Cherry II race car. That's.130" oversize. The only problem we have had is it leaves the space between the front and rear pairs of cylinders very narrow. At 10:1 compression it is difficult to keep head gaskets intact. We have had to put stainless O-rings on the block deck and use a solid copper head gasket made for us by Kevin. None of this should be necessary with a flathead but you may want to see if some of the gasket fire ring protrudes out into the cylinder.
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Topic author
Tmodelt
Posts: 146
Joined: Mon Jan 07, 2019 3:48 pm
First Name: Kim
Last Name: Wynn
Location: Morris, IL

Re: maximum cylinder bore

Post by Tmodelt » Sat Mar 09, 2019 1:39 pm

I don't think Grandpa would have kept any Chevrolet parts. Sac-religious to him!!! He had a several Model Ts and Model As. One was a 28 full cab pickup with a Model B engine. It was fun to pass people at highway speed out on the interstate.

I made an assumption. I will have to make a trip back out to the garage parts storage closet and check.


Adam
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Re: maximum cylinder bore

Post by Adam » Sat Mar 09, 2019 3:09 pm

It’s good insurance to ultrasound anything bored over .060”.

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