??Boring limit for '35 21 stud FH engine??

[JM 35 Sedan]

I've heard several different opinins on how much an early 21 stud engine can be bored. I know core shift, porosity, corrosion on the inner walls, etc., will play a part on the limit. I would like to get a suggestion on the limit from the engine gurus and also hear some actual bore numbers from those who have bored them to what they think is the limit. Thanks Fordbarners!

ps...I would also like to know the boring limit on a '37 21 stud block.

 

[rotorwrench]

I'm not a "guru" but just to keep a discussion going I'll input this. The old babbit bearing 21 stud V8s were usually set off under the work bench and a later motor was used if going over .060" OS. The LB motors or last of the 21 studs retrofitted for pumps in the heads were a common replacement to get the insert mains.

I read an article in a Tex Smith flatheat book about a later 21 stud that was bored way out to put 3 & 3/16" sleeves in it so they could have the extra power of a 239 CID motor but not have to worry about thin cylinder walls or overheating. I think they actually went through to the water jackets in places but then used JB Weld epoxy when they installed the sleeves. They ran the thing in the great american race and made the whole trip. I bet they spent a chunk of change getting the machine work done though.

Kerby

PS: I rechecked the reference "Tex Smith's - The Complete Ford Flathead V8 Engine Manual" and they did in fact use a 37 LB block. The article mentioned it was bored out to fit 3/16" sleeves for a final bore of 3 & 3/16". They used a late Mercury 4" crank modified to fit the motor block and 21A type conecting rods for a total of 255 CID. They also used a stock 1942 cam shaft and front timing cover for a crab type distributor. It's an interesting article (21-Stud Salute by Vic Thompson and Rex Gardner) but you can tell money wasn't an object for the build and I'm sure it was expensive.

 

[Walt Dupont--Me.]

This is my recomendation, I've built quite a few early flatheads. I wouldn't bore the 32-36 engine over .060 I've found alot of thin walls on these engines. The 37-38 21 stud I bore .125 and never had a problem. Walt

 

[jimTN]

Just look at a babbit or LB engine between the bores and you will see that there is very little material there.

 

[JM 35 Sedan]

Thanks to all for the info given. I had heard and read that. 060" is the safe limit on '32-'36 Babbitt blocks but a friend said his '35 has been bored to .120 over. Another friend has a '37 block that's been bored. 80 and he was thinking that was the limit for a '37. I'm also planing to build another '35 engine and wonder what I could bore it to without running into problems.