The Stovebolt Site Forums The Shop Area Engine Shop Cylinder wall thickness

I'm looking at a block that is .145 to .400 according to the sonic test. Would like to go .050 over, which means I'd be at .095 at the thinnest? Is that acceptable?

1. .050" only removes .025" from each surface
2. the thrust surfaces must be substantially thicker than the pin axis sides
3. for a street engine I like to see minimum of
Passenger side .150"
Driver side .120"
Crank axis .090"

Any rougher use needs more thickness

Your minimum thickness will be .120", not .095 with a 50 overbore. Back before the days of sonic testing, nobody worried about anything below 60 over, and the people who contracted rebuilding services to places like Sears and J.C. Whitney routinely went 80 0ver. If you're concerned about a thin spot, install a sleeve. I've repaired golf ball sized holes in cylinder walls with a .125" wall sleeve, and built 500+ HP round track engines with those blocks.

My father used to bore flathead Ford V8's .250" oversize by offsetting the cylinder centerline away from a thin area where the exhaust passed between the center cylinders and narrowing the small end of the connecting rod so the piston could center up in the cylinder. Then he ran them with 11:1 compression on alcohol!
Jerry

Just a point of interest, I've seen lots of Model A blocks that were bores 100 or even 120 over. Of course there was probably a lot more iron in those back in the 20's and 30's.

Isn't there a 3 7/8" diameter Chevy V8 piston that some people run in the Model A engine? That's a 1/8" overbore.
jerry

Don't know, as it's been almost 50 years since I messed with a Model A engine, but I think I saw 125 over stock style pistons available. I wouldn't be surprised if someone used Chevy V8 pistons in one of them.

I'm tinkering with one of those engines- - - -thinking of adapting a dual overhead cam cylinder head to it from a MOPAR 4 cylinder.
Jerry

Those were pretty torquey engines, kind of like a tractor. I think the stroke was 4 inches or so. Displacement of 200 CI for a 4 cylinder would be equivalent to a 400 CI V8. I ran a Model C engine in my first pickup, basically the same except bigger crank journals, counterbalanced crank, and a higher compression head. I know you could dump the clutch in high gear and not stall the engine. The guys on tour in the Model A club were jealous, because I was at half throttle when they were on the floor. A DOHC Model A engine would be interesting. It'll take some machining to develop a drive for the cams.

I’m sure someone in years past has developed A DOHC Model A head, they developed many other alterations.

Ed

Rajo and Frontenac made OHV heads, not sure about any DOHC conversions. Really, it would be fairly simple to adapt a belt drive setup to the front of the engine- - - -just sprockets, idlers, a tensioner, and a belt. No worries about the mesh of the crankshaft and cam gears, etc. That would make line boring the block for insert main bearings a simpler process, as well. I'm looking at a 2.4 Liter PT Cruiser head as a possible donor.
Jerry

HRL;

"2.4 Liter PT Cruiser head as a possible donor".... How would that work? I don't know if the bore centers are even close. Regardless it would be mic drop moment when opening the hood.

SimS

The "A" has a huge gap between the #2 & 3 cylinders to accommodate the center crank bearing.

It would require a little creative machining of an adapter plate, and probably custom pistons. For a running prototype, I'd rivet or bolt an aluminum shim to the top of the piston to take up the combustion chamber volume increase created by the adapter plate.
Jerry