Flathead Rebuilders (Please check me on this one)

OhioRick

OhioRick

Senior Member
I recently pulled the pan on my 1940 59A flathead chasing a broken ring. The engine is rebuilt now with 2500 miles on it. Found the culprit to my 30 pounds pressure in the no 7 cylinder. Luckily there was no damage to the cylinder walls only the ring grooves.

But upon inspection of the lower end I found the No 8 connecting rod loose at the journal with a backed off castelated nut and a broken cotter key.:eek: I also pulled off the adjacent No 4 connecting cap.

Both of the bearings were broken. I found the rod bearing surfaces only had very very minimal damage at the edge and no damage whatsoever on the crank journal. Am I lucky or what??

I have no idea how this happened. I can only guess the rear crank journal was over machined and they installed undersize bearings.

Now the specs and measurements. I am a metrologist and had my way around machining.

Stock specs and sizes...
Stock rod bore- forging number 99A and 29A size 2.3597 / 2.3600
Stock floating bearing size .1095
Stock Crank journal size 2.138 /2.139

My engine component measurements...
Rod bore 2.363 only about .001 out of round
Crank rod journal size 2.115 only at .0015 out of round

Now if
2.3600 - 2.1390 = .221 at the stock tolerance.

Then my engine measurements of
2.363 - 2.115 = .248 at present tolerance.

Those numbers of .248 - .221 = .027 oversize

Am I correct in assuming I can use a .030 oversize bearing????
Ha didnt know you guys were going to get a math quiz.
I am assuming that this must be a later model 59A
Rick



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Well, my math tells me this: Stock rod journal size 2.138/139 -.030=2.108/109 . Now, with brgs shells installed in the rod and cap torqued to specs, shell inside dimesions should be 2.108/109 + the .002 or .003 for clearance or 2.110. Stock rod journal - .020 gives you2.118, .003 larger than what yours is so you'll end up with.005 or .006 clearance .020 oversize will fit too loose and the .030 will lock it up tight. If I added it wrong, somebody straighten me out.
 
Your rods are too big by .003, your crank is down fron an .020 grind by about .003...
Grind the crank, may be able to go .030... rebuild the rods.... Karl
 
Check the thickness of your bearing shells. I think it's possible to buy floaters in oversize O.D. as well as I.D. to allow the big end of the connecting rod to be honed oversize to make it round again. I thought you were suppossed to have .001
diametral clearance between the rod and bearing and .0015-.002 between the bearing and the crank journal. The out of round on the crank and in the big end of the rod may have made the assembly "stick" when assembled. I spent days on this and the most out of round I had was .0005. The wear on the bearing edges might be the corner radius on the crank is too large. If it was mine, I'd check the rest of the rods before deciding what to do. JMHO
 
Thanks guys. I was figuring thats what answer I would get. This engine is installed. I was hoping to make it a quick fix. Never used plastigages??? Do they work and are they acceptable to use after truing up the out of round conditions and bringing the the connecting rod bore to 2.366?
Where can I get bearings with oversize ID and OD's?
 
Another thing to look at when you put it together is make sure your cotter pins fit tight. I've seen them end up as pieces in the pan if they are loose fitting.
 
O Rick,
Plasti-gages not so good on full floating bearings. Bite the
bullet and pull the the motor while the snow is still on the ground.
MHO.
Charlie ny
 
Charlie ny said:
O Rick,
Plasti-gages not so good on full floating bearings. Bite the
bullet and pull the the motor while the snow is still on the ground.
MHO.
Charlie ny
Click to expand...

Ok thanks. Speaking of snow Charlie, you guys had your share this winter with another 15 today. Yuk!

Where can I get bearings with oversize ID and OD's?
H&H? Speedway?

Rick
 
I don't like plastigauge, I use brass shim stock... it's a bit more work but it will tell you exactly what your clearances are... I mic the whole works, rod throws, mains, every bearing piece, block nad rod housing bores, (torqed)... Then I use shim stock, (paper would work) to check one rod and one main... Karl
 
I don't think anyone currently makes oversize OD bearings. Would have to find someone with old NOS stock and I've only seen them in .004 and .008 overzize. The rods can be resized to stock size.
 
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