21 Stud 37mod

JSeery said:
Nothing on the blocks is more irritating (and expensive) than putting a lot of effort into machine work and ending up with a hidden crack!
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This cost me the price of a complete engine job. My machinist (and engine builder) did the magnaflux, but not the pressure test. He is a very experienced flathead guy, and I trusted his call, and at the time, never thought of the pressure test. Anyway, it cost me. There were hidden leaks, causing water to exit via the RF exhaust port. Found this out after the engine was 100% complete, and on his engine run stand, for final checkout run. I paid the bill, and came home with nothing. Point is, I agree with above post that suggests a pressure test.
We speculated (engine builder and I) that my block was stored with the right front being lowest, and it was eaten out from inside rust. Besides the hidden leaks, it also leaked through numerous holes that put water into the timing gear area. The block material looked quite thin, where we could see. And, the decision was, even if we could fix the holes (at least the visible ones), we couldn't trust the block because it looked so thin in that area. (This was on a 59A block)
 
I don’t know how much the lumpy cam maybe smoothed out by a heavy flywheel but I have a Weber aluminum with a Harmon Collins cam, sound is fantastic with tube headers, iron probably muffles a bit.
IMO
 
Here's my thread about finding a crack in a 37 block in a dumb place after the block was magnafluxed and cleaned and declared good. Not fatal in this case but still would have been a pain if found after installing it in the car.
https://www.fordbarn.com/forum/showpost.php?p=1921710&postcount=1


I'm starting on a 36 block that has been magnafluxed and want to pressure test it before I go any farther. How do you guys plug the core plug holes in the pan rail to withstand pressure testing without leaking?
 
@rodrelic what cam are you using in your 21 studder , I am also using a aluminum flywheel and HC distributor but its a pancake type so cam maybe a issue
 
I will have to look at the end and confirm just know its3/4
Same lifters were run together so we’re matched
Not an ignition wizard but had good results with the crab dist and used 12v worked good Firestone spark plugs
 
Thanks for the info rodrelic on the crab and have one of them as well just have to figure cam out.
 
There are plates that block off the water passages in the head and the water pump areas of the block. The block water-jacket is then pressurized to see if there is any leakage. A flathead block has two separate water coolant systems/pathways in the block, so each side is checked separately.
 

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I was thinking you should also cover the expansion plugs on the oil pan rail on the early engines that had them. The expansion plugs should be replaced anyway it you are pressure testing and cleaning out the block prior to machining.
 
This may be alittle off topic, but, I've only worked on a very few 21 stud engines, including the 37. I don't recommend presuming any modification on these engine, as the internal rotating assy was used for two years in the 36 LB and early 38 21 stud engines. Best left to the people that want to restore the original cars. Late 38 24 stud engines can use all the late cranks and a 4: crank will fit, most of these blocks can be bore to 3 3/16 with some sonic testing, and all the " pieces parts" are available.
Gramps
 
One thing to clarify to what Ron said, the 38 24 stud blocks have the smaller diameter mains and short snout crank like the late 21 stud motors. The 39 engines got the larger mains.
 
The 38 91A crank has a 2.498 crank and is the same as the later cranks. It's also the lightest stock crank and was used in the early stock cars in the later blocks with bigger bores and the 91/21A rods. built quite a few of these back then in 8BA blocks.
 
Ron, we are agreeing except for the year the crankshaft was introduced. The 91A part number is explicitly a 1939 part number. The 2.4 main crank carried through 1938 including the 24 stud motors. I have a 1938 24 stud motor with the earlier shorter crank, it is an oddball engine that is basically a 21 stud engine with three additional fasteners per head.


Also, from the Green Book (please pardon the formatting, I had to use ___ to show the different columns):

68 6303-A___Crankshaft assy-2.40" dia. main bearing-24.47" overall length-used with 78-6335 & 78-6336___Pass, Comm & Truck 90 HP (8 cyl)___36-38

91 6303-A___Crankshaft assy-2.50" diam. main bearing-26" overall length-slinger type rear main bearing seal-used with 78-6335 & 78-6336-replaced by 91A6303-B, 91A-6335, 19B-6336 & 19A-6347___Pass, Comm & Truck 90 HP (8 cyl)___39-42

91 6303-B___Crankshaft assy-2.50" diam. main bearing-26" overall length-bus type rear main bearing oil seal having oil grovves-used with 91A-6335, 19B-6336 & 91A-6347___Pass, Comm & Truck 90 HP (8 cyl)___39-42
 
Well you learn sumpin every day, till they throw dirt on ya. So your saying that early 91a blocks were small bearing ones. Did they have a different prefix number?? interesting.
Thanks Gramps
 
I had an earlier 38 block that the machine shop lost the crankshaft to (this was back in the 60's). Had a difficult time trying to find a replacement.
 
I wonder if it has the slinger rear seal as well. Just a 37 crank. One thing about Ford, he didn't waste much.
 
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