Reground crank and bearings install question.

Mark's 37

Mark's 37

Senior Member
I put the .030" under crankshaft in this afternoon. Chased the main cap block threads and used ARP bolts to replace the 37 studs. Haven't done the rods yet. The main bearing clearances are a tight .001". I can't turn the crank by grabbing the counterweights and the pulley by hand. I can turn it using a large screwdriver in the crank bolt on the front of the crankshaft but it's a little stiff. Am I in the ballpark or should it be looser? Thanks.
 
I have never put in a crank I couldn't turn easily by hand, we're talking crank only correct?
 
I futzed around and determined the trouble was in the center main cap. If I backed off the torque on only those two bolts it would free up. After cleaning and rechecking, then swapping the front cap with the center, the trouble moved to the front main. Took it apart and sat the center main cap on its side and gave a whack with a rubber mallet. Reinstalled, all better. I will recheck with plastigauge in the morning. The only thing I can think is the bare block was stored with the main caps bolted on for a decade or more so possibly in moving it around it took a hit on the cap and tweaked it. Mystery motor blues. The front and center caps were marked but look identical. According to the book one is supposed to have a slight offset bolt hole and I measured them with digital calipers and all sides of both were equal. What is up with that?
 
The front and center caps are not interchangable.
As for clearance, you need to check it with plastigauge AFTER you reconcile the cap discrepancy.
With the main bearings lubed with engine oil and WITHOUT the front or rear seals installed and the crank in and caps torqued down, you should be able to spin the crank by hand and have it rotate at least one revolution by itself.

While you are checking things, check to see that the radius in the crank fillets is not binding on the bearing edge. You will have to open that up if it is.
 
Mark's 37 said:
The front and center caps are not interchangable.

How can you identify the front and center caps?
Click to expand...

If you look VERY carefully, you will notice the raised circular key is centered on the center cap. On the front one it is slightly offset.

Another thing to check is if the crank is bent. Just because it was reground doesn't guarantee it is straight.

If all of this checking doesn't resolve the problem, you may have to find a rebuild shop that has a mainline test bar to check the block.
 
Pete said:
If you look VERY carefully, you will notice the raised circular key is centered on the center cap. On the front one it is slightly offset.

Another thing to check is if the crank is bent. Just because it was reground doesn't guarantee it is straight.

If all of this checking doesn't resolve the problem, you may have to find a rebuild shop that has a mainline test bar to check the block.
Click to expand...

If its fresh reground and not dropped or mishandled it should be ok.
If its bent you should be able to slowly tighten the center maincap and find a sweetspot where the crank turns a few degrees free and then lock up.
If the drag turning it is constant line bore issue or bearings/crankgrind being out of spec.
And its a rough way of testing but would give you a hint.
 
If you are not able to detect any difference in the main caps it is possible that they are not the original caps for that block. The flathead main caps where close enough from engine to engine to come very close to interchanging and sometimes you could get away with it. I would check the caps and see if there are any obvious mismatches like a very slight "edge" when you run you finger along the seam where the cap and block meet with the caps torqued down (without the crank installed).
The block and caps really needs to be checked by a machine shop to determine if the main bores are all on centerline and the correct caps are with the block.
 
When you said the clearances were .001 - how did you measure this? As everybody noted, something is not right if you can't easily turn it by hand. My recommendation is that you have it checked out by a machine shop - once you get the caps in the right locations.
 
Talking about the off set bolt holes on the front cap, I think Ford didn't off set the holes until 39, SO, the early caps are easy to miss match, what you should do is remove the crank and install the front and center main caps, torque them down, feel with your finger the parting line and see if there is a hang over, If so swap the caps and see if the parting lines are smooth. You should mic the housing bore, I have the spec out in the shop, I believe the 37 is .100 smaller that the 39-48 blocks, I HAVE A QUESTION FOR YOU, does your rear main cap have a an aluminum slinger retainer or just the one in the block? I put the question on the barn a while ago and it seems some did and some didn't. I'm building a 37 engine right now and the cap is not machined to hold an aluminum retainer. STRANGE. Walt
 
Thanks for all the leads on figuring this mystery out. Back at it later today and this weekend. I found the very faint "dimple" on one of the main caps. The previous owner had the machine work done and the main caps were marked with paint dabs. The main cap with the dimple has two paint dabs indicating it would be the center cap as I see it. It is a 37 and the main cap bolt holes are not offset. I will be taking out the crank again and re-mic it again, install/torque the caps without the crank, measure and look for the clues explained in the posts including the fillets clearing the bearing edges. Walt, the original untouched 37 block had only the upper half of the rear oil slinger. Nothing in the rear cap, in fact, I spent a fair amount of time searching through the parts looking for the lower portion until I read that some did't have it. For clarity, I have the original untouched engine from the car on a stand, it is a standard bore and crank. The engine I am building is one I bought that was machined/etc. but never assembled (.100 overbore/.030 under rods and mains). Making my rookie run/mistakes on this one and saving the other to build after I get educated.
 
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Checking stuff today. Here are two photos of the original front and center main caps from the untouched engine out of the 37. No dimples, ****, markings, etc. to differentiate one from the other. No offsets that I can see. They appear identical to my eyes.
 

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Ol' Ron said:
Mine too, but they could be the wrong caps???
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Only if that was done at the assembly plant in 1937. Since it was the first year of insert bearings maybe Ford made some changes afterward. Sure as hell confuses me. Were pre 37 babbit bearing front and center caps interchangeable?
 
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Here are the two main caps that I am using on the engine today. Again they look identical. The cap with the two paint dabs has small dimple almost like a center punch between them. Not even visible in the photo.
 

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Mark's 37 said:
Checking stuff today. Here are two photos of the original front and center main caps from the untouched engine out of the 37. No dimples, ****, markings, etc. to differentiate one from the other. No offsets that I can see. They appear identical to my eyes.
Click to expand...

The cap on the left appears to have a #2 stamped on it.

247037
 
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