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Old 08-09-2020, 08:23 PM   #1
TMarsh
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Default crank shaft movement

A brief history. Had basket case 1930 Model A for 20 years. Finally completed total rebuild, engine, trans, rear end brakes, interior, paint, wiring, the works. Probably have twice what it is worth in. Love the car, probably as good as it was new. Issue, during routine maintenance on 1500 mileage motor I rebuild from ground up, noticed crankshaft move forward when clutch applied an amount your can easily see. My question, why would this be happening and what is the cure. Car runs flawlessly and is not just a cosmetic redo. Engine is babiit and bored 80 over. No leaks beyond normal. Worry are just drive and enjoy.
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Old 08-09-2020, 09:16 PM   #2
Bob C
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Default Re: crank shaft movement

First guess is thrust on rear main is worn or was not set correctly when
bearings were done.
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Old 08-09-2020, 09:44 PM   #3
40 Deluxe
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Default Re: crank shaft movement

Measure the end play with a dial indicator to see exactly what the end play is. Then decide what is needed.
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Old 08-10-2020, 04:18 PM   #4
Chuck Sea/Tac
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Default Re: crank shaft movement

There is a bronze thrust bearing that’s available thru the vendors when your engine is good, but have too much thrust. I personally wouldn’t want
more then 5 or 5 thousandths, but I believe it specs to 7 or 8.
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Old 08-10-2020, 04:55 PM   #5
TMarsh
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Default Re: crank shaft movement

How big a deal to change to bronze thrust bearing on my engine, it seems awesome in all respects and I just hate to monkey it up. I want to just enjoy it but do not want to damage it. Daily driver but awesome car.
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Old 08-10-2020, 05:12 PM   #6
David R.
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Both the worn out engines I just tore down had about .010- .012”
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Old 08-10-2020, 05:43 PM   #7
MAG
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Default Re: crank shaft movement

The part Post 4 is referring to is:
Brass Replacement Rear Main With Thrust Surface . Bratton's PN 8949.
It works very well. We just set one up with.002 clearance. No oil leaks yet.
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Old 08-11-2020, 10:51 AM   #8
katy
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Default Re: crank shaft movement

The bronze thrust cannot be installed w/the engine in the car unless all of the thrust babbit of the block portion of the rear main is missing or removed.
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Old 08-28-2020, 09:19 PM   #9
callcoy
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Default Re: crank shaft movement

Just did two engines with brass replacement for the factory zink/alum component. These do not always take all of the play out fore - aft, in my cases it didn't. Antique Engine Rebuilders makes the brass thrust and they also a much smaller brass haft ring about 1/4" thick that can be machined into front side of the rear main cap. The cap has to be removed and your can send it into Rich to have him machine it for you.

Yes you have to pull the engine to install both of these rings and you have to fit the smaller half ring, this procedure is an art not a simple drop in thing, it requires careful fitting. The smaller half ring has to be hand reduced in thickness, checked with a mike, then, sanded down and checked until you reach the desired clearance This brass thrust surfaces are so much superior and stronger than babbit and will last much longer. You should ask around and see if you can locate someone who can handle this this for you.
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