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AMC 20T engine assembly issue

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AMC 20T engine assembly issue

Post  rob spence on Thu Nov 16, 2017 1:04 pm

Hello,
I'm back on to my 20T rebuild. I've replaced all 3 bearings and the 2 oilseals. The crankcases are bolted up and the steel spacers are fitted in the oilseals, but when I put the crank sproket on the shaft and tighten the large nut the whole crank is impossible to turn, when I take the sprocket off again the crank returns to rotating easily.
Any ideas?

rob spence

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Re: AMC 20T engine assembly issue

Post  rob spence on Thu Nov 16, 2017 1:49 pm

I've just put the magneto flywheel on the shaft and tightened the nut and the same is happening ...the crank is nearly impossible to turn.
So it has to be the seals...as once the crankshaft spacers are gripped by tightening the end of crank nuts they stop spinning loosely on the crank and spin in the seals instead. I can't really believe that new seals would be this tight, I did grease them before assembly. Wonder if I have the wrong seals.?

rob spence

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Re: AMC 20T engine assembly issue

Post  rob spence on Thu Nov 16, 2017 2:19 pm

By the way the seals are of the double lip type...does this make a difference?

rob spence

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Re: AMC 20T engine assembly issue

Post  rob spence on Thu Nov 16, 2017 2:34 pm

I've just measured the crankshaft spacers which are 1 and 1/8th inch outside diameter...the oil seal internal diameter is 1 inch. Are they the wrong seals?

rob spence

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Re: AMC 20T engine assembly issue

Post  Cruiser79 on Fri Nov 17, 2017 1:07 am

Hi Rob,
Pic attached of old stock Payen crank and gear box seals for reference, they're buried somewhere in my shed but did find a used crank seal to measure. OD 1.747" ID 1.124" x .369" deep. New dimensions no doubt slightly different but not by much. Payen part number was B359 which was superseded by NA085. Give those dimensions to any bearing supplier and they'll match something to them. No harm to bring in the crank cases and the spacer sleeves which run in the seal for them to measure

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Crank

Post  kerabo on Fri Nov 17, 2017 8:24 am

When you slacken the nut and rotate do the seal runners stay still?
I have used double lip seals and fitting the seal runners was difficult but once in they were fine. You have to be sure you don't turn the lip inside out. Plenty of lube on them .
Also the seal runners are a fraction different in length but that shouldn't matter. I think they have a slight lead on one end but could be wrong on that.
Have you fitted the spacer between the bearings?
Ken
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Re: AMC 20T engine assembly issue

Post  rob spence on Fri Nov 17, 2017 10:59 am

Hello,
Ken, all is as it should be on the engine mechanicals...the only thing it can be is the internal diameter of the oil seals. The spacers are 1 1/8 inch external diameter and the internal diameter of the new seal is 1 inch. Cruiser79s post above seems to explain the problem as he measures the internal diameter of an original seal at 1 1/8 inch. I'll track some down and report on progress.

rob spence

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Engine

Post  kerabo on Fri Nov 17, 2017 11:34 am

Sounds about right.
Good luck

Ken
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Re: AMC 20T engine assembly issue

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