Strange symptom of overfilling oil tank

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Sarre
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Strange symptom of overfilling oil tank

#1

Post by Sarre »

Was riding with another pan owner this weekend, he has a '52 FL, so similar engine as mine, and after ±25miles his engine stopped running at a traffic light so we were forced pulled over.

After a few moments he started the bike and it fired right up, till next traffic light, it died again.

So we discussed what he did last and what he changed, my first idea was his gastank was not venting properly thus we tried it and no next traffic light he stranded again. This was getting annoying.

So we pulled the plugs, a bit dark but not really something that would explain the cause, bike was getting fuel and spark. So finally he said that he filled the oil tank that morning, horsehoetank with outside filter. So we check the current level, overfull. Apparently his bike sumps.

We drained the excess oil and the issue was gone, no issue the second part of the ride, ±50miles.

Now I am trying to wrap my head around what would be the cause of the engine dying out at lower rpms. Of course the vent line to the tank was getting oil and thus the crankcases might over-pressurize, which causes resistance to the pistons? But the crankcase should still be vented through the breather tube or not? And the oil should be puked out through the breather tube in his primary, instead of all collecting in the oil tank, or not?
nifty
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Re: Strange symptom of overfilling oil tank

#2

Post by nifty »

Sarre
Yes it should have puked into primary.
Check for free passage between primary & gearcase.
Remove primary inspection cover & oil tank cap, wrap a rag around air nozzle, apply low air pressure to oil tank, air should pass down vent line to gearcase and out to primary, you or your buddy should hear air at inspection hole.
If that is ok
All I can think of is with no air space in oil tank, when crankcase breather opens to eject oil & air from flywheel cavity, the increased pressure was enough to act on undersides of pistons and stall engine at idle. Wouldn't have thought it possible, but maybe?
Nifty
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