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#841552 03/01/21 7:55 pm
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1972 OIF A65L with a strange issue.

If you ride this bike 7-10 miles all the engine oil exits the breather. In other words it oil wet sumps and all the engine oil ends up being dumped. Bike has had the oil pumped swapped and the result is the same. Oil feed and return system is clear and seems to be in good working order. Gauges have been applied and the correct pressures and vacuums are present.

New owner (one week) has no experience to share, but has told us that the engine had recently been "rebuilt".

Our Theory: We highly suspect that a novice engine builder left out the breather timing disk, and without the disk that the oil is free to leave the engine. BUT in order to test this theory we'd need to pull the engine out of the frame and all the way apart, which is obviously a HUGE step just to check our theory.

So we're looking for someone who has experienced this symptom before. Do you know anyone who left the breather valve out of an A65 and what was the result ??

Thanks in advance for any help. thumbsup


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Do you have a magnetic drain plug fitted to the sump? If this is too powerful and or placed under the scavenge pipe this is known to be enough to stop return to the pipe and then blow everything out of the breather.


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If it were the same uncertainty on a Triumph, you would try lung pressure up the outlet pipe, while slowly turning the engine. If the breather disc is correctly installed, it will be easy to blow while the pistons are descending ATDC and impossible to blow during their ascent to TDC (turning the engine in its usual direction using the back wheel in top gear say).

I would think that would apply to the similar breather disc set up on an A65?

If it blows easily at all engine positions, that will strongly support your suspicion.

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You could maybe listen for the operation of the timed breather, take out the spark plugs , put a pipe down to the gearbox sprocket area, with one person kicking the bike over slowly, listen ( ear to the other end of the pipe) for the operation of the timed breather , it should huff as the pistons move towards BDC, if the noise is continuous then the disc valve isnt working.

The pipe may not be necessary I can hear mine huffing without it.


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Thanks for all the tips !!

We were able to pressurize the timing chest with air, then listen to the breather output. It does seem to switch between open and closed as the crank is rotated. So we are ruling out the breather valve theory.

I will pass along the information about the sump cover. That is our next area of investigation.


Thanks again for the ideas.


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The next thing I would check is the suction leg of the return half of the oil pump. Remove the sump plate, attach a short hose to the suction stub, put the other end into a jar of oil, run the motor and see if the pump sucks the oil from the jar.
its not unknown for suction leg to be loose enough to draw air where it is pressed into the cases, if that is the case it will fail to lift oil.

There is a non return "foot" valve in the end of the suction leg, the ball in this should be free and clean, if it fails then the pump will take longer to prime. This valve only holds back a small quantity of oil, that which is contained in the return line. on engine start up , oil should be observed returning to the tank just below the filler cap. If this isnt happening then the fault lies somewhere in the return pump/ pipework.
To expand further on the loose suction leg scenario, at rest the return line empties into the sump and the pump return side loses its prime. On start up the sump fills with oil from the feed pump until the level is high enough to seal the loose leg, at this level the crank is deep in oil and lots will be expelled through the breather. Observing in the filler cap no oil will be seen returning for a few minutes.At the same time oil will be spewing from the breather.

The other non return valve is on the feed side of the pump, this should stop the oil from draining to the tank to the sump, this is leaky usually.If the bike is unused for weeks / months then the sump will fill with oil.

A fairly common scenario goes like this.
new owner checks oil level in spine when cold, oil has leaked into the sump while sitting, new owner doesnt know this and tops oil up in the spine / tank. Goes for a run, oil spews out the breather. Make sure its not just new owner syndrome.

Last edited by gavin eisler; 03/04/21 3:10 pm.

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How did they check the return flow? Just look in the spine for something?
Maybe they left out the split pin in the head and more is returning through the rocker feed than should be.

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All excellent suggestions. Thank you.


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Just stumbled on this wet sumping tech article at JRC site.

Triumph, not BSA.

Lots of other good tech there too!

https://jrcengineering.com/technical-support/wet-sumping-problems/

Last edited by Nick H; 03/05/21 1:19 am.

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Originally Posted by Nick H
Just stumbled on this wet sumping tech article at JRC site.

Thank you for the very thoughtful link. I don't want to seem unappreciative. However, the BSA uses a gear pump that presents a whole set of different issues from the Triumph's piston plunger pump. Whereas the Triumph is more likely to oil wet sump going down the road, the BSA is more likely to oil wet sump only during long storage.

It's quite common for Triumphs to loose oil return ability due to small bits of trash in the pump's check valve. The gears in the BSA pump will pass that type trash right on through. So it's completely opposite.... which is the basis for all the head scratching.

All the best. thumbsup


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I had an issue with an A65 exactly the same,wet sump in whilst running,l checked most things including stopping the engine and measuring the oil content in the crank case which was in excess of 250 cc,depending how long the engine ran
I eventually found that the after market sump plate was so close to the pickup return pipe and causing a massive flow restriction.
I remove about 3 or 4 mm from the pickup pipe area on the sump plate and this solved the problem, l had considered fitting a thick sandwich plate but the machining operation did the trick for me.
This is worth looking at
Regards Ken

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We had a customer experience a similar situation on a 1968 Triumph 650 recently. Upon start-up, everything was fine until about 20-30 seconds after running. Oil started to belch out of the breather tube. An immediate check of crankcase oil contents revealed about 5 or 6 ounces drained from the bottom end. 100cc was then replenished through the timing hole aperture. The engine was started again, and sure enough, excessive oil blowing through the breather outlet hose again. The curious thing was that there was some oil returning to the oil tank, although a lower volume. After a lot of head-scratching and cussing, it was revealed the customer had replaced the original sump filter/drain plug with a shiny aftermarket plug complete with a magnetic insert. The scavenging pick-up tube was very close to the magnetic insert, effectively reducing the oil evacuation, and causing the crankcase to fill with oil. This was proven when the customer reverted back to the original filter/drain plug assembly.
-Dave


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I had the same problem. Check ball in return pipe sticking due to magnetic drain plug directly underneath it on cheapo aftermarket sump plate. I switched to one from SRM that has the drain plug in the back of the plate away from the return pipe. No more problems.

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OR, just cut a bit off the magnet...............

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Originally Posted by NickL
OR, just cut a bit off the magnet...............

That’s what I was thinking.


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68’ A65 Lightning “clubman”
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Quote
Our Theory: We highly suspect that a novice engine builder left out the breather timing disk, and without the disk that the oil is free to leave the engine. BUT in order to test this theory we'd need to pull the engine out of the frame and all the way apart, which is obviously a HUGE step just to check our theory

isnt the A65 camshaft fully drilled from breather disc side to gear side ?
so you could take the timing side cover off and have a peak down the center hole
with a
borescope . .. or use some plastic tubing to blow air from the cam gear end
... or back up the breather exit ?

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The anti drain back ball in the sump pickup can even stick from being left over winter, the fix is to probe with a thin rod it to lift it off its seat. It can also get gummed up with excess gasket goo, the fix is clean it all out. Recent rebuild suggests excess gasket goo is likely.

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Ok, first off I know little of the A65, but is the pickup in the sump the same or similar as the unit singles?
I had a similar issue, all was good a low speed but wet sumped during a ride and or higher revs. Problem was the pickup valve. The little pin that the ball bearing is sucked up against in the valve was broken so that when the oil flow was high the ball was pulled up and sealed (ish) the oil way. Perfect when the motor was not running. Took a bit of finding.

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I had the soldered end of the oil pick up line fall off. The pick up line goes straight up and there is a 90 degree corner. The horizontal end of the tube at the corner has a cap on it. After I first started the bike after rebuilding it, I opened the sump to make sure everything was ok, and the cap was sitting on the sump screen. Took me a little while to figure out what it was. You can get the pickup tube out and put it back in with the engine in place, but it is PITA.

Ed from NJ


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