No return oil

I just installed a Power Arc ignition in my bike after also rebuilding the transmission. It started on the 2nd kick and ran great. I started hearing the breather tube in the oil tank so I looked inside. The breather line was gushing oil at a terrific rate. I checked the return oil and there was none coming out of the engine. It is a good thing I have one of Jim's reed valve breathers.

The bike is a '72 Combat and I had to take the breather off to remove the transmission. The hole in the block stayed uncovered for a few days in my garage. The oil pressure is good. I can't think of anything else that would stop the return oil except some trash in the intake. Any ideas? (The pump has under 7000 miles on it.

Sounds like an obstruction at the return line, scavenging side of the oil pump. The oil had to go out somewhere, so up the breather. Unlikely oil pump damage on the scavenging side only and you said you are getting preasure feed so that side is working. I'd pull the return oil pipe and look for a plug then check the other direction into the engine. Just blow on these pipes or use low pressure compressed air to see if obstructed.

The scavenge pump likely just needs more time to prime and start returning oil. You can run it without fear of too much oil in the cases with my breather in place. It will keep the oil at a safe level in the cases even without a scavenge pump -not that this acceptable for the long term. Run it at 2500 rpm for a few minutes and see if it starts to pump.
You can also put your finger over the outlet from my breather for a few seconds which will cause the pressure to rise in the case and make the scavenge pump prime quickly. Jim

Jim,
I have been wanting to ask if that reed valve basically solves the Combat problem of pooling oil. Seems to me it makes the debate of machining cases and moving pickups moot.

Russ

rvich said:

Jim,
I have been wanting to ask if that reed valve basically solves the Combat problem of pooling oil. Seems to me it makes the debate of machining cases and moving pickups moot.

Russ

Click to expand...

I would still modify the combat cases as always. The breather may hide the problem but I would rather see the cases scavenged by the scavenge pump.

With the scavenge pickup at the front of the cases it is only picking up air when all the oil is being forced to the rear of the cases by crankshaft windage. That would leave all the oil returning through the breather which would not be good for breather efficiency.

As it is, my breather only returns oil when the bike is first started and when the engine is revved after running at low speed. When the engine is running slow the oil gathers at the front of the cases. [where the combat pickup is] but when you rev the engine the oil suddenly goes to the rear and my breather will evacuate the excess but the scavenge pump will remove the rest of the oil until it is well below the breather pickup. Jim

Thanks Jim. It turned out that you were right about the pump not priming. It is pumping fine now. I had checked the pressure side of the return for obstruction and found none. The "finger over the breather tube" trick worked to get the pump primed.

The reed valve breather works great and it gives a reassuring little chirp each time I shut her down. I took apart another oil pump I have on an Atlas block to see exactly how they are built. It all seems a little tiny to me and I am wondering if you plan to go into production on your high zoot oil pump. The Norton units seem pretty worry free but I'd like a little more pressure out of mine, especially when the system is hot.
Dan.

I have thought about building some pumps but they are far down on the priority list right now. Jim

The OEM pumps are mighty pricey, and seem to have a very high percentage of leakers after only moderate mileage.'

Seems to me a decent niche market, as a good replacement could fetch upwards of $300.