No oil return after rebuild

Gino Rondelli · Sep 23, 2011

I was helping a pal today to do the valve timing on a newly put together 750 Commando ( He aquired it as a non runner and no wonder, the valve timing was a mile out), It started no problem but smoked like a 2 stroke, after the usual wait for the oil return, it didn't. Seems the bike is sucking oil into the cases but not returning.
If I pull the return hose going to the filter off the engine and turn the engine over manually there is some oil exhaled (but not enough IMHO) I can blow up the pipe and it is clear through the filter to the oil tank. All the hoses are on the right way.
Any ideas guy's (and girls) before I start taking it apart again

rx7171 · Sep 23, 2011

If you have check valve in supply line from tank it may be installed backwards.
What caused initial non-runner status of bike prior to rebuild? Anything related to lost of oil pressure due to failed pump maybe.

rx7171 · Sep 23, 2011

Gino Rondelli said:
I was helping a pal today to do the valve timing on a newly put together 750 Commando ( He aquired it as a non runner and no wonder, the valve timing was a mile out), It started no problem but smoked like a 2 stroke, after the usual wait for the oil return, it didn't. Seems the bike is sucking oil into the cases but not returning.
If I pull the return hose going to the filter off the engine and turn the engine over manually there is some oil exhaled (but not enough IMHO) I can blow up the pipe and it is clear through the filter to the oil tank. All the hoses are on the right way.
Any ideas guy's (and girls) before I start taking it apart again

You mention oil sucked into engine. So you see il going down in tank and figure smoking is caused by wet sumping?

The type of oil line check valve I have has a ball with spring that requires some initial suction to pull the ball off its seat.
Maybe froze in place.
I primed my pump and line prior to first startup to be sure adequate suction achieved.
Any chance your pump is not getting enough suction to pull valve open?
Maybe blowing on line from tank to see if valve will open, although if pump full of oil may not be able to blow thorough. May require taking line off line from motor so you can blow through.

Hobot · Sep 23, 2011

A wet sumped Combat will jet oil via breather with in seconds of starting but oil pump takes like 20-30 seconds to add its spittle like return flow. A new start up w/o crank full can take about a minute to show up at tank. Drain sump and remove ball valve for another test of oil flowing. Only other place to suspect is the oil pump nipple crush sealing as the nipple and TS cover gasket must be matched set.

cash · Sep 23, 2011

Gino,
Oil pump knackered or gasket blew ( sucking air) , sump filter or return drilling blocked.

Best of luck.

Cash

ILLF8ED · Sep 23, 2011

Gino Rondelli said:
I was helping a pal today to do the valve timing on a newly put together 750 Commando ( He aquired it as a non runner and no wonder, the valve timing was a mile out), It started no problem but smoked like a 2 stroke, after the usual wait for the oil return, it didn't. Seems the bike is sucking oil into the cases but not returning.
If I pull the return hose going to the filter off the engine and turn the engine over manually there is some oil exhaled (but not enough IMHO) I can blow up the pipe and it is clear through the filter to the oil tank. All the hoses are on the right way.
Any ideas guy's (and girls) before I start taking it apart again

Hi Gino

How's the Tay Valley branch? Have seen your name in the Roadholder.
If the return isn't plugged at the oil tank side...any chance it's plugged at the crank sump? Blow back through the engine to see if there's any constriction.

dave M · Sep 24, 2011

A friend had the same problem and I found, on taking the oil pump off, that the scavenge gallery was blocked by gasket sealant applied too thickly when the cases were put together. I managed to unblock the hole and fish the globule out through the oil drain plug.

Gino Rondelli · Sep 25, 2011

Thanks guys, he stripped the timing side again yesterday (although never tried to blow through the oil way) and all seemed to be in order, no anti sump valve fitted. This week I'll get him to strip it again and I'll check all the return oilways are clear. It appears the oil pressure release valve had been dicked about with as well.
(Tay Valley Branch doing well thanks)

cash · Sep 25, 2011

If the pump gasket is put on the wrong way round it blocks one of the ports, the oil pressure usually blows a disc out of the gasket that then flows along with the oil, but for how long :?: .

Cash

rmullett · Sep 25, 2011

Take off the feed line and prime the pump... you will see the oil go down just by kicking over ( take the plugs out ) . The rule for oils lines are Feed forward ( outer pipe on engine ) and Return behind. I have never had a pump fail, weak yes but never fail completely.

rpatton · Sep 25, 2011

dave M said:
A friend had the same problem and I found, on taking the oil pump off, that the scavenge gallery was blocked by gasket sealant applied too thickly when the cases were put together. I managed to unblock the hole and fish the globule out through the oil drain plug.

I like this possibility, especially if by 'newly put together' that entailed splitting and reassembling the cases by your friend or the DPO.

No oil return after rebuild

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