Triumph 750 Bonneville wet sumpingII

[kevinlincs]

Hello,I have recently been restoring a 750 Triumph,the trouble is it is wet sumping while running.It has been rebored ,new oil pumps,new tubes,oil and airways have been checked, cylinder head with new valve guides ;and checked throughly for leaks.It has  a new 1976 crankcase fitted that has never been used before.It burns oil in the left cylinder and the crankcase fills up with oil,too much oil going in and not enough coming out,but the oil is competently returning to  the oil well.Has anyone had this problem before and is there a cure.

[joe90]

There is probably far better advice from experts here and I'm sure you'll get other suggestions soon, but for starters - did you check the scavenge pipe before putting the crankcases together? if this is damaged or leaking then it wont draw its designed quantity of oil from the sump.  I'm not sure how you can check this with the engine assembled but I am guessing you could push a tube on the filter end, block the oil pump drilling and see if it holds pressure.  You say oil is returning to the oil tank and the pump is new, otherwise I would suspect the pump - weak spring or ball not seating correctly.  Don't understand why the left hand cylinder is burning oil if you have rebored?  Could you have snapped a ring on assembly?  Might be an idea to add a comment on how many miles you have covered since the rebuild.

[L.A.B.]

First check I would make would be the scavenge side pump ball valve. And that all the holes in the pump gasket have been punched out properly, as sometimes they aren't and that there are no air leaks at the gasket?
As Joe90 said, if any air is being drawn in between the pickup and the pump then the scavenge won't work properly.

Are you sure all the return pipework is correctly fitted with nothing restricting the flow?

[pogotri500]

Hi there, This problem you describe is a carbon copy of the trouble I had on my 650 that  nearly drove me crazy for three weeks. I had bought a bottom end that I was assured had been totally reworked so build up  and away we go. Ohhhh Nooo  within a couple of minutes it was smoking, wet sumping, getting all hot and bothered etc. To cut a long story short my problem turned out to be the oil pressure releif valve. For reason unknown someone had decided to shorten the spring thus allowing the valve to open too early putting more oil into the crankcase  than the return could handle.New spring fitted, problem sorted! Hope this helps. Cheers, Dave