1971 Trophy 500 Oil Issue

[Bob Elwin]

I rebored my Trophy 500, stripped the motor down and gave it a general reconditioning.
It has good compressions (approx. 160 psi) and now runs well. It has a new oil pump and seals throughout. The oil return has good flow to the oil tank. It has the later type of breather system without a crankcase seal on the left side and the breather from the primary chaincase.
However, it has a problem on standing for any length of time. After starting, it coughs out smoke from both exhausts for several minutes and then clears up. By the time it is warm the exhausts are both clear. The smoke is way more than you would expect from valve guide wear.
If I drain the residual oil from the crankcase before starting, there is no smoke. The amount of oil draining from the lower case is 160 -180 ml. Does this seem excessive?
I am guessing there is sufficient oil in the case that it must be contacting the crankshaft and being flung up into the bores and overcoming the rings.
Has anyone encountered this before and have any suggestions as to what might be the cause and/or cure for this?
Cheers, Bob Elwin

 

[hemibee]

Sorry, I don't have the experience to help. Grandpaul or one of the others should be along to help.

 

[grandpaul]

You may be getting some wet sumping. Even a new oil pump can get a bit of grit stuck in one of the ball seats.

Welcome to the forum, Bob!

 

[Rocky]

Wet sumping would be my guess too.
180 ml doesn't seem like an excessive amount of oil in the crankcase, but by your own trial and error of draining it and there's no smoke, that's the problem.
Normally, oil can't drain past the plunger oil pump, but as GP said, a bit of grit could be holding a ball of its seat allowing the oil to seep by over time.
It may be a PITA, but pulling the pump off and cleaning it is worth the trouble.
The only other choices are to put up with it or drain the sump each time.

Suggestion:
The next time you ride the bike check the oil level when you park it and note the level after the oil has had some time to cool down.
The next time you ride it after that check the oil level before you start the engine and compare it.
If the oil level has dropped markedly, then you know it can only be in the crankcase.