Significant oil out the breather of a 1969 Triumph T120 Bonneville

[stevestriumph]

Hello again from across the pond. I recently acquired a 1969 Triumph T120 Bonneville which I was told by the seller and builder that the bike had a "complete rebuild". I have no reason to believe this fact is not true but everyone's interpretation of a "rebuild" is different. The question before the house, or in this case the Parliament, is that I am having significant oil coming out of the crank case breather, leaving small puddles right behind the back tire every time it is started and run. The seller/builder says if the bike sat too long this can happen and after it is "broken in", it should stop. I have had a number of Triumph twins and never had this problem. Can anyone give me advice as to the problem and how to address it? Thanks in advance, Steve

[R]

Its pretty tough to diagnose this without seeing the bike in question, we'd comment to begin with !

Part of an answer to this is next time before you go for a ride,
drain the sump and see how much oil comes out.
If it is much more than the traditional half a cupful or thereabouts,
you know it is 'sumping' - oil is draining into the sump.
Before you go for that ride, tip at least a half cupful back, into one of the rocker covers,
and leave it a moment, so the sump isn't too dry at startup.

This partly tests where oil draindown while standing is the problem,
or whether ring blowby while riding may be the problem.
It doesn't really determine if the oil return side of things is all correct and shipshape though.

The rings should seat better with some miles, as the seller says.
(Provided they were all fitted the correct way up).
Did he say though that the oil pump was new ?
If not, it sounds as though it could need more attention. ?
hopethishelps.

[stevestriumph]

Thanks for the info. Oil pump is the original as I was told. Could the problem also be related to the pump? That would be an easy change to fix. Can the pump function be tested without taking it out? There is a good return to the oil tank. Is the oil coming out of the breather originating in the sump? If it is "sumping" would that be due to the pump failing?

[R]

Without being clairvoyant, we can't see what is happening with your pump. !

Drain the oil out of the sump straight after a ride, and measure how much there is.
Drain the oil out of the sump again after its been standing say a week, and measure how much.

If a significant amount drained down during the week, its likely to be in your pump.
If there is a lot there straight after a ride, it might be a bit more involved.

If the oil is still nice and clean, add it back into your oil tank.
Better if some goes back into the sump too, if you are about to ride it.
Don't forget to replace the drain plug, each time, without over tightening it !

Someone who knows these engines well probably also needs to comment on how the breather functions,  in case it has been incorrectly assembled or parts left out.

[Rex]

Triumph's double plunger pump is excellent for holding back the oil ie not draining down, but one thing I've seen on these engines is a crack in the crankcase scavenge pipe, leading to poor scavenging and too much oil in the base of the engine when running. The old check for this is a rubber tube on the end of the scavenge pipe in the "sump", your finger on the scavenge pipe in the oil tank and suck on the rubber tube. Vacuum should hold, but if it doesn't then it's an engine strip to fix.

Rings (in my experience) seat/seal quickly and there is no "break in period" these days, but of they haven't sealed after a few runs they somethings wrong and they're never going to, so that would be a top-end strip.
There's nothing you could misassemble on this breather to cause oil to be spat out like this.

[mini-me]

My experience of modern day "rebuilders" would  lead me to surmise there are no bloody rings in it

thats looking on the bright side.

But its off with the top if you ask me, sound like too much blowback past pistons, like Rex says Triumphs do not usually wet sump.
Could be a bad bore, too much ring gap, even wrong size pistons[don't laugh,seen it].

If you find the slightest thing wrong or cocked up, Iadvise taking the whole lot down and start over again.

but everyone's interpretation of a "rebuild" is different.

you hit the nail on the head.

Good luck, these Triumphs are not a hard engine to work on, I used to be able,when younger, to get the engine in bits before lunch and have it reassembled and running by supper.

[stevestriumph]

So is there a test I can do to determine if in fact it is a ring issue? Will a straight compression test tell me if ring gap is too large?

[bollard]

 if oil is coming out of a breather then either the oil level is higher than it should be or compression is getting past the rings allowing the crankcase to become pressurised.
 first step is to check oil level, if OK then a compression test imo. Bit puzzled though as there is usually smoke in the exhaust in the latter case.