Engine oil blow out

[Craigy]

Hi Guys,
‘52 A10 plunger lost all engine oil today while I was riding. Luckily I noticed before anything went bang….sitting at road junction and nearly lost it when I pulled out, went straight through a large puddle of oil.
I’ve got the bike home, quick clean up and put oil in tank to see where the leak came from but nothing leaking.
Any ideas on what, where, why?
I did notice a short pipe located rear, bottom of the tank but assume this is a breather. It might have had flex pipe on but not now.
Any help would be appreciated

[limeyrob]

How hot was it?  There is a breather under the tank, its acts like an overflow. But to get oil out of it the oil has to get very hot so the level goes high or it boils.  I think boiling is very unlikely, I had it happen on a rotavator and the mess is incredible but the engine has to be so hot.
Any chance its a loose union on the return or rocker feed?
Could it have come out the engine breather?  If so check the sump gauze.

[CheeserBeezer]

Sounds like wet sumping, pump not scavenging?

[Craigy]

Air temp was about 23c, bike had had a clear run for about 30 miles, no traffic.
All oil seemed to be around the oil tank not the engine. It’s not long since I changed oil and cleaned filter, about 150 miles ago.
How would wet dumping cause this? Oil level was good when I set off so if any oil in sump it would have been minimal, also would that burn off during ride?
@limeyrob, as you know I’m new to this, so where do I find the engine breather?
Cheers for the help lads

[trevinoz]

Could be a sticky ball in the scavenge pick-up and the oil blowing out of the crankcase breather.

[limeyrob]

Its a long time since I had a plunger Flash apart, my recent work has been on a SA. If its the same then the engine/crankcase breather is on the rear of the crankcase aimed at the final drive sprocket.
You really need to work out whether it came out he engine breather, oil tank breather / overflow (the tube under the oil tank), one of the oil pipes or unions or somewhere else such as the rocker supply.
I'd give it a good clean and then let it idle for a while and see if there are any obvious leaks form the oil pipes as a start.

[Craigy]

Cheers. Plan is to check the filter, then refill and kick it over to see what happens. I’ll let you know

[Craigy]

Might be from here. Not sure if it had a flexi pipe on it beforehand

[limeyrob]

OK that's the oil tank overflow / breather.  Could be it was just over filled.  If it had been standing and oil had drained into the sump then that would have been returned and raise the level above the overflow, also when the oil get hot and aerated the volume increase quite a bit.  Have a look on some pictures (hand book etc) and see where the level line is.
You can put a tube on the overflow and route it to the chain so its not in line with the rear tyre.

[Swarfcut]

 I'd reckon Trev is on the case here. A fault in the scavenge side of the system results in oil accumulating in the sump, then exiting the breather. Stationary, you get a neat pool of oil, on the move, plenty of blue exhaust smoke, oil all over the chain, rear wheel and you! Standard Plunger breather exit is a small bore pipe from the back of the engine just above the gearbox sprocket, down to a crankcase stud adjacent to the sump plate. Over time, many have been discarded, leaving just a hole (as on later S/A bikes) to lubricate the chain.

 Causes range from simply overfilling, that pesky sump ball valve, sump gauze, pick up pipe fault, oil pump problems, oil tank obstruction on the return line.

 All covered extensively in previous Forum Posts, a search of "Scavenge" in the Engine Section of the Forum is a good place to start.

 Swarfy.

[Craigy]

Thanks guys,

As helpful as ever.

I was back in the uk for a few weeks and some oil had drained into the sump, but I drained that and topped up the tank back to the line.

I had been out on the bike twice before yesterday and no problem, putting in 100+ miles.

I think I may have found the problem, the oil filter was slightly creased - it was like that when I changed the oil after first 500 mile since restoration, so didn’t see too much of a problem. On closer inspection, it doesn’t have a ‘cap’ on the end of it and there seems to be a load of crud deep inside which may have caused a blockage.

I’ve ordered a new one - takes a couple of week to arrive here. So hopefully that’ll sort it

[limeyrob]

Sounds good.  Its a big step forward when you find a probable cause. I hate faults where there's nothing to find that's obviously wrong.

[Swarfcut]

 Craigy.... If that filter is in the oil tank, that is yet another system in its own right. That is on the feed side of the lubrication system. Your problem is to do with the return to the tank in my estimation, rather than a simple oil leak. Lucky you found this potential source of more trouble.

 When working as it should, there will be a good strong continuous flow of oil back into the tank, visible when the tank cap is removed. As a habit, once the engine is started, old hands take off the cap just to check all is well, a bit like a good luck charm.

 Look upon the lubrication system as two separate flows, the return having a greater pumping capacity than the feed side, hence a "dry sump" arrangement.

 Another recent thread to explore is titled "Baffled, Confused and Covered in Oil". Tells almost everything you need to know.

 Swarfy.

[Craigy]

That’s great info, cheers.

I’ll have a read of the other thread

[muskrat]

G'day Craigy.
Link to the topic Swarfy mentions. https://www.a7a10.net/forum/index.php?topic=14612.msg121892#msg121892
Cheers