A bit of background first. I paid to have this bike restored. The restorer has already rebuilt the engine at his expense twice since he completed the original restoration. At the weekend I started the engine for the first time after getting it back from the most recent rebuild. Oil return to the tank was immediate. I adjusted the carb settings and then took the bike for a test ride. I stopped for fuel after 4 miles and checked the bike over for leaks and anything shaking loose. All was ok, there were no leaks and the engine oil tank level had not changed, oil return was still good. I set off again, and after nearly 2 miles I almost lost the back end of the bike entering a very slow corner and pulled over. There was engine oil all over the rear tyre and a long trail back up the road, the oil tank level was now much lower. Back home I drained 1.2 litres of oil from the sump. Oil had clearly been blown from the breather.
Has anyone got a clue as to why the oil pump would continue to supply oil to the engine but stop returning it to the tank, or have any idea what else could cause this to happen? The bike is fitted with a return line filter.
If you take the sump plate off you will see a pipe sticking down through the filter this is the scavenge pipe it sucks the oil from the sump and returns it to the tank inside that pipe is a ball and if it is stuck then it cannot return the oil so it builds up in the sump and comes out the breather. Check to see that the ball is free to move.
my first question would be WHY? had he rebuilt it for the third time? what happened the first two times??
was it an original rebuild or a mechanical failure rebuild first time around?
presumably a professional rebuilder?
possibly excessive gasket cement blocking something. presumably if the oil was not returning to the tank the rockers have not been fed either?
Another possibility could be the oil pump itself becoming loose and sucking in air....
If it's not a stuck ball in the pickup pipe I guess it could be a blockage between the pickup and the oil pump itself - a blockage after the pump i.e. between pump and tank would likely result in a leakage around the return pipe due to the pressure.
Let us know if you want to diagnose the problem yourself - and we can post some more suggestions - or take it back to your builder again - but not sure if that's the best course of action!!
--Bernie
Quote from: berniej on 27 Aug, 2019, 16:07
- or take it back to your builder again - but not sure if that's the best course of action!!
--Bernie
I have had a couple of customers who took their engines to other shops but after failure would not return them, one a 125 that had left something floating below the crank,, top end went again same reason so I got them an engine from a breakers to keep cost down, another took his square four cases to a "shot blaster" to clean them up..totally wrecked the outsides and made the bores oversize for the bearings, new cases needed. other bike shop locally had a engine for 12 months before finding the cause of failure, they had asked the other bike shops in the area during the term..
The feed and return sections of the pump are separate so one part can fail whilst the other works.
The below BSA service sheet is worth reading.
Thanks for the replies. The first rebuild was due to the engine not having been started since the 1960's, the second rebuild was due to the rocker oil feed hose detaching during a test ride before he handed the bike to me. He stopped when the engine started knocking. He simply refitted the pipe, topped the oil up and noted that the engine was then quieter. I got about 5 miles before the engine started knocking. He hadn't told we what had happened. The third failure was due to him assembling the pressure relief valve backwards, i.e, seat, spring, ball, cap. Hard to believe I know.
Thanks for the suggestions, I'll drop the sump to start with and then probably have a look at the pump. I wont be able to do this until next week now. I'll let you know what I find.
Well I finally got around to checking out this problem. More first class incompetence from the engine rebuilder. He had fitted the SRM sump strainer upside down meaning that the scavenge pipe was pushed hard into the gauze rather than protruding through the formed hole in the strainer. Some fragments of cloth fibre worked there way down through the hole in the gauze and blocked the scavenge pipe. New strainer fitted and all now seems to be ok with a good oil return flow. Thanks for your help.
Back in the eighties, I had a customers bike that was wet sumping so did all the usual checks and found nothing wrong whatsoever. Decided to take the pump off and check the return side and blow out all oil passages from the pick up pipe to the tank but nothing seemed blocked.
Put it all back together and went on a road test. Nothing wrong, oil returning nicely, no leaks, so let the customer have it back. A week or so later, he is back, said he went on a run of about forty or fifty miles and the level had dropped. Sure enough, when I checked it, the crankcases were full.
After a bit of thinking time, I took the seat off to check the tank breather wasn't blocked only to find the owner had put a rubber pipe onto it held with a jubilee clip and then I find the pipe has been trapped further down, hence why every time he took the oil tank cap off, oil would return to the tank as he was releasing the pressure.
Yes sir, its the nut behind the bars!
Mel
customers, the bane of our life!!
I just finished restoring a 1969 A50 and am in the break in stage.
Bike rides and runs great.
Unfortunately I can't ride every day so it sometimes ends up sitting for 7-10 days.
During that time oil migrates to the sump.
Recently I drained the sump, after about a 10 day sit.
Out came about 1 pint.
I know oil sumping seems to be a fact of life with BSA's, but is a pint excessive enough to warrant tearing into the engine?
or
Should I just drain and ride?
Thanks.
1 pint is quite excessive for 10 days. If you left it for say 2 months, then the whole tank will have drained into the crankcases. Most likely problem is the check valve behind the oil pump and is easy to fix.
Take the outer and inner timing covers off and remove the oil pump. Behind the pump you will see a ball and spring. This fits over the feed outlet in the pump (noticeable as it has a small chamfer in the hole to enable the ball to be seated). The spring fits into a larger hole in the crankcase. Fit a new ball and spring but before that re-seat the ball with a sharp tap with a hammer using another ball (in case you create a flat on it with the hammer).
When you purchase a new spring, you will probably find the old one is much shorter as they do compress, losing their force over a period of time.
Always remember to fit a new gasket under the pump. That should do the trick.
Chris
Just to be clear, am I seating this ball into the oil pump or the engine case?
Many thanks. :)
Into the pump. The spring fits into the engine crankcase and holds the spring against the outlet of the pump.
Hope this clarifies
Chris
Got it.
Thanks
;D