I'm smoking on the right too!

[Steverat]

Hi Steverat,

I think it must be a delivery side leak perhaps from the PRV, overwhelming the scavenge which pumps a strong stream back to the tank but without any bubbles in it.

As I said earlier this is most unlikely to happen due to the greater capacity of the return side of the pump
The only way its possible is if the combination of the delivery and rocker feed  is greater than the return capacity

When You go back to the bike, drain the sump before you run it again, then when it starts to smoke stop and drain the sump. measure the amount and report back.

You could try removing the rubber connection on the return line and add a temporary flexible tube from the engine return pipe  to the oil tank filler hole bypassing the return oil connection to the tank,
This will remove the restriction at the top of the standpipe (and the rocker feed) to see if this is the cause of a (maybe) problem caused by increased oil flow from the new pump

John

Will do John, I had thought about that. I suspect the rocker feed is not much - the restrictor hole in the rocker unrion bolts are really tiny, only 1/64". But oil is still getting up there, the rocker spindles were full of oil when I took their bolts out just now. As you say, the stand pipe orifice in the tank is a restrictor too.

[berger]

don't want to open a can o worms mine had good compression good luck with the eliminating of possibilities of the cause

[Steverat]

REPORT BACK

1. Left bike overnight with full oil tank. Timing cover and sump plate removed - little or no seepage once the surface oil had drained out of the motor. Less than 10ml over 15 hours.

2. Replaced covers, ran motor for about 1 minute during which time the white smoke started again. Removed sump plate - 150ml of oil came out.

3. Replaced covers again, ran motor with return hose replaced by a free-ended transparent plastic one. Return oil got about halfway up the hose, but the white smoke seemed to start immediately. Shut down after less than 1 minute. Sump plate removed - 100ml of oil had accumulated.

And oh by the way the hole in the top of the stand pipe in the oil tank is 7/64" diam.


Ideas please.

[Swarfcut]

Steve.. With the sump drained out it will usually take a few moments for the "new oil" to work its way down, ready for the scavenge side to start to work. This is when the return "gulps" as the pump sucks air and the small amount of oil in the pick up pipe. The scavenge side should have no problem pumping oil through your temporary hose, way above the top of the tank. Once primed it should come out like a miniature fire hose. A good steady flow is what you would expect almost immediately from a bike in regular use, on start up. Are we actually getting a good return within seconds of starting up on a cleaned out sump? Not what should happen, there should be a delay.

  If it only reached halfway up, was that the best it can do? Or did you shut it down in disgust?  Just hope SRM haven't put another set of feed gears in the return side of the pump! No that's impossible isn't it?

  We need to establish that feed and scavenge are balanced as designed, and that the oil level is maintained. If it is constantly falling that is the reason for the smoke. Too much going in, not enough coming out. If the level stays the same, the system is working fine, and the fault lies within the cylinder.

  The overnight drip test would indicate the pump and crankcase ball valve are OK, but there still maybe a major leak on the pressure side, downstream of the valve. Rather unlikely, but possible.

  The PRV is the next suspect.  Dismantle and check carefully, making sure the ball seating area is undamaged.

  Too thick a fibre washer between the inner and outer parts of the PRV will decrease the spring tension on the ball. You need a thin one, copper or aluminium.  The sealing washer crankcase to PRV thickness is not critical.

    I think you have an early engine, which has no oil feed to the cam trough. If the PRV is faulty, opening at low pressure, it will dump pressurised oil directly into the oil pump cavity, which will fill up and pass from there very quickly through the keyhole vent into the sump....a possible explanation for the rapid appearance of smoke.

 Swarfy.


 

[chaterlea25]

Hi Steverat,
There is probably oil after gathering in the exhaust causing the smoke?
+1 on Swarfies comments
Did you look in the cylinders for oil ?
Or in the exhaust ports to see if oil is coming down the guides?
With the sump drained  it would take a minute to get  oil return

John

[Steverat]

Steve.. With the sump drained out it will usually take a few moments for the "new oil" to work its way down, ready for the scavenge side to start to work. This is when the return "gulps" as the pump sucks air and the small amount of oil in the pick up pipe. The scavenge side should have no problem pumping oil through your temporary hose, way above the top of the tank. Once primed it should come out like a miniature fire hose. A good steady flow is what you would expect almost immediately from a bike in regular use, on start up. Are we actually getting a good return within seconds of starting up on a cleaned out sump? Not what should happen, there should be a delay.

  If it only reached halfway up, was that the best it can do? Or did you shut it down in disgust?  Just hope SRM haven't put another set of feed gears in the return side of the pump! No that's impossible isn't it?

  We need to establish that feed and scavenge are balanced as designed, and that the oil level is maintained. If it is constantly falling that is the reason for the smoke. Too much going in, not enough coming out. If the level stays the same, the system is working fine, and the fault lies within the cylinder.

  The overnight drip test would indicate the pump and crankcase ball valve are OK, but there still maybe a major leak on the pressure side, downstream of the valve. Rather unlikely, but possible.

  The PRV is the next suspect.  Dismantle and check carefully, making sure the ball seating area is undamaged.

  Too thick a fibre washer between the inner and outer parts of the PRV will decrease the spring tension on the ball. You need a thin one, copper or aluminium.  The sealing washer crankcase to PRV thickness is not critical.

    I think you have an early engine, which has no oil feed to the cam trough. If the PRV is faulty, opening at low pressure, it will dump pressurised oil directly into the oil pump cavity, which will fill up and pass from there very quickly through the keyhole vent into the sump....a possible explanation for the rapid appearance of smoke.

 Swarfy.
 

Swarfy,
its actually a BA10 pair of cases, datestamped '52. But I like the theory that the timing chest is spilling into the crank volume, that would explain rather neatly why the RHS cylinder smokes more than the left. However I can't find anything wrong with the PRV - except the spring feels a bit soft but so does the one out of my spare PRV. It has a 1.2mm thick fibre washer in it, maybe I'll just leave that out and seal it on th thread with PTFE tape. That will uprate it a bit.

[Steverat]

Hi Steverat,
There is probably oil after gathering in the exhaust causing the smoke?
+1 on Swarfies comments
Did you look in the cylinders for oil ?
Or in the exhaust ports to see if oil is coming down the guides?
With the sump drained  it would take a minute to get  oil return

John

Hi John
Cylinders looking clean inside viewed thru the plugholes, I can see the piston crowns still shiny,   but the plugs are wet with oil.
I'll try again tomorrow with my "uprated" PRV (see above) and let it run a bit longer. 

[trevinoz]

BA10 should have the feed to the cam trough as does ZA10 & AA7.
The long stroke cases don't.

[Swarfcut]

Trev.. Very early versions of the shortstroke engine retain the basic oilways of the Longstroke design. I was well annoyed to find an internet purchase had no feed to the cam trough. It is in the shed, I'll dig it out sometime for the date and number which may be of interest to other sufferers.


  Steve.. So much for my theory. On the other hand there is an oilfeed to the back of the idler gear, via the oilway from PRV to Cam Trough, so the PRV could still be a factor. Keep an eye on the tank level, if all is well it should stay the same.

 Good luck, there are probably more than a few folks following this thread.

 Swarfy.

[Steverat]

Trev.. Very early versions of the shortstroke engine retain the basic oilways of the Longstroke design. I was well annoyed to find an internet purchase had no feed to the cam trough. It is in the shed, I'll dig it out sometime for the date and number which may be of interest to other sufferers.


  Steve.. So much for my theory. On the other hand there is an oilfeed to the back of the idler gear, so the PRV could still be a factor. Keep an eye on the tank level, if all is well it should stay the same.

 Good luck, there are probably more than a few folks following this thread.

 Swarfy.

Thanks Swarfy and Trev,
I'm to Shepton for a day off today, will be back on it tonight and tomorrow!
Steve

[Peter in Aus]

 Good luck, there are probably more than a few folks following this thread.

 Swarfy.

+ 1

[Colsbeeza]

+another

[Steverat]

Well I got back from Shepton and straight into the workshop.

Started with a drained crankcase. Assembled a PRV with no gasket between the spring cup and ball seating parts, in order to uprate the blow-off pressure. Instead of a gasket, I used PTFE tape on the threads to seal it. The ball seating and the ball itself are in good condition, so hopefully I have dealt with possible blowoff or leakage from this point into the crankcase cavity.

Then started up with the open-ended transparent oil return line - almost immediately the scavenge was sending oil and air up the line at speed. However, exhausts still smoking - not the billowing white smoke from first run, but still smoky, - from both pipes.

Stopped after about 2 minutes and removed the sump plate. About 200ml of oil came out. So is this wet sumping (again??) or is it just transient - since the  scavenge is picking up air  as well as oil it seems plausible to say it would have cleared this on further running. But still I don't understand how it accumulated there in the short time the engine was running. How much should there be? Does anybody know?

As for the exhaust smoke - maybe there was more than one thing wrong in the first place, and I have to look at the bores. Thinking of lifting the barrels tomorrow.

The valve guides don't seem at fault, I took a pipe off and the valve stem is dry and stays dry.

[Swarfcut]

Steve...With that much oil in the sump, there should be no air in the oil being scavenged. It should be a continuous flow.
 The sump ball valve should be well within the raised gauze of the sump plate, and protrude perhaps 10-12mm below the face of the sump plate mounting, almost to the bottom of the sump plate so that it is well below the oil level.....engines stored without the plate suffer bent up scavenge pipes.

 Air in the return all the time means a leak or split in the scavenge pick up pipe.

 Swarfy.

[berger]

steve leave the sump plate loose with a good oil catching thingy under it so the oil just runs out put some splash guards round it too , if it still smokes you know what's next, if it doesn't something else is going on but I am pretty sure mine drains about 200 ml after stopping the engine even after seeing the bubbles in the return .edit swarfy my sucky tube end just enters the gauze and the tapered bit sits in the gauze hole so maybe 3mm below the gauze if that