Engine done about 1800 miles since rebuild

[bikerboy]

Forgive my ignorance but what do you call a leakdown test?

I have not measured what is left in the sump to be honest. One I cant stop it leaking, which leads me to believe there is to much in there.

I seriously believe the only thing that can be causing it is to much oil in the sump forcing its way past the rings. I cannot for the life of me think of another possibility.

I aim to check the scavenge pipe, make sure (yet again) that all the oilways and breather pipes are clear, change the check valve and probably replace the oil pump (draganfly has recon ones with a different body for about £90, exchange of course) If all that does not stop it smoking I think I will set alight to the damned thing lol

[duTch]

 I'd call a leakdown test a "leakdown test"  ....but my understanding of what it is, is pumping a certain amount of compressed air into the cylinder under control, and with a pressure gauge in place, measure how much the pressure changes in a given time....or something like that?
 Someone posted a fairly detailed 'how to' on here a while ago...do a search....

 But before you go berserk, go for a spin, and then drop the oil from the sump...I measured about 160ml, recently with a standard old oil pump, without doing everything suggested you're pushing the proverbial........
   If there's a healthy return, I can't see how it's a problem, I'm interested how much other people measure too...??

 The check valve as I see it does nothing other than attempt to stop oil bleeding down from the oil tank when dormant(not running), when running, it does nothing.

  I suggested this on the first page, did you try it...works for me, but I 'didn't not' try it...

 

When I did mine, my mate said to wash the bores with soapy water and wipe it clean until no more black came off on a white rag, otherwise it'll smoke like buggery...so I did and it's not too bad- just a puff of smoke occasionally, but I think that's mixture issue...did you do that?
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[jachenbach]

Leakdown testing is, as said above, done by pressurizing the cylinder with engine locked at tdc. A compressor is connected to a pressure regulator, air then goes through a gauge and on to the cylinder by way of the spark plug hole. A valve after the gauge is closed with compressor on and the gauge (which reads percent leakdown) is zero'd. The valve is then opened and percent leakdown is read. A nice tight engine will imo be under 5%. If there is a serious problem (like 20%) you can hear the air. The nice thing about leakdown is by seeing/hearing where the air is escaping you can often pinpoint the source of the problem. For instance, air coming from the oil filler will be getting by the rings. From the carburetor is getting by the intake valve, from the exhaust pipe it's getting by the exhaust valve, etc.
Leakdown testers can be bought for under $100 US.

[bikerboy]

Thanks for explaining a leakdown test to me I have to admit I have never heard of it before but it does sound damned useful.

Dutch the reason I am doing the check valve again is it still has a tendency to wet sump despite the recent rebuild.

Anyway I still cant find anything wrong with it I have even gone as far as taking the sludge trap end caps off in case the guy who reground the crank and fitted it done something wrong in there. Yes I know there is nothing to go wrong in there really but I am really grasping at straws now

[jjbsa]

Hi,
Many years ago I had a home built RGS lookalike, which after a rebuild oiled up on the LH pot really really badly.  After looking at other possibilities, it turned out that the return side of the oil pump was sucking in air past the pump gasket, which isn't very wide at that point.  This was caused by me attempting to enlarge the hole in the crankcase from the sump oil pickup. I reshaped the hole and the problem went away.
HTH,
Jon

[bikerboy]

Jon

Thanks for that tip, I have stripped the engine and rechecked everything which still appears ok. I have yet to test it yet but if it still smokes and burns oil like there is no tomorrow my next move is a reconditioned oil pump, I see Draganfly are doing one which is a lot cheaper than the SRM one

[bikerboy]

Well I am a right happy bunny :)

After two years I have eventually found the problem

The only thing left for me was the pistons. I replaced them and hey presto. Smoke gone :) Plugs a lovely biscuit brown colour with a black ring around the outside.

The baffling thing is the compression is still the same? Odd but I dont care at least I can ride now without leaving a trail of gassed bodies behind me :)

[muskrat]

Good news. So what breed of pistons were they and what breed now? Could it have been the infamous JP rings? Or a slow run in?
Cheers

[bsa-bill]

traditionally Italian pistons needed a bit more clearance, maybe it had been re bored for them then other smaller pistons put in

[KiwiGF]

Well done biker boy, persistence is needed often with these bikes!

Edit: and many thanks for "completing" your thread and telling us all about how you solved it he problem.

[jjbsa]

If a change of pistons cured the oiling, and the oiling was on just one piston (the LH one) then I might suspect the up and down clearance in one or more of the piston rings in their grooves.  Excessive clearance there can allow the piston rings to move up and down and act like a very short stroke pump, letting oil past the rings round the back. Clearances generally should be 0.7 to 2 thou max.
Back in the 60s I once had a Hepolite piston where the oil holes drilled in the back of the oil ring groves were all over the place and drilled at an angle so that when the piston was descending they filled with oil and then released it back into the ring groove on the upstroke.  This caused oiling which was cured by using a needle file to open the hole out to remove its downward angling.  The original holes looked like they were drilled with a hand drill!  What a total difference from today's best pistons such as Wiseco and JE.

Re leakdown tests.  I have found these VERY useful in pinpointing where leaks are and they really do show that its possible to grind in valves and still have poor sealing if the seats weren't cut pretty damn accurately beforehand.  In fact the tests show that if the seats are cut accurately then subsequent grinding often doesn't improve anything.  I'm a convert to leakdown tests.  I clamp the cyl head with valves in to a metal plate with a thick rubber ring to seal it and put the compressor pressure through a blow gun to an old spark plug in the plug hole.  You don't have to have valve springs fitted, if I do then I generally use little weak checking springs.  If the valves seal well then there is no hissing and the head, once pressurised, will hold pressure for 20 or 30 secs before a valve (without a spring) drops down.  If it leaks you hear a hiss when the pressure is applied and a little strip of paper moved around in the port will flutter and quickly show just where it comes from.  It's embarrassed me a few times!

[mugwump]

Bikerboy, I'd be interested to know what the old pistons were and what you replaced them with.

[cableguide]

Hi there,
Glad to hear new pistons have sorted the problem, though it does make me think this....Imagine the bores were done a bit over and the old pistons where a bit under, might explain the problem to some extent..how do the bores measure up?. and how do the new pistons measure up against the old ones. Anyway great result.

[bikerboy]

Firstly I may be celebrating to early

Tonight after riding about 25 miles at about 65 mph I lost most of my oil out of the engine breather. But at least it never smoked lol.

These are the pistons I used and they are from TMS Nottingham

http://www.tms-motorcycles.co.uk/store/products/popup/?imgversionid=3&itemid=1685

Just to answer a few other questions in the last couple of posts.

I had the bores resleeved and bored to +20 imperial purely because I had a set of pistons that size.

The new pistons were metric which meant the bores needed to be 70.5 (I think).

What I did was take the barrels, the old pistons and the new pistons to the guy who done the rebore. He measured it in front of me and everything was great. He tried the rings, gapped perfectly as I already knew and told me there did not seem to be any reason for it to smoke.

He honed the bores for the new pistons while I stood there as the difference apparently is miniscule.

I put it together, smoking stopped, oil stopped pumping out of the breather and my world was complete for about 2 days. I deliberately put a pipe on the breather and threaded it thru to the top of the gearbox my side so that I could monitor it easily temporarily of course.

Drove to work this morning about 15 miles, no smoke, no oil loss and averaged about 65 mph as its all motorway.

Drove home via a friends house so it was about 40 miles (same average speed about 65 ish) and got home to an extremely oil covered right leg and an empty oil tank

I so hate motorbikes at this moment in time

[mugwump]

I don't think the problem is piston/bore related. Without reading back over the whole thread, has it been suggested that either-the feed /return oil pipes could be reversed or a leak on the feed side either the pump body or the anti sumping ball valve.