Author Topic: Black goo  (Read 183 times)

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ajb235

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on: June 29, 2021, 02:48:34 pm
I’ve had this problem for about 3 years now, it’s stopping me using my 1994 500 Bullet.
I rebuilt my engine with a new piston, phosphor bronze valve guides,and new valves. On start up I have a black sticky goo coming out of the exhaust port, past the exhaust pipe joint. The silencer and pipe are now clogged up with goo. So I strip the top end, check everything, clean the exhaust and pipe, reassemble, new crankshaft quill seal, new engine breather pipe, and still the dreaded black goo.
Is this a side effect of dry slumping?  My engine has an Alpha roller bearing big end fitted. The new piston does not have an oil control ring. Is excess oil passing up into the combustion chamber?

My oil is Millers pistoneze 20/50. I’ve tried the Hitchcocks crankcase breather system, but reverted to the simple ducks bill.

Would appreciate any theories or similar (solved) situations.

Thanks


Adrian II

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Reply #1 on: June 29, 2021, 10:55:24 pm
No oil control ring on that piston?  ??? ??? ???

Exactly what piston are you using?

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


ajb235

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Reply #2 on: June 30, 2021, 09:34:09 am
Thanks for your comment. I do have an oil control ring, of course, just below the top and second rings. What I meant was, I have no oil control ring  below the piston pin on the lower skirt. A few of my old bikes had these, but I can’t remember if my bullet had the lower oil control ring  on its original piston. Sorry for misleading info.


Adrian II

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Reply #3 on: June 30, 2021, 01:59:49 pm
OK, that makes more sense, having the oil control ring immediately below the compression rings is pretty universal practice for this sort of engine. Do you also get a lot of oil pumped out of the engine breather pipe? Is the black goo accompanied by white smoke? I'm guessing your cylinder head is not leaking oil at the gasket.

If this is ONLY on start-up and stops once the engine has been running for a while, that sounds a lot like what you call dry slumping, more commonly known as WET SUMPING. Oil leaks into the bottom of the crankcase, usually from the timing chest (though sometimes from the oil tank if there is a poor seal between the two halves of the crankcase). The oil sloshing around the bottom of the crankcase then gets picked up and flung around the crankcase an onto the cylinder wall when the engine starts, in quantities which are too much for the oil-control rings to cope with, at least until the scavenge/return oil pump has had a chance to pump out the excess, which usually takes a few minutes.

When you replaced the crankshaft quill seal did you ALSO replace the oil seal behind the crankshaft timing pinion (spring side facing outwards)?

If too much oil is getting past the oil control ring, it could be that it's not a good quality one, in which case you would be considering honing the cylinder and fitting a new set of good-quality piston rings.

The other common way for oil to get into the combustion chamber is past the valves stems down the valve guides. You say you have replaced these, though manufacturing tolerances could be a little on the sloppy side. You can buy valve-stem seals for the older Bullets, though these will not work if you have fitted high-lift performance cams.

The only other thing that occurs to me is that there could be an oil leak from the rocker area of the cylinder head directly into the exhaust port, which would be caused by a fault in the cylinder head casting itself, either through blow-holes in the casting or possibly a crack. Have you checked for this?

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


ajb235

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Reply #4 on: June 30, 2021, 08:14:02 pm
Thank you for your informed and constructive comments re this problem. This gives me some hope, and a plan.
I do lose oil from the engine breather, particularly at start up. Exhaust has white smoke.
The cylinder head gasket is a composite one, and I have lapped the head joint. Gasket compression is about 0.004 before the lapped joint seats.
Whilst I replaced the outer quill seal(I changed back to cork) ,I did not replace the inner seal, although I did check that it was the right way round, spring facing out
The replacement standard bore piston is running in a freshly honed bore. The piston is NOT a  top of the range item. I actually purchased +0.020 rings ( again , not top of the range items)and lapped them down to get the correct ring gaps. The oil control ring could well be poor quality.
The valve guides are phosphor bronze items from Mr H. I also purchased valve stem seals, but they would not fit these guides. In the end I machined down the ends of the phbronze guides to accept the seals. I’m running a standard cam.
Your final point may well be valid, and gives me some hope. I’ve had this bike for 14 years.  10 years ago at around 11,000 miles the big end gave up and I replaced it with an Alpha roller bearing. After the rebuild it ran for a short time and then overheated and stopped. I discovered that the debris from the failed big end had blocked the oil feed to the rockers, and the whole top end seized up, generating a lot of heat. My suspicion is that as a result of this , the head may have cracked, and oil is passing into the exhaust port, either directly or via the decompressor  bypass. The moral is of course to ensure all debris is cleared out of the rocker feed pipes after big end failure.
The combustion chamber has always seemed very “oily” on stripdown, see pic. The bike has used oil ever since big end replacement, which made me think that oil was flying out of the roller big end, rather more than the plain bearing, and causing oil to pass across the oil control ring into the combustion chamber.
So thank you for that suggestion. I’m not sure how I could check for leakage under running conditions, other than trying another cylinder head.

Thanks
J



Adrian II

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Reply #5 on: June 30, 2021, 11:41:28 pm
Quote
The bike has used oil ever since big end replacement, which made me think that oil was flying out of the roller big end, rather more than the plain bearing, and causing oil to pass across the oil control ring into the combustion chamber.

Oil flying out of the big-end is what lubricates the piston and rings, whether plain or roller big-end! If the freer-flowing nature of the roller big end makes any difference from the oil point of view, it will be to put less load of the oil pump drive gear teeth.

Your symptoms DO sound like classic wet-sumping, poor oil rings would make it worse, but I'd pay close attention to the seal behind the crankshaft pinion and (assuming it hasn't failed) make sure the inner lip is actually seating on the crankshaft. The size is 30mm O/D, 20mm I/D and 7mm thick. You can replace this with a 5mm thick one to move the inner lip inwards along the shaft by 2mm if you need to.

What oil pumps are you using, stock or performance? A performance scavenge pump (i.e. on with a larger piston) might clear the sump quicker.

Wet sumping is easy to check, run the bike for a decent trip until the exhaust smoke disappears, the put the Bullet on its centre stand, remove the scavenge drain plug with a bowl underneath and leave it overnight. If oil is leaking out of the timing chest past the crank it will collect in the bowl.

The next step is to check for leaks between the oil tank and the crankcase, so run the engine as before, and this time remove the timing cover to drain the oil from the timing chest. THEN remove the scavenge drain plug and leave with a bowl underneath overnight. If anything much collects this time, your internal crankcase joint faces need some attention, or at least a new gasket!

Then we can still get the "mystery" problems, my AVL hybrid engine can smoke very badly on start-up, and I've been though all the above steps with it! No wet sumping or oil tank leaks, new seal properly fitted. I checked with a Bullet expert (a REAL one!) and we concluded that the only logical explanation was poor oil rings, he mentioned he'd been dealing with a bunch of quad-bikes which had that problem, all down to bad rings. This was made more annoying in that my old 2005 Electra-X (the Electra has no seal behind the crank pinion) would get a gold medal for physically wet-sumping, BUT because the scavenge oil pump was so efficient, it would clear the oil build-up before the engine had a chance to start smoking...

At a guess I'd say your cylinder head casting probably IS sound, but you could still give it a really close look to be sure - perhaps if you have access to someone with a vat of trichloroethylene to leave it in overnight, it would be clean enough for you to check for tiny holes or cracks.

A.
Grumpy Brit still seeking 500 AVL Bullet perfection! Will let you know if I get anywhere near...


ajb235

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Reply #6 on: July 01, 2021, 08:40:15 am
Thank you.

J