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Oil,Oil, and Smoke
#437837 06/02/12 2:09 am
Joined: May 2007
Posts: 104
rickt Offline OP
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Last couple of rides last season I noticed some smoke from the mufflers before shutting down the '75 Commando. Was hoping the winter's rest would eliminate this potential problem. No such luck. When I restored the bike in the late 90's, I checked the bores and installed new pistons and rings. Should have given the head some attention but decided to just clean off the carbon. The bike has been ridden only a few thousand miles since the engine work. With my limited skills I'm hoping that the problem is valves/valve guides. What is the best approach to identify the source of the problem before I start tearing things apart?

The oil issue has me quite puzzled. Seems to happen more often since I retired. After a short (i.e. 20 min.) ride a couple of weeks ago, I checked the oil. It was about 0.5 qt. low based on the dipstick. Added enough to bring it to the full mark. A week or so later took another short ride and checked the oil when I returned to the garage. Level was a good 0.5 inch above the full mark on the dipstick. Probably a simple explanation for this and I'm very interested in knowing what it is. Do I now drain some oil from the tank?

Thanks for the help!


rickt

'74 Trident
'75 Roadster
'76 BMW R90S
'87 BMW K75C
'87 BMW K75C

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Re: Oil,Oil, and Smoke
#438136 06/03/12 5:14 pm
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rickt Offline OP
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Thanks for the input Steve. I certainly cannot rule out the possibility of wet sumping. My experience with this bike indicates that indeed it suffers from wet sumping but only after sitting unstarted for 4 weeks or longer. Also, as I understand things, wet sumping results in severe exhaust smoke when the bike is first started. In my situation the exhaust is clear when the bike is started and is only visible when idleling after a short fun. It has smoked the last four times I've ridden it.

I will certainly follow your advice and give it a longer ride. My problem (!) is too many motorcycles and not enough time to dedicate to any one of them.

Thanks


rickt

'74 Trident
'75 Roadster
'76 BMW R90S
'87 BMW K75C
'87 BMW K75C

Re: Oil,Oil, and Smoke
rickt #438288 06/04/12 11:55 am
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Hi,

the smoke could be a result of bad inlet valve stem seals. With bad rings or pistons you have smoke rather while riding.
To the oil issue - after a 20 min. ride all oil should be returned from the crankcase to the tank, but you have to check the level immediatley after stopping the engine. I can't imagine this could be the cause for the smoke.

Ralf

Last edited by Towner; 06/04/12 12:02 pm.

Triumph Bonneville 650 T120RV 1972
Norton Commando 850 MKII 1973
Re: Oil,Oil, and Smoke
rickt #438406 06/04/12 10:58 pm
Joined: Aug 2001
Posts: 1,368
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Crew Chief
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You may be interested to know that by my estimation 50% of RH4 heads are cracked at one ot two intake valve guides. The number of good uncracked RH4 heads is not as high as they should be. I am absolutely convinced they were broken at the factory during initial assembly by some gorilla with a sledge hammer pounding them into super thin port walls.
I had gotten a head from extremely low mileage RH4 MKIII and it too was cracked.


dynodave
BSA 3 1961-1963
Ducati 3 1992-2002
Norton many 1951-1975
87 Serv-Equip 100HP MC brake dynamometer,
Re: Oil,Oil, and Smoke
rickt #439110 06/08/12 1:40 am
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I would not tear down an engine before doing some basic troubleshooting. A leakdown tester will tell you a lot but if you don't have one a compression test will give you a clue. Check the compression on each cylinder with a guage, throttle wide open. Then pour a little oil in the cylinders and do a wet compression test. If there is a big difference in compression readings between the dry test and the wet test the problem is with the rings. Cheers!


reliccycles.com
Re: Oil,Oil, and Smoke
rickt #439160 06/08/12 11:58 am
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Posts: 338
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If the spark plugs or the mufflers are oily it is time to take the engine apart.


Triumph Bonneville 650 T120RV 1972
Norton Commando 850 MKII 1973
Re: Oil,Oil, and Smoke
Curmudgeon #439437 06/09/12 10:20 pm
Joined: May 2007
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rickt Offline OP
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Yes, this is the testing that I thought was in order. Given the bike has a Boyer ignition I believe I need to ensure that both plugs are attached to a good ground before cranking the engine.

Is this correct.

Thanks!


rickt

'74 Trident
'75 Roadster
'76 BMW R90S
'87 BMW K75C
'87 BMW K75C

Re: Oil,Oil, and Smoke
rickt #439641 06/11/12 6:17 am
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If the spark plugs are black and oily there is a problem with the head and you will get trouble with idling soon. If the spark plug faces are ok the cause can be the rings. The compression test can give you a hint. If the compression and the smoke are not too bad (and the spark plug faces) it is not necessary to take it apart immediately.
But I would check valve clearance, ignition , carbs adjustment, etc. at first anyway.

Edit: If the engine starts good warm and cold without kickback and runs without missing the ignition should be ok (at least not the cause). Rich mixture should be excluded. The valves should be adjusted before compression test.
If the compression reading exceeds 120psi on both cyliners with cold engine and open throttle, good spark plug faces and the smoke is not too bad, I would ride it.

Ralf

Last edited by Towner; 06/11/12 8:04 am.

Triumph Bonneville 650 T120RV 1972
Norton Commando 850 MKII 1973

Moderated by  Dave Comeau 

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