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Discussion Starter · #1 ·
Hi, I recently rebuilt a 76 CB200 engine using new pistons, rings, and aftermarket gasket set. All was well and the bike is running well. My problem is I have just noticed a small amount of oil on the lower left hand cylinder fins and I cannot find where on earth it is coming from. The head and base gaskets seem to be ok and the points housing and alternator cover gaskets also seem to be dry. If I wipe off the oil and leave the engine idling with the occasional rev there is no sign of a leak. It's only after a ride out that the oil appears, it starts on the lower front left fins then proceeds to the left cylinder fins ending up blown by the air passing over the oil onto the left side panel. It's not a great deal of oil but it's annoying after doing all the work on the complete rebuild of the bike including a full re-spray. Could there be something I've missed on the engine that could cause this leak. Is there anything near or around the starter motor housing that I should of replaced like a seal or O-ring.

Regards,
Glyn.:confused:
 

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Hi Glyn, the oil is not coming off your fork sliders is it? Worth a look under the gaiters.... and also worth checking the head bolt torque
settings to see if they haven't loosened off.
Nigel.
 

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Clean thoroughly then spray baby/talcum powder over the area. Let it run and watch for the spot that gets wet first. If necessary ride a short distance and then check. Repeat. Nigel's idea is also valid.
 

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Discussion Starter · #4 ·
Hi, Thanks for the input, I have re-torqued the head nuts twice and the area between the head and cylinders is bone dry as is the area around the base gasket. I like the suggestions about checking the fork seals for leaks, and using the talc, I would never of thought of that. So that's the next job.
Cheers Again,
Glyn.
 

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The oil seal behind the advance retard mechanism springs to mind, but you say that area is dry.

Wind rush on a moving bike does blow the oil around into unexpected areas. I was convinced that I had a leak from my cylinder base on the left hand corner ( oil riser on a 175 engine ), but it turned out simply to be a loose screw on the alternator side case, oil working its way up the threads then getting blow upwards on the cylinder fins.
 

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Discussion Starter · #7 ·
Just a quick update on the oil leak. I haven't found the problem yet but I have now noticed there is small amount coming out of the breather pipe and dripping on the garage floor every time I park the bike after a ride out. It's not emulsified with condensation it's clean engine oil. Is it possible to get the oil pressure so high that its forced out of the breather pipe ?
 

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It's crankcase pressure rather than oil pressure that causes this. Because both pistons rise and fall together in the 175/200 engines, there is a fair amount of air being displaced inside the engine. Add to that a bit of blow by past the pistons rings.

Both my rebuilt ( rebored ) 175 engines leave a drop of oil from the breather after a run. I can't remember if my brand new ( in '73 ) 175 did this as much. My badly worn Honda 50 C100 would pump most of its oil out through the breather. I fitted a catch can and poured the contents back in every so often. Not that I'd recommend this ..
 

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Discussion Starter · #9 ·
Hi Richard, Could there be a problem with the centrifugal oil filter/spinner, I've heard there is a spring loaded valve or bypass that is supposed to eliminate excess crank pressure. It's more than just a drop of oil that appears every time I stop for fuel or a coffee break and I don't fancy it getting on to the rear tyre.
 

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Hi Glyn,

It doesn't quite work like that. Engine oil pressure isn't linked to oil mist blowing out of the breather. I'm assuming that the engine isn't overfilled with oil, of course.

The spring loaded plunger on the oil spinner is there to make a good seal between the rotating spinner and the stationary plunger. Plenty of oil pressure is a good thing, keeps the plain cam bearings happy. Any excess oil pressure would be released via the roller crank bearings.

Excessive crank case pressure can only be due to bore wear or poor piston ring sealing. The crankcase breather is attached to the air space at the top of the engine. This space contains a labyrinth which is intended to separate the oil from the vented vapours, but I suppose excess crank case pressure would overcome this.
 
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