Clutch Slipping on R50; Oil turns Black quickly; Piston ring gap -all related?

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schrader7032
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What type of oil are you

Post by schrader7032 »

What type of oil are you using during break-in? I'm not sure I'd be too concerned about oil color this early in break-in...but I would recommend changing it early and often during this period. I changed my oil after the first 20 minute ride, then again at something like 50, 100, 250, and 500. New engine is putting out some wear products and the oil needs to be dropped to keep that stuff from getting into the slingers.

Before you dive back into the engine, be sure the clutch is adjusted properly. You want a little bit of free play at the handle which means you have free play at the arm at the back of the transmission. The ideal clutch adjustment should be that when you've pulled the hand lever about 1/2 way, the arm at the back of the transmission should be parallel with the back plate of the transmission.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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westeagle
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Clutch Slipping on R50; Oil turns Black quickly; Piston ring gap -all related?

Post by westeagle »

Hello

Recently dismantled the engine on my 1957 R50 a second time in a year to replace an oil-starved new piston which had serious scoring. Had the cylinder honed, replaced piston with another new one, and drilled out the right side oil passage which the R50's of this age did not have. Finally, I gapped all the rings to .5mm (-was this my fatal flaw?)

I am still very much in break-in mode with the new piston which has only about 30 miles on it. Lately the bike has felt "gutless" while accelerating. This morning, while accelerating in 3rd I definitely noticed the sensation of the clutch slipping: rpm increasing but no increase in speed. Noticed there is a bit of oil on the "shelf" -so it looks like leakage from the main seal may be getting into the clutch? The clutch friction plate is new.

I recently did an oil change and the oil level was slightly above the Max line. Could this cause excess oil pressure to leak through the main seal?

In addition, my new oil has turned black after about 10 miles. Is this normal?

I am thinking I will again take the engine out and probably change the main seal, however, any other ideas of what can be the cause of the clutch slippage would be much appreciated.
'57 R50; '73 R75/5 LWB

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schrader7032
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My Clymer says that ring end

Post by schrader7032 »

My Clymer says that ring end gap should range from 0.25mm to 0.40mm. Basically there's no adjusting these gaps. If you put a ring into the bore and square it up with the piston, if the gap in the ends is more than say the 0.4mm, then you either need new rings or you are at cylinder size where it needs to go to the next oversize. The rings do wear so the gap could grow and just putting a fresh set on could bring it back to within range.

If you're at 0.5mm, then you are getting quite a bit of blowby as well as more air entering the internal case, which as you suggested, can cause the air to find a way out which sometimes is past seals.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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westeagle
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Just checked compression

Post by westeagle »

I just came back from purchasing a new compression tester and cold I get to 115lbs after about 5 kicks.

The .5 mm I set the ring gap to was recommended by Duane A in one of his articles.

So it seems to me that the compression is decent? Could the blowby still be a factor?
'57 R50; '73 R75/5 LWB

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schrader7032
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This

Post by schrader7032 »

This article?

https://w6rec.com/test-compression/

He says that for most BMWs, the end gap should be 0.01" which is 0.25mm and that 0.025" (or 0.63mm) is worn badly.

I would say that 115 psi is about right for a '50s R50.

What do you mean by "I set the ring gap"?
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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westeagle
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I mean the piston ring end

Post by westeagle »

I mean the piston ring end gap.
It was the following article
https://bmwmotorcycletech.info/pistons.htm
where he says the end gap he usually went for was between .5mm and .6mm

'57 R50; '73 R75/5 LWB

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westeagle
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Oil type; black oil and ring gap

Post by westeagle »

Thanks for your reply Kurt.

I am using Lucas brand "Break In Oil" 20W50 containing ZDDP. I did change it out after the first 10 miles or so.

From reading through past posts, I have heard that poor compression can create pressure in the case forcing oil out.

I filed the piston ring end gaps to .5mm and am hoping that this is not the cause of my new problems.

I did play with the clutch cable adjustments as soon as I felt the slipping, but will look again.

Henry
'57 R50; '73 R75/5 LWB

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schrader7032
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Well, you were referencing

Post by schrader7032 »

Well, you were referencing Snowbum, not Duane Ausherman. Snowbum was writing about Airheads and may have been writing about Nikasil cylinders specifically which were used from 1981-on. My Haynes manual for Airheads shows end gaps in the 0.25-0.40mm range for the earlier bikes, for the /7 and 1981-1984 bikes it shows 0.40-0.65mm range. I think that's more like what Snowbum was discussing.

I see where Snowbum wrote he didn't like the lower numbers, but my limited experience would say that I would have gone with smaller end gaps than what you ended up using.

Snowbum speaks Airheads while Duane tends to be more of a /2 or early /5 guy.

I guess the only way to "set end gaps" is to buy/use new piston rings until you get the end gap you want. I have heard of people buying rings for an oversize cylinder which tends to result in near 0 end gap, then filing the ends of the rings down to the gap you want. I think, though, you end up with the ring ends not being properly parallel...and it's easy to break rings when you do that, and the only thing to do is to buy new rings and start over.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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westeagle
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oops!

Post by westeagle »

Ok then that was snowbum...

DO you think it would be safe to just replace those rings with new, tighter end gap ones without rehoning the cylinders at this point?

I have less than 50 miles on the bike with the new pistons.
'57 R50; '73 R75/5 LWB

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schrader7032
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You're getting pretty good at

Post by schrader7032 »

You're getting pretty good at this stuff! I'd certainly just try new rings...doubt much of the honing has worn off and you can always redo that down the road.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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