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Sharon's Burning Oil
Job Date 9/2/16
By Ren Withnell
Sharon's RKS 125 has been a splendid machine. Light, manageable, reliable, efficient and well made. Yet as many of my own motorcycles have done it seems to be having a crisis. I do not know why it is that when many motorcycles reach roughly the 20,000 mile mark they fall apart. My SLR 650 ate it's rear wheel bearings, shock absorber and all the linkage bearings. The CLR 125 ate it's rear wheel spokes and refused to run in the rain. The CBF 125 ate it's clutch basket! (Knocking CBF 125 Part 2) I suspect that most bikes are thoroughly tested to 20,000 miles and simply put into production.
Sharon's bike has got rust spots on the tank (Blisters On Fuel Tank) and it is using oil.
You don't want to be checking this ALL the time.
There are several reasons I can think of why a motorcycle will consume oil between services.
- External leaks
- Blocked crankcase breather
- Worn or hardened valve stem seals
- Worn piston rings and/or barrel
I am not an expert and I am sure readers can think of more, if so do let me know in the comments below.
1. Sharon did fix a crankcase leak a while back. Being the artistic type she cut a rather splendid new gasket out of gasket paper and with a little help from myself replaced it with much success. The motor is oil tight and as such we can eliminate external leaks.
2. A blocked crankcase breather will create pressure within the engine. This pressure, due to blow by and the moving piston, can cause oil to be forced into the combustion chamber. To eliminate this we fitted a cheap aftermarket crankcase breather filter. This had no effect at all on the oil consumption. Dagnammit.
3. Valve stem seal problems are typically indicated by smoke at startup. Sharon's bike doesn't smoke at startup, in fact it doesn't noticeably smoke at all. While valve stem seals have not been completely eliminated I do not think this is the issue.
4. Worn piston rings again would be indicated by a smoking exhaust. There is soot around the exit hole, enough to suggest oil is being burnt, but it's not a "smoker" like some of the older bikes I've seen over the years.
Regrettably I am very much thinking it is worn piston rings. Darn it and blast! While the exhaust is barely a plume of choking blue smoke the soot around the exit is thicker than my own 2 bikes and so I figure that oil must be being burned. But why? I've had a 40,000 mile CLR 125 that didn't use oil. My 49,000 mile CBF 125 doesn't use oil. Why would Sharon's 19,000 miles RKS be using oil?
I can hear a chorus of "cheap Chinese bikes!". Wait! Wait a moment, hold your horses, hang on there buddy. Yes yes yes, of course it is likely that a £1,500 Keeway is not made to the same exacting standards as a £2,600 Honda. And yet there are many other reasons piston rings can wear out prematurely. Just back up a little.
The quality of the castings and parts is very high indeed in the Keeway.
Having read a lot of "opinions" about this on the internet let me share a few. Sharon purchased the bike as a complete novice. As such the running in period involved a lot of slow and careful riding. While this is good for bedding in the crank and the valve train this can be detrimental to bedding in the piston rings - apparently. It is also possible this slow start caused the cylinder walls to become glazed - if there is such a thing. Maybe all the practice for U-Turns on car parks warmed the engine up too much before being fully run in. Maybe all the high speed riding around Scotland has taken its toll. The point is this - there are potentially many reasons the rings are worn other than "cheap Chinese bikes".
I am however also perfectly willing to accept that the piston rings are not of a high standard.
I will say this. Having stripped the engine with Sharon to replace the rings I am astounded at the quality of the construction. The castings are far better cast and finished than most Japanese motorcycles I've worked on. The cylinder itself shows no sign of wear. I know this engine is a copy of Suzuki's 125 that is used in the GN125, Van Van and several others, it is a simple and well thought out design and I would be happy to have this engine in a bike of my own.
Simple, effective, well made and well executed - the cylinder head.
Please also take a look at To Hone - Or Not To Hone (Or Deglaze) regarding the treatment of the cylinder's bore.
Reader's Comments
Henrik said :-
Interesting, I look forward to hear if new piston-rings will fix it,..
16/02/2016 21:38:30 UTC
Ren - The Ed said :-
So far Henrik the bike is back up and running just fine. It will take a few miles for the rings to settle in so it will be a while before we can decide if we have been successful or not.
16/02/2016 22:30:48 UTC
Bob said :-
New rings on a 20000 mile tiddler doesn't sound so bad to me. The revs the engine is sustaining for extended periods of time have to cost somewhere.
The camshaft and head look really good, so I'd have thought it'd be fine after the rebuild.
Maybe you've been spoiled by that Honda?
22/02/2016 13:20:26 UTC
Ren - The Ed said :-
Cheers Bob. Maybe I have been ridiculously lucky with that Honda! And yeah, Sharon's poor bike has been thrashed mercilessly around Scotland while trying to keep up with larger machines, been to Brighton and back and certainly not been cosseted on local roads at genteel paces.
I can't believe the quality of the castings on the Keeway. I'm currently writing a piece about that so there'll be more details. I think for a £1500 'cycle we can't complain now can we.
22/02/2016 16:33:40 UTC
Sharon said :-
I have to admit I am not gentle on my little bike. I do push him on the revs, but I get the feeling he enjoys revving high :-). I do however take the best care I can of him both mechanically and in the wash and polish department. I really love this bike.
23/02/2016 00:30:09 UTC
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