Low compression on one cylinder.

[siedlik]

Hello,
The bike runs, but the idle is jumping a bit and it drinks oil a bit.
I did the compression cold and the PSI is about 100,150,150,160. After adding oil it went up to 170,180,180,190.


I'm thinking about changing the piston rings with the engine in the bike. Is that possible? If not I will have to remove the engine.
Could the piston rings fail just after 30k miles? Best place to get the piston rings just for one cylinder? A piston ring compressor would be useful, should I get 2 or 4?


I did rebuild the Honda 125cc engine, so I know the basics. Hopefully, the 4 cylinder won't be a pain in the ass. 
Would I need some special socket the remove the engine bolts?

[BBROWN1664]

Could just be a sticky ring due to lack of use. Not sure how you could unstick it without pulling the piston out though. Maybe pour some petrol down the plug hole and let if soak for a while before doing a full oil/filter change. Dont forget another squirt of oil in the bores though before starting the bike again as petrol doesnt lubricate that well.

As far as i know, you cannot get the pistons out with the engine in the frame but someone like Gnasher will be able to confirm that.

[Gnasher]

Yes you can remove the pistons leaving the crankcase in the frame, that said and has been mentioned above your issue could well be just a sticky ring/s.

The fact you've run the bike, tested it, got low compression on 1 cylinder and I assume re started the engine after topping up the oil and got a higher readings all round.  Suggest it is/was indeed sticky rings and by running the bike has freed them all off giving you healthy readings.

I would give it a good spirited run, revving to 7, 10, etc working towards the red line in the lower gears for about half hour.  Allow it to cool and retest if the numbers hold up, you're not burning/using oil outside the spec, forget about the issue.

I would also mention, Fazers as a rule providing they've been maintained correctly, don't suffer bore/ring issues, if anything it's more likely to be a leaking valve/s. But again as a rule anything below 50k would be unlikely, as the rarely need shim adjustment below that mileage, even above that figure they don't go out much with normal road use.     

[siedlik]

Bought some Redex to clean the rings, and also an endoscope just to see what was going on in the cylinder. Hopefully, it will help.
I don't see the smoke, but it burns about 200-300ml of oil for around 600 miles.
If I will have to replace rings, will wait till winter and some snow. :rolleyes

[siedlik]

After a warmup, I did the compression test and I got about 180,180,190,190.
Hopefully that redex helped a bit and it won't drink oil anymore.
The idle jumps a bit, will balance the carbs and maybe it will work fine after that.