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I want to clean my piston in a small ultrasonic cleaner (with distilled water). Do I need to remove the piston rings to do so, or can I leave them on and make sure it dries completely?

If I replace them, do I need to hone the cylinder?

The piston has small scratches on it (can feel them with a finger nail).

The motorcycle is a BMW R80GS Bike with 60,000km.

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    What year is your R80? This is important. Newer BMW models of the boxer engine have a nikasil coating on the cylinder walls. If you have a nikasil coating you will have to get it recoated and honed for new rings. Personally, I wouldn't a ring replacement without honing the cylinder. Let us know the year and we can give you the procedure. – DucatiKiller Jun 8 '16 at 20:24
  • Its a 1991 but 25 years ago someone stuck Kolbenschmidt 1000cc pistons and cylinders on it. I can only assume they are nikasil. – Max Jun 9 '16 at 6:00
  • so new rings = new honing of cylinder and recoating? – Max Jun 9 '16 at 6:12
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You have a nikasil coating on your cylinder walls

You can't just bore, hone and assemble. You have to have a nikasil coating applied to the cylinder walls before reassembly.

Your model year of BMW has the nikasil coating.

I would not simply hone your cylinders, attempt to the coating, it may be required to put then next overbore size of piston in. If you did require an overbore the piston sizes come in .25mm step increases in bore diameter. You would also, of course, get new rings with the pistons.

You have two paths

  1. Clean the piston and rings. Take the rings off when you do this. Make sure they go back into the same landing of the same piston upon reassembly, the rings wear into the piston and match.

  2. Get the next size overbore piston and rings and send out your cylinders and new pistons for the machine work. If you take it to an independent shop they will have a relationship with a firm that does the coating and will usually be cheaper than going to the dealer. From there, reassemble and smile.

You can make your decision by measuring the bore of your cylinder at the top, middle and bottom of the piston stroke. If the diameter exceeds service limits in any of the locations then that can drive your decision to bore and rebuild or not. Hope this helpful.

Diagram of Components

Notice the lower image, the rings go in particular grooves on the piston. These grooves are called landings. You will want to ensure that you put the ring in the landing it came from. All of the components are wore into one another and as a result have matching wear patterns. Placing the rings on the incorrect ring or landing could accelerate the wear of the particular component and lead to an early failure.

enter image description here

  • Excellent, thank you.I will reassemble with the same rings after cleaning. You mean the openings of the rings should match the wear on the cylinders when inserting? – Max Jun 10 '16 at 8:40
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    @Max I added an image for you to see what the landings are, basically the ring grooves. – DucatiKiller Jun 12 '16 at 0:15
  • excellent, thank you very much. I have cleaned it all in an ultrasonic cleaner and then went at it with a brass brush. Will try reinstall everything tonight – Max Jun 13 '16 at 12:10
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Personally, I replace the rings every time a piston goes back in the cylinder. While I can't speak for motorbikes (*I know they get dismantled a lot more often than a typical car engine) I would assume like with most wear items, you'd want to remove it, then put new ones on after.

  • thanks. I've read that the cylinder is worn according to the last rings, is it alright then to put new ones on with the old cylinder? – Max Jun 8 '16 at 7:31
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    @Max I can't comment on that sorry, I was always taught to replace rings and now couldn't imagine rebuilding a motor with the previous rings – Aaron Lavers Jun 8 '16 at 7:40
  • thanks for your advice/experience. I suppose I'll replace the rings and circlips. – Max Jun 8 '16 at 7:44
  • @Aaraon, do the rings need any specific rotation or does it not matter where the ring opening is once installed? – Max Jun 8 '16 at 8:07
  • Some manufacturers specify alignment, others suggest aligning the breaks in the clips opposite from each other to avoid leaks, might want to check a guide to be safe :) – Aaron Lavers Jun 8 '16 at 8:09

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