Cylinder Bore Slightly Rusted

Paul Sutton

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I have my engine (14000 miles) apart and reground the valves by hand today. The valves/guides/springs are in specification. I noticed one cylinder has a light rust coating about 3 cm from the top, presumably where the pistons were left during their many years of storage. The rust layer is very thin without any pitting or flaking. Like the fine rust layer you see on old tools and drill chucks.

My Question: Could I use a rust removal treatment followed by a very light and quick hone (approximately 10 seconds) to break the glaze and then put the original pistons and rings back in? What are your feelings regarding this?

Thank you for your comments.

Note: I do not really want to rebore and go to the 1st over.
 
I would clean the rust off 1st with something like chrome cleaner, then hone. I'd use the bottle brush style hone too, not a 3 or 4 stone type.

If the ring end gaps are in spec then sure, you could re-use them. You don't find that too often though.
 
At 14K miles it may or may not be ok. If it was properly maintained it should be ok. Most Engine shops will for a small fee measure the bores and pistons to calculate the clearance. Your repair manual lists the specs. If the clearance is ok, you can go from there. If not then a rebore may be needed.
If the clearance is ok then you can measure the ring end gaps. Again specs in the book, should also tell you how to.
If the rings are out of specs new ones aren't much.
If you can reuse the rings you have, a hone may not be needed. Honing cuts ridges into the cylinder wall. It takes a fair amount of wear to smooth out these ridges, a lot of that wear will be on the rings. This will increase end gap to an excessive amount.
Rings don't really seal well until the rings and cylinder walls are worn smooth. Your cylinder wall and rings are worn smooth now. I would clean the cylinder walls very well, kerosene and steel wool should remove any glaze and get most of the rust, any left will get taking care of with a few minutes of run time.
Leo
 
Agree with 5twins, how ever that is with a nod to neither of us having seen the cylinders first hand. I know form experience working on heavy equipment for close to 45 years what some would call a little roughness on a part could actually be a major failure.

One other point I would need to bring up is how much is this engine going to be used and how hard? Point being if you are planning on putting say 10,000 miles a year on it at highway speeds it would need a much more perfect cylinder fit than a bike that may only see a few hundred easy miles a year. Or if this is an engine being built for competition that would also require a different level of precision!
 
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There is a good set of rings sold on ebay, sent direct from the mother country, at half the price for rings you can find anywhere else. PM me and I will look them up. Also, I might use a brass brush on the tarnished area but I suggest not honing or otherwise scratching up the rest of the cylinders at all. Oil consumption will be higher if you do. Especially at 14,000 mi. there will still be crosshatching in the cylinders from the factory,
 
Use the bottle bush and lightly hone both cylinders. Dont worry about what extra wear you are causing as it is minimal. Get a nice cross hatch and all will be good. You do not want a smoth cylinder as the rings will leach by.
 
Thank you everyone above for your kind advice. I am carefully considering all views. I have requested rebore and hone costs and await replies. I will get a good measure of the level of rust later this week when I remove the barrels and pistons and this may lead me to rebore or not. But a rebore seems quite attractive on cost grounds at present. I have plenty to think about now!!
 
Nice fine day with bright sun and blue sky - I removed the cylinders and cleaned the rusted area. It is clear that a rebore is needed as the rust is deeper that expected. I will get the bores measured so the engineer can tell me what oversize pistons to buy. I think they will be +0.50s.

That's life!!
 
Funny I just read the thread, and was thinking from the get go that rust is deeper than he says, grin If it's in a band like that, chances are......... Yup have had good experience with cruisinimage so far.
 
Most of the rust is superficial except in one cylinder where there are deeper pits in one location. A +0.25 would probably do except in all my searching I have not seen 1st overs. Hence my reference to +0.50.

Thank you 5twins, I have cross-referenced your Ebay link to the UK and they will cost £89 including postage from Japan. I will go for those once I know the recommended rebore size.

Thanks.
 
I think if you contact cruisinimage he does have the 1st over just doesn't list them on fleabay. But why not go to 2nd over? there 4 and 6 over sets.
 
The deeper rust was about 1cm across on one cylinder and the engineer said he had seen engines running with worse so proposed a hone and new rings. Based on the very reasonable price of new pistons I decide to go for the rebore.The engineer then said to go for +0.50 pistons so I placed the order today with cruisinimage .
 
Just to complete this little thread. The motor has now been bored to +50 and I reassembled it yesterday. Today I put the motor back in the frame and reconnected everything. The motor started up without any difficulty. Regarding the cruzinimage rings:
  1. The top ring gaps were just in spec. at the thin end - no filing required
  2. The 2nd rings were at the the top end of spec. i.e. slightly over 0.4mm - no filing required
  3. The oil rings needed a bit of filing as they were very tight
Due to rain I have not taken the bike out but have run it several times in the garage. The engine felt a little tighter than normal using the kick starter but now feels OK after 3 starts.
 
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