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Old 11-01-2014, 07:29 PM   #1
DR250Djebel OP
Joined: Nov 2014
Oddometer: 55
Cylinder Boring - Nikasil


I have a DR250 Djebel and have been having problems with my piston/piston rings/cylinder. The local mechanic has told me I need to re-bore the cylinder and get a new oversize piston and rings.

I'm concerned about this because the cylinder has a nikasil lining which would be lost if it was bored out.

I live in SE Asia and out here having it re-plated with nikasil is not possible. Sending the cylinder to the US to be done is not practical or economical given the high age and low value of the bike so I'm going to have to make do without the nikasil plating.

I've spoken to some other mechanics. Some proposed boring it out and fitting a sleeve to accommodate a standard 73mm piston. Others suggested boring out the cylinder to take an oversize piston (and presumably no sleeve).

I appreciate that neither is ideal as I will no longer have the tough nikasil lining. Can anyone suggest which of the two options I should go for?

As I see it, it could make more sense to use an oversize +0.25mm piston rather than put in a sleeve as this would be less expensive and there would still be scope to further bore out the cylinder to +0.5, 0.75 and 1.0 if the bike is still running that far in the future.

Am I right in thinking if/when the cylinder reaches it's max bore I could then fit a sleeve to bring it back to the original 73mm rather than fitting a sleeve every time it is bored to keep it at a constant 73mm?

Also, would a sleeve be more hard wearing or less hard wearing than the naked cylinder without its nikasil coating? If the sleeve would be stronger it may make more sense to use one and not have to re-bore the cylinder as often.
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Old 11-01-2014, 07:39 PM   #2
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The Nikasil should be harder than the piston and rings, unless theres excessive scoring why couldnt you just do new piston, rings and a hone job? have you seen the bore or are you just going off his word?
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Old 11-01-2014, 08:44 PM   #3
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You can't run the piston and rings on the bare aluminum under the Nikasil. It is too soft. You will either need to have it replated or sleeved. The sleeve should be good for at least one oversize.

You could also fit an oversized sleeve and piston like this, link, the piston kit is here. link.
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Old 11-01-2014, 09:23 PM   #4
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as above... the only options a re-Niksil after the bore or a sleeve. nothing wrong with a sleeve... thats the way they were/are done a hundred years. just need rings that are compatible with the sleeve

how about a replacement cylinder? there is a Chinee cylinder kit on ebay with piston & rings for under $80
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Old 11-02-2014, 01:39 AM   #5
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Just backing up what other people are saying. The aluminum in the cylinder is too soft to use without plating. The piston will just eat into it. If you can't replate, and very few places will do it, then your only option is to sleeve the cylinder.

Nothing wrong with sleeving and it will get you back to the stock size so you can use the stock size piston. If you seize that, you can bore it out and goto the next size piston, and so on.

It runs about $300 around here for a good quality job. I have seen people go cheaper and it ends up destroying the cylinder.
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Old 11-02-2014, 01:44 AM   #6
DR250Djebel OP
Joined: Nov 2014
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Thanks for the advice. I've got the cylinder and piston as I didn't trust the original mechanic and wanted to take it to some others for a 2nd/3rd opinion.

With the rings off there's space between the piston and cylinder. THe piston can rattle around slightly and I can see light through the gap.

The piston seems to be alu but the cylinder is iron/steel from the weight of it. The new cylinder + new piston kit from ebay would be great but the only ones I could find were for the older model DR250s from the 80s or early 90s.

As the piston and rings are softer then the nikasil cylinder like beemerkid says, I don't understand why it would be the cylinder that wears and needs boring and sleeving. All the bike shops I've taken it to have said I need to rebore the cylinder. They all give different answers on whether I can use the old piston or need to replace and whether to replace with standard or oversize.

Looking at the cylinder there is no serious scratching/damage. It looks smooth and polished but I can feel a slight ridge at the top of where the rings push up to. As I say, it seems odd that the cylinder should wear before the piston/rings.

Out here there are lots of scammers and dodgy mechanics all out to make as much money as they can from you. It's very hard to tell whether their recommendations are genuine or just designed to scam them as much money as possible. As a customer you have no comeback if the work they do is useless.

The most common view among the mechanics seems to be use the old piston with new rings and to bore out and sleeve the cylinder.

Does this make sense? I can't understand why the soft alu piston should be good to use but the hardened nikasil lined cylinder has worn and needs boring.

Thanks again.
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Old 11-02-2014, 01:50 AM   #7
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Also, thanks for the comments confirming that if the cylinder is bored it has to be sleeved. At least now I know not to trust the mechanic that was just telling me to bore it and use an oversize piston. I wasn't sure at first as my piston is alu and the cylinder seems to be iron/steel. I thought with the cylinder being harder than the piston this might be a reasonable suggestion.
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Old 11-02-2014, 08:39 AM   #8
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Post up some photos of the inside of the cylinder along with piston. Get them as clear as you can. Then we can tell you what type it is along with what you need.
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Old 11-02-2014, 09:22 AM   #9
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I'm guessing this is a 2 stroke? Pics are needed. and it you want to know if the cylinder has a steal sleeve in it and can be bored and a over sized piston used just get a magnet and see if it will stick to the inside.

also I have never seen a Nikasil cylinder that was worn that didn't look like hell. The Nikasil isn't very thick and once its warn through the soft aluminum will melt and then deposit in a line up and down the cylinder.

Get us some pictures and we'll get you the best information we can.
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Old 11-02-2014, 11:25 AM   #10
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Stop guessing

Once you have the piston & cylinder off, the next step is to measure them to see where the wear is. You may find the cylinder is okay.

Or, just guessing, maybe it isn't.
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Old 11-02-2014, 11:59 AM   #11
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if you can feel a ring ridge the bore is worn. sometimes it's just a build up of carbon that can be scrubbed off, but if the bore itself is worn then it needs to either be sleeved or bored. a new piston is in order too. there are other fixes that will make it run again but they won't last very long. as above.... pix will help. does a magnet stick to the bore? if so, it's already got a steel liner
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Old 11-02-2014, 03:07 PM   #12
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Take a picture and email it to me I can host it if you don't have a host. Like everyone has said, Nikasil should look perfect even with a worn piston and rings.

To make sure you have Nikasil plating, it should be magnetic on the inside (if in an aluminum cylinder). If it isn't magnetic it could still be Alusil coated which is also hard.
Your cycle had a bell on it.
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Old 11-03-2014, 01:47 AM   #13
DR250Djebel OP
Joined: Nov 2014
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I checked with a magnet and the cylinder is alu and does not have an existing sleeve.

I've taken some pics but keep getting "upload failed" when I try to add them so they are hosted at this link:

It's a 4 stroke engine.

Any advice would be very welcome. Every mechanic out here gives a different suggestion and they seem to be mostly based on which parts each mechanic has available for sale. If he only has rings, that's all I need. If he has a piston, I need that too. If he can bore, I need that doing too.

Thanks again for your help and advice.
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Old 11-03-2014, 04:37 AM   #14
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if the crosshatching is still good on the nikasil, there should be no need to do anything with the cylinder. you need to take precise measurements of the bore, and check the ring end gap when fitted inside the cylinder to see if it falls within spec.
no need to EVER bore a nikasil coated cylinder unless damage was done, and in that case, best to just buy a new cylinder.
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Old 11-03-2014, 06:34 AM   #15
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To my eyes from those pics it looks like the piston and cylinder are worn out.
The best course of action is to get the cylinder sleeved to the original size with a cast iron liner and a new piston and rings.
Cast Iron liners are fine, they work well, Nikasil is used because its lighter and can be made in one process rather than fitting a sleeve to the block.
Looks like a high hour engine or lack of maintenance to me.
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