Starting a tear down. To Nikasil or sleeve?

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P1KL3
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Location: Sydney, AU

Starting a tear down. To Nikasil or sleeve?

Post by P1KL3 »

Hi guys and gal's
I am commencing a kr1s engine rebuild. In initially tearing down the top end I discovered that at some stage the cylinders have had a steel sleeve pressed in. They measure 56.51mm. One cylinder is still very good condition with a very fresh hone cross hatch. The other seems to have suffered a cold start up seizure or an issue with the intake on that cylinder creating too much heat. I have not spent too much time measuring port timing tho I have noticed quite an excess of sleve windows interfering with the cylinder exhaust port and its much more pronounced on one cylinder than the other. There is also a deposit of piston material on the cylinder walls of one cylinder.
I have the option to use a standard kr1b pair of cylinders on the on b sized pistons.
I believe timing is improved on the s cylinders but I'd hate to go ahead with the sleeves if sleeve/port timing is going to cause issues.
Ideally I'd like to prep both sets and have the sleeves as spares in times of recoating or ordering pistons (will be a daily rider) but could use the funds on other items of repair...

So asking a couple of basic questions...
Pros and cons of steel bore on kr1s?
Am I better off using the kr1b cylinders or the kr1s steel sleeve?
Can a sleeve be coated? Is it worth doing?
Any advice in this area is greatly appreciated.
I am sure I will have more.

Oh and as soon as I figure out the pics I will start a proper resto/custom thread.

Thanks heaps in advance.
Dill.
09 zx10r only owner 100k odo
92 aus kr1s
89 vj21
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James P
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Location: Sydney, Australia

Re: Starting a tear down. To Nikasil or sleeve?

Post by James P »

If the sleeving job is good, you could just have them bored and/or honed and use oversize pistons for Yamaha TZR250 (1KT-based models) - these are practically identical to KR-1/1S pistons, the slightly larger bore size being the only real difference. There are also other TZR125 and DT125R pistons which will work.
If there are any areas where the sleeves don't match the cylinder casting, it may be possible to clean these up. However, it may be worthwhile spending a little extra time to make sure port shapes and sizes are the same between the two cylinders. If there is any sign that the sleeve has moved in the cylinder since being pressed in, it may be a bit risky to use it.
I understand that sleeves can be plated, but there should be no real need to do this unless they are particularly soft, or if you can't get oversize pistons.

If your bike will just be a road bike in fairly standard trim, I doubt you would notice much/any difference in performance between KR-1 cylinders and KR-1S cylinders (everything else being equal).

I would have no qualms using sleeved cylinders if I knew that the sleeves had been fitted properly...but I suppose that is yet to be determined in this case. If you have a set of KR-1 cylinders in good condition with matching pistons (also in good condition), that may be the most cost effective option.

Let us know what you decide...or if you discover anything else about the parts you've got.

Regards,
James
stevo135+
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Re: Starting a tear down. To Nikasil or sleeve?

Post by stevo135+ »

If I'd followed this advice my KMX would have been off the road a week or so at the most. It would have only probably needed the old steel sleeved cylinder honing and a new piston to match.

But my sleeve was pitted, scored and was a terrible match to nearly all of the ports. Only the main exhaust port was close to matching. The ports that were supposed to be rectangular were all either oval or shaped like a hovis loaf.

I guess it was fitted and then someone went in with a die grinder to hand match the port windows to the sleeve as best as they could this way. Don't get me wrong, I'm not saying that I could do a better job myself, I'm sure I'd balls it right up. But compared to standard it was inferior in several ways.

If having the bike running as well as it possibly could in standard form would bother you then it wasn't acceptable from a performance point of view I'd say. But then again it still ran ok and rode ok too, but the dyno number was lower than expected. If I'd never been to the dyno I wouldn't have known really that it wasn't great. I'd ride a bike that's had a sleeve fitted if I needed to, or didn't want to spend much on it, or didn't use it enough to justify extra work and expense.

I probably should have listened to my own advice there, but it's a slippery slope doing extra work or fitting aftermarket parts to a bike as you don't like to think your leaving untapped potential behind by just putting it together and riding it if it runs ok and is reliable.
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