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Cylinder integrity - need opinions
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Posted by: Canon---------------------
Hey people, need advice. I am in the middle of restoring an 89 KDX200. Supposedly just before I purchased this bike, the top end had been rebuilt. Since I had the bike torn down to the frame, and the engine on the bench, I decided to remove the head and check the status of the KIPS section. Will say no more about that other than I am getting ready to order valves. 
Here is the deal. It is obvious top end work has been recently done, head is ultra clean, piston and rings are new. The engine prior to my disassembly ran excellent even with the valves in a state of disrepair. Upon close inspection of the cylinder wall, I notice what seems to be a couple of spots just above and below a cylinder port where the chrome is worn away. Was this a high place on the cylinder wall that caused premature where in that area alone? Is this common? And lastly, should I be worried about
major engine damage if I install the new valves, reassemble, and run the bike as is. I have found no cracks in the cylinder wall...and
as best I can tell...this is the only questionable spot on the wall. Below I will place a link to a close up picture of the area in question. It would be great if any of you would take a look at it and give me an opinion.
http://www.stormpages.com/kdxsquared/picz/cylinder.jpg
Thanks in advance.
Posted by: iainross---------------------
You're not alone.
Your pictures aren't up yet and I'm no expert but I can repeat advice I have been given from other people. Check the thread "converting SR to R" as well, it's where some advice has come from.
I'm in pretty much the same situation. I thought my bike was running fine except a bit flat and lacking some bottom end compare to a mates new 220. I stripped it down and found good rings but a buggered exhaust valve, scored bore and marked piston.
I took the parts to a mechanic friend who said dress down any rough parts with 400 grade wet&dry and plenty of WD40 and put it back together with a new exhaust valve. He went on to suggest selling the bike in a few months to buy something less powerful to get more grip. He doesn't like KDXs and like CRMs.
Another friend, a bike shop owner and mechanic, suggested putting it back together and selling it to get something more powerful. He sells GasGas and wants some extra business.
I spoke to a few firms who sell pistons and carry out replating and they said the rough edges will tear up a piston and cause seizure and further damage. They obviously want some business too.
The last bit of advice came from a friend with years of experience and no financial interest. If you like the bike and want to keep it, it's worth spending the cash. If you're not sure, fix the valves and put it together. Try it for a month or 2. If you're sure you want to keep the bike, then spend the cash. All you will lose is the cost of a gasket set and a few hours to fix it.
You might also ask yourself that if the piston and rings are absolutly mint, are they actually catching on the damaged area. Wouldn't this damage the piston and rings? If there is no damage evident it should be OK to reassemble with new valves. Why spend **** loads on a replate if you don't have to. Remember a replate will probably also mean another new piston set.
Please don't take just my word for it though. As I have already said I am not experienced in either off-road or 2 stroke bikes. There is lots of info around. Check a thread on honing, It contains a link to Eric Gorrs pages on maintenance which includes a section on honing bores and replating.
Hope this has helped.
Iain
Posted by: Canon---------------------
Thanks for the advice....I was hoping to replace the KIPS, put it all back together...and give it a whirl. Still have my ears open for any advice. The
piston seems to travel smoothly thru the entire stroke. Just don't want to wear the cylinder to the point of non-repairability. If I hear no different...will assemble and ride. Sorry about the bogus link to the pics. In order to get there, go to this address, and click on the bottom of the monkeys head. When you get to the pic page....it will be the last thumbnail towards the bottom. Thanks again Iain. Here is the link http://www.stormpages.com/kdxsquared/
Posted by: iainross---------------------
Looks fine to me. Dress down any rough edges and put it all back together. Your valves look pretty bad though, much worse than mine. You should notice a big difference when it's sorted.
Iain
Posted by: Sage---------------------
Looks like the cylinder needs to be replated, its only going to get worse from there.
Posted by: KDX-Jack---------------------
Can a 89-94 KDX Cylinder be bored out ?
My cylinder is 65.85mm ?? The manual say 66.10 mm is the service limit.
EKK....What should I do ?
Thanks ( In advance )
Jack
Posted by: iainross---------------------
Jack
I spoke to a firm over here that specialises in sleeving engines. They said that a kdx can't be sleeved because the barrel is basically a bored out 125. Instead it has to have the plating removed and be replated. They also said that a 89-84 kdx is not nikasil plated but something much softer is used instead. They offered to replate it with nikasil and claimed that this was better than new.
Canon
have checked my bore and although mine is scored, there is hardly any damage around the valves. Yours is worse. It is worth checking whether a replate will require a new piston. I'm pretty sure it will. In that case I would put it back together with the existing piston and new valves and run it for a while. That way you can see if you like the bike before spending big bucks on a replate.
I don't think you will be dissapointed. I've just come back from a 20 minute trip round the local lanes after rebuilding mine. To call it transformed doesn't do it justice. It easily pulls high gears from low revs which it wouldn't touch before. I can climb in a higher gear with more power and have more control since I am not screaming it in the power band. I finished off coming up the lane by my house with a 30 yard standing up wheely in 2nd, totally controlled on the throttle. I nearly shat myself and I'm still grinning now!
Iain
Posted by: KDX-Jack---------------------
Thanks alot for the response Iainross...I think I may use the Eric gorr 225 or 240 big bore kit to fix it.......
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