KX Riders
Maintenance & Technical => KX500 Original => Topic started by: ktmdude on August 14, 2010, 06:22:48 PM
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So I striped the top end down on my uncles 91 k5 today. It had boiled over and lost compression during a race and would not restart. Once I got it apart I found that the edge of the piston had melted, some of it melted to the cylinder, but I do not see or feel any gouges on it. When I turned over the cylinder to remove the power valve I saw cracks on the back side of the sleeve where it connects to out side of the cylinder. Not real sure how to explain, but hear goes, on the sides, not front or back of the cylinder there is two(one on either side) "braces" that support the sleeve. They are both cracked where they hold the sleeve. I also found cracks in the intake on the two vertical bars at the sleeve. Can I have it welded or is it a paper weight? Does anyone here fix this type of stuff? Or does anyone have a good cylinder to sell me? What would you guys do?
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Unless the cracked parts are moving it'll be fine. I had a Suzuki LT500 that had cracks in the intake and near the same areas you speak of. I inquired about them and was told it'll be fine. I ran the snot out of it that way and didn't blow the motor.
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some photos would be usfull. mark the cracks with a marker pen
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sorry to hear bout that ktm dude.
I`m sure you will find the best fix fix for the problem.
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I have cylinders and heads for sale. let me know if you are interested.
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If your racing that thing then junk the cylinder and find a stock sleeveless cylinder and have it plated or coated from US Chrome or Max Power. That stuff holds up way better to race loads than a sleeve.
Did you figure out why you had a meltdown to begin with ? lean jetting will destroy a top end and or cylinder, maybe water pump failed. Are what appears to be cracks really cracks or casting marks ?
get some pics, the guy's on this sight are a wealth of help
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It is a stock sleeveless cylinder, and it is definitely cracked. I said "sleeve" for lack of a better word. We think it was jetted well, not sure about the water pump, I'll have to take a look. There was a couple of bad bottle necks on the harder rock garden sections. It boiled over at idle. Think it melted due to lack of water. I'll try to get some pics later, I'm a lot better on a bike than on a computer, I'll see if the gf can help me. lol I'm thinking of starting fresh with new (used but in good shape).
The rod feels good, no up and down play. Do you think that anything could have happened to the bottom end?
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Maybe the plating is worn off the cylinder wall in that spot or maybe real thin due to age , that would cause major piston failure and overheating. you did say it was a 1991. do you know if it's ever been replated ? if not thats a long time on the junk factory eletroplate. Maybe the piston and rings were too aged to handle race loads. any idea on the age of those ? I once was stuck at a bad bottleneck at a GNCC race for porbably 10 min at idle with mud packed around motor and radiators and did not overheat. I was surprised I didn't break down, Four stroke bikes were dropping like flies. The steam from boiled over bikes was like a swat team smoke grenade. Most of the two smokers made it thru.
If your crank still cycles smoothly and has no noticeable play, run it....
get a new cylinder, im sure someone here could get you one for short money, once again go back to the water pump for certainty and double check jetting once you get cylinder issue fixed.
I'm surprised no K5 experts have chimed in yet ??? anybody ???
Hope some of this info might help as I once experienced this with an older bike also. my problem ended up being worn plating and poor jetting ( the bike was an 87 K5)
Keep us posted with your results and good luck
PS - just thought of this, check your stator plate position to make sure it didnt move from normal setting maybe the screws loosend up and the timing advanced a little and overheated
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It had 35 hrs on complete rebuild, top and bottom, and fresh dip. He was running the some jetting that he ran last year at the Rubicon, witch is the same elevation as the race that we did. About the same temp. also. The bottle neck was just like how you described, 4st blasting tear gas, But rich 2st exhaust was pretty thick also. I was glad to get threw it. I re jetted my 300 to the factory chart and had no problem. But this post is not about me and my bike,... he is thinking about asking the Destry Abbott site if they would sell him any old race bike stuff(cylinder and head). Get a new piston and rings slap it back together and mix up some race gas and let her fly. I will take a look at the water pump, and stator. What should I be looking for? What are your thoughts on old race parts?
P.s. We road the Rubicon last year with 10 hrs on his fresh motor, so not much had changed.
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My cylinder was cracked, and the welding to fix it was only $60 on top of the replating. For me this was better than getting someone else's old junk. The left side in these is rewelded, the right side is original. It looks cracked as well, but that is actually just the parting line on the casting. From you description I think you are describing a crack in this location.
(http://i106.photobucket.com/albums/m252/snoopjonnyjon/100_0044.jpg)
(http://i106.photobucket.com/albums/m252/snoopjonnyjon/100_0046-1.jpg)
As well as a crack on the two webs shown on the underside here? Mine weren't cracked, but had the same grooved out casting flaw that sure looked like they would be prone to cracking there.
(http://i106.photobucket.com/albums/m252/snoopjonnyjon/100_0045-1.jpg)
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You nailed it, two cracks on the intake in the same spot as you. I am not to worried about having them repaired, it seams straight forward. At the web where it becomes part if the "sleeve" (it is a stock sleeveless cylinder) there it two long cracks on the web not the "sleeve". I don't see how someone can fit a tig torch in that small of area. Please let me know if anyone has had a repair like this done. Does anyone know the correct word so I can stop saying "sleeve"? Sorry for not having pics, I am lame with computers. My uncle called LA Sleeve, they said that they can fix it, but my uncle has not seen the cracks, so I know that they don't know where the cracks are. Has anybody had any experience with LA Sleeve, good, bad, or indifferent?
Thanks.
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Here are the pics of the cracks
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Last I read somewhere that cracks in this spot is common in k5s. Anyone had anything similar. Can it be fixed?
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Cracks are very common and can be fixed good. I would say the cracks you have there are uncommon and catastrophic. I would scrap that jug.
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Get a base pan and fill it with sand...makes a great ash tray.
Buy a used one and get it plated here....
http://www.maxrpms.net/shop/index.php/extra-nav/plating-repair.html
or you can get a brand new one for around $550.
Factory plating isn't as good though.
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It's real hard to tell from those photos if that is a crack or just another badly blended area caused by the sand cores not being properly pasted at the foundry. The exhaust ports and intake - boost port ribs suffer from this problem. They look like they're broken when new. The sharp lines create a stress riser that helps bad dreams come true, a real crack.
The transfer rib is an area of low stress and relatively thick material.
Take a small diameter round file and remove some material from the area you believe to be cracked. The flaw may be only skin deep.
Larry