KTM Top end question

[MikeS]

Strick

You may indeed have a lean condition. Just curious though. Did the Exhaust side of piston actually melt or is it beat up???

I just caught a disaster just in time thanks to Denny at HS. I put in a set of rings,OEM,ouch. and did one ride. I noticed a ticking noise when I kicked the bike over. Dealer said it is normal they all do that. Well I pulled the pipe to find the Power valve hitting the top edge of piston. Dimensin "Z" was perfect in fact alitte + side,allowing more clearance. I had cleaned the PV that was gummed up from previuos owner castor type oil. What I failed to notice was the lateral play in the PV shaft. Denny had mentioned that sleeves are used in the 300 not bearings and the shaft can wear. I did a quick mechanics fix (trimmed valve,new orings) just to get by this weekend.I hope.....

As for mobil that is good stuff. I use Amsoil and the cylinder ports and head are squeaky clean. Even when I switched over oils on this bike it cleaned up everything.

Goodluck,Have a good weekend riding.

Mike S

[This message has been edited by MikeS (edited 03-01-2001).]

 

[Strick]

Mike, My next door neighbor tore his '99 380 down last night. His power valve has the lateral movement you mentioned (side to side). My PV was first stuck closed. After the cylinder cleaning (acid etching) it was stuck open. Now it still does not move as freely as I would like, but it does not open all the way with the linkage on. With the linkage off, it will open all the way. It seems the additional restitance the linkage provides, in combination with its' gummy state has created my dilemma. I did clean it with solvent then WD-40 in large doses, next Easy Off.

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Strick '99 KTM 300mxc, AMA & BRC member

 

[EnduroAddict]

Strick,

I have no experience with power valve cleaning & service, but I have a copy of a Dirt Rider Mag article on power valve care. They used a KTM for the example. They used Easy-Off, but no longer than the specified time period. Then a second coat with a Scotch-Brite pad. Another option, and sounds more reasonable to me, to have the parts cleaned with a glass bead blaster at a machine shop.

They also mentioned that a stuck power valve can cause overheating and seized piston. Your power valve may be at root of these problems.

 

[Strick]

EA - Do you know which Month/Year Dirt Rider? I would like to read the article, and probably have the issue at home. Thanks!

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Strick '99 KTM 300mxc, AMA & BRC member

 

[EnduroAddict]

My buddy copied the article for my archives. He cuts out the important stuff and tosses the mag. I don't have the month, but I'd guess it's from a 2000 issue in the Tech Tips section.

 

[erdento]

Strick: Sounds like you've got a problem. What seemed a little odd was that you stated earlier you've been running a 178 main in our current temps. I've been running a 170. The lean condition that caused the burned piston was with a 168 during the peak heat of the summer out at Sand Mountain. I may be a little lean on top now--I'll try to check before this weekend--but not much; I don't have the lean miss syndrome the 168 presented. The KTM jetting charts show the 300 taking smaller mains compared to the 250. Also, I am running c-12 mixed 32:1 (but ran straight pump gas with the 168 this summer). You are running 40:1. This should make the 250 run leaner than the 300. It appears odd that our bikes could be jetted so differently and with the fuel differences and you have had such a problem. Have you ever boiled over? Any signs of an air leak?

 

[Strick]

erdento-

I was going to post my diagnosis later, but I will post it now.

I am not jetted too lean!!! However a WFO desert race with a stuck power valve, maybe I was too lean given those two factors. Having said that I am going to a 180 main for breakin. Here's what happened: My power valve stuck closed at some point during the last race. The race was very sandy, and some very long WFO straights. I feel this generated my over heating problem. The piston actually started to melt. The bike did not leave me stranded and actually ran strong all the way to the pits (95 miles worth).

I ran Golden Spectro Pre-mix (a blend)in my bike for the first four months or so. Golden Spectro is notorius for being gummy and messy (spooge). It does lubricate well, however. I switched to Mobil MX2t about 3 or 4 months ago. I really like the way it lubricates, and the way my bike runs & smells on it. The Golden spectro left the power valve gummed up. After a couple of months of a cleaner 2-stroke oil (MX2t), it created a very sticky power valve that eventually stuck altogther. To some this may sound unreasonable, but I think it is very sound logic.

Anyway I think the bike will be back together tonight. Are you riding Sat or Sun? Let me know

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Strick '99 KTM 300mxc, AMA & BRC member

 

[Strick]

Top end finished, rode 50+ miles, after a 15 minute break-in. The thing flat rips. Wiseco pro-lite piston, and I did add a Delta II-VForce reed cage. Thanks for all the replies!!

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Strick '99 KTM 300mxc, AMA & BRC member