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KLX 300: serious overhaul

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Ok so its december now in wyoming. After a long hiatus from dirt bikes I picked my 98 KLX 300 about 2-3 months ago. I put off the major check up because I was having too much fun riding it to pause and tear up. That's not an issue now(its about 0 F right). The bike has a good compliment of stroker products (365 cc, pumper carb, compression release, goldtech valves). I think the bikes been ridden hard, but maintained. Obviously I'll check the valves, take down and lube the linkages, I should probably inspect the piston and rings as well. I was thinking of sending off the stator for a rewind as well. I've got the 250/300 manuals and some experience with auto repair, but not much with dirt bikes. So what else should I be on the lookout for? and the frame needs a paint job...any recommendations on color?

Thanks

Brad

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If it looks like the bike's seen some mileage (and from your description it does), I'd put in a new cam chain. If the valves are nearing the end of their spec, I'd suggest kibblewhite SS valves and springs.

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I'm not a KLX expert, but for engines in general, do a compression test. If that is up to spec, get the valves set if they are out of spec, and don't worry about it. Well, maybe the cam chain. I hear that is the weak link in the engine, especially on a bike that has been run hard. I assume the starter idler gear has already been replaced.

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Thanks Bill, by valves nearing the end of their spec, do you mean shims no longer being able to place the valve correctly? or some other sign of wear. Any recommendations on where to get SS valves and springs?

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Thanks Bill, by valves nearing the end of their spec, do you mean shims no longer being able to place the valve correctly? or some other sign of wear. Any recommendations on where to get SS valves and springs?

Not a good measure of the general valve condition. General running condition of the bike is your best measure. When the valves go, the leak/seal is best measured with a compression test. If the compression is low and you're not burning oil then it's usually the valves and their seals.

Best direct meaure of the valves is removal of the head and spraying WD40 into the head and seeing if the lubricant stays or leaks away.

BTW, I'm not a mechanic, these are just things I remember from AutoShop 101 in high school. I wish I had taken metal shop. I really feel I could use some welding skills to better use. 😢

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Not a good measure of the general valve condition. General running condition of the bike is your best measure. When the valves go, the leak/seal is best measured with a compression test. If the compression is low and you're not burning oil then it's usually the valves and their seals.

Best direct meaure of the valves is removal of the head and spraying WD40 into the head and seeing if the lubricant stays or leaks away.

BTW, I'm not a mechanic, these are just things I remember from AutoShop 101 in high school. I wish I had taken metal shop. I really feel I could use some welding skills to better use. 😢

I haven't heard of anyone's KLX burning the valves while there was still clearance. Zero clearance is a problem with our bikes.

How do you monitor the WD40 after you spray it into the head? Head removed? Back in auto shop, we would shoot a bit of oil into the spark plug hole and then take a second compression test and see if the compression went up. If it did, it's rings.

Wrench on

Brewster

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Yes. Put your valves back in spec by shimming them. Note the size of the shim you are using to get them in spec. Then, after a few rides, check them again. If they are staying in spec, you're good to go. If the intakes are starting to close down, you will most likely need to shim them again fairly soon - and fairly often. If you are using a pretty thick shim, you have some adjustability left. If you're getting near the thin side of shim spec., then you need new valves.

If you do valves, I would only do Stainless. Kibblewhite has the springs and valves. The springs are around 60 for all 4. Valves are about 32 each. I would not do a half a$$ valve job with stock valves, keeping the stock springs again. Last time thumper racing told me that was OK. Now, after a lot of research, I vehemently disagree.

That valve job only lasted about a thousand miles before we went through all the adjustment and were left with tight valves and no room. Talk to George at ESP. They have a valve guru that has been around for 40 years doing nothing but valves for race cars and motorcycles. Their # is: 818.951.9144.

Ask me in about a year what I think of the job. 😢 For right now, I'm happy with the job. The proof will be in how long they hold up. We only have a couple hundred miles on the new valves right now.

BTW, it is my experience with 2 KLX's that once the intake valves start moving (closing up) after a seemingly unreasonably short amount of time, your valves are shot. If you let them get to zero tolerance, they are shot. If you let a bunch of dirt get into the intake, they are shot. If you are a schreechingly high rever and combine that with any of the above, they are shot really fast (3 months of hard riding/racing).

Good luck, Bill

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I haven't heard of anyone's KLX burning the valves while there was still clearance. Zero clearance is a problem with our bikes.

How do you monitor the WD40 after you spray it into the head? Head removed? Back in auto shop, we would shoot a bit of oil into the spark plug hole and then take a second compression test and see if the compression went up. If it did, it's rings.

Wrench on

Brewster

Me neither. More about valve wear. Years and years ago I had a bike I drove into the ground. Still ran great, but far far weaker then it once was. My brother took the head into a shop and the mech did the WD40 thing and the liquid quickly passed thru the worn valves and their seats.

Right about the oil in the cylinder thing. I had forgotten about that simple trick.

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Once your valves go on the KLX, it will not run "poorly". It will just not start. The first KLX we had that had the valves close down on a long hot sandy run up from Mono Lake to June Mountain took us 2 hours to get started. Once you let the bike cool off it will be very difficult to start. If they are completely closed, it will be almost impossible. They only way we eventually got it started was with a tow rope and another bike. Don't let your valves close down - or they're cooked. Check them every 500 hard dirt miles or so. As long as they're not "moving", you're good to go. After they start showing signs of closing up, prepare for the valve job. This is a know issue with KLX's - as well as most other high performance 4 stroke motorcycles. Guys that used to race KLX's hard like Gary Hazel at Thumper Racing put in new valves every 30-90 DAYS!

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