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KLX 300 Jumped Timing After Valve Job


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I recently picked up an 01' on a trade. It had slightly bent intake valves (no damage to piston & head). Timing was spot on prior to disassembly, exhaust valves were on spec. I put new intake valves in, lapped them for good measure. After cams were in I measured .30 clearance on the new valves so I shimmed them within spec. All timing marks were good, brand new tensioner (old one was bad), torqued all to spec and I put engine ass'y lube on the cam lobes etc.

The bike fired right up and ran great on a test run. It would not start afterwards so I double checked the timing again....off by about 2 teeth 😏, timed it up again and it fired right up. It ran for a minutes minutes and shut it's self off. The kick start was stuck 😏 so I checked timing again....Off again by about 3 teeth and my intake valve clearance is way off (telling me my new valves are bent).

What are the symptoms that would cause timing to jump like this ?

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Wow!...taking for granted that you indeed had the cams timed properly as you state...and that's not suggesting that you didn't...I'm guessing that something is amiss in your tensioner and/or the cam chain guides. This engine just won't throw the cam chain like that if the tensioner and guide blocks are doing their job. Since you state your cam chain tensioner was defective, I'm thinking something is going on with the new tensioner and guide blocks. Are you sure that you got those long cam chain guide blocks into their appropriate locations in the cases?

The KLX has been showing some issue with the OEM tensioner for some reason. My '06 had the cam chain worn out in 11,000 miles because of the tensioner. The tensioner shows no wear or malfunction signs, but it does not do its job. This is not an isolated incident. Mark Kreiger of Kreiger tensioners made a manual tensioner for the KLX, and I may have the prototype arriving today to try out. That's what I'm going to do to eliminate the sketchy performance of the OEM tensioner. Many never have an issue with the stock tensioner, but many have reported this problem. Surprisingly my cam chain guides showed almost no wear when compared to new units, but the chain made a nasty slapping/knocking sound and was out of spec at the mentioned mileage.

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Right on...the old tensioner was sprung all the way out. If you would try to push it in it would just pop back out. I did push the new tensioner all the way to reset it (per manual specs).

I am 100% sure of my timing set-up, even put a dab of paint of the # 32 pin for extra re-assurance.

The guides could possibly be the issue, maybe I didn't do something quite right when feeding them through the head. I will run out to take some photos to help illustrate everything.

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Right on...the old tensioner was sprung all the way out. If you would try to push it in it would just pop back out. .

That's the way it should work. The ratchet prevents the plunger from going back into the tensioner body. When remounting the tensioner, remove the spring, move the plunger into the body, mount it on the engine, and then put the spring in.

Ride on

Brewster

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There are two cam chain tensioners. One of them pushes on one of the cam chain guides. This one is just spring loaded, no ratchet. It is located a couple inches below the ratchet unit.

Ride on

Brewster

Heck, I wasn't aware of a second unit 😏 ... I'll check it out and come back with some pics

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That's the way it should work. The ratchet prevents the plunger from going back into the tensioner body. When remounting the tensioner, remove the spring, move the plunger into the body, mount it on the engine, and then put the spring in.

Ride on

Brewster

The old one would not ratchet, it would allow to chain to float back and forth at will. It was prob the cause of the bent valves when I picked it up. I did take the proper installation steps per the manual. Just like you mentioned and torqued to 11 ft lbs.

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There are two cam chain tensioners. One of them pushes on one of the cam chain guides. This one is just spring loaded, no ratchet. It is located a couple inches below the ratchet unit.

Ride on

Brewster

Brewster...I believe that both tensioners push on the same guide block...the one to the rear of the cylinder and head. I'm wondering about this two-part tensioner design. I can't recall a setup like this on any of my other bikes over the years, even those with double overhead cams. If I recall, they all operated with one tensioner...even my KLR600/650's. I wonder why the KLX has 2 tensioners?

KD...the front guide block is the one that is critical about placement when you make sure it's bottomed out down into the case...it fits a certain way in a kind of slot there. The rear guide block is the really tall/long one, but it's bolted to the case. I had to be careful when installing that front one, as I thought it was bottomed out but really wasn't when checking everything out before installing the cylinder. In your case I know you had the head off, but I'm thinking...it's been several months since I did mine...that front guide block may not be disturbed if you didn't pull the cylinder.

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