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rush66

Looks like I get to replace a few parts and I have a few ?'s

4 posts in this topic

Well due to some misfourtune and stupid mistakes I lost the case drain plug and ran my bike without oil. The engine started to seize when I killed it coasting down a trail. The bike is a 99 400

I tore into it and found most everything in the head to be OK. There is slight wear on all the cam sprocket teeth but all the lobes check out. The head and valves appear to be in good shape too.

As for the piston and cylinder, they're toast. The piston was badly scored and the cylinder isn't pretty either.

Due to the lack of lubrication the crank did blue a little bit but the bottome end from what I can see looks to be in good shape too. The rod looks OK. The crank bearings look OK too, it turns over smoothly.

Is a blued crank cause enough to replace the crank and everything else in the bottom end?

As for the piston and cylinder if I could leave the bottom alone I think I'd probably just do the 420 kit. I know that I'd like to go with the 426 parts if I have to split the cases.

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If it were mine, I'd definatley have the crank rebuilt. A new crank pin, bearing, rod, and main bearings would be installed. I would also take a close look at the oil pump because it might have some damage too. Most likely the wear on the cam sprocket has nothing to do with a lack of lubrication and is just normal wear. Sounds like it may need to be replaced as well as the cam chain.

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The "Bluing" around the big end of the crank is done at the factory, and is normal. If the big end suffered that much heat in operation, the bottom of the rod would have turned an ugly black color.

Remove the cams and check the bearing surfaces in the head and cam caps. If badly galled, Engine Dynamics can repair it.

The piston failed because it did not get any oil. The source of oil for the piston is the oil thrown off at the rod bearing. You follow the logic, right? The piston needs oil much more desperately than the rod bearing does, and will normally suffer damage long before the crank is injured, but my advice is that you take the crank (in or out of the bike) to a competent mechanic and enlist his opinion if you have any doubts about your own.

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It does seem that I recall the same blue marks on the crank last time I had it apart. The rod is it's normal color.

The cams and all the surfaces in the head all are fine. The only damage I can really see is on the piston and a little scoring in the cylinder.

Do you think I might be ok if I just put a new top end in it? I just talked to a machinist friend and he said the same thing I was thinking. There is still a little aluminum buildup on the cylinder wall but the scoring is deep enough that it has taken of some of the coating. It would run with a good hone but not to it's full potential.

I've been looking around and found that if I wanted to do a 420 kit that Pro-action has a place near by that would do it and they have the piston kit to go with it. Anyone had Pro-Action do motor work for them? They list their prices at $225 for boring and re plating and $131 for the 420 piston kit.

Anywhere else that would have as quick turn around time and be close price wise?

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