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Rings Or Top End Kit?

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I have a 2001 XR400 that I am planing to use to commute to work and hit the trails on the weekend. The previous (original) owner says that it is still on the factory bore. I checked the valves and only had to make minimal adjustment to bring 2 of them into spec. It is smoking and looks like it needs new rings at the very least. I don't know if I should just order rings and gaskets or go ahead and get a piston also. I hate to spend more money on it than I need to.

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Smoking while running, I'd suspect rings.  Smoking only after sitting for a while, i'd suspect valve seals. 

 

Also, you can further see if rings are bad, by getting compression check, then adding a bit of oil in chamber and checking again.  If the numbers go up, then rings are probably faulty.  THough i suppose that wouldn't be as easy to see a difference if the rings already had oil on them.  hmmm.

 

I've also seen on here that a hone is a good idea when replacing rings.  I haven't on a few bikes I've ringed, inconclusive results.  So I'd defer to others that know more, and research it further. 

 

Course, if you'd get a piston, a bore hone would be a real good idea. 

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Measuring and inspecting the bore and piston is the only way to tell what is needed.  Your choices are:

 

Hone and new rings in what sounds like a worn out bore, and probably keep adding oil as you ride.

 

Or, a precision rebore with new piston, rings, and valve seals, then you probably don't need to add oil between oil changes.

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Measuring and inspecting the bore and piston is the only way to tell what is needed.  Your choices are:

 

Hone and new rings in what sounds like a worn out bore, and probably keep adding oil as you ride.

 

Or, a precision rebore with new piston, rings, and valve seals, then you probably don't need to add oil between oil changes.

 

So over time the rings will wear the bore? Sounds like the smart thing to do is just get an oversized piston and bore it. Should going to 86mm be enough? Is it worth it to go to a high comp piston at 11:1? Would that require me to use premium gas?

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I think I answered my own question about the high comp piston. It sounds like they are not worth it and that stock comp almost needs premium gas as it is.

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I have a 2001 on it's stock bore and it don't smoke.  Oil changes is the key.  If I was going to tear it down I damn sure would go for the 416 kit with higher comp.  Why not.  The bike is a pig, the parts add no weight and you get more ponies and better response.

 

...unless that's not your thing.

 

And yes I run nothing but premium now.

Edited by XR-rated

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For me, with the hot summer, low compression.  I like to be able to run pump gas and sometimes 87 if that's all there is.

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Decided to order an 86mm (1 over) Wiseco pistion at 10.1:1. Now to find a machine shop that can bore it.  

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