08 rmz250 smoking bad

JakeqB97
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JakeqB97
I have an 08 rmz250 that I bought recently. The guy said it stopped running and smoked real bad before it stopped. I replaced the head and transferred the three good valves into it and replaced the bad exhaust valve. I lapped them all and put new valve seals and hot cams. I had the clynder professionally honed and the same man got a pro x piston specifically for the new bore size. All new gaskets. The bike runs great but smokes bad after it warms up and is going through oil pretty quick. I don't see any oil in the intake port but there is obviously some in the exhaust port but not on the valve stems. This is the second cylinder I've had on it and second piston. I've torn the motor down three times now. The oil screens were covered in nasty dirt but I thought I tore the cases down an cleaned everything well. I'm lost.
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Paw Paw
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Paw Paw 9/28/2017 1:22pm
9/28/2017 1:22pm
FYI: You can't lap these valves as it removes the special coating on them. They will not last .
Did you have the valve seats cut?
Did you put in new valve seals?
Did you check the valve guides on the exhaust side?
What was your ring end gaps?
Was the cylinder checked for size?

Paw Paw
JakeqB97
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JakeqB97 9/28/2017 1:30pm
9/28/2017 1:30pm
How do you insure a good seat then? And no, the head is brand new OEM and it came with the guides installed. Yes brand new valve seals. And don't know, I had the cylinder professionally honed and he got me a piston for the specific size. I took it to a professional engine machinist.
Paw Paw
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Paw Paw 9/28/2017 6:31pm
9/28/2017 6:31pm
If the valves are new ( and 3 of yours were reused and not new) and the seats are new, then they will seal. The lapping of the valves will shorten their life at 10 fold.

If you had the work done by a good machinist , then you need to visit with him on the oil usage. I do however suspect bad blow by with an ill fitting piston and rings and or bad valve seals.

I would also suggest that you redo the valves with new ones as the ones you have will not last now.

Paw Paw
JakeqB97
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JakeqB97 9/28/2017 6:41pm
9/28/2017 6:41pm
So here's what I found. I understand your point on the valve seats and that's a lesson learned. I will replace the valves before putting it back together. The gasket kit that I bought included the valve seals which I have just discovered are way too big. They did seem loose when I put them on but i trusted in the gasket kit (tusk) and thought it would be ok.

The Shop

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JakeqB97
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JakeqB97 9/28/2017 6:43pm
9/28/2017 6:43pm
Do I need to have the valve seats redone as well?
JakeqB97
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JakeqB97 9/28/2017 6:47pm
9/28/2017 6:47pm
I've also never heard of not being able to lap these valves. I've seen it done in a few bikes and quads and have never heard of anything happening. Are you saying you have to redo the seats every time and get brand new valves when they go bad?
Paw Paw
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Paw Paw 9/29/2017 8:27pm
9/29/2017 8:27pm
JakeqB97 wrote:
Do I need to have the valve seats redone as well?
They may need a light touch up cut.

Paw Paw
Paw Paw
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Paw Paw 9/29/2017 8:35pm
9/29/2017 8:35pm
JakeqB97 wrote:
I've also never heard of not being able to lap these valves. I've seen it done in a few bikes and quads and have never heard...
I've also never heard of not being able to lap these valves. I've seen it done in a few bikes and quads and have never heard of anything happening. Are you saying you have to redo the seats every time and get brand new valves when they go bad?
When the valves go bad the seats are normally damaged and need to be recut or replaced for new valves.
Lapping valves now a days with them having special coatings on them shortens the valve life. If stainless valves are used ( they are weigh more) then lapping can still be done.
The best match is Ti coated valves using copper bi seats. This combo will save the valves as the seats will take all the abuse. This combo does cost more, but yields very good hp and revs. Re-shimming the valves becomes more frequent as the valves do tend to beat the seats a good bit.
So you can go OEM, stainless or go big dollars for the most bang, but each has it's draw backs and good points. You just have to choose. Remember ... "speed cost money...so, how fast do you want to go".

Paw Paw

ktm-5
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ktm-5 9/29/2017 9:01pm
9/29/2017 9:01pm
I agree with everything paw paw said

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