Shaw520

Damn Yankees
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I just did valve adjustment on my new 400SX, and all four valves were tight!! I have aprox 20 hours on it,... I was contemplating waiting till after my next ride this weekend,..... Glad I didnt wait. The manual says valves should be adjusted every 15 hours.

This is strickly theoretic, but; could this be somewhat related to cam bearing failures, without sufficiant valve clearance, the impact during combustion could be placing an extra amount of pressure through out the valve train,...??? Ordinarily, this pressure would be transfered to the valve seats, where it should be.
Any comments?
 

Anssi

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May 20, 2001
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My valves have not lost adjustment or worn out since the first time I adjusted them (and I have several times). My cam bearings on my -02 520 SX went at about 70 hours of riding time.
 

SFO

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Feb 16, 2001
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Originally posted by Shaw520

This is strickly theoretic, but; could this be somewhat related to cam bearing failures, without sufficiant valve clearance, the impact during combustion could be placing an extra amount of pressure through out the valve train,...??? Ordinarily, this pressure would be transfered to the valve seats, where it should be.
Any comments?

The valves get rid of 80% of their heat through the valve seat/valve face junction.
If the valve has insufficient clearance the valve face stops shedding its heat into the seat and the valve starts to lose thermal stability.
Maybe the valves were on the tight side out of the gate?
On fleas 520 after it ate the 3rd decompressor bolt we took the head apart and there was enough face errodsion on the intake valves to justify replacement, even if they weren't bent.
If the cam brg was loose it would create more cleareance?
 

Shaw520

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Originally posted by SFO


The valves get rid of 80% of their heat through the valve seat/valve face junction.
If the valve has insufficient clearance the valve face stops shedding its heat into the seat and the valve starts to lose thermal stability.[/ QUOTE]

This heat you speak of,.....then gets transfered to where,..????
[ QUOTE]Maybe the valves were on the tight side out of the gate?[/ QUOTE]
could be,....
[ QUOTE]On fleas 520 after it ate the 3rd decompressor bolt we took the head apart and there was enough face errodsion on the intake valves to justify replacement, even if they weren't bent.
If the cam brg was loose it would create more cleareance?
If the cam brg where loose, I think its already too late, what I am trying to say is the lack of valve clearance COULD be creating undo stress on the entire valve train,.. which would include the decompression bolt,..?
 

SFO

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The heat passes from the valve face to the valve seat to be cooled by the surrounding material in the cylinder head.
Insufficient clearance has problems unrelated to the cam brg~decompressor bolt IMHO.
The husaberg head which is nearly identical had fewer issues when the decompression cam was replaced with a older non-decompressor style cam sprocket and the rockers were converted from bushed to needle brgs on the pivot shafts.
They would run for a whole season at the national level with the only maintenance be occasional valve jobs and spring replacement.
If your valves sucked all the clearance out already I would pop the head off and identify the point of wear. (Thats just me and I am a bit rectal about these things having a cylinder head shop.)
Or seeing as you buy a new bike each year forget about it and just monitor the valve clearance and document it closely clearance vs. engine hrs or gals of fuel.
This makes good science and I appreciate your insights.
 

70 marlin

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Originally posted by Shaw520
I just did valve adjustment on my new 400SX, and all four valves were tight!! I have aprox 20 hours on it,... I was contemplating waiting till after my next ride this weekend,..... Glad I didnt wait. The manual says valves should be adjusted every 15 hours.

On a scale #1 to # 10. how tough of a job was it? also could you give a detail explanation of the process? as I'm planning on my nexted bike will be a used 400exc. thanks!!!!!!!!!
 

Shaw520

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Marlin, I have maintained three different RFS, and have adjusted valves a total of five times, the more you do it the easier it gets. Remove the radiators, it makes life alot easier. Many guys have a hard time locating TDC. I have found that with a good pen light, you can see the top of the piston through the sparkplug hole, rotate the engine by hand, ( I put it in 6th gear and use a 17mm box wrench on the counter shaft) Turn the engine over very slowly with the coutershaft till you see the intake vaves open, (they will compress), at this point hold the wrench tightly cause the engine is going to want to spin ahead, right after the intakes close, look into the sparkplug hole, you will see the piston coming up, now you can visually get the piston a TDC, At this point you can adjust all four valves, use .005 angled feeler gauge. Always recheck the clearance after tightening the lock nut.
Ive got it down to about 45 mins. Do a search here before you begin, there is a very informative thread in archive.
As far as #1-#10,......If changing the oil is a #1, then this would a #3. :thumb:
If you have any questions PM me and I will try to help.
 

70 marlin

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First I need a bike :whiner: but till then I can research the bike and motor! I was really intrested on what was stated about the cam deterioration. what I've heard about motor cycle valve's have the habit of going tighter. and the damage cause would be in the line of cam's & retainer bolt failers? what have you seen on the RFS motor? :think:
 

Shaw520

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On the RFS's I have ridden and maintained, I have experienced zero failures,...cam bearing / valve train or otherwise.
But, I'm not trying say that this is, or is not directly related to valve clearance maintnance, I'm sure there are people who may have maintaned there valves and still had failures! >shrug<
 
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