When is time for Valve & spring replacement

I have 24000 hard KM’s on my 2007 DRZ400sm with stock muffler with powerbomb, hotcam intake, with MX-FCR and 3x3, I do regular check of valve spacing, say once every four months of riding, always need to make a small change to one of the valves clearances. To me the bike runs fine from what I can tell power wise, but nothing to compare to.:thumbsup:

-I would like to know when or how do I tell when, it’s it time to replace all valves & springs? Or just valves??

-In addition how to replace the valves, I understand how to get the valves physically out and in, but is there anything that is needed or should be done to do with seating new valves, or is it just a straight replacement?

-In the future I would like to do a big bore, would the OEM valves and springs be acceptable. Alternatively, is there a more suitable make of springs and valve required of a future big bore?

I don't think there is any standard time for valve and spring replacement. The fact that you are constantly replacing shims several times a year leads me to think it is time. Clearances can remain very stable for a long time. But when they start to move they can move quite rapidly. I would say if you have changed shims 3 or more times on any one valve, it is probably time for a valve job. The valve seats in the head will need to be refinished when new valves are installed. I'll let some one else comment on brand of valves and springs. For most people stock is fine but there is other stuff available. A good valve job using good parts will be fine for a 440 kit. If you are going bigger than that, then some additional valve work would be in order to take advantage of the larger displacement.

for bigger valves you need different cams than the hotcams, you should have a big bore and stroker crank too if you want to take full advantage of the bigger valves. take your head to a reputable machine shop and have them check the whole head. they'll check your springs to make sure they're within specs. the need for shimming isn't normally a sign that the springs are bad, it usually means the valve seat/valve meet point is worn. a good shop will even reshim your cams if you give them the cams.

39Fcrmx, hotcams and stock valves will limit the potential of a stroker motor..

You could stay with the above and have a strong mid range engine, but your top end will struggle to produce HP...

I have ran the above on my 485..and then went to 41fcr, RHC187 cams and +1mm RHC valves ( with stage 2 spring kit)...Supplied by Eddie..

and head flowing

Resulting in substantial overall improvement, especially the top end...:thumbsup:

Edited by CraigoDRZ400sm

the big bonus with the RHC gear is the reliabilty factor .

the stock valve gear would be a concern to me in a modded motor

always need to make a small change to one of the valves clearances.

change in clearance is a sign.

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