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wweagleflyer

Valve Spring Compression Test

7 posts in this topic

I have searched the forum and can't find any reference to how to do a spring rate test on the valve springs for an 06 YZ450F. The manual says to do a spring rate test on the valve springs by applying a specific force to the srings and measuring the deflection. I can't think of a good way to do this while being able to take an accurate measurement.

I noticed that there is almost no reference on the forum to either doing this test, or replacing the springs. Do the valve springs seldom need to be replaced? Has anyone else done this test?

Also, I understand that the titanium valves are not to be lapped (per multiple references on this forum) despite the manual saying to do so. I don't undertand how you can match the valves to the seats then without lapping them to the seats, for example if you need to replace a valve in the head?

Thanks

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You need a valve spring tester or make one using a scale and a drill press of some sort ( not a good system with the low rates they use) The springs are pretty tough but new ones are not too costly so replacing them is the way to go. If the seats and valves are true and flat they will seal as with fresh cut seats and new valves. What most engine builders do is lap the seats with used valves and install new parts.

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The way you match the seats and valves is by precisely cutting the seats to the correct angle. If they are finished round and concentric, and at the correct angle, they don't need lapping.

Lapping with used valves is improper because it imparts the worn condition of the old valve to the freshly finished seat, essentially destroying the work already done.

As far as springs go, just replace them. They are dirt cheap compared with the trouble one could feasibly cause.

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Lapping with used valves is improper because it imparts the worn condition of the old valve to the freshly finished seat, essentially destroying the work already done.

Then I guess that leaves my original question unawsered if you need to replace a valve. Do you buy one new steel exhaust valve and one new steel intake valve and use those only once to lap the valve seats, or do you just have to take the head to a machine shop get the seats recut?

If you remove the valve to inspect, decide it is good and reinstall it, do you need to be concerned about how the valve is rotated in the valve seat to match with the original wear pattern, or do the valves rotate around enough while the engine is running to create a uniform wear pattern circumferentially around the valve face/seat?

I also recently read that you are not supposed to use chorinated solvents on titanium valves due to the potential for stress-corrosion cracking. Before I read that I had used a chorinated solvent to clean the valve seats, which means that some could have got on the valve faces when I reinstalled the valves. How big of a deal is it if I did use a chlorinated solvent? I know to be careful not to get chlorinated solvents on rubber seals, but I generally use them liberally to clean other metalic parts. Is this a bad practice?

Thanks

Edited by wweagleflyer

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Actually, it did answer your question:

The way you match the seats and valves is by precisely cutting the seats to the correct angle. If they are finished round and concentric, and at the correct angle, they don't need lapping.

When replacing a valve, have the seat refinished by a machinist equipped for the task. Lapping will not refinish a worn seat.

Chlorinated solvents (which are mostly "brake cleaners") are only an issue if a significant amount of it remains on the parts for an extended period. I know of no problems I've ever experienced from their use. OTOH, I don't use them much. The carb cleaner (Berryman's B12) that I use for all kinds of stuff doesn't have any chlorine in it, and neither does shop solvent, mineral spirits, or paint thinner. I use brake cleaner on brake hydraulics and as a prep for some sealers because it dries without any oily residue at all.

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