New Valve Installation?

[400ex2072]

Hey guys, as Ive said before, Im completing rebuilding my top end. I just got my new valves in today so I was wondering about installing them. I have lapping compound here, but is there anything special I got to do to install them? I also have a valve spring tool, so thats not a problem either. Ive heard some speak of "grinding" the valves before installing them, but Im not sure if this just means lapping them up with the compound or not. So what is the procedure for doing this, can I just put some lapping compound on them and then install them right in? I just dont want to leave out anything important, so thanks alot for the help....

[400exredrider]

grinding just means lapping, which really isnt good it causes abnormal wear on the valves.

[MIKE400EX]

You need to have the valves and valve seats ground to true up the angles. Then you should lap them together to obtain the best seal. Lapping & grinding are not the same process. If done properly it will not cause abnormal wear. Sorry, been doing it for 40 years.;)

[wilkin250r]

Lapping compound is an abrasive. The theory is that you put the lapping compound on the valves, and then pull them against the valve seats, and rotate them. The valves and the valve seats sort of "grind" against each other, smoothing imperfections, and allowing for a good seal. Then, you clean them off and install them.

It requires a tool to hold the valve against the seat, and hold it perfectly straight and true while lapping them. If not done correctly, you won't have a good seal.

If you don't know exactly what you are doing, I would either have somebody that DOES know teach you and walk you through it, or else send it to a shop to have it done. In my opinion, its far too critical to learn by trial-and-error.

[400exredrider]

is it the 400 or the 450 that has the coated valves that arent suppose to be lapped? i belive its the 450

[dork]

you're not supposed to lap titanium valves. the oem valves are stellite coated, so you're not supposed to re-grind or dress them, you just replace them when they're worn. but light lapping is fine. you can check the valve seal after you put them in by pouring water or kerosene in the ports and seeing if it leaks out or not.

[MIKE400EX]

"the oem valves are stellite coated"

I just took apart a 450R head and the valves were not coated, they were not in too good of shape either. Maybe someone was in there before?!

[dork]

i meant the 400ex and xr valves. doesn' the 450 have titanium valves? they don't seem to last as long.

[MIKE400EX]

The 400 valves are not coated, at least none that I've ever seen. The CRF450's are titanium, the TRX450's appear to be the same steel that the 400's are. The ti CRF450 valves do need to be replaced often - that's the price of a little more performance.

[TC426EX]

The stock 400ex valves need to be lapped I know that much. I always use a special tool with like a suction on the end which holds the top of the valve shaft once you put it through the guide. You put some lapping compound on on the grooved edge of the valve at the bottom and pull it all the way into the seat throught the top. Then you spin the tool in your hands like trying to start a fire until the valve and seat are matched and seal properly. I use the trick above and pour liquid into the guide to see if its sealing. If you have a good service manual, there are pics and specs of what the valve looks like under different conditions that'll tell you if its done correctly or not...

[Mickey Dunlap]

It is best to always do a good 3 angle valve job on any 4 stroke. Even brand new the valves can leak from the factory. I like to turn the head upsidedown so you can fill the combustion chamber with acetone (or something like it). Then I use a rubber plug with a hole in it and blow 150 psi of air in the intake port. If you have any bubbles coming out around the valves you know it's not sealed up good enough. Do the same on the ex valves. Sealing up the valves will make the difference between a good running motor and a great running motor.