valve problems

[webbnaste]

any one have an easy way to re-seat the valves on a 300ex? i think one of them is not tight, and im losing compression....help!

[the Z Man]

There is some kind of gritty paste youi put on there and spin with a drill, are you sure its not bent?

[TRXRacer1]

To do what the Z man is talking about you need to remove the head and lap the valves with "lapping compound". You can use a drill but you need to be very careful to not grind too much. The safe way is to do it with a special dowel that has suction cups on each end. It's a complete tear down of the head to do this. Have you checked your valve clearances? Maybe you're simply to tight.

[wilkin250r]

Why do you think it's your valves?

Lapping the valves is generally beyond the average tinkerer. For example, I know a bit about engines, I'm not afraid to install pistons, camshafts, ect ect. But I don't do my own valve work, I simply don't have the equipment for it.

My first piece of advice is to determine what the actual problem is. I'd hate to see you throw money into a solution, only to find out that it's not really the solution. What kind of problems are you having?


Second peice of advice, if it IS the valves, just take the whole head in to a shop and pay them to do it. It's a few hundred bucks, which is never fun to part with, but it's MUCH better than the hassle of trying to do the valves yourself.

[webbnaste]

im pretty sure its a valve thats not seated right...piston and rings all brand new, checked the clearences with feeler gauge, and their right on...it tries to start, everythings moving, just not enough compression. Cant find anywhere else it might be getting lost....??


What is this dowel tool you mentioned?

[John451]

just a thought, i problably would over look it, does it have a decompression lever? Make sure it's off! Hate tryin and tryin and adjusting to find out that i left the kill switch off, or choke, or decompression.

[86 Quad R]

if it is infact a valve giving you trouble then it is likely that a simple valve lapping may not work. there maybe something wrong with it. i've seen some OEM's that show symtoms of what you describe and it ends up being that one is starting to pull through the seat. if you do one ya may aswell do the other.

i too am fluent in building engines but will farm out the head work. the main reason as mentioned is the tools...... its not a simple matter of just lapping them and sticking them back in. most good shops will put a 3 angle face on them ect ect and there is a special clamp for re-installing the spings.

if you do end up carrying it to a shop, dont carry it to one that charges a few hundred ..... thats nuts :eek: :huh

[dustin_j]

I just had C&D racing do my valves on my 400, and he charged about $70 to do a 3 angle grind and install with new seats.

[wilkin250r]

Originally posted by 86 Quad R
if you do end up carrying it to a shop, dont carry it to one that charges a few hundred ..... thats nuts :eek: :huh

Maybe I should have been a little more specific. How's a couple hundred sound?

The 3-angle valve job itself will only be about $100 or so, but that's for the grinding only. Chances are, he'll almost certainly need a new valve and guide for that valve that's not seating, and it's not uncommon for the exhaust valves to need replacing. For roughly $30 per valve, that's cheap insurance.

All told, he should be looking at right around two bills. He might get cheaper, but I can't possibly see it being any less than $130.

[400exrider707]

I agree 100% with Wilkin... do it right or dont bother. That paste stuff is a total waste IMO.

[86 Quad R]

Originally posted by 400exrider707
I agree 100% with Wilkin... do it right or dont bother. That paste stuff is a total waste IMO.


not really........... if its a simple case of carbon buildup or where an engine may have set with a trace of moisture, the compound would be great. :cool:

[wilkin250r]

The valve lapping compound works just fine, it's the exact same stuff they use at the shop to fix your valve seat along with the proper equipment and a 3-angle valve job.

The shop will also generally use a coarse and a fine lapping compound.

[blue_ex_rider]

I would check the decompression mechanism as well you can lose compression if its not working right threw the rigth exhaust valve. Which will make it not start,

[250X_project]

What's the story here? It was lacking compression, so you rebuilt it and still has insufficient compression? What are you reading for compression?
I had a pair of valve spring keepers fail once, robbing me of compression. I had to put a new ex. valve and keepers in it. Luckily I had the parts lying around...:D