Jump to content
Sign in to follow this  

Fresh valve job, already shimmed out!

Recommended Posts

Well, I just rebuilt my bike (.5hrs on it now). I sent the head out for a valve job to MX TIME. They installed faction MX stainless Intake and exhaust valves as well as their high rev spring kit, and cut the seats. However, when I installed my cam assembly on my bike i swapped shims in and out until I was at the right tolerance. I'm at my smallest shim I have on the left intake which is 1.20mm. and my tolerance is .004" I'm going to be shimmed out if my valve seats itself even the slightest bit, because as far as I've seen, 1.20mm shims are the smallest made. Not sure what happened, or what to do. please help.

Share this post


Link to post
Share on other sites

It seems the seats were cut too deep, perhaps because they have been cut before. This would cause valve stems to stick up too high underneath the cam. If this is the case you will need to get the valve seats replaced and recut.

Share this post


Link to post
Share on other sites
Well, I just rebuilt my bike (.5hrs on it now). I sent the head out for a valve job to MX TIME. They installed faction MX stainless Intake and exhaust valves as well as their high rev spring kit, and cut the seats. However, when I installed my cam assembly on my bike i swapped shims in and out until I was at the right tolerance. I'm at my smallest shim I have on the left intake which is 1.20mm. and my tolerance is .004" I'm going to be shimmed out if my valve seats itself even the slightest bit, because as far as I've seen, 1.20mm shims are the smallest made. Not sure what happened, or what to do. please help.

you might be able to have a few thou. ground off the valve stems as long as the shims still hit the stem before the retainer, that would mean you would have to pull the head and take the valves out so they could be ground though

Share this post


Link to post
Share on other sites

Just a word of caution. Make sure you measure the installed spring height. You will have less pressure from the spring with the valve deeper in the seat and loose a slight amount of compression. You may need to install a thicker base washer on that valve if it is out of spec.

Next time you take it apart have new seats installed to get it back to stock unless you want to have to cut new valves each time you buy them.

Share this post


Link to post
Share on other sites

Check here; http://racetoolz.com/

See the valve height tools. They are used when setting up the head to prevent what you are describing. If you can't find someone local to tip the valves for you, send it to us and we will do it very fast and get it right back to you.

Share this post


Link to post
Share on other sites

Well, I'm going to run it until it 0's out.. then I'll pull the head off, take the valve out, and grind a couple (maybe .008") off the stem. I'll keep APE in mind, thanks!

Share this post


Link to post
Share on other sites
Well, I'm going to run it until it 0's out.. then I'll pull the head off, take the valve out, and grind a couple (maybe .008") off the stem. I'll keep APE in mind, thanks!

just make sure the shim is pushing on the stem not the retainer or it will loosten the keepers , and Rocksalt made a good point , it could need spring shims under the springs for the correct spring pressure , because it look's like they cut the seats too deep and that makes the installed hight of the springs taller and means less spring pressure , 8 to 10 thou. doesnt sound like much but it is probably a fair amount of spring pressure over the nose of the lobe where you need it to keep the bucket following the lobe

Share this post


Link to post
Share on other sites

I would grind down the shim before grinding down an expensive heat treated and hardened valve. After you replace the seats you also might have a problem with a shortened valve.

Share this post


Link to post
Share on other sites
I would grind down the shim before grinding down an expensive heat treated and hardened valve. After you replace the seats you also might have a problem with a shortened valve.

thats a good idea , but it wont hurt anything to grind on the top of the stem if you dont get it too hot , I just thought he would have an easier time grinding a few thou. off the stem than paying someone with a surface grinder with a magnetic table to grind down the shims ( if he want's them flat and paralell ) , and at some point the shims probably get weak when they are ground thinner than the thinnest ones they sell , and on the valves I dont think they would be worth using over on a new pair of seat's after he is shimmed out even though they probably make shims thick enough :bonk:

Share this post


Link to post
Share on other sites
grind down the shim.. haha good idea a lot easier too. thanks!

if the shims arent flat and paralell they will wear fast or wear the stem down at a angle , you need a surface grinder to do it correctly

Share this post


Link to post
Share on other sites

You'd be a lot better off getting the valves tipped off .012" or so than trying to cut down a shim, especially on a new head. It doesn't happen often, but if you get one of those shims nonparallel it can spit the shim out and cause all kinds of havoc.

Share this post


Link to post
Share on other sites
You'd be a lot better off getting the valves tipped off .012" or so than trying to cut down a shim, especially on a new head. It doesn't happen often, but if you get one of those shims nonparallel it can spit the shim out and cause all kinds of havoc.

agree. I have never heard of anyone grinding shims down, tipping down valve stems to fit yes.

Share this post


Link to post
Share on other sites

Seems to me you could take a really fine whet stone or diamond hone and with lots of oil lay the shim down on it and with a one finger just make a light circular motion and get it down where need it and it would stay flat and parallel

Share this post


Link to post
Share on other sites

how much can you grind the thinnest shim down before the bucket rides on the retainer?

Edited by MELK-MAN

Share this post


Link to post
Share on other sites
Well, I'm going to run it until it 0's out.. then I'll pull the head off, take the valve out, and grind a couple (maybe .008") off the stem. I'll keep APE in mind, thanks!

And this folks is why you factor in the price of a brand new top end when you buy a used MX bike no matter what the seller tells you has been done on it. For me it means that I will NEVER buy another used 4 stroke. It is either new 4 stroke, or a used 2 stroke.

Share this post


Link to post
Share on other sites

I would call them and ask what kind of deal they'd give me on new valve seats. How many valve jobs on that head?

Share this post


Link to post
Share on other sites
Seems to me you could take a really fine whet stone or diamond hone and with lots of oil lay the shim down on it and with a one finger just make a light circular motion and get it down where need it and it would stay flat and parallel

that might work for the first .001" before it starts to go south

Share this post


Link to post
Share on other sites

One thing that seems to have been overlooked so far is have you called MX Time where you had the head done and asked them to stand behind their work? Seems this should have been step one. The longer you wait or alternatives you try then the less I would expect them to stand behind it. I would hope the would offer you a solution at no charge or have a legit reason not to.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×