HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
Cadoewen

Yz450f time for valve job, who does it best?

9 posts in this topic

I rebuilt my yz450f in the summer and adjusted the valves. they were tight almost with zero clearance. i rode it for about 5 more hours and i decided to check the valves again before storing it. needless to say they are tight again. what is involved with replacing the valves? do i need to send the head out to get new valve seats? should i go with copper seats? what company can do this all at once?

Share this post


Link to post
Share on other sites

What's involved is that the old valves have to be removed, everything cleaned up, and the condition of the guides evaluated. Any that are worn need to be replaced to ensure that the new valves will last.

Next, the valve seat angle should be "rough cut". This is something of a misnomer, because only the absolute minimum required to get the seat about 90% "clean" should be removed (normally, it won't take much). At this point, the width of the seat, and the point at which it contacts the valve face are checked, and then a ~30 degree angle is cut above the seat and/or a ~60 under it to move the seat up or down the valve face and narrow it.

Once that is done, the finish cut is put on the seat. I very much prefer this done by grinding with the finest possible stone, again removing only the minimum necessary to clean the seat. I believe this is important in order to reduce the wear on the hard coating of the valve face. Too rough a finish will accelerate the wearing through of the coating, and you'll be back where you are in another year. This is the same reason guides are important here. If the valve is able to move off center of the seat, it will scrub as it seats, again accelerating the wear.

If you want to send the head to where it will be done the best, then I suggest Eddie Sisneros at Out the Door (OTD) Cycles in Colorado (Denver, I believe) is the best bet I know of. His valve jobs are absolute precision. After that, Engine Dynamics, or Millennium Technologies are good. Ron Hamp cycles is likely better than either of those two, and definitely worth trying. Otherwise, contact the machinist that the big local shops use, and have him tell you how he does them. A local shop should be able to do a very good job if they are attentive enough. In Eddie's case, his equipment is top of the line, and that makes a difference.

Share this post


Link to post
Share on other sites

When i took a tour at Pro Circuit a couple of months ago.

We were able to look at a lot of the work they do and it is amazing how precise it was.

Kinda pricy

Share this post


Link to post
Share on other sites

Next, the valve seat angle should be "rough cut". This is something of a misnomer, because only the absolute minimum required to get the seat about 90% "clean" should be removed (normally, it won't take much). At this point, the width of the seat, and the point at which it contacts the valve face are checked, and then a ~30 degree angle is cut above the seat and/or a ~60 under it to move the seat up or down the valve face and narrow it.

That is pretty much old school. Todays modern cylinder head machines use cutters that have all of the angles and the 45 in them and do all the cuts at once, or CNCs the seat. These machines can also perform radius cuts in place of the 60 which is not possible with an old school seat grinder.

Jay

Share this post


Link to post
Share on other sites

In a shop with the most current modern equipment, on which the depth of the cut and the feed rates are machine controlled, a cutter, correctly used is fine. Smaller shops still using hand cutters face the same problem they always had, which is that such tools are difficult to produce a truly fine finish with, and the seat needs either to be finish ground or lapped. Since lapping is out of the question with Ti valves, that really only leaves one option.

It is possible to do a very precise valve job by using "old school" tooling, although it does require skill, practice, and takes a good deal more time than the top of the line modern stuff does.

The point I regard as most important in my original post is that the finish of the seat needs to be as fine and as true as it can be, and the guides in good condition in order to avoid rapid wear of the new valves. A lot of small repair shops still haven't adapted to this, and may be more focused on knocking out "production grade" work quickly with hand cutters, costing their customers money in the long run.

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  
Followers 0