Valve job do's and don't

[Guest]

I am going to do a valve job on my GS650G. What are some of the tips and tricks I may need to be aware of before I get started.

Thanks.
Will

[tkent02]

Valve job or valve adjustment?

[Willmrx]

A complete valve job.

[Steve]

What makes you think a "complete valve job" is necessary?

That is usually only needed if the adjustment has been neglected and the valves are burnt.

If you DO find that a full valve job is necessary, you have to be careful that the installed height of the valve in the new seats falls in the range that can be accommodated by the shim sizes that are available.

.

[chef1366]

So you plan on cutting the seats and valves (or replace)
And get new guides installed?
For one get new valve stem seals.
Are you doing the work or a machine shop?

[tkent02]

Did you try to adjust them or are you just into tearing it apart to see what's inside?

[Nessism]

Tips and tricks:

Measure all the various parts to assess their condition. For example, valve stem outside diameter in various places, and valve guide inside diameter, or at least the valve to guide clearance. The factory Suzuki service manual details how to perform a "wobble test" to judge clearance using a dial indicator. The service manual details a service limit of .014", which is crazy sloppy in my opinion. I'd install new guides and valves if the clearance exceeds .006".

If the head needs new guides it's best to heat up the head before driving the old ones out. Suzuki's service replacement guides are oversize and require reaming the head so they will fit. Ape sells some non oversize guides so that may be the way to go.

If the valve stems check out okay, you can have the valves faced to clean them up. Have the stem cut down a few thousands at the same time otherwise your engine may require overly thin shims.

When you cut the seats be careful to measure the margin. Suzuki specifies a pretty thin margin so measure to know where you are at. Typically, you cut the 45* face first, then thin it up and position it in the center of the valve with the 15* and 75* cutters. The service manual details the procedure so check that out before you do any cutting.

Good luck

[cowboyup3371]

If you decide to do a valve lapping job, Basscliff just posted up a small tutorial on how to do the job.

[Willmrx]

The heads have about 26,000 miles on them and have some slight pitting on the seats. I think from the looks of the seats, some small amount of lapping is required. So far all of the valve stems, springs and guides are with in specs. I have been told that you should not lap the valves. Is that true? I was thinking of taking it to a machine shop, but I am not all that confident that I can find a shop that I can trust.

[cowboyup3371]

You do need to lap the valves and it's not that bad. Like I said, take a look at the guide just put up...http://members.dslextreme.com/users/...LAP_VALVES.pdf

[tkent02]

How is the compression?

[Willmrx]

I am rebuilding the engine too. Rings,bearings, orings and all that stuff.

[Steve]

Generally, the head is left alone until it NEEDS the work, because of the tight tolerances with valve clearance. Feel free to replace the seals and clean up the seats and valve faces, but when you start cutting the seats or dressing the valve face, you might also have to trim some off the small end of the valve, so you can still use standard-size shims.

As you cut away on the valves or seats, the valve will recede farther into the head. This will require the use of thinner shims. After a few thousand miles of use, most of our bikes are already using shims that are about half a milimeter from the smallest shim, so use that as your guide.

Oh, and our valve clearances only get tighter, so make sure you trim enough off the end of the valve to get you to where you need the thicker shims at first.

.

[Nessism]

26,000 miles is nothing for a GS engine. A light lapping is all that should be required to clean up the seats. It's perfectly safe to lap the valves but don't go too hard or you will create a ridge in the valve head and round off and widen the seat margin.

Standard forum wisdom strongly suggests using stock Suzuki OEM gaskets when you put the engine back together. Aftermarket gasket kits are very spotty quality wise. Valve stem seals seem less critical though.

[tkent02]

26,000 miles is nothing for a GS engine. A light lapping is all that should be required to clean up the seats.

Actually riding the bike with the valve clearances adjusted correctly will allow the valves to go on working fine, the seats will get better as it wears more.

Unless the valve is too burnt to seal, in which case it will get worse.