Valve adjustment procedure

[Guest]

Hi all, I've just started with my first valve adjustment on my 1978 GS750 8-valve and I think I may be doing something wrong. I've followed the shop manual with the exception of turning the engine over via kickstarter rather than with a socket. I ordered a set of metric feeler gauges that range from .02 mm to 1 mm and got started. The problem I'm having is that every single one of them seems to be too tight. 2 or 3 of the valves I can get a .05 mm gauge in, and many I can't get the .02 mm gauge in. I can't get the .08mm gauge in any of them. This is my first experience with the shim style of valve adjustment so is the goal to get slight drag on the gauge just like a normal adjustment or am I looking for something else? I just wanted to make sure I was doing it right before changing out all of my shims

 

[sam000lee]

If you can get the .05mm gauge in, and not a larger one than that valve is withing the .03 -.08mm spec. You are checking each valve with the lobe pointing up, right?

It's common for PO's to ignore checking the valves and letting the clearances get too tight, sometimes to the point of zero clearance (which you can check by seeing if the bucket spins), so it wouldn't be surprising if several or your valves did not have enough clearance to fit any gauge through.

 

[hampshirehog]

You're on the right lines. The feeler gauge should just fit with slight drag between the shim and the cam. Also worth checking if the shims spin at all - that shows that although the clearance is below the minimum spec there is som clearance. Plus make sure you follow the manual to set the cam in the right position before testing - use the Suzuki manual as they have it right whereas some others may not.

 

[sam000lee]

Just re-read your post. The goal is to fit the largest shim in the clearance possible and then that is your `reading'. For example if you put a .55mm shim in and the .68mm (next largest in my set) one didn't fit then you know the gap is between .55mm and .68mm, which would be within limits.

I always end up drawing a crude picture of the whole set up to make sure I don't mess it up:

U <-cam lobe
--- <-gap you are measuring
=== <- shim
MMM <- bucket

If the gap is too small, then you want to decrease the size of the shim and similarly if it is too large, you increase the size of the shim.

 

[Hinermad]

I just set the clearances on my 750 a couple months ago. It's had so many owners I don't know the last time it was checked, but I had to replace five of the eight shims. (All four exhaust and #4 intake.)

Shims generally are sized in 0.05mm increments (with some exceptions), so if one valve clears a 0.02mm gauge but not 0.03, then replacing the shim with the next size up (say, going from 2.55 to 2.60mm) should put your clearance at 0.07mm, which is in spec. But if you can't get a gauge in there at all, you know that your shim is at least 0.05mm too thick. (That's 0.03mm minimum gap + the size of your smallest gauge.) But you may need a shim that's thinner still. You can either order the next two smaller sizes and hope one of them brings you in spec, or you can try swapping out the shim on that valve with a smaller one from another valve and see if you can get a positive measurement. (You are pulling and measuring all your shims with a caliper, right?)

If you go swapping shims around, be sure to put a quarter in any empty bucket before you rotate the camshaft. Rotating a cam against the bucket will screw up the lobe. The quarter, being cheap soft metal (it's made by the government you know), acts like a pad to cushion it. You may ruin the quarter, but it's cheaper than a new camshaft.

If you don't have it already, I highly recommend you get forum user Steve's valve spreadsheet. It does all the math, all you have to give it is the thickness of your existing shims and the measured clearances. Steve's also who told me about the quarter trick.

 

[Guest]

Thanks for all the responses. It seems I'm doing it right and the PO never checked them at all. That would explain my issues tuning the #4 carburetor I've been checking them by aligning the exhaust cam parallel to the valve cover surface and pointing the intake straight up for #1 and #2 Just like the manual says. Where can I find the spreadsheet for the valves?

 

[Hinermad]

Where can I find the spreadsheet for the valves?

You'll have to email Steve. Find a post he's made (there are lots) and click on his user name. You'll get a little menu with an option that says "send email."

 

[hannibal]

I just set the clearances on my 750 a couple months ago. It's had so many owners I don't know the last time it was checked, but I had to replace five of the eight shims. (All four exhaust and #4 intake.)

Shims generally are sized in 0.05mm increments (with some exceptions), so if one valve clears a 0.02mm gauge but not 0.03, then replacing the shim with the next size up (say, going from 2.55 to 2.60mm) should put your clearance at 0.07mm, which is in spec. But if you can't get a gauge in there at all, you know that your shim is at least 0.05mm too thick. (That's 0.03mm minimum gap + the size of your smallest gauge.) But you may need a shim that's thinner still. You can either order the next two smaller sizes and hope one of them brings you in spec, or you can try swapping out the shim on that valve with a smaller one from another valve and see if you can get a positive measurement. (You are pulling and measuring all your shims with a caliper, right?)

If you go swapping shims around, be sure to put a quarter in any empty bucket before you rotate the camshaft. Rotating a cam against the bucket will screw up the lobe. The quarter, being cheap soft metal (it's made by the government you know), acts like a pad to cushion it. You may ruin the quarter, but it's cheaper than a new camshaft.

If you don't have it already, I highly recommend you get forum user Steve's valve spreadsheet. It does all the math, all you have to give it is the thickness of your existing shims and the measured clearances. Steve's also who told me about the quarter trick.

I'm pretty sure he meant to say go down a size as in 2.60 to 2.55.

 

[Hinermad]

I'm pretty sure he meant to say go down a size as in 2.60 to 2.55.

You are correct. Thanks for catching that!

 

[Steve]

You are checking each valve with the lobe pointing up, right?

WRONG!!! You do NOT check them with the lobe pointing up on all the valves. The Suzuki manual has the best description of the lobe positions, but briefly, the two lobes on each side of the cam will be at about a 45-degree angle to the valves. Neither lobe should be pushing on its valve. Yes, one lobe will be pointing UP, the other will be pointing FORWARD on the exhaust cam and REARWARD on the intake cam, but while in that position, measure BOTH valves. Using any other positions will give you false readings. It's also easier and quicker, so why not do it right?

It seems I'm doing it right ... I've been checking them by aligning the exhaust cam parallel to the valve cover surface and pointing the intake straight up for #1 and #2 Just like the manual says.

Apparently you find the picture just as confusing as everyone else. See the first part of my post.

Where can I find the spreadsheet for the valves?

Take a look in my signature.

.

 

[Guest]

FWIW - the Sacajawea Dollar coin is a better fit than a Quarter -

 

[Hinermad]

FWIW - the Sacajawea Dollar coin is a better fit than a Quarter -

True, but most people would rather mangle a quarter than a dollar. Whetever coin you put in there is going to get chewed up a bit. (Although the vending machine at work accepted the quarter I used, so maybe it doesn't matter.)