1978 GS750 Broken Valve Shim

[alkswheetinjur]

My 1978 GS750 has had some trouble with cold starts lately. I would usually end up draining the battery cranking it over before it would fire. When it finally would start it would smoke a little at first but went away as it got warmed up. Figuring the valves were getting tight, I picked up a set of feeler gauges and a valve tool from motion pro. I was a little nervous since I have never done this procedure before. The first shim I checked was tighter than all of my feeler gauges (smallest it goes is .0015/.038, Do I need a smaller set?) While removing I realized it was split in half! Its was a 2.65 so I replaced it with a 2.50 (still too tight) that I had and continued to check the rest. Only #2 and #3 exhaust valves are within spec. Everything else is too tight, most tighter than .0015/.038 but still spin freely. So I am not really sure where to start as far as purchasing new shims. All clearances were checked with the cam lobe facing straight up but after further research I am not sure if this was the proper position. I kept a detailed log of everything I will try to upload later. In the meantime...

Is the broken shim something I should be seriously concerned with?

Do I need a smaller set of feeler gauges?

What is the proper cam positioning for taking measurement?

 

[Guest]

My 1978 GS750 has had some trouble with cold starts lately. I would usually end up draining the battery cranking it over before it would fire. When it finally would start it would smoke a little at first but went away as it got warmed up. Figuring the valves were getting tight, I picked up a set of feeler gauges and a valve tool from motion pro. I was a little nervous since I have never done this procedure before. The first shim I checked was tighter than all of my feeler gauges (smallest it goes is .0015/.038, Do I need a smaller set?) While removing I realized it was split in half! Its was a 2.65 so I replaced it with a 2.50 (still too tight) that I had and continued to check the rest. Only #2 and #3 exhaust valves are within spec. Everything else is too tight, most tighter than .0015/.038 but still spin freely. So I am not really sure where to start as far as purchasing new shims. All clearances were checked with the cam lobe facing straight up but after further research I am not sure if this was the proper position. I kept a detailed log of everything I will try to upload later. In the meantime...

Is the broken shim something I should be seriously concerned with?

Do I need a smaller set of feeler gauges?

What is the proper cam positioning for taking measurement?

I have never come across a broken shim, but that doesn't mean it couldn't happen. My guess is someone tried to pry it out without depressing the bucket first or the shim wasn't seated all the way in the bucket the last time adjustments were made. I say the latter is most likely. What is the thinnest shim you have? The 2.50? I think a 2.15 is the smallest shim available, but it's hard to say where to begin.

 

[alkswheetinjur]

I have a handful of shims 2.50-2.90 that came with the bike. I believe that they are mostly too large for what I need at this time.

Here is everything I recorded earlier:

 

[chuck hahn]

Heres what ya do.

1... Measure clearance on all the valves and write it down. I number a piece of paper I1, I2, I3, and I4 on one side leaving 4 or 5 lines between each heading. Make the other side of the paper E1, E2, E3, and E4. Measure Intake 1 and write down the clearance under I1...and so on till all are recorded.

2.. Go to I1 and remove the shim. MEASURE it with calipers to see what it is REGARDLESS of what printed on it. Put it back in the bucket and remove another shim ad record that...do all 8 valves.

3... Refer to what your clearance was for I1. Lets say the .03MM feeler gauge would just barely go in..but it was kinda tight. So lets say the shim in I1 is a 2.70 I would put in a 2.65 or 2.62 and recheck the clearance. If its around .05 or so I am usually ok with that. Some like to get as close to the .08 as possible and there isnt anything wrong with that. Me, personally am ok with a MINIMUM of .05.

4... Note that a shim for say E3 may be the shim that will get I2 within spec...so move whatever shims you can to get as many valves set before getting new shims. Once youve played the shim shuffle game you may only need 3 or 4 to finish up...follow me so far??


5... go to the services section and find the shim club post. read the requirements and send Ray a PM with what shims you need. When they arrive you swap your tight shims out and send Ray your unneeded ones. If on an off chance Ray doesnt have one you need THEN see a dealer or get them off Ebay. Remember the Suzuki shims are 29.5 MM around.


Any questions PM me your number and I will call you.

 

[Nessism]

The valves tighten with mileage and eventually they don't close anymore. When it gets to this point damage occurs on both the seats and valves. Hopefully it's not too bad in your engines case.

Your only option at this point is to get at least one thin checking shim; something thin enough to allow some clearance so you can calculate what shims are needed.

Oh, and your cam positioning method is incorrect. Follow the procedure in the factory service manual.

 

[chuck hahn]

Service manaul




http://zeus.mtsac.edu/~cliff/storage/gs/GS750_Service_Manual_early8valve.pdf

 

[alke46]

Another thing to remember is when changing shims, rotate the engine a couple of turns to firmly seat the newly replaced shim for an accurate reading. Also, do not rotate the engine without a shim in the bucket as that can damage the cam lobe.

There's also a specific way outlined in the FSM to position the cams so you can read two cylinders at a time.

There will also be more replies coming along to help you out. Good luck.

 

[Steve]

Is the broken shim something to be concerned about? YES. Make sure you have ALL the pieces. That likely happened because the shim was not fully in place and the tool slipped off the side of the bucket, allowing the valve to slam home. You don't have to ask me how I know this, I will show you. This did not happen with a GS, but on a Kaw, the procedure is basically identical.

Do you need to get a thinner set of feelers? NO. Not sure there are any readily-available feelers that are thinner, anyway. Your thinnest feeler is just above the minimum clearance. You can be assured that if that one does not fit, it does not matter what the actual clearance is, you need to change the shim.

What's the proper position? It's outlined in the FACTORY manual. Clymer and Haynes show the same goofy line drawing of "position the cams like this", and then leave you to your own imagination. The factory book tells you how to position the cams, then to check BOTH valves on that side of the cam without moving anything. Checking clearances is relatively quick and easy, with minimal turning of the crank. The "fun" part is figuring out what you have in there and what you need to have in there.

Speaking of which, be sure to take advantage of the offer in my signature. It's just an Excel spreadsheet that keeps track of your clearances and shims, which will help you plan what shim(s) to have on-hand for the next adjustment. There is also a handy summary page that you can use as a maintenance log book. Look down there.

.

 

[alkswheetinjur]

About to recheck everything with cams in the proper position. Hopefully with some better results. I got a photocopied service manual when I got the bike but a lot of the pages are missing so the pdf. doc is a huge help. As for the shim it was ​luckily snapped in half Just two pieces.

 

[Nessism]

That broken shim is an aftermarket type. K&L, which makes a lot of valve shims, had quality problems a few years ago so maybe that one was affected. Good thing it didn't damage a bunch of parts.

 

[alkswheetinjur]

Not gonna lie I'm still pretty confused by the cam positioning but I got measurements positioning the cam with one lobe straight up and the next lobe on the same cam horizontal facing the front wheel on the exhaust and facing the rear wheel while doing the intake basically making a 90 degree angle. I also got measurements positioning both cams horizontal with the lobes facing out away from each other. Don't know which way is correct or if they are both wrong but I got the same results both ways shown below...

 

[Nessism]

There are dozens if not hundreds of threads in the archives discussing how to position the cams. Basically, just follow the factory manual process but if that's to confusing, look for Basscliff's tutorial, and if that's too confusing just point the lobe away from the valve. If you use the point away method increase the desired clearance to about .07-.13mm and you will be good to go.

 

[Steve]

Not gonna lie I'm still pretty confused by the cam positioning ...

Have you downloaded the GS750 manual from BassCliff's site? :-k

When you have done that, go to pdf page 65, where the adjustment procedure starts, it can't be much plainer.

Paraphrasing the manual: Position EX1 cam lobe FORWARD, measure clearance at EX1 and EX2. Rotate the crank (using a 19mm wrench on the right end of the crank) 1/2 turn. You will find IN1 cam lobe pointing UP. Measure clearance at IN1 and IN2. Rotate the crank another 1/2 turn, measure clearance at EX3 and EX4. Rotate the crank a final 1/2 turn, measure clearance at IN3 and IN4.

Hopefully that clears the confusion.

.

 

[alkswheetinjur]

Thanks for clearing that up. Sorry that was hard for me to explain but I think I did do it correctly. I do have the Manual saved. The "A" and "B" positioning was what had me scratching my head.

Today after work I stopped at my local cycle salvage to try and get my hands on some shims. They did not have any 29.5s but the did have some 29s (I believe from a Kawasaki?) so I got a 2.00, 2.30 and a 2.40. Would it be an issue using these strictly for measurement purposes? Mainly to get a better idea what shims I will need on the tighter ones where my feeler gauges won't fit.

 

[1948man]

Should be okay for measuring, just don't forget and leave one in there.

 

[Steve]

I would REALLY hesitate putting one in there. Yeah, it sounds great "for measuring purposes", but it will be SO easy to forget to take it out. Even worse would be if you used more than one. Theh 2.30 should be great for "measuring", don't worry about the others. When you get your "measuring" shim installed, measure the clearance, enter that value into the spreadsheet you just received, it will give you the value of the shim you should have. Please note that you still have to think a bit. If the new shim will leave you at the very bottom of the clearance range, consider a shim one size thinner. Yes, it might leave you just over the specified clearance, but many of us will go to 0.10mm for our upper clearance.

.

 

[alkswheetinjur]

Today I was able to get my measurements with my 2.30 shim and with a little math (2.30 + feeler measurement - .076 = new shim size) which I was able to confirm with Steve's handy spreadsheet. And now for (hopefully) my final question on this topic. All of my exhaust shims I need are in the 2.70 to 2.75 range but my intakes are all smaller at 2.40 to 2.55. Is this something I should be worried about?

 

[Steve]

No worries. Just change what you need to change. When you have all the shims replaced, spin the engine for 5 or 10 seconds with the starter to make sure they are all seated, then check your clearances again. If they are all in the upper end of the clearance range, you might not have to change anything the next time around. Anything less than half, I would have a shim ready. That "next time" might be the last time you have to change a shim for a while, but you still need to check them every so often.

Looking at your math again, what was the 0.076? :-k

.

 

[alkswheetinjur]

.003 in = 0.0762 mm

 

[jdion81]

spin the engine for 5 or 10 seconds with the starter to make sure they are all seated, then check your clearances again.

.

Ok, a question on spinning the engine while checking the clearances. Would you put the valve cover on before running the starter? I got my clearances dialed in, while the engine was on the bench then due to a timing chain tensioner issue decided to pull the valve cover after the engine was put in the frame (and verified that the engine ran). When I pulled the cover there was oil in parts of the head under the cams. Wouldn't running the starter throw oil all over?