1977 GS750 Valve Issue ?

[8ball]

Read the manual again...or type the right measurements..but its .08 MM as the MAX gap and .03MM as the minimum. A .80 MM gauge is wrong to use.

He got .8 mm with a toonie (Canadian $2 coin) in place of a shim because he couldn't get a feeler in with the shim in the bucket.

 

[8ball]

I used my larger set of feeler gauges as the toonie was only 1.80 mm thick and created a pretty significant gap. I went up in feeler gauge sizes until the gauge just barely fit which was .80mm. Adding those two thickness together would create a 2.60mm "shim" which would have no clearance. I then subtracted .05 mm which in theory would then be my clearance (right in the middle of spec). So as mentioned I think 2.55 mm shims should be a safe starting point.

Maybe my previous post made no sense but to me these numbers make sense or am I from Mars - which is totally possible!

Your math made sense. I think Chuck missed the fact that you had a coin in the buckets. Most of us Yanks don't know a Toonie from a three fer. LOL I just have happened to work for Canadians much of my career, so I am familiar with your Monopoly money and crazy coins. I have returned from the Great North more than a few times with my pockets too heavy with Loonies and To
onies

 

[XGS750X]

Thanks 8ball! I'll go for 2.50 mm shims and see what happens. Appreciate the help guys!

 

[XGS750X]

Your math made sense. I think Chuck missed the fact that you had a coin in the buckets. Most of us Yanks don't know a Toonie from a three fer. LOL I just have happened to work for Canadians much of my career, so I am familiar with your Monopoly money and crazy coins. I have returned from the Great North more than a few times with my pockets too heavy with Loonies and To
onies

Next time keep the toonies! They are the perfect size for doing valve shims and now are worth basically nothing.

 

[chuck hahn]

Dont get TOO high 8ball. S hims have been known to jump out of the bucket a little on way loose valves and get snapped...and then its a torn up bucket and cam lobe.

 

[8ball]

Dont get TOO high 8ball. S hims have been known to jump out of the bucket a little on way loose valves and get snapped...and then its a torn up bucket and cam lobe.

Noted. .1 mm is less than .004", and I wouldn't ever suggest going more than that. My suggestion is, merely go for the high end of the spec. but don't sweat it if it was just out. But you are correct. Most of the motors I have dealt with are shim under bucket, so there is no risk of a dislodged shim. But the lash spec on these engines is the tightest spec I have ever dealt with.....STUPID tight! My R6 valve lash spec is 5 to 6 times bigger than my GS!

 

[XGS750X]

New shims in! I started the bike, it warmed up much quicker than before, great throttle response and no smoke either but it did have a bit more or a valve rattle / noise? it was never perfectly quite and it did have louder spots at certain RPMs but it seems more consistent now? Either way, I haven't had a chance to ride it yet, I'm planning to do that tomorrow but here's a quick rundown of the shims originally found in the bike, the new shims I put in and the clearances i'm now getting. Thanks again for the help. Will report back after a good rip.

Cyl #1 EX
Original shim: 2.70
New shim: 2.50
Clearance: .07mm

Cyl #1 IN:
Original shim: 2.70
New shim: 2.50
Clearance: .07mm

Cyl #2 EX:
Original shim: 2.75
New shim: 2.55
Clearance: .09mm

Cyl #2 IN:
Original shim: 2.75
New Shim: 2.55
Clearance: .08mm

Cyl #3 EX:
Original shim: 2.75
New shim: 2.55
Clearance: .07mm

Cyl #3 IN:
Original shim: 2.75
New shim: 2.55
Clearance: .09mm

Cyl #4 EX:
Original shim: 2.70
New shim: 2.50
Clearance: .05mm

Cyl #4 IN:
Original shim: 2.80
New shim: 2.55
Clearance: .08mm

 

[Nessism]

Those numbers suggest damage occurred. You best recheck them in 500 miles or so.

 

[XGS750X]

Thanks, will do. Took it to work today and it ran like a champ! Seems to have a lot more power.

 

[2BRacing]

Wow! Never before seen the need to go down 4 (and even 5) shim sizes!

 

[XGS750X]

It did seem like a big jump to me as well and I'm definitely riding it cautiously for the time being. I'm planning to check the clearances again after a few hundred KMS. I haven't touched the shims or valves in the last year and a bit (since I've owned the bike) and have no idea when they we're done before that. Can pure neglect cause this size of change or should I be leaning towards taking it apart further to check for burnt valves / damage to the seating areas?

 

[chuck hahn]

Neglect will for sure cause extremely small ( tight ) clearances..but to have to drop that much on them is kinda hard to explain. Run it and see what the next readings bring is about all you can do for now.

 

[Big T]

It did seem like a big jump to me as well and I'm definitely riding it cautiously for the time being. I'm planning to check the clearances again after a few hundred KMS. I haven't touched the shims or valves in the last year and a bit (since I've owned the bike) and have no idea when they we're done before that. Can pure neglect cause this size of change or should I be leaning towards taking it apart further to check for burnt valves / damage to the seating areas?

I'd go about 2,000k and check them again

That should give you a good idea of the wear rate. I wouldn't be worried about tearing into the motor just yet. A compression test comes first

 

[XGS750X]

Ran it about 200km and starting to get some exhaust popping at lower RPMs, so I took it apart and remeasured the clearances. It seems that the clearances are already getting bigger. Any idea what this means?

Cyl #1 EX
Previous clearance: .07mm
New clearance: .09mm

Cyl #1 IN:
Previous clearance: .07mm
New clearance: .07mm

Cyl #2 EX:
Previous clearance: .09mm
New clearance: .10mm

Cyl #2 IN:
Previous clearance: .08mm
New clearance: .10mm

Cyl #3 EX:
Previous clearance: .07mm
New clearance: .08mm

Cyl #3 IN:
Previous clearance: .09mm
New clearance: .08mm

Cyl #4 EX:
Previous clearance: .05mm
New clearance: .08mm

Cyl #4 IN:
Previous clearance: .08mm
New clearance: .10mm

 

[Nessism]

There was carbon on the valve faces. It's wearing off so your clearance is increasing.

I wouldn't worry about the valves at .10mm.