JSG's 1978 GS750

[JonathanGreene]

Sorry, tiny picture, not sure how to fix it without finding my external HD with photoshop on it.

Well I was hoping I wouldn't have to get into too much mechanical stuff before the spring/summer but the bike had a different idea.

The thing just started running really funny, (especially/only so while in gear). So I guess it's time for me to learn a bit about the inner workings of a motorcycle engine/drivetrain.

How do I plan to achieve this goal? The same way I learned how to replace a FWD car clutch when I was 17, just start disassembling and visit google.com and any applicable repair manuals/forums/websites when necessary(sorry guys)

I'm told valve adjustment is important, and as far as I'm concerned that could be the problem so I figure I'll start there.

However, I am afraid that there's something wrong with the transmission.

To get me started:

My bike is a '78 GS750E, which of the service manuals on http://members.dslextreme.com/users/bikecliff/ would apply best to my engine etc.?

I've been looking for a chart or anything that catalogs the differences in the GS750 bikes across the years but have not had any luck.

Jon

 

[TheCafeKid]

I dunno bout valve timing, but your valve clearances could likely be the culprit. The valves should be checked every 3-5000 miles. If you haven't done em, they're likely way past due. Adjusting the clearances is actually pretty easy. It's a simple shim over bucket design, 8 valves so 8 shims to check. The clearance between the cam lobe and the shim should be between .03-.08mm. If your .04mm feeler gauge doesn't fit, you need to change the shim for the next smaller size. I'm making this a little simple and there is a proceedure you need to follow to assure there is no loading on the cam shaft while you're taking your measurement and you also need a special tool or to make a special tool to access the shims. BassCliff has a nice tutorial with great pics on how to do it and really it's not hard. Just takes some patience and time.

This would be where I would start first. Tight valve clearances lead to valves not seating well, which can lead to compression loss, hard starting when cold rough running etc etc. Before you look elsewhere, a valve check/adjustment will give you a good baseline to find and hunt for other problems.

 

[JonathanGreene]

ignore this message

 

[JonathanGreene]

I got the valve cover off just to inspect visually(no shims yet...) it would appear that they're a little off; there's even some wear on the edges of the #4 exhaust cam.

I also went to drain the oil today so I could check out the transmission to see if its in bad shape, when I took the plug out a round piece of metal and some metal shavings came with it....

Haven't looked into it yet as a couple of the screws didn't want to busge so I'm letting some penetrating lubricant sit for a while before trying again, I don't want to strip those buggers.

 

[justin caise]

Suzuki
GS750 Service Manual
at Knucklebusterinc.com
http://www.knucklebusterinc.com/features/category/tech/

 

[JonathanGreene]

So I've really started tearing into it and even went out and bought a new engine to throw in while I work on the original(and probably do a full rebuild now).

That plan is now in action but I realized the problem may have been much smaller than I had anticipated. I thought it had to be the tranny because I had no idea what else would bog down the motor more in gear than in neutral. However, I think it may have been an electrical problem, maybe getting no spark to 2 of the cylinders or something.

Either way, I'll be making some real progress soon and I'll be sure to post pictures when theres anything to take pictures of...

Also, the PO was using exactly ONE of the 4 front engine mount bolts... What a champion.

 

[JonathanGreene]

New Engine in, valves adjusted, electronic ignition installed.

It lives! Took it for a test drive today, the clutch is very slippery but was improving as I rode, I'm guessing the discs were probably just a little glazed over because the engine thats in it now had been sitting for a while? Either way if it doesnt improve all the way soon I'll be tearing into that. Other than that and the left side signals its about road ready.