1981 GS 750 cam chain broke in 1989

[laverda1200]

Hi all

I introduced myself here in this thread http://www.thegsresources.com/_forum...d.php?t=180899

I am in Calgary, Alberta, Canada, and I just rescued a 1981 Suzuki GS 750 EX with the square headlight and sort of lunch bucket looking headlight pod.

I was originally told the bike had been off the road since 1998. I talked at length to the original owner by phone today, who clarified for me that the bike has actualy been off the road since 1989, so over twenty years since the cam chain broke. The original owner is a very friendly "good ol boy..." who seems to have a bit of an imagination.

The original owner's story as to how the cam chain came to break is very highly animated, and boils down to roughly the following - back in 89 he were layin on the tank doin 160 mph at 13,000 rpm when he heard the durndest BANG and the motr just loked up, he were lucky to still be live.....and he ain't ben near a motorbike since

very entertaining.... anyway, I have pulled the motor and stripped it to the bare cases to see if the bike will be rebuildable. What I found was one broken rocker arm on exhaust 4, a bent rocker arm shaft for 3 and 4, a cam chain broken into 4 pieces, the cam chain tensioner plunger inside the motor, and a lot of debris and swarf in the bottom end which wil need to thoroughly cleaned out.

I traded a bottle of whiskey for the bike, so I am not in too deep financially, and with the bike having sat outside for at least a few years of its long slumber, the bike needs pretty much everything, so I am thinking it would be a good base for a special build of some sort.

I have sourced a used rocker and rocker arm shaft locally, as well as used cam chain guides, there are no witness marks on the valves or pistons, but I haven't yet got out the valve spring compressor to strip the head to see if any of the valves got whacked, and I haven't yet checked the rods/pistons to see if anything happened to them.

a couple of questions.

is a rocker arm failure common on these engines?

what cylinder blocks/pistons/heads will swap onto a 1981 GS 750 bottom end? Can I stuff any of 1000/1100/1150 cylinder block/head onto the 750 bottom end, and if so, what years and models?

I found that AirTech still sells a Wes Cooley fork mounted fairing replica in fiberglass and without mounting brackets, what other Wes Cooley fairing look alikes are available, if any?

any other advice to offer?

Thanks in advance.

Paul

[Nessism]

Hey Paul,
The 2nd generation 750 engine is problematic. The only GS engine that isn't bulletproof. The oiling system is suspect and wiped out cranks and cams/rockers are common. I doubt the cam chain snapped before something else happened, such as a cam seizing in the head or similar. At any rate, I don't think you can swap any other cylinders on that bottom end, but I'm not sure about the head. You can stuff a 1100E engine into that chassis though - they call that a 7 - 11 swap. As far as replica 1000S fairings go, there is some guy that markets on ebay that makes some high quality pieces, or so some members here claim. I'm not sure how to chase that guy down, so you might want to try to search out the info in the archives here.

Good luck with your new project.

[laverda1200]

this engine is the only GS engine not bulletproof, you say.... well, I guess I got what I paid for, maybe I should ask for my bottle of whiskey back!

with that info, I am not sure what to do with this project. I did hear about an oiling problem with this 750 engine series and supposedly some factory tech tip to increase oil pressure by shimming something somehow, anyone got any details on that supposed oiling fix?

I do museum quality restorations on Laverda triples and twins, Benelli's, Ducati bevel's, etc, and recently did a bare frame/bare crank on of all things a Kawasaki 1978 KZ 650 SR just for fun, but even the proper resto on the KZ 650 was close to $2,000 just in consumable parts (bearings/seals/gaskets/piston rings/valve guides and valve springs/shocks/drive chain and sprockets/cam chain/tires/rubber bits/seat recover/clutch plates/painting supplies, etc., etc), I don't think I want to sink that kind of money into a project like this 81 Suzuki 750 if it has known engine problems, doesn't cost any more to restore say a Suzuki 1000.

I think I'll get this 750 motor sorted and back together, fire it up, then decide......

any other suggestions and info for me?

Paul

[Nessism]

Shimming the oil pressure relief spring is the recommended fix, only I'm not sure how much to shim it - 2mm comes to mind but I'm not positive. You also might be able to run a top end oiler, but they are not cheap.

Good luck with what ever you decide.

[Flyboy]

What Ed means by not bullet proof, is that tey only run 100 000 miles if looked after, not the normal 200 000 miles.
Seriously, though they were the weakest of the lot, but not t fault, they are still very good motors, if cared for and maintained properly.
I am sure you wil find the botton end to be fine, I peak under correction here, but the rocker arm is a designed weak point, to break and save the rods etc, so don't worry too much about it.
As Ed said, just check around for a possible cause for the cam chain breakage, sounds like a normal engine rebuild will see you good again, with said mods to the oil system.
Or you could just hunt down a second hand motor and slap it in and call it done, if you not going for a museum quality refurb. In which case, no question on the 1100.
Talking of which.......you know we like pics, lots of 'em, not of you, of the bikes.

[TheCafeKid]

You'd be better served to either find another motor for it, or do a 7-11 swap, or part it out to be honest.

Check the cam journals, lobes, etc. If they're scored or heavily blued, it's trash. Not worth the money to repair given what it would be worth in the end.
If you pull it apart further, check the rods for play. These were/ are insert bearing motors. If this one had an oiling problem, those would have/could have suffered damage as well. I'm honestly not sure if these motors, in any variation, were "crashers" (id assume that they probably are) but if the cam chain broke, likely ya bent or broke some valves... And the money keeps adding up. It's not worth it.

[Sunburn]

The only GS engine that isn't bulletproof. The oiling system is suspect and wiped out cranks and cams/rockers are common.

Yeah, I smoked one of them motors one day. @ 25,000 miles comming home for work something don't sound right. Made it home with a little luck.

Pulled the cover and the cams were toast. Figured it was an oil issue.

Now a large paperweight with wheels.

[laverda1200]

1981 GS 750 cam chain broke in 1989

interesting replies, thanks.

I have the motor apart to the bare crank, and everything quite frankly looks pretty good. I stripped the head earlier today and put the various valves on V blocks with a dial indicator, everything looks OK, especially the two valves on exhaust 4 where the rocker arm broke. I checked both cams, and the crank, on V blocks as well, everything is wel within runout specs.

the story from the former owner included that the cams were worn so he replaced both cams with brand new cams back in 89, rode the bike about 300 miles and the cam chain went bang....

I ordered an aftemarket cam chain for about $50, while I am waiting for that I will run the carbs through my ultrasonic, when the cam chain arrives it will only take a couple of hours for me to stick the engine back together, stuff it back in the chassis, and fire it up to see what happens. Worst case is I am out the cash for the used rocker arm/shaft/cam chain guides, a cam chain, a few gaskets, and a bit of my time, and I ebjoy doing this anyway.. I have a good spare battery laying around to fire the bike up with.

if the motor runs fine, I will have a running bike for less than $125 total and a bit of my time, if the motor is toast I should be able to make a significant profit parting the bike out, no problem.

I'll report back after the cam chain arrives, and I'll post a few photos.

Paul

[Sunburn]

the story from the former owner included that the cams were worn so he replaced both cams with brand new cams back in 89, rode the bike about 300 miles and the cam chain went bang....

l

Don't forget he was doing 160 mph at 13,000 rpm. lol He was already into your whiskey bottle telling fibs of all sorts..

[laverda1200]

Don't forget he was doing 160 mph at 13,000 rpm. lol He was already into your whiskey bottle telling fibs of all sorts..

laughing out loud......!

in fairness to the redneck former owner, the bike came to me complete with the owners manual, and folded into the owners manual is a hefty stack of parts receipts from January, 1989 from our local big box Suzuki retailer, where he spent $179.66 for a brand new exhaust cam, $169.92 for a brand new intake cam, over $200 for 8 brand new rocker arms, and a wad of further cash on stuff like 4 brand new carb slides/diaphragms, a new O ring chain and new drive sprockets, etc., etc. He clearly loved his 160 mph, 13,000 rpm turning motosickle.

the drive chain , although it only has about 300 miles on it is rusty junk now from sitting outside, but all the other stuff he replaced back in 1989 seems for the most part in good shape (other than the one broken rocker arm), which is part of the reason I have been going ahead with getting the engine running

yesterday I stripped the carbs and ran the carb bodies through my ultrasonic cleaning tank while all the brass bits and the disasembled fuel tank petcock soaked in HydroSeal, I had forgotten how stinky 20+ year old fuel residue is the carbs actually cleaned up quite well, the petock internals, not so much at least so far....

Paul

[laverda1200]

1981 GS 750 cam chain broke in 1989

if I had known how tough it was going to be to put the little spring loaded clip dealy thingy back into the original petcock I might never have taken it apart...... Anyways, soaking the petock parts in HydroSeal overnight, then running everything throught he ultrasonic tank a few times actually got all the petrified stinky crud out. I re-assembled the petock, stuck it back ont eh tank, amazingly enough it works, at least in the "prime" postion, and more importantly, doesn't leak!

I also pulled the fuel level sensor out of the tank, absolutely seized solid with petrifed dinosaur juice as well, cleaned it up as well, as well as unsticking the fuel cap itself,

I presure washed the fuel tank with really hot water and soap, rinsed, and then rinsed with gasoline until crud stopped coming out of the tank. I think I now have a workeable tank, the original paint actually cleaned up quite well.

can anyone tell me why the sheet metal cover that screws on over the fuel sensor assembly into the tank has a spigot on it going to no-where? It looks like a fuel line or vacuum line should hook up to it, but it isn't attached to anything and doesn't go anywhere.....curious.

the carbs are finished and all back together, they came out like new, al the dired up fuel residue came off and out, HydroSeal, ultrasonic, compressed air.

Cam chain and gasket set won't be here until end of the week, soonest, I hate waiting for stuff to arrive.....

Paul

[Kaiser Sosei]

can anyone tell me why the sheet metal cover that screws on over the fuel sensor assembly into the tank has a spigot on it going to no-where? It looks like a fuel line or vacuum line should hook up to it, but it isn't attached to anything and doesn't go anywhere.....curious.

It drains the fuel to the back of the bike and onto the ground instead of dripping onto a nice hot engine when the rubber seal for the sensor goes bad.

[laverda1200]

It drains the fuel to the back of the bike and onto the ground instead of dripping onto a nice hot engine when the rubber seal for the sensor goes bad.

thanks for that, then I shall attach a drain hose to it and run it out the back of the bike. Imagine, Suzuki planning for a fuel leak in advance, I don't know whether to be impressed or frightened......

Paul

[TheCafeKid]

thanks for that, then I shall attach a drain hose to it and run it out the back of the bike. Imagine, Suzuki planning for a fuel leak in advance, I don't know whether to be impressed or frightened......

Paul

It's rubber soaking in a petrol product... I think they assumed it would eventually go bad. Be impressed. (makes ya feel better that way )

While oil starvation is an issue with this particular motor, it seems to most often rear it's head in bikes of unknown maintenance history prior to the poor guy it went boom on. Many of the owners of this model, with religious oil changes at 1500-2500 miles, and those who keep them in good shape don't have problems. Let the level get low, or some filth clog a delivery port and then you may have problems. But, if you've broken it all the way down, and everything looks spec, and she's been cleaned out throughly, you may never have a problem.
As much as I dislike that model for it's less than GS-like reliability, it is probably one of the smoothest running, nicest sounding motors in stock form they built. (I didn't personally care for the body style either, but they are smooth and when in good tune sound like a Singer sewing machine...)
Good luck with it!

[laverda1200]

1981 GS 750 cam chain broke in 1989

thanks guys, appreciate the experienced advice.

so, sounds like I need to solve the oil pressure issue on this 81 750 GS motor once and for all before I put it back together.

Can anyone point me to detailed instructions as to how to shim the pressure regulator to ensure a higher oil pressure, or explain it clearly for me?

thanks in advance.

Paul