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1981 GS 750 cam chain broke in 1989

  • Thread starter Thread starter laverda1200
  • Start date Start date
The 750 you've got is a really good engine - it is only crap maintenance that brought them down (or overloading the top end). It is the smoothest running motor of the range by a mile - really silky when compared to the roller bearing motors.
 
I always wondered where the coffee cup went in an engine....I know you'll show me later....
 
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So it's not possible that he WAS going 160 at 13Krpm's? Sounds feasible if the engine didn't detonate....oh wait it did! lol I mean top end on my 700EF is 140 at I would assume redline which is 10Krpms...just sayin...Might have hit it for a few seconds :D
 
dueller said:
So it's not possible that he WAS going 160 at 13Krpm's? Sounds feasible if the engine didn't detonate....oh wait it did! lol I mean top end on my 700EF is 140 at I would assume redline which is 10Krpms...just sayin...Might have hit it for a few seconds :D
Click to expand...

laughing out loud again. The previous owner was very animated telling his story, lots of beer bottle wavin in the air, various engine noises being made, and quite insistent about the 160 mph and the 13,000 rpm, especially when I said "really, are you sure" and he says yepp'ers she was a wailin;)

I was just happy to trade a bottle of whiskey for the bike, I wasn't going to challenge a good story and **** him off......:)

Paul
 
and the reason it blew was the low tension on that oil pressure relief spring!!! lol...I don't think I'll bother messin' with the washers in my 750t....I'll just keep it below 110mph!!
 
chirobo said:
and the reason it blew was the low tension on that oil pressure relief spring!!! lol...I don't think I'll bother messin' with the washers in my 750t....I'll just keep it below 110mph!!
Click to expand...
You understand why the mod right? Increasing the pressure on that spring makes the oil go thru the passages and not blow off (back to the sump I assume?) creating a lack of lubrication up the chain of oil passages. Not trying to be condescending.....just makin sure you understood the idea ;)
 
the full engine gasket set and the new cam chain I ordered finally arrived today. The new cam chain is a Japanese manufactured 120 link endless "DID" Daido Bush Chain, (DID219FTS(S)120L) and the cam chain box has a large warning on it all in capitals as follows:

CAUTION: DO NOT INSTALL THESE ENGINE CAM CHAINS BY YOURSELF. BE SURE TO ASK YOUR LOCAL DEALERS.

then goes on to say that incorrect fitting is excluded from DID's warranty

I was laughing out loud....;)

Paul
 
dueller said:
You understand why the mod right? Increasing the pressure on that spring makes the oil go thru the passages and not blow off (back to the sump I assume?) creating a lack of lubrication up the chain of oil passages. Not trying to be condescending.....just makin sure you understood the idea ;)
Click to expand...

Got it...but I thought that the low pressure was only a problem with un-maintained engines...extended oil change interval specifically...I live to change my oil out!! so r u going to get a new spring and shim that??
 
Hi all

new cam chain and full gasket set and full seal set all just arrived, so beginning reassembly of this engine which hasn't run since the cam chain snapped in 1989.

and yes, I do know the manual calls for assembling the transmission and crank into the upper engine case then installing the lower, I simply find it easier and neater to lower the very light weight upper engine case onto the lower case. The only "trick" is to install the cam chain guide and rubber cam chain guide isolator bushes a couple of hours earlier into the upper case, with a dab of silicone on each of the two rubber isolator blocks so nothing falls out when lowering the upper case....

Paul
 
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Did you remove the rods from the crank and look at the bearings? Highly recommended if you didn't. Also, I'd plastigauge the rods at least to make sure the bearing clearance is to spec.

Oh, and did you get an OE gasket kit?
 
Hi Ed

yeah, I used plastiguage on all the rod bearings, and also on the main crank bearings, everything was OK except two of the crank main bearings, which I replaced with proper size. Oddly, the pairs of center main bearings were fine, it was each end of the crank that was having bearing wear issues, the alternator end particularly

the engine gasket kit is aftermarket, made by Athena, I can't say I much like the look of the valve guide seals or the head gasket, I haven't decided if I am going to use either, I might just order a Suzuki head gasket, but the rest of the stuff looks pretty much OK.

Paul
 
laverda1200 said:
Hi Ed

yeah, I used plastiguage on all the rod bearings, and also on the main crank bearings, everything was OK except two of the crank main bearings, which I replaced with proper size. Oddly, the pairs of center main bearings were fine, it was each end of the crank that was having bearing wear issues, the alternator end particularly

the engine gasket kit is aftermarket, made by Athena, I can't say I much like the look of the valve guide seals or the head gasket, I haven't decided if I am going to use either, I might just order a Suzuki head gasket, but the rest of the stuff looks pretty much OK.

Paul
Click to expand...

Paul,

The Athena base gaskets are horrible. These photos were taken after mine failed after only about 150 miles. I torqued the head after the first few heat cycles and all the nuts were loose. Check again after a few more heat cycles and once again, loose nuts. The base gasket was extruding out of place and the head wouldn't stay tight. The head gasket was fine though.

IMG_1929.jpg


IMG_1928.jpg
 
I would highly recommend using OEM Suzuki gaskets, unless you like oil leaks that is. Many of the aftermarket gaskets are inferior to the OEM pieces, and as I understand it the difference in gasket thickness between AM and OEM can lead to problems.

edit: Looks like Ed beat me to it :)
 
Athena gaskets

Athena gaskets

those Athena base gasket photos are horrifying, as well as the thought of having to pull the head and barrels only 150 miles after a full rebuild....

I went to the local big box Suzuki store and ordered a full gasket set, it was about $110. When it arrived (after a two week wait) I saw it was an aftermarket gasket set, the parts guy assured me it was as good or better than stock Suzuki and that is what they provide for "those really old bikes".

it is a holiday Monday here today, I was going to finish the motor build today, but looks like I won't be using the Athena cylinder base gasket, guess I'll have to sit in the sun and drink beer all day instead.......;)

thanks very much guys.

Paul
 
so, since I am waiting to order an OEM Suzuki cylinder base gasket, I am thinking "while I am at it" that I "might as well" replace the piston rings and run a hone down the cylinder liners.

what is a good source for reasonably priced and reasonable quality replacement stock size piston rings for an 81 GS 750 16 valve motor?

Paul
 
I'm unaware of anything other than OEM.

I'd talk to Z1 Enterprises. Good folks to deal with and they ship international, or so I've been told.

BTW, don't forget new valve stem seals. I think Athena includes them so you should be good there.
 
yes, new valve stem seals came with the Athena full engine gasket kit, and yes, I am lapping in all 16 of the tiny little valves and replacing the valve guide seals...

I put the clutch back together earlier today, odd setup for the clutch actuator, I am much more familiar with a push type assembly, that weird square geared pull assembly caused some head scratching working out how to get the outer clutch cover on and the gears engaged with each other.

I do not understand why Suzuki painted all the engine externals, I am really fighting the urge to just spray everything with paint stripper and have at it with a polishing rig...but I will resist, looks like a lot of unnecessary work for now, I'll get the engine back in the frame and running for the first time since 1989, then decide.

Paul
 
If I'm not mistaken, 81 should have an unpainted engine. At least my 81 750E did.
 
Just got caught up reading the thread Paul..the real trick to assembling these motors is to put the pistons and rods into the bores then put the top case onto the barrels. Place the crank in position and assemble the rods onto it.Working with the thing inverted of course.
The box can then go into the top case and the lower case gets offered on.Only a couple of selector forks to guide into place.
Much easier than those roller bearing cranks....LOL
 
Hi Greg

sounds like something I should do while standing on my head>>>>;)

Paul
 
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