750 TSCC Rebuild or Replace?

[dorkburger]

Always nice to see some goodness.

 

[Rich82GS750TZ]

When the engine is over-revved the valve train floats. The rocker arms are not following the cam lobes smoothly anymore but are being hammered open and slammed closed. All of this causes wild harmonic vibrations which can loosen the valve adjusters and even cause the screws or nuts to back out. When an adjuster screw separates from the rocker, especially the ones closest to the cam chain tunnel, they frequently get drug down with the timing chain. When the screw gets jammed between the crankshaft sprocket and the chain the sprocket teeth jump the chain links throwing camshaft timing out of synchronization. The results can be bent valves or in this case the valve to piston interference was significant enough to break the rocker arms. I have personally found valve adjuster screws backed out on engines that the owners admitted to missing a gear and severely over-revving the motor. In one instance several screws/nuts had fallen out of the rocker arms. All but one screw was still laying in the head. The last screw was still in the crankshaft sprocket area and had cause the cam timing to jump time. All 8 of the intake valves were bent and required replacement. Dar

Dar
Thank you for this explanation. It leads me to believe that I'm 99.9% positive that all of my adjuster nuts were tight, and that I'm 100.1% sure it was because of the way that I routed the clutch cable, and it's interference with the throttle linkage on the carbs, that caused by bike's demise. Totally my fault either way. Just good to be able to piece together this series of unfortunate events.

 

[GSXR7ED]

I’m interested in how you routed your throttle cable that caused this demise.

Ed

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[Rich82GS750TZ]

I’m interested in how you routed your throttle cable that caused this demise.

Ed

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See posts 34, 35 of this thread.
https://www.thegsresources.com/_forum/showthread.php?258181-Before-I-start-clutch-work

The piece of bent wire I so cleverly made up did a fine job of keeping the clutch cable away from the valve cover/engine. It kept the cable so far away from the engine that it pushed it in the the path of the throttle linkage. I was getting more confident in my clutch repair and the last time I pulled out, I poured on the throttle pretty hard, the throttle linkage stuck and when I left off, pulled clutch to shift to 2nd, the throttle was hanging. Never got it into second, then...WEEEEEEEEEE, CLANK, CLANK, CLANK, CLANK, CLANK, CLANK, CLANK, CLANK, CLANK. Hit the kill switch. Got it started, limped the bike for 1/2 Mile (I measured it yesterday). That was all she wrote. And here we are.

 

[GSXR7ED]

Ohhhhhhhhh!!!!!!!!!!

Yeah, I wondered why that guide was attached to the carbs...it's very important...APPARENTLY!

Thanks for explaining.

Ed

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[limeex2]

As far as I know it's the same.

Those engines have oiling issues. One of the few GS engine's that are not bulletproof. There is a fix that involves shimming the oil pressure relief valve. Details available in the archives. That said, don't think that's the cause of this engine failure.

Not sure why these get such a bad rap? I road raced mine for a year before it got bent up. Pounded the hell out of it. Changed oil and adjusted the valves after every race week end. Just by getting rid of the 630 chain it was the fastest bike in the production class. I was NOT the fastest rider! 80-82 motors are all the same. I believe the motor my have changed in 83.

 

[Nessism]

Not sure why these get such a bad rap? I road raced mine for a year before it got bent up. Pounded the hell out of it. Changed oil and adjusted the valves after every race week end. Just by getting rid of the 630 chain it was the fastest bike in the production class. I was NOT the fastest rider! 80-82 motors are all the same. I believe the motor my have changed in 83.

They get a bad rap because they tear up cranks and top ends due to poor oiling. Don't believe me? Go search through the archives. There are several threads detailing the horrors.

 

[Rich82GS750TZ]

Making progress on cleaning up the donor engine. Got the barrels off last night. Valve cover and head cleaned up really nice. Most of the base gasket is stuck hard to the bottom of the barrels. That one’s gonna be some work. Filling my shopping cart on partsoutlaw I’m over $200 for all the gaskets, orings, copper washers, half-moons, etc. for the base, barrels, tensioner, head and valve cover.

I have a Clymer’s and the factory manual pdf from BikeCliff’s. Clymer actual may me a little more thorough. Been reading a lot, but I’m sure I'll have questions as I get on with it.

 

[Big T]

You do realize that, with the engine disassembled, you're going to have to go all Chuck Hahn on it and make it all clean and shiny?

 

[Rich82GS750TZ]

I’m gonna spiff it up a little, without going full Chuck Hahn. I’m not that patient. Though I do admire his work. I wanna ride.

 

[Rob S.]

See this month's Bike of the Month for a classic 7/11 conversion.

 

[Rich82GS750TZ]

Well, one thing led to another today and...

Overall, things look pretty good.Swingarm bearings look and feel in great shape. It gave me an opportunity to inspect the goofy wiring by the PO to the rear that I knew was there but never investigated, until now. There are no ground wires going to either turn signal like shown on my wiring diagram. Lots of bare wires twisted together and taped up. And only 2 strands of copper running one of the signals. I’ll want to put it back together better than I took it apart. Should there be a ground wire with a lug under each turn signal mounting nut?

 

[Big T]

Correct on the ground wire and location

 

[zuluwiz]

GSs have 2 types of turn signals: A) with running lights, and B) without running lights. A) type have 3 wires. B) type have 2 wires. That said, i'd wanna be replacing all that blodge with decent wiring.

 

[Rich82GS750TZ]

On the plus side, I figured out how to haul my bike in my MINI. It?ll fit, now.

 

[93Bandit]

Wow, you're getting serious about this bike.

 

[Rich82GS750TZ]

Once I got started, it turned into one of those “while I’m at it” situations. So now I’ll be fixing rusty spots and painting the frame, swingarm, center stand, side stand and engine mounts. Every nut and bolt’s been wire wheeled, bagged and tagged, every wire connection that I took apart will be cleaned with deoxit before everything goes back together.

The whole front end was removed intact. I only removed the instruments, ignition lock, and top triple so I could remove the front end from the frame. Didn’t have the heart to pull all the wires apart in the headlamp housing. All bearings look great. And I refurbed the forks and front caliper last year.

Once my new gaskets, etc. arrive I’ll finish cleaning up and putting the donor engine back together with my original case covers.

At least that’s the plan.
I’m trying to keep everything as organized as I can.

 

[Rob S.]

Every nut and bolt?s been wire wheeled, bagged and tagged...
I?m trying to keep everything as organized as I can.

That's the easy way. If you were up for a challenge, you'd skip the tagging, bag them all together, then give it a good shake.

You youngsters - always looking for the easy way out.

 

[GSXR7ED]

Wow, you're getting serious about this bike.

Very true...I have a thread called “breakdown” but it is nothing compared to what Rich is doing.

Ed

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[Rich82GS750TZ]

Covered all the rusty bits the other day....

I?m fortunate to have a big paint booth at work to hang and paint all the pieces.