GT750 starter clutch woes

[jabcb]

Put the gray 75 GT750 in storage a few years ago because of petcock problems.

Recently got it out of storage & did the manual petcock conversion. Got a new fully charged battery & fresh gas.
Almost got it started. Now a few tries later the start motor spins but the clutch doesn’t engage & turn the motor.

Service Bulletin GT-4 covers the GT750 starter clutch mod: http://www.ozebook.com/compendium/techb ... 0001-6.pdf

The motor had been rebuilt by the prior owner. Don’t know if it has the modified starter clutch design.

Any tips of suggestions?

[jabcb]

Figured out the problem.

Prior owner installed the early version Newtronics. First time I’ve had that cover off — will need to check the routing of the red wire.
GT750_1967 by jabcb, on Flickr

[jabcb]

Starter clutch.
GT750_1968 by jabcb, on Flickr

[jabcb]

The nut was loose. Apparently wasn’t properly torqued down.
GT750_1970 by jabcb, on Flickr

[jabcb]

After the nut worked loose, the tight fit on the taper popped, and that tiny key didn’t stand a chance working against the starter torque.
GT750_1971 by jabcb, on Flickr

[Alan H]

First time I've had a look at that side with its clothes off. Interesting.

[jabcb]

Same here. The repair will be much easier that I expected.

Also of note is the infamous cracked plastic gear. The PO drilled stress-relieving holes at the end of the cracks to prevent further crack propagation.
It’s a simple fix that should greatly extend the useful live of the gear.

[tz375]

Interesting fix for the shrinking plastic boss syndrome. Over time, the center of the plastic gear shrinks and cracks but they rarely fail. for some reason. I like that fix though. Makes sense.

BTW, what was the cause of the rust on the clutch gear? Looks like the flange on the points shaft has rusted at some point.

[jabcb]

The plastic gear may be large enough that the crack tip stresses drop to the point that it takes a really, really long time to propagate further.

The important starter clutch surfaces are good. I’ve seen parts on eBay with similar rust problems.
Might be parts inventory shelf wear. Where Suzuki protected the important surfaces, and some other surfaces look ugly after a few decades on the self.

[jabcb]

Took a look at the service manual. Torque spec for that nut is 33 ~ 40 ft-lb.
A much larger torque that I would have guessed. So it shouldn’t be surprising that the nut hadn’t been torqued properly.

Suzuki had a special tool for holding the gear when torquing down the nut. Any suggestions on how to holding the gear?

Manual: https://www.oldjapanesebikes.com/mraxl_ ... /index.php

[tz375]

Try holding the alternator bolt as you tighten that nut.

[jabcb]

I have the GT750 rebuild info DVDs from some guy in England. Had forgotten about them.
The service manual doesn’t say anything about using Loctite. Elsewhere on the same page they used Loctite for something else.
The DVD says Suzuki didn’t use Loctite, but they used red paint.

Also found an old topic about pullers for the alternator & starter clutch.
viewtopic.php?f=2&t=9813
It refers to another reference that recommends using an impact driver + blue Loctite on the nut.
http://pinkpossum.com/GT750/Crank%20pullers.htm

Had wanted to get an impact driver for some time. Now I have an excuse.
Being a novice impact driver operator, I’ll also get a torque limiting extension so I don’t screw things up.

[tz375]

I wouldn't use an impact wrench as well as holding the other end of the crank. That is most likely to make it twist.

But an impact driver on its own would work.

The simple alternative is to make up a holding tool to bolt to the drive gear through the three threaded holes MAke up a plate and weld an arm to it to allow you to restrain the gear from moving.

You might be able to cut a short section of a spare gear to drop in between the starter idler gear and the running gear on the crank - assuming that torque applied to the nut causes the shaft to lock on the starter clutch. I haven't tried that approach.

[jabcb]

The DVD covers a complete rebuild. He installed the alternator & starter clutch before installing the pistons. Made the issue easy — he used the nearest connecting rod & a holder.

Mechanics don’t need to stop tire rotation when they use an impact wrench on the lug nuts. The impacts work aqainst the momentum of the wheel. Same with the GT750 crank.

I already bought a torque limiting extension rated at 40 ft-lb. A neato device — it twists to absorb the impacts when the torque exceeds the rated amount. It doesn’t work against continuous torque, so there is no point in using one with a regular wrench.

Was a bit confused about impact drivers & wrenches. Drivers use bits & wrenches use sockets. I’m actually getting a cordless 3/8” impact wrench.

[jabcb]

Impact wrench + torque limiting extension worked great.
Based on what I found on youtube, you should test your setup before using it on the intended project. Results seen to vary quite a bit depending on what you actually have & how you use it.

GT750 now runs & is a smoke signal generator. Will try new plugs.