GT750 Timing Slipping

[sodium.filled]

Just brought home a '76 GT750A - motor was done 2 years ago (only 300mi on rebuild). PO was a bike guy now in his eighties and giving up riding. Motor was done professionally with seals replaced. Compression is ~130psi on my tester. I picked up the bike which was not ridden since the rebuild 2 years ago, battery on charge stabilizer in the tank, prodded on the kicker starter and it ran.

Road it home parked it. 2 days later took it out cleaned it and it would not start.

Pulled the SRIS valves, drained a smaller amount of fuel/oil from the crankcase (most likely from my repeated attempts with the starter to get it to go). replaced plugs. checked points etc. Nice spark. Drained tank and replaced all fuel.

Today pulled it out and still no go... Started to look at the timing. When the marking disc (L,C,R) shows up in the window the Left Cylinder is close to or about BDC. At same time Right Cylinder is close to TDC.

Swapped plug leads on L and R cylinders (HT lead from Coil closest to L Cylinder now on R Cylinder and HT Lead from Coil closest to R Cylinder now goes to L Cylinder).

Bike now pops and almost starts - has some life where it previously had none.

After searching and ready some posts I suspect that the starter clutch woodruff key may have sheared leading to the timing slipping.

Before I dial in the timing I would like to pull the cover and remove the starter gear. What is the right procedure for this? What do I need to drain etc.? I know I need to use a Sears Steering Wheel puller to get the gear off.

Am I missing something else more obvious or given that this is a simple enough procedure and removes a variable I should proceed with ensuring that the key is intact and correctly located?

Your recommendations are appreciated.

[oldjapanesebikes]

Could be the woodruff key I suppose, but you said it ran fine initially ? If it had sheared then all the timing marks would be out the same amount eh ? How did you clean it - pressure washer ? What I would do is ensure things are nice and dry, do a static timing check with something that will show you TDC and each timing mark for each cylinder (dial gauge, or even a stick), and pull apart the connectors in the harness and ensure the contacts are clean - also clean the engine kill switch. The check to ensure you have power at the coils and try again.

And where in Canada are you located ? A group of us get together in Calgary each week, plus other board members are scattered across the country.

[sodium.filled]

Hi Ian,

Thanks for the reply. No pressure washer. Yes the bike ran fine. I'm a bit baffled by this.

I'm in Vancouver BC. I've visited your site several times and seen that Calgary has a keen interest in the Buffalo.

I road the bike from Vancouver Island home to Vancouver via the Ferry. Started and ran each and every time. I was carefully not to run water all over the bike. (Owner of Brit Bikes as well).

I've done a rough check on the timing with a stick in each cylinder. Stick in the L Cylinder when the L Mark shows up in the window indicated BDC, but R Cylinder is near TDC. Hence me swapping the plug leads.

The fact that I have to do this to make the bike have any signs of life makes me suspect something is slipping?

Thanks,
Rob

[yeadon_m]

The L mark in the window indicates approaching TDC, not BDC, for the left cylinder. If you take the plugs out, pop them into the caps, and slow rotate the motor in the correct direction then, in a quiet shed when ignition and kill switch are on, you should hear the snap when the points open and the plug fires. Have a look at the window and see if the correct paddle is passing the mark when that happens.
Mike

[Suzukidave]

It is sounding like the key may have sheared , there have been several that have posted this happened .. from gas flooding and injector oil filling the bottom end and one the nut holding the starter clutch on had loosened . Time to do a side cover pull and check it out , like you posted a steering wheel puller takes off the starter clutch without damage .

[sodium.filled]

Thanks I'll remove the cover tonight and take a look and update.

[oldjapanesebikes]

It is sounding like the key may have sheared .

+1 to Dave's comment - but it does seem odd given you were able to run it for quite a while. Any I've seen this happen on, it happened on the first couple of crank spins after firing and not after several miles of riding. And the timing on the middle and right should have shifted as well - not just the left. That's a puzzle.

[sodium.filled]

Took the cover off tonight and does look like the gear has slipped. I will pick up the steering wheel puller tomorrow night.

I can see swarf and it looks like the keyways are not in alignment.

My T500 was also out of service but I've sorted her out tonight with some new coils, condensers, 1K ohm plug caps and new HT leads.

1 2 stoker working is better than none!

Will post pics of the gear when pulled off...

[Suzukidave]

Any update ?

[Barry S.]

Mine has sheared 2 keys when the petcock let it flood, I solved that with a brass inline cut-off valve.

[sodium.filled]

Had to source a puller here in Kanadia; picked-up a harmonic balancer puller from a auto parts store.

Key is sheared in two. I also suspect a leaky petcock. On my T500 after rebuilding the petcock I ditched it for a Pingel Dual Outlet w/ On/Off/Reserve. Looks better too!

I'll pick-up a few spare keys and rebuild the petcock.







Thanks for the help guys - so far this is a very helpful forum, and I thought you only meet nice people on Hondas...

[oldjapanesebikes]

I edited your photo links for you.

[Suzukidave]

9 out of 10 times a leaky petcock means the O ring attached to the diaphragm has failed .

[Coyote]

Speaking of that o-ring, anyone know where I can by just that? I don't need a full rebuild kit. I need the o-ring, the 4 hole gasket and the V seal. As the 4 hole gasket and V real are external parts, they are easy to source. Not so for the o-ring as you all know. Once I tried one of the 6 o-rings from under the oil pump manifold. It didn't work. Cross section too large.

[oldjapanesebikes]

Speaking of that o-ring, anyone know where I can by just that?

I just took the old one to a local jobber supplying seals and things to the oil patch here in town, and they were able to get a close match in viton material. They usually work fine. Full (and I do mean full) rebuild kits are available from these folks in Germany - you will have to translate the page. The quality is excellent.

http://www.hard-to-find-parts.de/pi-550 ... egoryId=53

I suspect Reiner may also be able to supply just the o-ring - you'd have to email him and ask.