75 860GT Timing Question

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jcroson
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75 860GT Timing Question

Post by jcroson » Fri Feb 08, 2019 6:08 am

My 860 has been leaking oil from the front cylinder for some time, and in my haste to fix it, I pulled the heads off to do both before turning the motor to TDC (I think).

I now find myself in a pickle so I start reading the manual to determine how to set the timing. I think it involves removing the right side cover and line up the marks on timing gears, do the same for the bevel gears on the head and slip it back on.

So I have a look at the rear cylinder bevel marks...this is the one off the vertical shaft.
https://drive.google.com/file/d/1FlH9-J ... p=sharing

This is a view of the mark on the bevel gear off the horizontal shaft, 180 in the opposite direction of the other mark.
https://drive.google.com/file/d/1h2YvPV ... p=sharing

Seems like whoever put the Lucas ignition on rotated the top bevel gear 180 degrees?

So then I look at the valves and they both look to be at the TDC position...
https://drive.google.com/file/d/1BdWclo ... p=sharing

Opinions appreciated.
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

Lumpy
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Re: 75 860GT Timing Question

Post by Lumpy » Fri Feb 08, 2019 1:19 pm

Maybe it`s camera angle or my fading eye sight but the 3rd photo doesnt look TDC to me. The exhaust valve is partially open. Interesting camera angle too..............looks like the camera is on the piston at the bottom of the stroke. At TDC on any given cylinder your cam lobes viewed through your tappet covers should be at 4 and 8 o`clock, so 12 o`clock was pointing straight up away from the piston. 6 o`clock was straight down. There should be clearance at the valve and cam follower. The timing marks on the bevel gears are hunting teeth. That is they will align only after X amount of revolutions.

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Gardner
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Re: 75 860GT Timing Question

Post by Gardner » Fri Feb 08, 2019 6:50 pm

I use this - https://willyg.homelinux.org/Bevel_Timing/timing.html
Makes it easy to understand.
1978 SD Darmah
1979 SSD Darmah
1981 900SS
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ducadini
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Re: 75 860GT Timing Question

Post by ducadini » Sat Feb 09, 2019 5:54 am

It isn't as easy on a springvalve as on the desmo but here's the method.
Turn the bevel-shaft of the heads untill the marks on BOTH gears lign up exactly.
For one cylinderhead, this is with both valves closed, for the other one valves are open (but in fixed position).
AND the Oldhamcoupling should be facing to the spot where the cylinder is going to be.
Brainfade : can't remember which one is which : horizontal or vertical.
Now You can deduct (nice appropriate word) which piston has to be on TDC.
Now turn the crank (or if You don't want to take off a cover) the rear wheel in 5th gear untill the correct piston is at TDC.
Then check the alignement of the Oldhamcoupling (the "half-shaft) which has to be parallel with the length of the bike.
If this isn't (and BOTH oldhams should be in the same angle), turn the engine over until this is the case.
Fit new o-rings, put on heads, torque.
Sounds easy, just practice a lot.
Of course : when a PO juggled all settings, take the manual and follow those instructions (removing covers etc etc).

ciao
ducadini
Nego i ricordi peggiori
Richiamo i migliori pensieri

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jcroson
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Re: 75 860GT Timing Question

Post by jcroson » Sat Feb 09, 2019 1:01 pm

Lumpy wrote:
Fri Feb 08, 2019 1:19 pm
Maybe it`s camera angle or my fading eye sight but the 3rd photo doesnt look TDC to me. The exhaust valve is partially open. Interesting camera angle too..............looks like the camera is on the piston at the bottom of the stroke. At TDC on any given cylinder your cam lobes viewed through your tappet covers should be at 4 and 8 o`clock, so 12 o`clock was pointing straight up away from the piston. 6 o`clock was straight down. There should be clearance at the valve and cam follower. The timing marks on the bevel gears are hunting teeth. That is they will align only after X amount of revolutions.
Thanks for the reply. The 3rd pic looks like that because the cylinder is still attached to the head, and I flipped it upside down to take the pic.

I'm still struggling trying to get the timing cover off. I've got the gear changer, kick starter, all bolts and the plastic screw plug that holds in the wire and still, after beating (gently, kinda) on it with a plastic dead blow hammer, it won't budge.

After a bit of fiddling, I've managed to rotate the bevel gears until the marks match, and when I rotate the motor until the top piston is at TDC, the flat of the drive tongues facing in the correct location as Gardners documentation provided here: https://willyg.homelinux.org/Bevel_Timing/timing.html

I think I might be moving in the right direction!
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Re: 75 860GT Timing Question

Post by jcroson » Sat Feb 09, 2019 1:02 pm

Gardner wrote:
Fri Feb 08, 2019 6:50 pm
I use this - https://willyg.homelinux.org/Bevel_Timing/timing.html
Makes it easy to understand.
Thanks so much for this, it does help. I was able to manually rotate the bevel gears on the head until the marks lined up, and moved the top piston to TDC. You really helped, thanks!
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Re: 75 860GT Timing Question

Post by jcroson » Sat Feb 09, 2019 1:13 pm

ducadini wrote:
Sat Feb 09, 2019 5:54 am
It isn't as easy on a springvalve as on the desmo but here's the method.
Turn the bevel-shaft of the heads untill the marks on BOTH gears lign up exactly.
For one cylinderhead, this is with both valves closed, for the other one valves are open (but in fixed position).
AND the Oldhamcoupling should be facing to the spot where the cylinder is going to be.
Brainfade : can't remember which one is which : horizontal or vertical.
Now You can deduct (nice appropriate word) which piston has to be on TDC.
Now turn the crank (or if You don't want to take off a cover) the rear wheel in 5th gear untill the correct piston is at TDC.
Then check the alignement of the Oldhamcoupling (the "half-shaft) which has to be parallel with the length of the bike.
If this isn't (and BOTH oldhams should be in the same angle), turn the engine over until this is the case.
Fit new o-rings, put on heads, torque.
Sounds easy, just practice a lot.
Of course : when a PO juggled all settings, take the manual and follow those instructions (removing covers etc etc).

ciao
ducadini
Thanks, I'll try to figure out how to get the front fitted now!
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Gardner
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Re: 75 860GT Timing Question

Post by Gardner » Sat Feb 09, 2019 7:08 pm

Both heads go on at the same time.
1978 SD Darmah
1979 SSD Darmah
1981 900SS
2017 Desert Sled
1982 Bimota HB2

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Re: 75 860GT Timing Question

Post by jcroson » Tue Feb 12, 2019 7:14 am

Gardner wrote:
Sat Feb 09, 2019 7:08 pm
Both heads go on at the same time.
Right, but how do I know the proper orientation of the front cylinder bevel gears?
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Gardner
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Re: 75 860GT Timing Question

Post by Gardner » Tue Feb 12, 2019 9:10 am

The rear piston is at the top of it's stroke, the front piston is moving down. Use the rear wheel rotating in proper direction to see the direction the engine rotates. Both flats on engine bevel shafts should face out at this point. Rotate head shafts till punch marks line up, flats should face in. Make sure the coupling sleeve is on engine bevel shafts and slide the heads on. You may have to wiggle and adjust slightly to get the flats to line up.
1978 SD Darmah
1979 SSD Darmah
1981 900SS
2017 Desert Sled
1982 Bimota HB2

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Re: 75 860GT Timing Question

Post by jcroson » Wed Feb 13, 2019 4:05 am

Gardner wrote:
Tue Feb 12, 2019 9:10 am
The rear piston is at the top of it's stroke, the front piston is moving down. Use the rear wheel rotating in proper direction to see the direction the engine rotates. Both flats on engine bevel shafts should face out at this point. Rotate head shafts till punch marks line up, flats should face in. Make sure the coupling sleeve is on engine bevel shafts and slide the heads on. You may have to wiggle and adjust slightly to get the flats to line up.
Thanks!
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Re: 75 860GT Timing Question

Post by jcroson » Sat Mar 02, 2019 2:04 pm

So I've read through the comments and consulted my manual regarding timing.

My understanding is that if I put the rear cylinder at TDC, line up the timing marks on the head all should be good for the rear cylinder.

I've also tried to line up the timing marks for the front cylinder, but the horizontal marker is either hidden by the washer or absent. There is a bit of red paint on the inside of the shaft....(see pic). In this position, the flat on the bevel shaft is in the correct position.

https://drive.google.com/file/d/15ZlI5r ... sp=sharing

The valves, however, are closed.

https://drive.google.com/file/d/1xUdAPr ... sp=sharing

So IF I assume that's the correct mark for timing, would I be good to go, or will I be screwing things up?
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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Gardner
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Re: 75 860GT Timing Question

Post by Gardner » Sat Mar 02, 2019 6:30 pm

You can usually see the timing mark with a small light while rotating and looking under the washer.
I have heads off that are assembled at the shop that I can line up the marks and take a pic to compare to yours in the morning after breakfast.
1978 SD Darmah
1979 SSD Darmah
1981 900SS
2017 Desert Sled
1982 Bimota HB2

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Re: 75 860GT Timing Question

Post by wdietz186 » Sat Mar 02, 2019 7:11 pm

On the horiz. cyl. the intake valve will be partly open when in the correct position to install. Keep turning the bevel shaft until the dots line up. A light helps if the dot on the cam gear is under the washer. I think they only line up every four revolutions.

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Re: 75 860GT Timing Question

Post by jcroson » Sun Mar 03, 2019 6:33 am

Found the other dot. Had to pry the washer up a bit to see it!

All lined up and installed.

Thanks all!
1975 Ducati 860GT
1974 Kawasaki Z1 900
1999 Yamaha XVZ13TF

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