Sync beavel gear

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dessmo
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Sync beavel gear

Post by dessmo » Fri Jan 05, 2018 12:15 pm

I have removed the tops for some cleaning and maintenance. The dots at the top is aligned. But I had to turn the engine around without the top on the engine. Will it be in synch as long as the shafts are in the correct position correct (the half shafts fit together) and the dots are aligned? If not, what do I have to do to make sure it is the right synch?

Thanks!
Magnus
Norway
83 900 SD Darmah

ducadini
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Re: Sync beavel gear

Post by ducadini » Fri Jan 05, 2018 2:39 pm

UHOH, You're in trouble now :-)

Unless You are VERY sure how many turns You did on the crank, best thing is to take the RH side cover of and align the dots on the gears.
Done that, the halves of the Oldham coupling should both be in a 90° or 180° angle as to the crank . Can't remember which.
If the dots on the heads are still aligned, You could check the halves of THOSE oldhamcouplings, they should be opposite.

Better check this before fitting the heads and damaging valves.

ciao
ducadini
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dessmo
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Re: Sync beavel gear

Post by dessmo » Sat Jan 06, 2018 12:53 am

Thanks for your reply Ducaldini,
So this means that even if both shafts will fit (the two half of the shafts fit together), it might not be in synch with the heads even when dots at heads are aligned? Iow one 180 turn of the shafts does not bring the engine back to the same position? Or am i misunderstanding you. Both cover on the tops and the right side with the alternator are removed, can't see any dots down by the alternator.
Thanks for your assistance, it is highly appreciated.
Magnus
Norway
83 900 SD Darmah

ducadini
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Re: Sync beavel gear

Post by ducadini » Sat Jan 06, 2018 2:59 am

OOPS :oops:

Forgot about the support plate that's hiding those bevels. And it’s not really easy to take the support off to check the bevels
I open Steve’s site (thank You Steve) two times so I can open both the 860 GT-GTS workshopmanual on page 103 AND the 860 parts manual on page DS.
On page 103 WSM you can see what it should look like on assembly.
On DS you see the parts.
I’m assuming the engine did run before You took off the heads and turned the crank.
Now turn the crank ANTI-clock until the vertical piston is at TDC. THEN the oldhamcoupling should be perfectly in-line with the crankcase-split (see pic 83).
From that side ALWAYS turn anticlock, that's the way the engine turns AND You avoid turning the starterengine.
If not, repeat, being sure the VERTICAL piston is at TDC and checking the oldhamcoupling (both) for the correct position.
It could take several turns until BOTH oldhamcouplings are in-line AND the vertical piston is at TDC.
That’s because the upperbevel and the crankgears have uneven teeth to avoid excessive wear.
When vertical piston is at TDC and the oldhamcouplings are inline with the crankcase (pic 83) then You could feel with a small dentist hook (<2mm) if the 2 dots on the lower bevels are in line.
It’s a bit moving around but can be done.
You could try with an endoscope but not much place downthere.

Keep us informed about the progress 😊

ciao
ducadini
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dessmo
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Re: Sync beavel gear

Post by dessmo » Sat Jan 06, 2018 9:36 am

Thanks again Ducldini, this was way more complicated than I initially thought. But I think I slowly get it. As of now the to shafts/Oldham couplings are both in the same position with the "face"/flat part facing out to the right. But the vertical piston is more or less at the bottom and not at the Top Dead Centre as you are explaining. Can't see the dots on the top crank wheel, so it hidden behind the plate somewhere. So if I understand you correctly I should continue to turn counter clockwise until vertical piston is TDC and the shafts are facing as now. The engine worked just fine before I removed the heads and cylinders. The pictures you are referring to is it from the 860/900GTS workshop manual? the pages/pictures in the 860 GT/GTS workshop manual does not make sense to me. Will try to see if I can feel the synch marks, but it is quite cramped. Thanks again.
Last edited by dessmo on Sat Jan 06, 2018 11:06 am, edited 1 time in total.
Magnus
Norway
83 900 SD Darmah

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Re: Sync beavel gear

Post by ducadini » Sat Jan 06, 2018 10:08 am

Indeed, the flat sides of both couplings must face the righthend side AND the vertical piston must be at TDC.
THEN the dots are aligned at the bottom.
Could take several turn to get to this.
If the cylinderhead beveldots are aligned (could take several turns and those flat sides are facing to the lefthand side) everything fits nicely together.
It should've been the 860/900GTS manual but almost all pics about that chapter are the same.

ciao
joseph
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dessmo
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Re: Sync beavel gear

Post by dessmo » Sat Jan 06, 2018 1:32 pm

Thanks Joseph, I think I got it now. I am waiting for some parts before I put i together again.
Magnus
Norway
83 900 SD Darmah

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abmartin
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Re: Sync beavel gear

Post by abmartin » Fri Jan 12, 2018 12:12 pm

I don't think you have to worry about the alignment of the bottom bevel gears. If the vertical cylinder is at top dead centre, the dots on the upper bevel gears are aligned and the shaft couplings fit together then install the cylinder head. There should then be only one way that everything will line up for the horizontal cylinder and that is when the shaft couplings fit together and the dots on the bevel gears for that cylinder are aligned. Just to make sure turn the engine over by hand to make sure that the valves don't hit the pistons. At top dead centre on the compression stroke for each cylinder the valves should be fully closed. You can check this by looking at the camshaft lobes position with the end plates removed. They should be in the eight o'clock and four o'clock position.

Bruce
1979 900SS
Fredericton, NB
Canada

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dessmo
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Re: Sync beavel gear

Post by dessmo » Fri Jan 12, 2018 12:29 pm

Thanks for your reply Bruce. I have worked on the engine today and mounted back the cylinders, will go for the heads tomorrow. After playing around with the engine it seems like there are 3 different positions for the bevel when the vertical cylinder is TDC, an only one where the shaft couplings fit nicely together. That should be in accordance with your description. I will check the valve clearance tomorrow before I install the tops, do you measure the clearance with the valves open or closed? After what I read the cylinder should be at TDC, but there are three different TDCs. If you use the one where the dots are aligned, the valve is fully open and the rocker arm is pushing on the valve and there is no clearance.
Magnus
Norway
83 900 SD Darmah

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abmartin
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Re: Sync beavel gear

Post by abmartin » Fri Jan 12, 2018 4:36 pm

Hi Magnus,

The valves should be adjusted with each piston at top dead centre on the compression stroke. I don't look at the dots on the bevel gears, all you need is to have both valves fully closed. Rotate the engine a few times to get a feel for it. Setting the clearances can be a bit tricky so go to this site for a good description of how to do it: https://www.ducatimeccanica.com

Lots of great information on that site if you haven't seen it before.

Bruce
1979 900SS
Fredericton, NB
Canada

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dessmo
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Re: Sync beavel gear

Post by dessmo » Sat Jan 13, 2018 3:24 am

Thanks again Bruce, that makes sense. I have the heads of the engine now, so I guess both valves being closed with no pressure on the valve is what I should measure?
Magnus
Norway
83 900 SD Darmah

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abmartin
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Re: Sync beavel gear

Post by abmartin » Sat Jan 13, 2018 11:20 am

Magnus - it sounds like you have it figured out. Just remember you have to press down on the closing rockers to take up the spring pressure before you can get an accurate measurement.

Bruce
1979 900SS
Fredericton, NB
Canada

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Gardner
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bevel gear timing marks

Post by Gardner » Thu Jan 18, 2018 8:04 pm

I found this article years ago and printed it for reference and just found it again!
https://willyg.homelinux.org/Bevel_Timing/timing.html

Mark
1978 SD Darmah
1979 SSD Darmah
1981 900SS
2017 Desert Sled
1982 Bimota HB2

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dessmo
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Re: Sync beavel gear

Post by dessmo » Thu Jan 18, 2018 11:41 pm

Thanks Mark, that was a very useful article to understand the synchronization of the engine. I think I got it right, but will double check once more before I try to fire up the engine. The engine is still out of the frame, so it won't happen before in a month or so, depending on how I am progressing putting the bike together again.
Magnus
Norway
83 900 SD Darmah

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dessmo
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Re: Sync beavel gear

Post by dessmo » Mon Mar 12, 2018 12:50 pm

Started the engine on my Darmah today after assembling the bike after a total strip down, repainting, rewiring and some service on the engine. The good news is that the engine started immediately and ran very nice. The bad news is that I think I might have a minor oil leakage from the lower bevel support at the rear cylinder.
Is there a way to replace the bevel tube O-ring in the lower bevel support without taking the engine out of the frame? And if not, what is the best/smartest way to get the engine oft the frame to replace the O-ring.
Magnus
Norway
83 900 SD Darmah

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