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Discussion Starter #1
Little help on this one would be appreciated before I redo a load of work...

I, replaced the belts whilst the engine was out of the 748, marked the old belts, replaced them and matched all the marks - this was done whilst the Cam pulley was lined up with the crankcase mark. However I never checked the TDC mark on the flywheel.

So before getting ready to fire the engine up now it's back in the frame I wanted to check everything over to be safe, So I line up the pulley mark in the window and then look at the marks on the cam pulley and it's out, needless to say so are all the other marks now...

How can the cam pulley not be lined up when it's at TDC? Should I continue to rotate the crank and see if the pulley comes back into line? Or is the pulley out of sync - it looks like it might have been removed at some point...

I'm not going to try and start this up until I'm sure this is all sorted. There's no problem rotating the crank, there's compression and nothing obviously wrong apart from the marks...

Thank you!
 

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there are 2 tdc marks, one for the vertical and 1 for the horizontal. take out the plugs and put a long screwdriver in the horizontal and slowly turn the motor, watch for when the screwdriver stops moving, that should line up with the correct timing mark on the flywheel. here are some photos of the timing marks. that dot isnt the timing mark anyway. there are 2 hash marks on the magnet, one for the vertical one for the horizontal. some times they can be hard to see. use the screw driver method as a reference. hash marks are on the 9 o clock and 12 o clock in the picture. those dots are all around the magnet.
 

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On my 996 when the crank mark is lined up in the window the horizontal cylinder is at TDC and the cam marks match the notches on the cases (horz. Cly). At the same time the cam pulley marks on the vertical cylinder match the notches on the case, BUT the vertical cams are under tension as the valves are ever so slightly open (not TDC on vertical cylinder). WHEN THE CRANK MARK IS LINED UP ONLY THE HORIZONTAL CYLINDER IS AT TDC.

Hate to say it but....you might have to take off the belts and start over to be sure.
1. Line up crank mark.
2. Line up cam pulley marks on Horizontal cylinder with marks on the horz case (TDC).
3. Line up the cam pulley marks on the vertical cylinder with the marks on the case...Don't move the crank!! The vertical cams will be under tension......install the vertical cam belt.
4. Install the horizontal cylinder cam belt. Recheck that the crank has not moved.
5. Adjust the belt tension on both belts.......
 

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you will need a cam holder for the vertical cams as they want to turn by them selves. the cam gears can only go on one way so no way they are aligned wrong. almost looks like a oil spot on the glass instead of a mark.
 

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Discussion Starter #5
Thank you Gary, Thumper. I used the screwdriver method to identify a faint scratch on the flywheel that then also correspondingly meant the pulley marks all lined up! I clearly remember paint marking the belts with all the timing marks in the correct places originally (except TDC on the flywheel) so I assumed as long as it all went back on the same and nothing moved (apart from the cams) then I was replacing as it was.

The flywheel looks different to the pics you posted Gary, it's got a bevelled edge and that punch dot is clearly a timing mark as there is only one... There are a few faint marks and probably two I could identify for Horizontal and vertical TDC's. But I ma happy that horizontal is at TDC, there is a matching line on the flywheel and the cams all sit at the right places. I wonder if it's a replacement flywheel, not the OEM one?

I made my own tool to hold those cams in place originally, but I rather not try another belt replacement with the engine in place!

Much appreciated
 

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Surely if the pulley marks all align then it's good. The drive pulley runs at half engine speed so only lines up with the marker at the 'correct' TDC.

Depending on engine work you may find that the cam pulleys don't align perfectly with the marks due to offset woodruff keys/adjustable pulleys etc. making them slightly out.

I used to slip the belt over the rear cam pulleys whilst holding them by hand, a bit tricky but doable. To make it easier I bought a cam holder but it doesn't quite fit under tension due to the offset key on the intake cam moving it around half a tooth out so I still have to do it the hard way...
 

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i always mark the old belt and the new belts just to make sure everything was the same before and after. i see you have a 97, so thats why its different. you have a different stator system.
just looked at my 98 flywheel, it has two dots for timing. what looks like the problem is the fly wheel was put on improperly with the alignment mark on the pully not lined up correctly on the crank so the timing marks dont line up correctly now. would suggest next you are tearing into it to fix that problem.
 

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Pull the plugs, if not already, and put your thumb over the horizontal cylinder's plug hole. Use your turning tool to rotate the engine in the correct direction until you just start to feel air / compression at the plug hole. Then gently and slowly rotate the engine while looking at the timing window and stop at the first dot you see. That should be it. Horizontal piston needs to be a TDC compression for the marks to line up.

Your bike has a single phase generator if it is a 1997 and the flywheel will not look like the one pictured.
 

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Discussion Starter #9
i always mark the old belt and the new belts just to make sure everything was the same before and after. i see you have a 97, so thats why its different. you have a different stator system.
just looked at my 98 flywheel, it has two dots for timing. what looks like the problem is the fly wheel was put on improperly with the alignment mark on the pully not lined up correctly on the crank so the timing marks dont line up correctly now. would suggest next you are tearing into it to fix that problem.
I'm in agreement with this, the two timing marks I saw look like they've been hand scored and the original punched dot must have been the timing mark once. So the wheel hasn't been replaced correctly - are these not keyed on the shaft?

As long as it's on TDC and the marks of all the pulleys line up we know we are OK though, the cam pulley is keyed to it's shaft and would be an accurate timing mark (I didn't remove that or the flywheel, just checked they were tight) There's no problem rotating the engine, it's certainly compressing when the plugs are in so unless I'm missing something else it should be good to go for a start in the next week or 2...

Appreciate the answers guys, very helpful and saved me a lot of ball-ache and grief!
 

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my 98 is not keyed so it can be put on in any direction, it does have an alignment dot to match up to the crank. probably why the timing mark is scratched on. when you have the cover some time fix the problem.
 

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I use a 12" 3/8 extension to check tdc if need be when I do belts. If you're not 100% sure, take them off and start from scratch. Another 25-30 minutes is cheaper then a set of valves and head work lol.
 

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If you dont have the tool to lock the cam pulleys, here is what I do when putting on the belts on the vertical cylinder. I rotate the crank pulley 5 teeth CCW. I then rotate each cam pulley CCW by 5 teeth. This removes the spring force from the cams. Slip the belt on, tension them, then rotate the crank pulley 5 teeth CW. I then check to make sure all the dots line up. Been doing this method for many years on all my 4V bikes.

Mike
 

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Discussion Starter #13
I use a 12" 3/8 extension to check tdc if need be when I do belts. If you're not 100% sure, take them off and start from scratch. Another 25-30 minutes is cheaper then a set of valves and head work lol.
Thanks Danbuc, I've used a screwdriver to see TDC and the cam pulley dot lines up with the crankcase mark. If I were to pull all the belts and start again I'm still going to to use the cam pulley mark rather than the flywheel marks as they are unfortunately, not necessarily correct. So I think I'd end up exactly where I am. As I mentioned before, the engine rotates and achieves compression without any valves fouling so I hope I'm safe to attempt a start. It seems the flywheel marks might not be the most reliable starting point as the wheel isn't keyed to the crank whereas the cam pulley is...
 
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