Evening Does it matter if you set the belts tension on the exhaust or compression stroke as long as it is TDC? If you set the horizontal to TDC via the timing marks then rotate the engine via turning the rear wheel is the first TDC the compression or exhaust stroke? Thanks
At the timing position the horizontal cylinder is at TDC at the start of the firing stroke and the vertical cylinder is halfway down the inlet stroke. So if you turn the engine through 270° the vertical cylinder will be at TDC at the start of it's firing stroke. So yes, it's the first TDC that comes after the timing position.
just out of interest why does it matter re tension . no valve springs to over come. not trying to be a smart arse. btw. :smileys:
Actually there is valve spring tension to overcome. At the timing position the inlet valves are fully open and the closer springs are trying to pull them shut. They maybe relatively lightweight "helper" springs but just try holding the cam in position while you fit the belt and you'll see just how much tension they can apply. For this reason it's best to tension the belts at TDC with inlet and exhaust valves closed for each cylinder. The adjustable pullies on the later engines are to help setting the tension. The cams should be locked then the locking screws loosened to allow the pullies to move. This ensures there is no load on the belts while tensioning and the timing isn't lost because the cams are locked, as long as you remember to tighten the lockscrews again before removing the cam locks.
feckity, feckity, feckity! At least I spotted 2 different TDCs. Don't think I've seen it mentioned before. Either it's so obvious everyone knows to only check every other TDC. Or people only check it in the first place and don't rotate the wheel to check again. Or they do and keep getting varying results so either ignore it or go for an average/middle4didle. This is what happens when I just do something without a massive thread first!!!!
cool cool. thought it could be down to vernier pulleys to once i had a wee think, hmm i didnt do mine at tdc ether. another case of "little knowledge can dangerous" doh.
Didn't do at TDC or the correct TDC? How many miles you done and for how long a time? Thing is, using the 5mm deflection method it's ok and the 45+45deg twist is fine too. The guitar tuner must be a lot more accurate.
As an experiment set the "wrong" cylinder up for TDC firing and recheck tension and it will confirm that belt is slightly slack. You're not the first person to do this by far, and it's not the end of the world on a two valve but does need to be right on a 4 valve.
Am I right in saying that a full engine rotation is 720deg then? A TDC is achieved every 360deg. Lining up the timing mark, and turning the rear wheel to it reaches the timing mark again will be a 360deg rotation on the shaft but a 720deg rotation of the pistons?
power stroke every two turns or 720 Deg. tdc every one turn 360Deg. tdc top dead center. bearing in mind you get about 10 Deg of crank rotation at tdc
Correct. The crossover shaft turns at half engine speed. Get yourself an engine turning tool, it makes life a lot easier when changing the belts.
I'm not really surprised and I think there is far too much obsession with getting exact tension values.
Absolutely Steve.............It amazes me the number of people that seem to think the camshaft position makes a cylinder change length.........however I still do it with all the timing marks lined up. I have tried two methods of adjusting belt tension.........the 5mm / 6mm allen key seems OK, but I have also used a sprung load fishing weight scale whuch is not that much different to the Ducati gauge..........and I still check it with the allen keys.
I did both on mine when I did my first set this last year. Alos down loaded the Gates frequency Ap which gave a good reading on one belt and frack all on the other
