I have a question about valve timing. If during the process of valve shim adjustment I take the belts off (having marked them at the appropriate points next to the dots on the case and flywheels) does it matter if I have spun the cams (to move the rocker sideways to remove the shims) as long as when I put the belts back on all the dots and marks line up? Or put it another if the dots line up could it still be 180 degrees out or something like that? Hope this question makes sense. Thanks Smon
If all the dots line up then it can't be wrong. If the cam shaft dots were lined up on the wrong TDC, then the dot on the layshaft won't be lined up. I take the belts off and spin the cams to do the valve clearances, it's the only way to get a 'feel' for how tight, tight is...
Look through the inspection window in the left side casing, through there you can see the fly wheel on which are 2 dots - one for each TDC.
I replaced the belts today. When the dots on the pulleys lined up there was a fine line visible on the flywheel lined up with the pointer in the window.
When all the dots line up on the pulleys, can it only be the compression stroke TDC or could it be exhaust stroke TDC also?
When all the dots line up, the front cylinder is at TDC compression and if you fit the belts at this position (and check again after turning) then the timing is correct. Also one of the lines (or dots) on the flywheel will line up at this point, if you then turn it until the other lines up it will be at TDC rear cylinder. When on exhaust TDC all of the dots/lines won't line up. You really can't (or shouldn't) get it wrong, the only slightly tricky bit is that the rear cylinder camshaft is under tension/load when fitting the belt and has a tendency to move a tooth when fitting.
Thanks. Yes that all seems clear. Some shims will need lapping down - need 1-2 thousanths of an inch removed on the openers. It seems that its easiest to do shim changes with the belts off as the cam needs turnng to get the rocker off the valve. Clearly the cam should not be turned with the cylinder at TDC as valves may hit the piston. So only turn the crank over when both valves are fully closed. On the front cylinder this is when the dot on the cam pulley lines up with the dot on the belt casing. What about the rear cylinder?
That's what the other line on the flywheel indicates. I always take the belts off, then turn the engine so that the piston is away from the valves to check the clearances - doesn't matter where they are in the cycle as the valves are not connected to the engine when belts are off. That way, not only can you easily turn the cams in either direction you can also feel if there is any drag on the closer shims - I set them tight (0.05mm) but check there's no drag when turning the cams and then confirm this by inserting the 0.05mm feeler and turning the cam, so that I can feel exactly how tight it is. You won't feel this from turning the crankhaft with the belts fitted, or worse still by turning the rear wheel in gear. Note if you need to change a closer shim, leaving the valve unsupported then it is a good idea to bring the piston up first to stop the valve falling in to the cylinder, in case it slips out of the head.
Thanks for the advice. If you are rotating the cam freely, how do you decide its at TDC for the valve clearances? Do you use the dot on the pulley for the front cylinder? Is it just where the clearance is loosest or can you see the cam lobes - knobbly bit 180 degrees from valve.....
So far I have checked the valves on the horizontal cylinder only. Openers are about 2 thou inches - to tight - Can I lap off a couple of thou?
With the front cyl, TDC is where the dots line up, for the rear you could mark/note where the cam sits at TDC whilst the belt is fitted but really the clearance should never be more at TDC than slightly either side anyway so no need IMO. That's why I rotate the cam with a small feeler in the gap to feel if it binds anywhere, to make sure that the clearance is the clearance at whatever the tightest spot is, although it should be the same both at TDC and either side until the cam ramps up. But I suppose there maybe minimal differences? e.g. if you have a 0.05mm closer clearance then the cam 'should' rotate by hand, albeit tightly, with a 0.05mm feeler in the gap and freely without or even with a 0.04mm feeler in it. As for clearance at 2 thou tight, you could lap the shim but 2 thou is 0.05mm which is the next shim size so best to fit the next size down and save the old shim as you might need it somewhere else yet. Plus you never know, that 2 thou too big shim on one valve might be just the one you need on another? (more so on 4-valve heads). The best way is without a doubt to have a selection of shims, to avoid to-ing and fro-ing to a dealer for different sizes. I'd recommend getting a shim kit from EMS in the USA; https://emsduc.com/ and then topping up with individual shims as required.
Dukedesmo thanks for taking the time to explain all this. I only just got the 900ss, having had some Pantahs in my youth. My other bike is the Guzzi pictured. I picked up the 900 for £1750 - 11000m 1 owner and don't want to commit too much money yet. Its been a bit neglected. First impressions - Huge tires and silencers. The seat and gearing are too high, the bars are too low but I love the frame and engine. Needs to lose the fairing lowers and gain a 2 into 1 pipe. Got some 1" raised bars coming from China via EBay for £30. Makes me realise how my 40 year old Guzzi is still a great bike.
