|Basic Instructions for a Guzzi Big Twin Valve Adjust
1. Put machine on stand then remove spark plugs.
2. Move back wheel back and forth. Select a high gear, at least fourth.
3. Remove both rocker covers.
4. Obviously the rocker to the front of the bike is the Exhaust rocker, the one nearest the
carb/injector is the Inlet rocker.
5. Now watch one cylinders rocker gear at the same time get a friend to rotate the rear
wheel in the normal (forward) direction of rotation (DOR) slowly,
6. Now what you want to do is first watch the EXHAUST rocker go down and come back up,
carry on rotating and do the same to the INLET rocker but as soon as the rocker stops
cease rotating the rear wheel for a moment, then find a small piece of rod say 2MM wide
by at least 300MM long, insert through the spark plug hole and rest on top of piston
then continue rotating wheel slowly until the rod comes up toward you to the highest
point then stop. The piston will be near enough at TDC to set valve clearances.
7. You will need to know the clearance for you're particular machine stated in the (ManSpec)
Manufacturers Specifications, look in the manual under rocker / valve clearances.
8. Select a Feeler Gauge as stated by you're manual and insert it in the clearance between
the rocker arm and the valve stem, so if it is a sliding fit with no excessive clearance the
valve will not need resetting. If the stated clearance is say 0.35MM, and a 0.37MM gauge
will slide slightly tight in the clearance I would not adjust it, but any clearance larger than
this then I would. If in the manual it states two clearance sizes, the larger clearance will
always be for the EXHAUST.
9. The same routine applies to the other cylinder, it doesn't matter which is done first.
10. The clearances are adjusted via undoing the Locknut and rotating the screw in the
required direction, then retightening the locknut.
11. Once you have done the above the valve clearances are set.
12. Replace all covers and plugs "rock" the rear wheel to select neutral gear.
13. At the end of action #6 with the piston at the uppermost position, if you wanted to find
true TDC this is normally located on the flywheel, by removing the rubber bung on the
clutch housing and looking in you will see a scribed line on the surface. These marks
will be also used for setting the ignition timing. You may have to "rock" the engine as
prescribed above about 25MM either way to accurately align the line with the associated
14. So if you’re setting the IGNITION timing, you MUST use the timing marks on the
flywheel, but if you’re just setting the valve clearances Nos 1-12 will suffice. Please note
that each cylinder will have its own marks (2) on the flywheel for both ignition and tdc,
you cannot use ONE set of marks for BOTH cylinders. The two marks per cylinder
scribed on the flywheel will be within 30MM or so to each other. If you rotate the engine
the way it runs (via fourth gear) the timing mark that appears first will be for IGNITION
timing, the next mark will be TDC. To make life a little easy after you have set the piston
via small rod to the highest point, highlight the flywheel marks via white paint or use
Tipex as i do.
Well I know this was quite long, but it will suffice.