Gregory Bender
 

Setting valve clearances on Moto Guzzi Tonti-framed machines

Moto Guzzi V7 Sport, 750 S, 750 S3, 850 T, 850 T3, 850 T3 California, V1000 I-Convert, V1000 G5, 1000 SP, Le Mans, Le Mans II, Le Mans CX 100, Le Mans III, Le Mans 1000, 1000 SP III, 1000 S, California II, California III, California 1100, California Jackal, California EV, California EV Touring, California Aluminium, California Titanium, California Special, California Special Sport, California Stone-Metal, California Stone-Touring, California Classic, California Touring, and California Vintage models

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Background: Moto Guzzi provides D (right) and S (left) marks on the flywheel to identify when each piston is at Top Dead Center (TDC). The D and S marks on the flywheel can be visible on the compression stroke, but they can also be visible on the exhaust stroke (when the exhaust valve is open). It is important that you locate TDC on the compression stroke when both valves are closed.

Here is the approach that I typcially take to finding Top Dead Center (TDC):

  1. I remove both spark plugs.
  2. I rotate the engine counterclockwise (counterclockwise as if you were viewing from sitting properly astride the motorcycle facing foward). I typically do this by using a hex key in the bolt that secures the rotor to the crankshaft (after removing the alternator cover, of course).
  3. As I am rotating the engine, I place my finger on the spark plug hole (sealing it) and wait for pressure to start to build against my finger. When I feel air pressure against my finger, then I know that I am on the compression stroke.
  4. You can then continue to rotate until you see the correct D or S mark on the flywheel (depending on which side you are doing). You will need to rotate the crankshaft again for the other side.
  5. Be advised that it is possible for the flywheel to be bolted onto the crankshaft in any one of six positions. Only one of these positions will result in the D and S marks being visible at TDC. Therefore, if this is the first time that you'll be setting the valve lash on your engine and you aren't 100% certain that a previous owner didn't re-mount the flywheel in the wrong position, you'll want to verify that the piston is truly at TDC when D or S is visible.
    • To check to be sure that you are at TDC without referencing the flywheel marks, you can use a popsicle stick, plastic drinking straw, or even a screwdriver if you are careful. Insert it into the spark plug hole such that you are NOT going against the wall of the cylinder but rather gently feeling for the top of the piston. You then rotate the engine around as you hold the stick, straw, or screwdriver in your other hand and get a feel for when the piston reaches TDC.
  6. Remember that you are not setting valve timing and you are not setting ignition timing. You are only setting valve lash/clearances. I mention this because the most important thing in this operation is to be certain that the valves are closed. The above procedures should help you get there.