500 Valve TIming

R

Rob7

Full member
Location
Perth, Oz
A question regarding valve timing on a 500. When refitting the camshafts/timing chain (the latter being new as are the chain guides) I am unable to line up the two sprocket timing marks and the TDC mark simultaneously. I have checked TDC with a dial gauge and the marks on the flywheel are correct.

The sprocket marks are slightly off - if I move the flywheel approx 3 degrees after TDC (clockwise) they line up perfectly - but are not out by enough to support moving the chain a tooth. If I move a tooth they line up well before TDC.

Is this OK?

R
 
Head and/or barrel been skimmed? This would retard valve timing as described.

While not being ideal, 3° isn't enough to totally knacker the engine behaviour and valve/piston clearance will remain in the ball park. Give it a try, easy enough to slot the cam flanges to correct it later.

piet
 
Thanks - engine has not been modified and clearances appear to be OK. Must have been set up like this before cam removal - but didnt check before I took them out - probably should have in hindsight.
R
 
Same problem for my 500 : my camshafts are 4° late to the crankshaft. This is about 3 mm to the chain.
I checked my cam chain length : 901 mm what makes 5 mm lengthening (112 x 8 = 896 mm). About one third of these 5 mm (1.7 mm) delay my camshafts.
The other cause is my head that has been skimmed. I don't know how much, the bike seems to have a bad story and I don't know it. The pistons are the high comp Formula type (maybe because of the skim head) but the camshaft are standards 14.
My questions :
Do you think the engine can work (even badly) with this timing defect?
For the chain, I’ll wait and pray for a new batch. For the head, is there a way to compensate the heigth reduction? Thicker gaskets or other ?
Thank's for your help,
Fabrice
 
very rare to find a Laverda engine where the cam timing is within 2 degrees of factory spec
finished 3 x triple engines over the last 10 days and had to adjust the cam timing on every engine, one Exhaust cam was out by 9 degrees

built a 500 engine few years ago that was going to be raced so changed the cam timing by vernier drilling the Camshaft sprockets
each threaded hole changes the cam timing by 3.14 degrees at the crank, you manipulate the 7mm threaded holes and changing chain position on the sprocket until you find the cam timing figures you want, mark the sprocket, remove and machine in a new timing mark
see photos

4 degrees is not going to make much difference to the running of the engine

19th Nov MN cam timing inlet

19th Nov MN cam timing exhaust
 
FaNa01 said:
The pistons are the high comp Formula type (maybe because of the skim head) but the camshaft are standards 14.
Click to expand...
That would have the opposite effect - skimming eh head has already raised the compression ratio. Easy enough to add thickness to gaskets (base gasket is the cheapest and easiest). Worth getting an accurate measurement of CR using a burette or similar with very accurate cc measurement. I found that SF motors are well below what is specified.

CR = swept vol (3.14 x 0.5 bore squared x stroke) PLUS the measured volume of the combustion chamber (engine assembled, piston at TDC, filled to halfway up the spark plug hole), total divided by combustion chamber volume. Not adding the chamber volume to swept volume gives an incorrect figure.
 
Fingers crossed someone comes up with a new Cam Chain availability for all these engines, including my Atlas and those racing these engine types.
 
Thanks a lot for your answers. I'll try the bike like that for this time (it was working but I don't ride with it before dismantling).
I’ll do a better job next time. What is exactly the way to add thickness to base gasket ? Is it possible to simply put two gaskets ?
I love the vernier drilling solution. I guess it’s ideal for a racing engine.
For the piston, I thought that the valves recess of formula pistons could secure the clearance. I understand I'm wrong.
 
Checking cam timing doesn't rely on the marks - it can only be done by measuring the actual opening-closing degrees of the valves (but nearly always done by calculating degrees at max lift). Timing marks could be wrong but cam timing spot on ... and obviously vice versa.

On SFs and triples different thickness base and head gaskets are available (and probably are for 500s) ... and if not, I'd hazard a guess two base gaskets could be used (if it got you the correct. I'm usually going the other way and fitting a thinner base gasket to raise CR.
 
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