How to make adjustable camwheels on Laverda sohc twins (by courtesy of Phil Todd)
The following advices and informations are purely indicative and by no means the
responsability of the author of this article and/or the webmaster. Everyone has
sure that he is able to repair or maintain himself his motorbike, if in doubt, leave it to professional mechanics.
I've not seen any threads about the twin's cam setup details - I presume everyone's
happy with theirs, or, probably as it's such a pain in the backside job to sort
out no one wants to approach it - I suspect the latter!
I've not done this job for about 10 years - I hope my recall is accurate enough.
Firstly, obtain a couple of triple camwheels - most dealers will have an excess
of these - especially used - and be delighted to "offload" some of them - don't
get fleeced - phone round!
out the triple camwheel's centres to be a snug fit over the twin's centre boss.
Mount both wheels over the centre bosses, then align the teeth - the duplex chain can be looped round and secured to do this.
Using a 6mm drill, carefully bore 3 holes spaced equally at 120? through the whole assembly. These holes are at a larger PCD than original tappings - you will see why when doing the job.
Set up wheels to make sure you will miss the original tappings during this procedure.
Separate wheels - Tap 3 holes to 7mm in one wheel and increase the other wheel's and the "new" centrepiece's (CP) holes to 7mm.
Bolt whole assembly together with new 7mm bolts, then make a timing mark in the same place as original, using your previous record.
Mount the CP on a rotary table and, with a 7mm slot drill or end mill, elongate the 3 holes to allow the teeth of new camwheel to move just over ¼ of a tooth. This job can be done, or completed, carefully with a file.
The whole assembly is, unfortunately heavier than original - I have drilled lightening holes in mine, but still am a tad heavier. As cams run at half engine speed it is not so bad. I lap the new wheels to the CP with grinding compound - not sure if this is necessary - don't get any between centre boss and wheel.
You now have the facility to adjust the overall cam timing.
For this procedure the right hand cam (RH) is the dynamo drive side, the left hand (LH) is the primary drive side. This will enable timing to be adjusted between cylinders. This job can be done on its own, no need to do procedure 1 first. Obtain a length of 4mm keyway steel - a bearing shop or engineer's supplier will have this.
a 4mm carbide or similar tipped end mill, elongate the woodruff key slot in each
cam half to full length of flange. |
Elongate the 6mm mounting holes in the LH cam flange to allow just over ¼ of a tooth of movement either way - this will only be a couple of mm at this PCD.
The holes can be elongated on a rotary table with a 6mm slot drill or end mill. Once again - they could be done, or finished, with a file.
Cut and shape the 4mm keyway metal to finish up so that it does not protrude past the mounting end of flange I.E it does not enter camwheel.
Fit flange to cam half. For the RH cam - cut & shape the keyway metal so that it protrudes into about halfway of the thickness of camwheel, but must not touch the LH cam half when bolted up. Fit flange to cam half. You may be wondering why I suggested elongating the RH half's slot, as it really is no different in operation than it was. - It is because I consider the original to be a weak point anyway.
As the flanges are removed/replaced, each time they lose a tiny bit of their grip. If flanges are a loose fit on shaft, no extra pins, grub screws or whatever are likely to stop disaster happening. I would be among the first to point out that the key only locates an outer in normal circumstances, but there is, I believe, a design "blemish" here. I believe that, as the flange has quite a thin wall, the key, which is a good tight fit, actually embellishes (I've found another good word) the metal to metal contact in this application and benefits from being present along the whole length of flange.
I do lap the flanges to camwheel before fitting to cams. Bolt the two halves and camwheel together and check that the movement is available.
ASSEMBLY & CHECKING:
For this I am presuming both procedures have been done - for those only doing
procedure 2 - the last bit will apply.