triple cam chain confusion

19753C(E)

19753C(E)

Full member
Location
Wisconsin, USA
So I checked out my valve clearances on the triple - everything is ok, thankfully.  Figured I'd check the cam chain tension while I'm at it.  The Green Book says there should be 10mm total (up and down) movement with the outside cylinders at TDC.  Fine.  Get the cylinders where they should be...hmmmm...only 5mm total.  Loosen the adjuster bolt...keep on loosening it until its almost out - best I can do is 7mm.  So I decide to rotate the crank and check the chain at different spots...it varies with position but at the point  where the exhaust valve on cylinder #1 is just starting to open the chain movement is 15mm!!  Holy crap - the last thing I need is to lose the cam chain mid-ride.  What's going on?  Is this another Green Book snafu?
 
Not sure what model you have, 120 or 180. On a 120 (RGS) the centre cylinder should be at TDC.
 
Its a 180. 

Just did what I should have done before sending my first post and checked the archives.  There's a thread from 2005 that says, check the chain when the middle piston is TDC, as you say, and don't worry about it if the tension changes at other cam positions.  As it happens, when the middle cylinder is at TDC is when I see that 15mm play in the chain.  Another thread, from 2015, says turn the engine until the intake on one of the outside cylinders is just starting to open while the exhaust is just opening on the other.  On my 180 motor that is TDC on the center cylinder.  We seem to have a pattern here.  I'm still a little worried about the chain being too tight in spots though.
 
The orientation of the cam lobes results in the lobes slackening the chain through valve spring pressure in one certain position.  It is in this position that chain tension must be checked and adjusted.  The tighening of the chain as the engine is turned is simply a matter of the valve springs acting on the cam lobes in the oposite direction and is normal.

piet
 
Assume its a 180 by his title.

To adjust you need to understand a little of how the valve train operates and when the chain is under load and when its not in the valve operating cycle...  as ideally you will want to adjust the free play when there is no load on the chain.. hence why its called free play.

Here is what I do, simply  turn the engine so that the outer cylinders ( on a 180 that is ) are coming up to TDC, you will see that for one of the cylinders the cam lobes are pushing the tops of the cam wheels towards each other ( so the corresponding other outer cylinder will then be what is called rocking ) which is therefore  - putting 'slack' into the top run.
This makes it easier to establish the 10mm total free play... ( 5mm in one direction ) ...........25/64 " total for those who think like me.. its more about the feel I guess.
 
And, if the maintenance history of the bike is unknown, it is always a good idea to check the condition of the chain tensioner blade.  With age, the rubber lining becomes brittle and starts cracking, too tight chains rip off a lot of the centre guide ridge and sometimes the rubber seperates from the metal backing.

piet
 
I'm going through this exact thing at the moment, have done shims,
re-fitted cams and chain.
I  presume it has new cam chain and tensioner.
With pistons 1 & 3 at TDC--5mm slack.
With piston 2 at TDC--15mm slack.
All this with tensioner wound all the way out.
 
Read what both Piet and myself have wrote.

Am sure if you drop Dave a line he can send you a cover gasket during the week.
 
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