Valve timing on Mk1 Montjuic

[redceph]

Just like last winter I'm trying to get my Monty finished this winter, but as it's currently 2 degrees C in the garage my brain has shut down and I've come in to thaw out.  Can anyone provide guidance on setting valve timing on a Monty and whether the Alpino workshop manual is relevant in this regard?

When I set the right piston to TDC using PMD on the flywheel as a guide, and line up the mark on the exhaust cam sprocket with the mark on the central bearing cap, the cam lobes are at approx 9 o'clock but are depressing the buckets by a couple of mm.  Exhaust valve clearence is set at 0.20 mm (inlet 0.15 mm) as per Alpino.

The engine has been in pieces for some time and the cam sprockets were certainly taken off at some point.  The exhaust sprocket is marked S, and the inlet is marked A.  The markings on each sprocket face the marks on the respective central bearing cap.  Have I put them back together correctly?

Many thanks

Martin

 

[bob]

Hi Martin,
'A' stands for aspiraz [inlet] and 'S' stands for scarico [exhaust], so it would appear you've got that bit right . Alpino and Monty cam timing is quite different so unless you've got a 500 manual with a Monty supplement you're might be going in the wrong direction.

 

[redceph]

Thanks Bob - I just have the standard Laverda 500 Workshop Manual without the supplement you mention.  ??? 

Can anyone send me a copy?

 

[sfcpiet]

Martin, basically the Alpino and Monty valvetrain are identical.

Seems to me you have just mounted the sprockets incorrectly.

With the RH piston in TDC/PMD, the RH cam lobes should be roughly pointing at each other, ie, the exhaust 180? opposite of what you've got!  The Inlet should just begin to open, the exhaust should almost be closed.  As there is quite a bit of valve overlap with the Formula/Monty cams, both the inlet and exhaust valves will be open for a bit around TDC.

piet

 

[redceph]

Piet, many thanks. 

I'll double check the positions of the inlet and exhaust cams relative to each other using the timing marks on the sprockets and bearing caps for guidance.  It is reassuring that there is some overlap and that the exhaust valves are not fully closed at TDC.

Having read through some previous posts on this topic it seems that Alpino valve clearences are too tight for the S1 cams.  Mike's (Waugh) preference for 0.20 mm (inlet) and 0.25 mm (exhaust) is easily obtainable from the current setting of 0.15 mm and 0.20 mm.  Sadly missed by all.

Also, the Monty timing figures posted a while ago (at 0.30 mm clearence, 1 mm lift) of:

Inlet open at 24 BTDC
Inlet closed at 43 ABDC
Exhaust open at 39 BBDC
Exhaust closes 29 ATDC

are also very useful to cross check so I'll sacrifice that old Johnny Mathis CD and get it marked up. 

Thanks again

Martin

 

[sfcpiet]

Martin,

All the Lav 4-valvers like a bit more valve clearance.  0.20-0.25mm inlet, 0.25-0.30mm works OK.  Adjusting them all to a fixed clearance will get you stark raving mad in a single afternoon, best to give yourself a bit of tolerance to work with.  

The cam/bearing clearances are enough to throw your measurements overboard every time you loosen the cams......

piet

 

[GregT]

Where there are problems like piet quotes, I've always found it easier to work to lobe center figures as these are not dependent on using a fixed clearance.
On that point - and having no personal experience of the Monty motors - i note that the quoted valve timing has what I'd describe as odd lobe centers by modern standard. Most good 4 valve heads now run approx 102 - 104 inlet LC and 104 - 106 exhaust.
Has anyone played round with cam timing ?

 

[bob]

Hi Greg,
You're absolutely right about the Monty cam timing, quite radical and peaky by modern standards
My bike has the cam timing set at 106 degrees inlet and exhaust, it runs very well indeed , in fact it's so tractable I might introduce a bit more overlap and see if we can gain a bit more top end .
Bob

 

[GregT]

I've not seen a Lav 4 valve head so I'm guessing....but if they're quite wide valve angles try around 100deg inlet 105 ex. This works well on the early wide angle Hondas.
If they're reasonably "modern" angles then all I'd try on yours is to move the inlet to 104 deg LC - leave the exhaust where it is.

 

[bob]

Hi Greg ,
The 500 head has a combustion chamber which is quite similar to a Suzuki one of the same era, so you could say it's relatively modern with fairly shallow angles, at least when compared to the triple [see pic] I don't think I'll going as far as 100 degrees as we'll almost be back where we started [Monty inlet lobe centres are 99 degrees]  My motor runs so well and strong that any incremental changes will almost certainly be very small.
The 500s will rev quite happily to 9500 rpm, in fact they feel quite happy at those revs and will go beyond 10,00rpm. At these revs they still feel OK but unfortunately they tend to have a reduced service life!
On my racer I've got the rev limiter set at 8600 and most of the time I shift up at about 8000 [the bike is an endurance racer], so I'm not looking for lots of top end. My motor is bored out to 603cc and has been tuned specifically for mid-range and its characteristics are quiet different from most 500s Bob

 

[GregT]

The air/oil cooled GSXR's love 104/104 - some speedway TQ engine builders here go to 103/104 for a wider spread of power but 104/104 is best all round I find.

Explanation...TQ = three quarter midget. Speedway car class using a lot of 750GSXR's on alky and single geared.

I hear what you say about broad spread of power. Our local circuit has an average lap time of say,1min 50sec. Of this about 18sec are spent on the fast part. Convincing people that a better midrange will pay off in the minute plus of infield is often hard...