34a/Hawkestone barrel

[greeves246]

I'm surprised at your reference to the powerband of the Stiletto, Greeves246, they are my favourite bike, having raced one MANY years ago. I found them very rideable, with good midrange, helped no doubt by the double needle carburettor, which when set up correctly (not by me) gave excellent throttle response through the rev range. Much better than my Bultaco Pursang of the time, even though it had more peak power.

i like the sdr my father has a MAR years ago my father pitted his montessa against one on the moors on a sunday yes any sunday ! and he found the ossa to be very fast !

i had a ASPES 50 ! MY FRIEND HAD A ITALAJET !

[ADickerson]

The original question was raised as my 31a engined Scottish had been pinking and siezing from time to time and the big end developed play over a period of just 6 months.
I replaced the crank with a better one (standard - not full circle) and placed a 1mm spacer between the barrel (iron scrambles barrel) and crank case mouth. I ran the bike up the other day and noticed that it had the effect of softening each power stroke just noticeably and that is with exactly the same ignition settings. I will let you all know how the bike reacts to sustained high revs and if it has cured the pinking issue when I get the chance (young family to look after and all that..).

Hi 249XUU, or can I just call you Reg! I've suffered from similar problems with my Hawkstone in the past, similar setup to yours, and the problem is possibly down to one of two things. Ignition timing too advanced or too high a compression ratio! Unusual in a Trials bike unless someone has fitted a high comp head. They are easy to spot as the combustion chamber is hemisherical and measures just 46mm diameter where it meets the face of the cylinder head. It gives a ratio of about 12:1 which is a bit high, 10.5:1 is recommended by those who know. The effect you've achieved through adding the spacer under the cylinder will give the same effect as under the cylinder in respect to lowering the comp ratio although of course the Port timings will be affected as Peter originally suggested. Hope your efforts have at least cured the pinking, and maybe even added some interesting power characteristics to boot as well! Let us know how you get on, family allowing of course. I think most of us have been there too, just enjoy both as time permits.

[Peter Rotherham]

Hi, (again).

"unless someone has fitted a high comp head."

Once again, this is the old problem arising from 'bikes being used after 50 - 60 years of use, mis-use and 'tuning'.....

As I've said, Villiers parts are extremely interchangable, and at first glance, all 9E/31-37A casings, cylinders & heads look alike. I always take a Villiers parts list (VEC245?) with me to check part numbers when I'm at Autojumbles. I also take a cloth & WD 40 to clean items up.
Heads are often found to be surface ground either to increase compression, (as Adrian says), or to repair warpage. Gear Box Casings were 'mated' to ensure correct endfloat on lay-shafts, and should have matching 3 figure codes on each case. However, judicious use of glass/grinding paste or gaskets can solve the problem of odd casings.

The other point is that different owners want different things from 'bikes. Personally, I never liked 'Choppers', seeing them as a waste of a good 'bike. But, as works of art they do look nice. Likewise, although I started my riding with the 1960's Clip-ons & rear set brigade, I found that I suffered cramps in my thighs from the 'Bum in the Air' position, so have tried to be as upright as possible in over 40 years of riding now. That's why I liked my 1960 Scottish so much, it was comfortable, and in 1970/71, there were no Japanese Trail Bikes around.

So, i'd approach the problem thus...What do I want the 'bike to do/run like. If I need to, I'll have to change a few things. I'll start at Standard and alter it as neccesary.

It sounds as if you've made a good start.