improving VB performance

[Graeme.crawley]

I had the inlet port opened and polished and the valve guides shaped by a local Drag racing Machine-shop. Did not increase the inlet valve size and have not changed the carburetor so it was a bit pointless really. Anyway there is no head gasket which probably raised compression a little bit but might also have restrited gas flow from the barrel but I radiused the barrel on the valve side so maybe not! Did it help? Nope! Still a sluggish old thing totally unsuitable for the hills here in NZ. Yesterday we did a 150km run which involved two hills each with a pretty steep climb of about 5 Km. It got 2/3 up in third at a snails pace but had to go down to second for the last 1/3 and meanwhile the OHV's were still in top as they passed me. Maybe a different cam and no oil ring would help more than the little bit I did but I also have a bike with a VB bottom end with a 1937 OHV barrell on it and it pulls like a train but guess that's not quite as much a challenge as trying to get some power from the VB. Incidentslly my friend has a Norton SV which eats the Ariel on hills, not sure why.

[nevhunter]

Open up the exhaust tappet clearance to about .012" and also make sure the Muffler is not restricting it and the ignition timing right on for the engine revs you are doing. How BLUE is your exhaust pipe? Nev

[Roger Gwynn]

I had similar on my SB after a 100 miles or so and then was a bitch to re-start. Checked the usual and it went fine after I opened up the tappets by a smidge (British Standard measure for a small amount - see also Firkin, as in too Firkin much)

[Simon.Gardiner]

Are you using one of the very sloooooow cams??
(Seriously!)

SG

[Karol Burger]

so for SV models is it advisable to leave a small clearance for the exhaust valve? 0.012" I am currently upgrading SB/1932 and any such information is important to me

[david.anderson]

Graeme
As Simon suggested it could be one of the slow cams that you have fitted. Do both lobes look the same or is one more pointy than the other ie the slow cam. My VB when standard showed almost 70mph top speed. Ariel claims 65mph.
While Brenton has not posted here for a long time I built a warm side valve and am happy with its performance. My motor is a 1952 alloy head. It is fitted with the early larger inlet valve and late smaller exhaust valve. Firstly I cleaned up the ports using a flow bench and was able to get rid of turbulence and improve flow. I fitted a 30mm concentric on a short manifold that I made. The manifold is needed for the carb to clear the generator but the length is restricted by the oil tank. Next I had the head and cylinder, which was badly distorted, skimmed a total of .040”. I found a hot A6-664 cam at a swap meet. The cam had been ground back to a 1.25” base circle and it was pitted. I checked the lift every 5 degrees and the cam looked like it should perform, although possibly hotter than I wanted, so I sent it the Franklin cams NZ and asked them to build it up with stellite to return it to a 1.5” base circle while maintaining the same profile. Franklin did an excellent job. The cam as fitted has a valve timing, measured at .050 lift of 24btdc 72 abdc 68bbdc 29atdc intake duration 253, exhaust duration 259, and a lift of .337”. The standard VH cam A6-664 measured at .050 lift has a valve timing of -7bdtc(7atdc) 49abdc 44bbdc -6atdc(6btdc) intake duration 222, exhaust duration 218, lift .313” The uneven lobe side valve cam has a much slower valve timing than the A6-664.
The bike now performs very well, having almost the same top speed as a VH although it does not have the acceleration of the VH, and it has not lost any of its character.
Franklin have a lot of Ariel cam profiles that they can grind. I know that they have Hartley profiles that were supplied by Brenton. I do not know if they kept the details of my cam.
David

[johnmack]

Hi Dave what cam 2 lobe cam would you recommend using on a VH other than the A6/664 that would enhance the performance without causing excessive wear to the cam followers.I guess that that the raised oil level in the cam and follower housing would prolong the life of the followers particularly the exhaust one. Franklin cams as you suggest would probably have a suitable profile but someone who has tested one in a bike would perhaps have a better take on the performance.

[david.anderson]

John
PM sent
David

[nevhunter]

Because of the Large surface area of the sidevalve combustion chamber and it odd shape it doesn't breath well and has a lot of extra heat to get rid of.
They also need more advance and a High compression ratio is impossible. In addition the Cylinder is very un evenly heated because of the exhaust Port location and the bore warps excessively when Raced. An OHV will run Much cooler in any given situation. The exhaust valve has to be very good metal and preferably rotates a bit each time it opens to reduce warpage. You can use pretty "sharp" valve timing as there's a direct valve to camshaft action. so you can rev them if the rest of the engine is strong enough Nev