A matter of weight...

[Paul Slootheer]

Well take a look at this: a 1948 > 1951 KH crank and the later one, according to Ariel it was 20% heavier, ''for smoother riding, without affecting acceleration or pick-up''... Compare the size of sludge traps, the older one takes nearly twice the amount of sludge!

[nevhunter]

I don't think they are intended to trap sludge. They just happen to do it quite well. Most car and in line multi cylinder bike cranks are just drilled on an angle straight through from a main to each big end. Hollow cranks are quite strong and weight saved near the crankpins is less required on the counterweights. Nev

[brenton.roy]

I'm not sure I buy the idea that 20% more flywheel mass has no effect on pickup and performance.
Nev, did you write that the early flywheel showed up other engine balance issues? A heavier flywheel seems to be a lazy fix..
Aren't these motors essentially the same as a pre war t100 / speed twin?

[Leejm]

Val page did design the first Trimuph twin. And the kh so they very well could be alike in some way But I have never seen one!
I wonder why they felt the need to add weight for! After all the kh had been around for four years. Tests of the bike was done in 46 so it's not like they didn't have the time to test things out.

[nevhunter]

The placement of the camshafts (front and rear) is the distinct characteristic of the Page KG, KH as well as the single piece forged crank. which would have to be considered a GOOD thing technically.. Dimensions are very close to the Tiger 100 /Speed 500cc twins. Much better oil pump but the triumph is more suitable for modification having separate inlet ports and did allow being stretched. They are both pretty lightweight engines at the time..
The first Triumph twin By Val Page is indeed a RARE thing . I've seen one all pristine and restored beautifully on a run recently. They resemble an A 10 with the camshaft position and look expensive to make. COST may have been a reason for their lack of success..
Flywheel weight doesn't affect power as such and heavier is smoother at LOWER revs so you can run slower in top gear and generally have a more pleasant feel. Lighter flywheels will rev quicker so acceleration figures will be better. Light flywheels are also more likely to kick back when kick starting advanced. The same Balance Factor is used whether light wheels or heavier are used. In line motors need dynamic balancing as they have considerable length of crankshaft.ON a single or V twin with a built up crank, you get a good result balancing each flywheel separately to the same factor. NOT the same weight. Nev

[Paul Slootheer]

1935 Triumph Model 6/1 650cc. What a lovely machine! Found this one on the Net...
(Photograph, Andy Tiernan)

[PeterW]

Spooky, at lunchtime I was reading a 1945 edition of The Motor Cycle and the letters page had one from some chap called Hartley listing all the benefits of heavier flywheels.

[nevhunter]

The first sidevalve 1200 CC Harleys in 1930 were recalled (over 3000 of them) to fit bigger flywheels and crankcases and required new design frames to accommodate them as the flywheels were considered too light. Major expense and bad look. HD supplied the Parts but the dealers had to supply the labour. This was at the beginning of the great depression. That year they sold over 10,000 of that model and it ran till 1936 including a 1340 cc version. with average sales around 3,000 per annum. Hard times. (American) Excelsior folded up motorcycle production at end of 1931 because of the depression. Nev

[Paul Slootheer]

Spooky, at lunchtime I was reading a 1945 edition of The Motor Cycle and the letters page had one from some chap called Hartley listing all the benefits of heavier flywheels.

Makes me curious, what are the benefits of heavier flywheels according to this ''chap''?

[paul.jameson]

It will be interesting to see PeterW's reply.

Meanwhile, in the 1970s I ran a VH and Watsonian Monza sidecar which had highly polished steel flywheels which were completely flat on the outside and stamped C&H on the rims. I assume C&H stands for Carter and Hartley which was the dealership where Lawrence Hartley was a partner. Anyway, the big end began to knock so I acquired another set of flywheels, a new big end for them and swopped the flywheels over. The new flywheels were the heavier VG type. The improvement in performance was considerable. I have always thought that this might have been due to the extra weight of the sidecar. Perhaps the lighter flywheels are better for high revs racing but the heavier ones are better for low revs normal use.