ET: Engine (Twin) Effects of Cam Timing

[Bill Thomas]

Bob Dunn didn't want to fit me another Bigend in these wheels
Said there was a slight crack bigend eye ! , So sold me a set that were smaller outside dia',
I never bothered altering the oil scraper and have had no problem,
They make the Bike a bit more easy to rev'.

 

[greg brillus]

Hi there Bill, do you know how much lighter they are........cheers.

 

[Bill Thomas]

Morning Greg, 3582 grams,
But Bob's one I don't know, It feels more like my old Triumph T/Bird ,
Not so light, I would think, But a better way to go ?, Turn down outside edge ?.
I only have a Standard COMET one to compare = 4194 g.

In the old days I would try anything, But I was not a good rider and I was TOO big,
But found it very interesting.

If I ever get my New Comet done ?, It will be Bigger Than Yours ,
92 mm Bore, I have a Piston !, Very nice looking, T.P. I think and 102.5 stroke = 681 cc,
Must ask Conways to do me a barrel, When I have some cash !.
Cheers Bill.

 

[greg brillus]

Neal Videan has the liners for the 92 bore pistons....... I think he may have the muffs too, but these might need machining........he is away for a couple of months, but I can ask him when he returns........Cheers........Greg.

 

[Bill Thomas]

Thanks Greg, But I want to try it on the cheap !,
With a standard Muff and Normal type liner, I think it will Just !, Work,
I can grind a bit off the studs where they would be in touching with the top liner flange,
I also want to try Trev's idea of drilling a few holes on the bottom of the liner for oil,
Splash from the flywheels,
Just a bit of Fun.

 

[ericg]

My experience with Terry's cams, not so great.........basically, wrong type of bushes, wrong cam material, machined not ground finish, base circle eccentric not concentric.........and no quality control........so basically rubbish........This is common issue with loads of Vincent parts. The Vincent cam does not allow for much performance, the surface areas on the lobe and followers are way too small.......(Rolls Royce Merlin cams suffered the same issues) This means that performance upgrades are limited........so in a 500 single you are looking at around 40 odd Hp max, 1000 twin about 70 to 80 Hp max........bigger engines only gain the extra HP due to the extra capacity........most 1200 to 1300 cc engines seem to be around the 90 to 100 Hp figure at most....... Lets go to.......symmetrical cam lobe with roller followers, with say 400 lift at the lobe.......then ratio the rockers and add rollers in the pin/bush........larger say 2" or more inlet valve and even go smaller on the exhaust.......Inlet lift of around 600 less on the exhaust........Obviously a decent oil pump system and almost certainly a one piece crank........lets shave a load of weight off the crank and run much lighter short skirt modern pistons........ideally you want a big diameter piston with short stroke........starting to sound more like a modern engine isn't it........so now you are looking at putting out some better HP figures........just like the Horner's engines........It's all doable but costly and very time consuming.......If you look at a lot of the repro classic engines in racing, this is exactly what these engines have.......that's why they go so much better than the originals from years ago. The Godet Flash 500 engine puts out about 53 HP roughly, these go to 9000 RPM easily........big bore short stroke........full oil pressure one piece crank........nothing like an original, but go much better........This bike still way down on power verses some of the trick Norton's and G 50's out there.........Is there anyone out there who will carry out these mods........a bit slim these days......If your up against modern classic race bikes, then your 12:1 specialoids and a set of Mk 2 cams just ain't gonna cut it........Just having the extra capacity of a twin isn't enough........well from the racing i've seen down here anyway.......there are too many trick engines out there that perform very well.

Would love a couple of pics of this machine Greg.

 

[greg brillus]

Sure, It's sort of in bits at present........but i'll try and put some pics on here as it goes together........I have a race meeting coming up in early July so keen to get it back together and test it before the race.........Then we have the Queensland state titles in September, and the national titles in October........Now you can see why I need more bloody horsepower........cheers.

 

[Monkeypants]

Many of the race Nortons and Triumphs in the UK and North America use crankshafts made by Dave Nourish. His Weslake 8 valve complete engines are also known for winning races.
His cranks are very heavy, heavier than stock. Stock Norton is already heavy at 23 lbs, but not strong enough for racing.
There are fans of both heavy and light cranks in those bikes, but the heavy Nourish cranks sure do not stop them from winning.

Glen

 

[davidd]

The heavier the flywheels, the higher the top speed. But, it is a bit slower to get there. AHRMA runs at small tracks except for Daytona. Thus, there is not much of a penalty for running lighter flywheels. Some riders believe that the lighter flywheels are a benefit for better acceleration. between corners on a tight track.

I tend to prefer the stock flywheels with no lightening of the timing gears. The extra weight seems to provide the valve gear and drive train with extra damping that helps the big singles run smoother. Irving was dead-set against lightening the timing gear as it would only promote valve bounce.

None of this is particularly beneficial for street riding. But some racers want a slower revving motor that acts like a punchier street bike. Most older riders want a fast ride on the weekend and not necessarily a series championship. A mostly stock Vincent with some careful preparation will do this quite well.

David

 

[Monkeypants]

That's true, I was out on the Rapide yesterday, wee 28 mm carbs, 8 to 1s and MK1 cams. It felt great, no problem leaving traffic behind.

Glen