Camshafts. R45 cam in a R90!? 😳

[slyngej]

Can you put a r45 cam in a 247 engine? The reason I ask is because, as far as I know, the general cam specs of the 284 cams in the r50 and r45 are the same, except that the lift in the r45 cam are slightly higher. I use a r50 cam in my r90/6 with sidecar. The 284 cam gives a lot more torque in the lower rpm range. Generally I’m very satisfied, and I am no speed devil. But when not driving with a sidecar, the 284 can loose torque a bit early in the higher revs. I don’t want to change the final drive each time I go without sidecar.
But if the r45 284 cam could fit, and it has 0,6mm more lift, I would not really loose any low end torque, but would gain a bit more midrange torque.
I have electronic ignition on the crank, so I don’t use the “points” tip, so that would not be a problem.

[barryh]

No I don't believe it will work at least not while maintaining the same cam timings.

As you say type 248 R45 and R65 cams have the same basic timing as type 247 cams so the the standard 35hp R45 cam is a 308 and the 27hp R45 cam is a 284 and those 284's by the way are very rare outside of mainland Europe. But in any case the they are not the same cam as a type 247 equivalent because the shorter stroke of the type 248 changes the angle of the pushrods which changes the timing.

[Rob Frankham]

But in any case the they are not the same cam as a type 247 equivalent because the shorter stroke of the type 248 changes the angle of the pushrods which changes the timing.

Absolutely right. The effect of changing the angle between the pushrod and the camshaft will move the timing for one 'engine' forward and that for the other 'backwards so that each will be out by the same amount but in opposite directions. I don't suppose this would stop the engine from running and I doubt it would cause any intereference between piston and valve (although I would want to check very carefully before I buttoned the engine up) but it would inevitably mean that the engine would run unevenly and be impossible to balance.

Rob

[Todd]

Can you put a r45 cam in a 247 engine?

Hi,

I'll be the first to admit that I am new to BMs and know nothing about them ... but reading up on them, I am really surprised at how limited or backwards the choice of alternative valve train components is, and also the general awareness of how many opportunities or services there are out to change them. In comparison to, say, Harley-Davidsons ... where you can be offered a selection of 30 or 40 different cams, each with well documented specs, able to dial in torque or horsepower to whichever rpm or compression ratio you wanted, I found it really shocking. And I'm not talking about "horsepower cams", i.e high rpm, I'm talking about dedicated touring/outfit or "torque cams", i.e. designed for cool running with maximum torque at lower rpms that people actually use.

Given that a BM is basically the same as a Shovel or Ironhead Harley that's been squashed flat, i.e. a hemi-head with two big valves and pushrods, I'm surprise cam manufacturers have not just copied findings from them, and applied it to BMs.

Ditto, you get high lift (ratio) rockers to subtly change timing, shortened or adjustable pushrods to accommodate them etc.

Looking also to the car world, there are still remaining some engineers whose business is altering camshafts and rocker arm ratios to whatever spec you want. And I know in BM racing, many have used significantly shortened pushrods, so that must be available too.

I couldn't even find a good documentation of OEM and "performance" cams for BMs with a couple of manufacturers being very cagey and defensive about their "woo" asymmetric products ... seemingly because it just turns out to be a rip off of someone else's product (asymmetric tells you nothing in real terms about how they perform).

If I had some money to play, I'd be looking at the specs of something like an Andrews Andrews PB+ or a mild Andrews J grind, or a Woods W-6S, and asking the engineers to regrind a BM one to suit. Something with a torque peak south of, say, 2,500 to 4,000 rpm, where most people spend most time riding.