650 Max revs?

canolman · May 7, 2014

Does anyone know what would be considered maximum safe revs for a 650 berg? (Yes I know nothing is safe!) I've fitted a rev counter to my track bike and don't know what to set as a limit, a rough idea helps with gearing.
Would there be a difference between the 628 and the 644, long and short stroke engines?
Thanks

Taffy · May 7, 2014

for the 644 it would be around 7,800 revs and for the 628 it would be 8,000 revs. however, the later engine is safer than the earlier one so you may want to give the early one more space?

this is working on the principle of the piston speed being 4,250ft per second.

regards

Taffy

canolman · May 7, 2014

Cheers Taff,
I can work with that, p'haps about 7500 Max on the 644? Peak power would probably be a fair bit lower in the rev range anyway?

Taffy · May 7, 2014

well yes it is of course - as with all singles. your dyno sheets will help you, you should calculate the gearing and revs from that.

regards

Taffy

Idle · May 7, 2014

IIRC, it's 8,400 for 628 and 8,200 for 644. At least that's what the owners doc says..

I take it your bike breathes well enough to keep pulling past 7,500?

You know, I recall you are road racing your bike.. A 17 tooth counter shaft sprocket is/was available. Rick Bozarth fitted one for his western states tour and may be able to point you in the right direction.

bushmechanic · May 7, 2014

some of the rfs strokers are going out to 10K with 78mm stroke and 119mm rod

compared to that 8500 on the 80mm stroke seems pretty "safe" except that their (rfs) stroker cranks are lighter

canolman · May 8, 2014

Cheers lads,
I'm not looking to rev the **** out of her, 6th gear seems quite tall so I should be able to keep the conrod inside the engine!!

bushmechanic · May 8, 2014

fwiw there is a close ratio 6th option if you need it. Dr_C uses one

I run one because the older gears are tougher and "6th" has the dogs which engage 4th ...... but I prefer the higher ratio.

Taffy · May 8, 2014

I have a spare pair of close ratio 6th gears Canolman. why not call me sometime, I'll see if I can't help you a bit.

regards

Taffy

Vegard · May 9, 2014

Taffy said:
I have a spare pair of close ratio 6th gears Canolman. why not call me sometime, I'll see if I can't help you a bit.

regards

Taffy

Maybe this is something for my rebuild?

bushmechanic · May 9, 2014

FWIW the numbers of the 2 gears are H24007601 and H24008601

Taffy · May 10, 2014

Vegard said:
Maybe this is something for my rebuild?

very special occasions only!

regards

Taffy

canolman · May 10, 2014

Diolch Taff,
But it will have to be for another day, up to my arse with alligators and Visa bills, gonna try and get some racing done with what's left of my budget!

650 Max revs?

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