Double Pinning

[topcatcustom]

When does it become essential? Just before I put my blower back together I am wondering whether or not to do it- would rather not if it doesn't need it, and as the rotors are so short on the 4-71's I thought there would be a good chance they don't need doing like the long rotors of a 6 or 8-71 would!

p.s. I am only going to be running about 6/7psi boost
TC

[Paul B]

When does it become essential? Just before I put my blower back together I am wondering whether or not to do it- would rather not if it doesn't need it, and as the rotors are so short on the 4-71's I thought there would be a good chance they don't need doing like the long rotors of a 6 or 8-71 would!

p.s. I am only going to be running about 6/7psi boost
TC

I think you need to contact UK Blowers. Can't remember his e mail, but I he posts here on occasion. I recall being told I'd need to double pin my 6/71 if I planned using much more than 4-5 psi.

[bigaldart]

Our rotors are not double pinned and the rotors timing and clearances are the same now as when built about 20 years ago. Not a lot of mileage as its a drag car but really a lot of abuse, it has been sneezed plenty of times during our fuelling experiments. Never had a problem with it. It does suck oil through the seals if overfilled, maybe seals are shot but for us its not a problem, once it finds its own level it runs perfectly, will spin freely by hand, no noise and no slack in the gears. Be careful the seals are the right way for your application. Petrol will not tolerate oil in the combustion chamber without expensive detonation. As to oil level as long as the gear teeth touch it slightly the oil will climb the gears and lubricate just fine. We use a mix of synthetic gear oil, stp and molyslip, not sure of the proportions anymore. The moly makes it a dead giveaway where any oil comes from because of the colour.

Alan

[topcatcustom]

Cheers Alan, wish you were on here a few months ago!!! I did them anyway, bit of a pain but no biggy really, I guess with the 4-71 the rotors are so short they dont really get enough torque to rip the pins.

TC