Straight cut primary gears

[JPark]

Is there much difference between the helical primary gears of a 92 and the straight cuts of a 93 rat?

Even with the helicals, my motor whined a lot, probably due to a shot pinion bushing and rumbly main shaft bearing. I suspect that the side load on the big gear coupled with its diameter/leverage is hard on the ball bearing, and the wear pattern on the bushing shows that the actual load is toward the countershaft rather than away as one would suspect.

I never heard the primaries on my Rat, or much of anything else other than the pipe, but would it be really annoying on a muffled [such as it is] bike? I'd prefer getting rid of the side load if I could. I'm not that convinced that straight cuts are significantly more efficient but bearings are sure to lead an easier life.

[Al Harpster]

Swapping out to the straight cut primaries on my Ace 100B gave me audible gear whine that I didn't have before.

But I solved that annoiance when I swapped out the Ace "flamethrower" pipe with a Rat pipe and DH silencer. Quieted them right down.

I can't tell you anything about noticeable power increase with the straight cut. I just don't remember if they went in alone or I put in some other enhancements at the same time.

I think I'd advise making sure you cure your existing whine first if you haven't already. Then if you're looking for just a bit more power you could swap.

[JPark]

Actually, according to testing, there isn't any significant difference in power loss between straights and helicals. Both are between 93 and 98% efficient depending on the ratio and other variables.

The Rat may have got straights because they would not be able to generate snap side loads [axial bearing load] when shifting without the clutch. Plus, the mainshaft bearing would be better off being another 6204 but all there is room for is a 6203.

Did you find the Rat pipe reduced the induction roar as well?

[Al Harpster]

I find that I can't hear much of anything over the rat pipe.

I don't think I've ever heard induction roar with the ACE, but I swapped to reed intake over a decade ago. And had the reed manifold modified for two pedals & modern reed material.

Took a quick search on the net. Seems helical & spur efficiency are equal. I thought otherwise.

"What you don't know won't hurt you, what you believe that isn't true will"

[dirty_rat]

The gear ratios are also different from the Ace primary gears to the Super Rat primary gears.

The Ace gears are 19T x 69T for a ratio of 3.61:1
The early Super Rats are 17T x 63T for a ratio of 3.71:1
The late chrome tank Super Rats are 21T x 59T for a ratio of 2.81:1

The Super Rat straight cut gears were also forged, where the Ace gears were cast and not as strong.

[JPark]

I'll remember to use late Super Rat gears if I ever go to Bonneville.