The Hodaka Club Forum

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.

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.

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?

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"

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.

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