bottom ends- 92 ace 100/93 super rat

[fullchoke]

are they the same? everything I looked at in the schematics looks the same but I didn't look at everything, cranks are the same too.

[Zyx]

Ace 100B had helical primaries. Rat had straight cut primaries.

[hodakamax]

The 93s had caged needle bearings on the main and countershaft replacing the bronze ones. The clutch discs, springs and cage had a new 93--- number. As AZ said, straight cut gears replaced the helicals on the primary drive. Thats all I can think of.

Maxie

[dirty_rat]

If you are just looking for a replacement, the Ace 100 bottom end will work for a super rat. The bearing/bushing difference is insignificant as the later super rats came with the bushings instead of the bearings. While the clutches might be a little different, I have placed the two side by side and couldn't see any differences. The biggest difference was the primary gear, with the Ace having helical cut gears and the super rat having straight cut gears. The primary gear ratios were different as was the material they were made of. I have seen many of the Ace gears shatter under the increased HP of the super rats, but I have never seen a super rat primary gear break.

[Zyx]

The Ace primaries were 19/69 for a primary ratio of 3.63:1. SR were 17/63 for a ratio of 3.71. Gear tooth module for the Ace was 1.5, and for the SR it was 1.75. The larger tooth module is at least part of the reason they last longer. I switched from Ace to SR back in 1973 along with a Webco 125 kit, and the gears were fine when I pulled them out this spring. Helical gears are technically quieter, but frankly it is hard to hear the difference over the exhaust note. I would agree that if you are thinking of building a bottom end, use the straight cut gears.

[hodakamax]

The 93 straight cut primary large gear was machined from steel but the pre 93s were cast.

Max

[taber hodaka]

They both used the ace90 racing crank.-----------Clarence

[hodakamax]

Hey Clarence, I do remember ordering the new 91 series rod for the 90 racer. The 90s had a bushing upper end and I replaced it with the new upper needle bearing rod along with a cool blade job. As I recall the rod was the change that made the 91 crank assembly for the new Ace 100s. (You're testing the old memory now!)

Max