Ace 90-100 Rods

[bobwhitman]

OK, all you small motor experts, I want to rebuild an Ace 90, with a bad rod. What is the difference (if any) between Ace 90 rods and Ace 100 rods? Stroke is the same, crank pin/bearing is the same. Small end differ, but does it matter? Looks to me (in my ignorance) as though one could likely swap a 100 rod (912710R) along with a n Ace 90 piston, with minimal problem, perhaps none, if the top end bushing used in a 90 happens to be the same diameter as the bearing from a 100. Oh, then there are the odd-looking (Crank pin thrust washers) shown for the 90 - what's that all about?

Guidance needed from those of you who work with the little folk.

Bob

[rlkarren]

I can only give you conjecture since I was looking at this same issue awhile back. Keep in mind that the Ace 100 was an "improvement" to the Ace 90. I think that would explain the differing thrust washers as not an issue. The only difference between the two models is that the top end uses a bearing and the oil cutouts are larger for an Ace 100; and of course the piston itself. I know that an Ace 90 piston fits perfectly on an Ace 100 rod with the bearing. The only thing I don't know is piston height at TDC which should be the same, but I haven't measured it. I haven't made it that far yet.

But in summary, yeah should work fine, just use the bearing. Wrist pins should also be the same.

$0.02

Roger

[MTrat]

I believe that early '90s had bushings for upper end bearings while later ones had roller bearings. This may enter into the picture as your project evolves...

[hodakamax]

Ace 90s came with a bushing upper end. Before the Ace 100s a 91 prefix rod or R rod was offered with a upper needle bearing. It came as a kit as I remember and my Ace 90 soon had one. The 91 "R" rod became the standard for the Ace 100. Everything is interchangeable. 912710R rod still has the R for racing.

[viclioce]

So Maxie. Does this mean the Ace 90’s & 100’s have the same stroke & just a wider bore? Just asking.... Victor

[hodakamax]

Victor, Yes, all gains in displacement are bore. Everything is interchangeable.

[Joe Ormonde]

You can replace the ACE90 Crank with the ACE100 Crank. Neat Engine! You can also Bore it to +.080 and use a Standard Model 93 Piston and Head to clear the Piston dome or a Model 92 Head. You can upgrade the clutch to one from the early Model 92 or from the 100B, B+ or 93 Super Rat. Same with the Primary gears. A set from a 69 70 71 or 1972 Super Rat. The 72 (93B) are cheaper and all of these parts are plentiful! The possibilities are endless! Joe Ormonde.

[matt glascock]

Cool observation, Joe. They really are the chameleons of the motorcycle world.

[thrownchain]

And that's why sometimes you don't know what you're buying.

[matt glascock]

Very true, Thrown. But it also shows the genius of PABATCO in their design concept in that the bikes are relatively simple to wrench and that parts interchange, across models and time, facilitates keeping the bikes operational. What a refreshing notion when one considers the current "lets make everything disposable and irreparable" modern design ethos.

[matt glascock]

Bob, check PM.

[bobwhitman]

Matt-
No message(?) here. Send me a note directly: [email protected]

[matt glascock]

Will do Bob.