correcting a 'frankensteined' HPI 2 speed

[SSnarf]

So I bought an incomplete frankensteined HPI RS4 3 - MT2 - MT1 on ebay for spare parts and upgrades for my MT1. Unfortunately whoever put it together didnt use any matching parts, but it had a 2 speed that i wanna put into my MT1. The set fits just fine into the carrier, but the gears don't match up, when the high gear is meshed, the low gear hardly touches.

I have a 13-20T clutch bell and 43T and 47T on the transmission. I did some measuring and i need to make up roughly 1/8 of an inch in diameter to get the low speed to mesh. I think i want a larger low gear anyway so the 47 tooth gear needs to go, what size should fit and/or should i get a different ratio on the clutch bell? I'm thinking a 50 tooth should be the right diameter but i'm not sure, or a 15-20 clutch bell if that's an issue.

okay, nevermind it looks like a 49T gear is the correct diameter.

 

[markallen]

I always thought the differences in the tooth count must be the same.Clutch bell 13/20, 7 teeth.Spur gears 43 /50, 7 teeth.That should work right.

 

[SSnarf]

well the dimensions for the 49 seem to be right to fit. the 43 is 1-3/4" diameter the 47 is 1-7/8", the 49 is 2"... the 13 is 5/8" and the 20 is 7/8", so the difference between the 43 and 47 are 1/8" and the difference between the 13 and 20 are 1/4". at 2" the 49 tooth will make it 1/4" as well... if that makes sense with all the numbers and fractions.
The difference in the diameters between the high gear set and low gear set needs to be the same so both sets will mesh properly and the engine can sit square. right now if you tried to mount it, you would have to mount the engine at a big angle and make the holes very big to get the gears to mesh the same. Plus HPI doesn't make a 2 speed gear in 50 tooth so that pretty much makes my choice easy.

 

[markallen]

I willing to bet the 13/20 clutch bell is from an older nitro rs4 2.The spur gear came with that clutch.The included spur gear was a 37 tooth.And first gear would have to be a 44 tooth for it to work..

 

[SSnarf]

okay the 49 tooth fit just fine and both sets of gear mesh nicely, but now i have a new problem.... No shifting. looks like there may be other parts missing like the adjustment screw to adjust the shift point. I dont have a parts breakdown of the 2 speed so i can't tell what's there and what's not there. there's also a catch somewhere in the forward dogbone and drive cups, but i think i can fix that by putting the drive cup from my other spur gear assembly.

 

[SSnarf]

ok everything is working good now, except the high gear is just too much gear and it wont accelerate much in 2nd. I could probably re-gear it and/or put a good tuned pipe on. Maybe 47-52 instead of 43-49 and just make sure it's in optimum tune. I was holding the car off the ground and letting it shift and the front tires ballooned more than i have EVER seen an rc car tire balloon! it was flat as a pancake.