Primary reduction and clutch question

[JerboaJohn]

I have both and wonder at what point the plate fails, if it's reliable up to say 5hp. I've yet to test it since I don't have an engine mount yet for my 118. I'm gonna guess it fails because that jackshaft is only supported narrowly and if you honk on the throttle it'll get a seesaw load.
looks great and costed $99 but I'm not going to baby the bike. if it breaks it breaks and I'll go cvt I suppose
I only got it bcs CVTs seem just too wide but there has to be good reason everyone uses them.

 

[willis617]

I purchased one of these:
79cc-transmission-for-predator-engine-4-stroke
https://www.gasbike.net/products/79cc-transmission-for-predator-engine-4-stroke

I made mine, 3/8 thick 6061 aluminum, and find that it flexs under load. How thick is your bought plate, what is the center distance between shafts?
At this point I'm thinking about going with a plate supported jack shaft assembly with out board bearings similar to what I've seen used on some 212 builds

 

[willis617]

Btw, your buid looks great, what frame is that?

 

[JerboaJohn]

mine's 3/8 too, and tape measured it to 6-7/8".
I wonder if I can just use a longer shaft and add a pillow block to hold the other end to the seatpost or lower frame

 

[CrazyDan]

If you can secure the output shaft to the seat tube with a pillow block then it should fix the flex issue.

 

[willis617]

If i go with a separate jack shaft assembly, with pillow blocks mounted at both ends of a plate, the plate would then mount to the seat post, is there then some sort of "strap" that ties it back to the motor to prevent the assembly from turning on the seat post?

 

[MotorBikeFab]

I have both and wonder at what point the plate fails, if it's reliable up to say 5hp. I've yet to test it since I don't have an engine mount yet for my 118. I'm gonna guess it fails because that jackshaft is only supported narrowly and if you honk on the throttle it'll get a seesaw load.
looks great and costed $99 but I'm not going to baby the bike. if it breaks it breaks and I'll go cvt I suppose
I only got it bcs CVTs seem just too wide but there has to be good reason everyone uses them.

Good to know.
I am going to put a 19mm carb, free flow exhaust, and 18# valve springs on the 79cc engine. That will increase the HP a bit but probably not take it over 5HP.
I have some 1/2" x 1" alu bar that I can screw onto the plates while keeping out of the way of the chain and sprockets, which should strengthen the plate and reduce the plates ability to flex.

 

[MotorBikeFab]

Btw, your buid looks great, what frame is that?

Thanks!
It's a GT Dyno MoonEyes cruiser frame.

 

[JerboaJohn]

If i go with a separate jack shaft assembly, with pillow blocks mounted at both ends of a plate, the plate would then mount to the seat post, is there then some sort of "strap" that ties it back to the motor to prevent the assembly from turning on the seat post?

the SBP kit for 2 strokes does mount the engine, it's integral, but the 4 stroke is a different beast. I've looked at a couple pics and they had a plate that the pillow blocks are mounted to, welded on. but I'm missing or not seeing something. I need to see more pics how ppl are mounting a jackshaft on the 79s and 212s. Im sure a U-bolt will turn

 

[willis617]

the SBP kit for 2 strokes does mount the engine, it's integral, but the 4 stroke is a different beast. I've looked at a couple pics and they had a plate that the pillow blocks are mounted to, welded on. but I'm missing or not seeing something. I need to see more pics how ppl are mounting a jackshaft on the 79s and 212s. Im sure a U-bolt will turn

I've seen pics where the jack shaft plate if mounted to seat tube with 3 u bolts, but cant tell what is attached to keep it from turning