90cc Diesel engine

[BrotherAnon]

This is my first time on this forum, and if I'm doing something wrong let me know.

Anyways, I want to convert my 2002 Polaris Sportsman 90 to diesel. I need to find an engine that will work on this particular frame. I would prefer it to have an electric start as this was the first Sportsman 90 to have one.
Do any of you know of one?

Thanks in advance!

[coachgeo]

What do you plan to use for transmission? Diesels have much lower RPM so you need different ratio gears and/or sprockets. Is this a shaft drive polaris or chain drive?

[boertje-jr]

It's me,
The Polaris is chain drive. I don't know what I would use as a transmission.

[tappy]

First off, you don't want a 90cc diesel engine.
The engine in it is a 90cc petrol 4-stroke so probably makes about 8hp. The brochures say 8.82NM @ 6000rpm which is about 7.5hp so it might make a little more power at higher revs.
At that amount of power your engine choice is limited to industrial engines - something like the Changfa CF178 engine, or 186 engine - these are 300cc and 400cc diesel engines making about 7 and 8.5hp respectively.
They'll be physically larger and heavier than the existing petrol engine and if you use the electric start versions they'll need a bigger battery to cope.
They'll need a different exhaust system, and might need extra plumbing to & from the fuel tank.

Diesel engines make their power at much lower rpm - 3600rpm compared to 7000rpm of the petrol engine, and they do this by making more torque at lower rpm.

The transmission in you Polaris is a belt CVT (continuously variable transmission) system, designed to transmit 8.82Nm at 6000rpm. If you connected the diesel engine straight to it, it would now need to transmit 16.8Nm at 3600 rpm. It won't behave as it should, will have the engine over revving all the time, and will break fairly quickly.

At this point you have two options:
1) Find a Comet CVT system (or similar) that's man enough to take the higher torque at lower revs and then put a suitable output sprocket on that to mate to the original chain final drive. There are plenty of CVT systems man enough to cope, but again they'll be physically larger and heavier than the original.--
2) Run a chain drive or belt drive from the engine to the CVT driving sheaves, gearing up the output from the engine so that the CVT is now handling roughly the speed and torque it was designed for.

In both cases you'll have to spend some time adjusting and tuning the CVT system to behave correctly with the different engine power delivery.

I'm sure there are other ideas that people will offer, but that's my 2 penneth..

[boertje-jr]

Thank you so much for you answer! I probably won't do that anymore. Instead I might just buy a used larger polaris. That might be better. I appreciate it!