GX390 Reduction Box w/ Torque Converter?

[jorgy]

Hi All,

I've been having a good read on the forum and thought i could use some input from someone here.

I recently acquired a Honda GX390 LXQ4 that has an inbuilt reduction box, 2:1, that cannot be removed and does not have an inbuilt clutch.

Does anyone know if i can run a Comet (or equivalent) 40 series with the max RPM for this engine at 1800RPM? Will the Driver engage? Or is the only option to use 2x jackshafts, 1 to increase the RPM then 1 for the Driven?

Or, is it possible to get a torque converter to work in the lower RPM ranges?

Thanks

 

[landuse]

You should be able to. you can then have an axle sprocket that is half the usual size. It will have to be a comet 40 series though with that engine

 

[Half-breeder]

Hi All,

I've been having a good read on the forum and thought i could use some input from someone here.

I recently acquired a Honda GX390 LXQ4 that has an inbuilt reduction box, 2:1, that cannot be removed and does not have an inbuilt clutch.

Does anyone know if i can run a Comet (or equivalent) 40 series with the max RPM for this engine at 1800RPM? Will the Driver engage? Or is the only option to use 2x jackshafts, 1 to increase the RPM then 1 for the Driven?

Or, is it possible to get a torque converter to work in the lower RPM ranges?

Thanks

I recently got a 30 series TC/CVT. I studied its performance and functions, and noticed that it did engage at a lower rpm(not sure what the rpm was... but alot less than a cent clutch). If youre 'MAX' rpm is 1800, then 2x JShaft, are in order, or youll never be able to reach the fullest potential out of the TC(and might as well use a cent clutch)... but not fully sure how you would go about getting the speed up w/ 1, to turn the TC/CVT, then another from driven(i understand the 'idea'.. just not seeing the construction). Just remember to get a shaft spinning at 1800rpms is one thing... but to have a chain, spinning a shaft to 3600rpms is another(can you imagine the racket?!).

So... is it possible... yes, but itll come at a cost and fabrication that I personally wouldnt wanna endure(Id rather CL/HF a motor personally). Your gears would have to be something like motor 20T, JShaft in 10T(to get your rpms up to speed), TC out 12T and axle 60T... that would run you w/ a 5:1 ratio(I think I calculated that right w/ the 2:1 gearing from the motor). Depending your tire size would determine your top speed...

...but im positive that 'if' this is what you are wanting to undertake in your project, there WILL be someone on here that will chime in their experiences/thoughts to help you out.

 

[itsid]

Does anyone know if i can run a Comet (or equivalent) 40 series with the max RPM for this engine at 1800RPM? Will the Driver engage? Or is the only option to use 2x jackshafts, 1 to increase the RPM then 1 for the Driven?

Or, is it possible to get a torque converter to work in the lower RPM ranges?

I say no you can't..

according to
the comet series 40 spec sheet
http://www.bmikarts.com/PDF/Comet_40series.pdf

the minimum engagement speed is 1600rpm

so you'll end up with just having 200rpm to control your speed, and about 1000rpm where you rev the engine and nothing happens.

Even if the comet's clutch survive (and I assume it will only a short time) you couldn't use the potential of the TC at all.

So you can do two things if you want a TC...
1) find a new crankcase cover and use that (maybe you need a new crank too)
2) add a jackshaft with a 2:1 gear ratio so that you end up with a shaft running twice as fast again.

'sid

 

[landuse]

Hmmmm. I didn't think of engagement speed

 

[OzFab]

Yeah, I'm with 'sid on this one, RPM range is too limiting.

I'm curious to know why the redux box can't be removed though; AFAIK, the housing bolts onto the engine side cover...

 

[mckutzy]

Are you sure it cant be removed, it sure does look like it me???...

If most of the unit can be, at least the gearing/clutch/whatever in it can be, and can mount to the main crankshaft PTO for your jackshaft( or clutch if room on the shaft itself to do so.)????

 

[rmm727]

He can remove it but will need a new crank and side cover.

 

[firemanjim]

If Im not mistaken, he ONLY needs a new side cover. The crankshaft is still the same, keyed, and the drive gear for the reduction ,runs off that shaft. Honda didnt want to have to make a different crankshaft , so the gear box was designed "around" the existing engine.
I could be wrong so dont shoot me,.....

 

[rmm727]

Its real short I believe. The gx200 ones are splined so a gx390 version might be as well. If its a cost thing, I would look into a clone crank and side cover.

 

[OzFab]

Correct me if I'm wrong but, it's my understanding that the housing bolts onto the side cover; once removed, the side cover is the same as with any other engine...

 

[rmm727]

pg 203 of the GX390 service manual

here...

http://www.seddonplant.co.uk/downloads

 

[jorgy]

Thanks for all the replies and suggestions. I can indeed remove the reduction box which I have done and the current crankshaft is as rmm727 said, short and splined.

I think i will have a go at replacing the crankshaft and side cover. It looks like cost may become a factor here so I wonder if anyone has recommendations for decent sellers that may send international? Other than ebay?

Without trying to start a new topic, while i have the engine apart, is the general consensus to remove the governor on these engines for use on a buggy/kart?

 

[OzFab]

Hey, I didn't notice your location before, where in NSW are you?

If you can find some way fo cutting internal splines, you could make (or have made) an adaptor...

There's no general consensus on the governor, it comes down to personal choice but, I don't know of many who insist on leaving the governor intact; given the opportunity, most will remove it

 

[jorgy]

Fabroman, I'm from the Blue Mountains.

Been having a look at sourcing the parts and the price for a new crankshaft and side cover including postage makes a complete clone engine look appealing.

 

[landuse]

Fabroman, I'm from the Blue Mountains.

Been having a look at sourcing the parts and the price for a new crankshaft and side cover including postage makes a complete clone engine look appealing.

Yeah, getting a new crank can be very expensive. Sometimes going new is the best way

 

[OzFab]

Fabroman, I'm from the Blue Mountains.

I just spent the last few days in St Marys, I live in Bankstown...

Have you tried Aussiespeed small engine preformance? They don't have a crank listed but, I'm sure they could give you a price...

Other than that, on some products, it actually makes sense to import form the US, even with the, sometimes, massive shipping costs. I bought a clutch & chain &, even with shipping, it was still cheaper than a local clutch...