Chinese Torque Converter with Tecumseh H40?

DaddyJohn

Well-Known Member
#1
I recently acquired a Toro snowblower with an H40 engine, hoping to transplant it into a Doodlebug or similar inexpensive mini bike chassis.

After removing the engine, I discovered it has a 1" output shaft. :( I guess this isn't uncommon, but it limits the selection of centrifugal clutches I can use.

Typically, I'd use a 3/4" bore clutch with 10T/#35 sprocket to use the original rear sprocket and maintain the standard gearing. However, it seems all the 1" bore clutches I see are 14T for use with a 420 chain. Now, I could theoretically get a new rear sprocket to fit a 420 chain, but worry I'd have to get a bigger diameter to lower the ratio down to something similar to standard (due to the 14T front sprocket). Doing that might get it too close in diameter to the rear wheel and limit cornering. Not to mention the expense of buying said sprocket...

So... I got to thinking about the possibility of using a 1" Chinese torque converter from eBay, like this: http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=390581280696

It could be a good solution, but my concerns are:
a. Will it bolt to my H40 engine case?
b. Is 4hp enough to drive it?
c. It's output is designed for 420 chain, necessitating a new rear sprocket (which I hoped to avoid). That being the case, what size should I get?

Does anyone have any ideas I haven't thought of? I'm trying to keep it somewhat inexpensive, otherwise it would just make more financial sense to buy a Predator and go from there. That being said, I would like to make it something unique and like working with the old American engines. :)
 
#2
I recently acquired a Toro snowblower with an H40 engine, hoping to transplant it into a Doodlebug or similar inexpensive mini bike chassis.

After removing the engine, I discovered it has a 1" output shaft. :( I guess this isn't uncommon, but it limits the selection of centrifugal clutches I can use.

Typically, I'd use a 3/4" bore clutch with 10T/#35 sprocket to use the original rear sprocket and maintain the standard gearing. However, it seems all the 1" bore clutches I see are 14T for use with a 420 chain. Now, I could theoretically get a new rear sprocket to fit a 420 chain, but worry I'd have to get a bigger diameter to lower the ratio down to something similar to standard (due to the 14T front sprocket). Doing that might get it too close in diameter to the rear wheel and limit cornering. Not to mention the expense of buying said sprocket...

So... I got to thinking about the possibility of using a 1" Chinese torque converter from eBay, like this: http://rover.ebay.com/rover/1/711-5...0001&campid=5335845805&icep_item=390581280696

It could be a good solution, but my concerns are:
a. Will it bolt to my H40 engine case?
b. Is 4hp enough to drive it?
c. It's output is designed for 420 chain, necessitating a new rear sprocket (which I hoped to avoid). That being the case, what size should I get?

Does anyone have any ideas I haven't thought of? I'm trying to keep it somewhat inexpensive, otherwise it would just make more financial sense to buy a Predator and go from there. That being said, I would like to make it something unique and like working with the old American engines. :)

Following that link, in the top part of description it “says it comes with a 12 tooth 35 “. I’m assuming that you would get both a 35 sprocket and a 40/41 sprocket..... as far as bolting up, you need to find the bolt pattern on that H40 where the TAV will bolt up before you buy it. Just my 2.5 cents ;)
 

DaddyJohn

Well-Known Member
#3
It does say that up top, but in the contents blurb, it says it comes with a 40 sprocket. However, I guess I'm generally wondering if anyone has mated a 30 series Comet clone to an H40, if the bolt pattern was compatible (thinking probably), how well it worked, etc. I can get a new rear sprocket to suit the up-sized chain if possible; was just hoping to avoid it.
 

cfh

Well-Known Member
#5
that looks like an HS40 (not an h40). but having an HS is probably better anyway. the bolt pattern will definitely support a china torque converter.
 

DaddyJohn

Well-Known Member
#6
Good point, I goofed the engine model, lol... HS40!

Anyway, good to know those parts will play well together, so I can avoid the gear ratio problem the added 3 front teeth on a 1" clutch would cause (just don't think 4hp is going to pull that lower gear ratio).

Now, I guess I could still run a clutch if an 80 tooth rear sprocket wasn't to big in diameter to allow proper cornering with the stock 145/70-6 wheel/tire.

Now, with either strategy, I just need to find where I can get 420 rear sprockets with the 6-hole Baja Doodlebug hole pattern that don't cost a fortune... If it gets too costly to put a drive system together, I may as well just buy a Predator 212, a 3/4" clutch, and use the standard rear sprocket!
 

65ShelbyClone

Well-Known Member
#9
You know you can change the sprocket on the torque converter, right? Just because one comes with a 420 or #40 doesn't mean you're limited to that.

A TC incurs about a 20% driveline power loss and the 6" driven unit is also going to have a 0.90 overdrive at top speed. You might have to play with the gearing anyway.
 
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