Gearing/Driveline Suggestions on Sears / Roper

DaddyJohn

Well-Known Member
#1
I posted this mini in the Whatsit section (Sears/Roper), and in the course of forming a strategy for putting it together, noticed I might be missing some parts, and developed some concerns.

Anyway, I plan to use a 5hp HSSK50, and think that would work nicely. However, if you’ll notice, my bike has some alien (to it) 10” wheels, and it appears it has no jackshaft assembly (as I’ve seen on most of these). The rear sprocket is a 52 tooth, and the tire OD is about 16”.

At first, I though I’d go the simple route, slap a 10T clutch on there, and direct drive it. However, that gives me about a 5:1 gear ratio driven through that 16” OD tire. I’m concerned that’s too high for a friction clutch and the 5hp engine.

Question is, does anyone think it necessary for me to build a jackshaft assembly to lower the ratio? Is a TC a better option (would it fit?). I’d rather not do either of these things if not absolutely necessary, but if direct clutch drive isn’t going to be very usable, I’m welcome to suggestions!

IMG_1991 small.jpg
 
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#2
Didn't they make a Roper with 10" wheels? To me a TAV would be best once you get to a wheel of that diameter. A jackshaft will work, but gearing it low enough to have any kind of torque will kill the top end.
 

DaddyJohn

Well-Known Member
#3
Didn't they make a Roper with 10" wheels? To me a TAV would be best once you get to a wheel of that diameter. A jackshaft will work, but gearing it low enough to have any kind of torque will kill the top end.
The pics I could find of 10" models show them with a TC driver and a jackshaft, which is further than I'd like to go with the project expense and time-wise. If I were to do a jackshaft (which I'd like to avoid having to fabricate), I'd just combine it with a clutch. Then again, I do have a Chinese TAV sitting on the shelf that I could use in lieu of a jackshaft if necessary, but am concerned with getting it to fit.

My overall goal is just to make the bike decently usable with a minimal outlay of cash and work time.

Here's a pic of a 10" wheel model I grabbed of an old Letgo sale ad, and assume it's what mine would look like if it had the original parts on it..

 
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DaddyJohn

Well-Known Member
#4
Using a gearing calculator, with a 10T front, 52T rear, and 16" outer wheel diameter, I get a 5.2:1 ratio, that yields 33mph at 3600rpm.

That sounds pretty acceptable, but then again, you don't want it to take off slowly or have excessive clutch action that heats it up and wears it out.

Wondering if anyone has experience on their mini with a similar set-up...;)
 

cfh

Well-Known Member
#5
The 10" wheel ropers are GREAT. and yes more rare. but they are awesome. the 6" wheel variety kind of suck to be honest. Here's mine with 10" wheels and a HS50 engine. And yes you want a jackshaft and a torque converter. I made some other modifications to mine. For example re-positioned the rear shocks to give more angle. also used different front springs, to give a bit more rake. this really makes the bike handle better. I also changed to a DB30 style disc brake. And a series20 comet clone torque converter.





and here's a more original 10" wheel version...


 
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DaddyJohn

Well-Known Member
#6
The 10" wheel ropers are GREAT. and yes more rare. but they are awesome. the 6" wheel variety kind of suck to be honest. Here's mine with 10" wheels and a HS50 engine. And yes you want a jackshaft and a torque converter. I made some other modifications to mine. For example re-positioned the rear shocks to give more angle. also used different front springs, to give a bit more rake. this really makes the bike handle better. I also changed to a DB30 style disc brake. And a series20 comet clone torque converter.
Sounds like there's no real cheap and cheerful way to get this thing rolling properly...:(

I could always (gasp) explore putting 6" wheels on there; it does need new tires anyway...
Then again, I'd lose the back brake assembly if I did that, and would initiate new work fabbing a new set-up.

Incidentally, I need a rear brake cable. Any idea where I might get one specific to this model?
Need a lever and perch too, but I think I can pull that out of the motorcycle junk drawer. :D

Good thing I only paid $50 for it, or I might be a bit less philosophical about the challenges, lol... :)
 
#7
Hello John.

I think either way you go, you'd benefit by setting up a jackshaft.

The nice thing about the Roper frame for this scenario, they use a bolt on jackshaft plate.

The mounting holes are already there in your frame...the upward part of that angled piece of iron, that the swingarm stops at...see the holes...2 on each side of yours, front hole almost lines up with the footpeg:

Screenshot_20200501-112635_Gallery.jpg

The tav driven is mounted on that jackshaft on mine:

20200501_090826.jpg

Here's view from the other side. Please excuse my chain being off.
20200501_090750.jpg
 
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delray

Well-Known Member
#10
I see you mention about keeping the bike at 3600 rpm's so yes you will need more gearing for sure. completely stock tune 4 or 5hp will struggle with a full ground adult on it. like cfh was saying with a torque converter and jackshaft it will pull you all day. with just a clutch only and jackshaft it could still work,but you will need some good gearing on the jackshaft and it won't hurt to run little higher stall(2500) so the bike can come out of the hole/ from a dead stop and up. with any of these mod's done I think you will be happy with it.
 

DaddyJohn

Well-Known Member
#11
I see you mention about keeping the bike at 3600 rpm's so yes you will need more gearing for sure.
I won't be doing this, but assume the governor will do it for me. ;)

Seriously though, I probably won't spend a lot of time optimizing things, as I won't spend much time riding it.
I just want to get it reasonably operational, and would probably tolerate a lower top speed more so than a boggy take-off.
 
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