Roper Rebuild

#1
I started the rebuild of my recently acquired Sears Roper mini bike, it's not a restoration I'm just bringing it back from the dead to ride. I was looking for a cheap mini bike to ride around when we go camping. I camp at Lime Rock Park for their vintage races twice a year so a vintage mini bike was what I was hoping for. The bike pictured below is I purchased it, almost as much rust as there is paint. I didn't know what it was so I got help from the "What Is It" forum to verify it. It didn't help that the shocks were missing and that the frame was rusted together.

Here's the bike as purchased:
1.jpg 2.jpg 3.jpg
 
#3
The bike is yellow over a faded purple, both are not original. I found purple overspray on the foot pegs. I'm thinking it may have been purple to start with since the seat is white with purple glitter. I disassembled it last night and started the sanding process. It took me a bit to figure out that I needed to spread the frame to get the pivoting section out of the main frame. I tried hammering what I though was a bolt only to notice that it was welded in place.

The seat bolts pulled right out of the rotten wood base which I will have to replace. I had hoped to simply re-cover it but that's not possible. The roper seat is wider than all of the replacement seats I could find for a reasonable price. I don't need to put a $125 seat on a $100 mini bike.

It turns out that the handlebars were originally chromed, the thinnest possible chrome it looks like. They are really pitted and whatever chrome is left is pealing. They can't be re-chromed even if I wanted to because the pitting is just too bad. I'll be painting them like it has been done previously.

I can't figure out how or if the sprocket is removable. That is going to make sanding, painting and fitting new tires a real issue.

I intend on putting a small 75cc Predator engine on it, I have a new one on hand. I think a 6HP 212cc engine would just be too fast for my needs.

Pictures will be uploaded shortly.
 
#4
Personally, I would have had the frame and forks sandblasted rather than trying to sand it (what is your time worth?). The sprocket is not removable- it is welded to the wheel hub. Not just your rear shocks are missing- it looks like the original upper mounting plate/gussets are gone (cut off?) as well. You will need to get that (welded) bolt out of there, and rework that area as that entire motor plate pivots (that is how the shocks work). You really have your work cut out for you on this one...
Michael
 
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#5
I don't have access to a sand blaster and I'm trying to get it done fast. I'm not stripping the entire frame to bare metal, just removing rust and loose paint. I'll see what it looks like once I prime it with primer with filling primer and give it a light sanding. Like I said, I'm just getting it to running condition but I don't want people to need a tetanus shot to ride it. Pictures below as it stands right now. I haven't touched the sprung frame section yet but I have rough sanded the forks and main section. You can see the upper shock mounts in one of the pictures as well as the degree of pitting on the chrome.

main frame.jpg motor mount.jpg pitted.jpg pivot frame.jpg shock mount.jpg
 
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#9
One coat of Rust Reformer, two coats of filler primer, light sand, one coat of white primer, two coats yellow, two coats clear. Yellow pops better over white primer. I forgot how tough it was to remove and replace those little tires. The HF tire changer made it a lot easier.


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#14
It barely moves under power, I think the rear bearings are seized. That's a pain, I needed it this weekend for a camping trip.
Likely the very underpowered engine , that small engine was a mistake in my opinion , could be wheel bearing issue and those at $2.50ea. should have been replaced. Hey the bike looks good , it's a learning experience and you have your vintage cruiser !!
 
#15
It barely moves under power, I think the rear bearings are seized. That's a pain, I needed it this weekend for a camping trip.
In addition to that small engine it could be your gearing. How many teeth on the clutch sprocket? If I remember correctly the original rear sprocket is 60 tooth on Ropers.
Michael
 
#17
Likely the very underpowered engine , that small engine was a mistake in my opinion , could be wheel bearing issue and those at $2.50ea. should have been replaced. Hey the bike looks good , it's a learning experience and you have your vintage cruiser !!
I did this all at the last minute before my trip, not great planning but it is what it is. It rained for about 70 hours straight so the minibike would not have worked out anyway. When I say it barely moved I mean I had to push it along with my feet to get it to move on level ground. I wasn't looking to go fast, it was just going to be transportation to and from the bathrooms to our campsite. It's pretty common for folks at Lime Rock park to have mini bikes or golf carts for this.

I would assume that 3hp could get us to 15-20mph on level ground, that's all I needed really. The bearings are cheap and easy enough to install. It's the first mini bike I've brought back from the dead so I got a nice little lesson. Funny, I'm restoring two old Honda motorcycles and I did order new bearings for them ahead of working on them.
 

DaddyJohn

Well-Known Member
#19
I agree that the engine is simply underpowered; pretty common story with those 79cc Predator units. It’s true that the Predator 212 can be too squirrelly for certain uses, so something around the 5hp mark can be tame yet potent enough. I like to put flathead Tecumsehs on the vintage minis. If you’re anywhere that derelict snowblowers are plentiful, a running HS50 shouldn’t be hard to locate for cheap.
 
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