Question for rear sprocket welders

[race]

It appears that on the rolling chassis I picked up recently ('70 Taco 44) the sprocket / rear brake drum was not centered properly before it was welded to the wheel hub. The rear brake cable was not hooked up (still not) when I picked it up but once I got it home, I noticed that with no axle inserted I can set the rear brake into the rear brake drum and it rotates freely. But when you insert the axle thru the wheel the brake now hangs up and no longer spins freely. Depending on how it is oriented it is free from about 12 o'clock to 4 o'clock ... after that it takes some effort to rotate it back around to 12 o'clock.

I can only conclude that it was welded to the wheel slightly off center. I'm no machinist or welder but I am hoping I can take it to a welding shop and have them take it off the wheel, center it properly and then weld it back on. Any major hurdles with that plan? Are there tricks to get it centered properly?

I attached a couple pics.

Also, for any Taco experts, I believe the rear brake cable goes thru the threaded hole at the end of the anti-rotation bracket shown in bottom pic. In the pic you can see I have a 3/8" bolt threaded into it to check what size it was. What is the correct fitting that normally threads in there to receive the brake cable housing?

 

[O.J.Didit]

Check to see if the drum has 'run out'. If not check to see if the brake shoes have a high spot.

O.J.

 

[desert rat]

It should not be welded to the rim. If it is your options are limited. So lets see what we can find out with simple tools, I don't know how tooled up you are. Bolt the assembly back in the frame with no chain or brake cable. Find a #2 lead pencil and a 90 deg. device, a small peace of wood, small box, hose clamp around the frame will work you must be able to hold the pencil still. We now are ready to check the first two things that are the most important things, sprocket run out. We will be looking for "in and out and left and right". Place the mini so you can rotate the rear tire. Hold the pencil with the point at the base of the teeth just off the sprocket do not let the pencil move and rotate the tire. Move the pencil in until it touches the sprocket. It should touch 2/3rds of the sprocket and remain constant at the teeth (left to right). If this is off more than 1/16 of an inch there will be chain adjustment problems and the sprocket will need to be reset on the rim. If this passes you can place a piece of sand paper in between the shoes and drum and rotate the tire, sand the drum not the shoes, until you get an even run gap. Cooling welds "shrink"and I see four at the drum to sprocket connection these may be what the problem is. Sorry for being so long, I would just throw a mag mount dial indicator on the frame and be done( you can get a cheap one at Harbor freight). Hope that helps.

 

[race]

Thanks for the replies guys. I will def do the pencil test on the sprocket. And go get a dial gauge. I'm actually leaning towards a high spot in the brake shoes now. You can see them in pic 1 at the ends of the shoes where the shoes are thicker for some reason.
So I drew a line down the center of each shoe and then put the brake assembly back into the drum and rotated it a bunch to see where the wear would show. See pic 2.
The wear spots showed at the ends of each shoe ... but at the non active cam ends. See pic 3. You can also see the U-shaped bracket that grabs onto the non active cam is bent a little but I don't think that affects anything.
I could sand down the two areas with sandpaper ... or just ignore it as it will wear down from riding use. Probably Chinese made and not exactly done to aerospace standards.

Once the bike is all together the real test will be how well I can stop the thing. I have a Frank Moore ported WB 820 going into it!

 

[desert rat]

You will gain nothing by sanding the shoes they are not your problem. If you leave the drum in this condition it will try to lock up when you apply the brake. I have been out to 190 mph a lot, if you can't stop that will kill you. Ok I'll get off my soap box sorry.

 

[Havasu Dave]

Yes, these look like Azusa repops, but even the original Taco brake drums were welded. It is extremely difficult to attain a perfectly centered sprocket to hub weld that retains concentric perfection. It is very common to have to shave the brake shoes to comply with "mini bike" quality components, not to mention the fact that your shoes are warped or worn.

Sanding the shoes and reversing them was common practice in the days where these were used on competition karts. Arcing brake shoes for motorcycles is still done, though it's becoming a lost art. I would not hesitate to take these down, as I have done so many times. Bu then I've never been over 40 MPH on a mini bike. Your WB won't have you going much past that, if you push your throttle past the point where it feels comfortable. There is a whole bunch of vibration at 7K RPM, and your front end is going to start bitching at about 40 MPH.

 

[desert rat]

These are just toys to me. My "Fast" bike was a TL1000 gray market that was full race built with the rev limiter defeat after 3rd gear. The fastest I "left" a bike was at 120 mph, I just could not get it slowed up any more than that in time. I could not put a helmet on my head for 6 months and took some were around two years too recover as much as I was ever going to. All that being said this is my point and i don't care how you get there, treat your ability to stop the same as a sky diver treats his para shoot. I still ride but I'm one of the lucky ones. I'm out

 

[race]

Thanks H-Dave and D-rat. I will check for run out and try some machine shops to see if they can re-arc my brake shoes. They way they look in pic #1 (you can see the shoes are clearly thicker at the ends) almost looks like they were done that way on purpose. ?

I will probably be doing 90% or more of my riding on dirt tracks so I currently don't have any really high speed plans. Still need to figure what gearing to use. Any good tools for that? My rear sprocket will be fixed at a 60 tooth and the clutch will have a 10 tooth. I would think 45mph would be more than enough for dirt riding. Would like to have really good acceleration out of the turns. Not sure how to calculate what jackshaft gears to try.

 

[Havasu Dave]

First things first: Here is a link to a spreadsheet done in .XLS by our friends the Pardue Brothers. It's a down load, but it is safe and it is accurate. I've used it for years. Click here I should note the Pardue spreadsheet is good for me because it allows for Jack Shaft gears. Most on line calculators do not, and quite frankly, it should never be about hitting top MPH, but attaining max. efficiency within the power band. I like lower gearing with two strokes. 7 or 8 to one. Four strokes, I go much higher.

You are going to want to check with Frank Moore to get a sense of where he is going to recommend you run it RPM-wise for max. power. You need engine RPM to determine speed, but one thing no calculator will give you is best torque range. You need a dyno for that, and "then" you'd mess with gearing. The kart racing versions did about 8K RPM, but you are not going to want to twist it that high.

Having said all of that, using a vintage bike and a vintage engine-in design if not age, so let me be blunt and say "archaic" is not what I would do with this bike. There are plenty of machines you can set up to beat around in the dirt that are not so valuable. I would not under any circumstances run any Taco at 45 MPH in the dirt or anywhere else. I had a 99 which is essentially the same bike, with a high performance flat head on it, and "Trail Tamer" (Earles) front end, and at about 40, it wobbled. I always had more throttle than I did "bike." They can be modified of course to run much faster, and it starts with the front end, then the front end geometry, and pretty soon they aren't mini bikes anymore.

I would not hesitate to build a Taco 44 with that engine and use it for occasional riding however. (My two strokes piss off the neighbors and we live in a hot rod town) Sorry to sound like a know it all ass here. There are many who have different opinions on things, and that's fine. I do hope you keep making plans and taking photos and sharing what you are doing. Mini bikes are cool. Dave

 

[race]

First things first: Here is a link to a spreadsheet done in .XLS by our friends the Pardue Brothers. It's a down load, but it is safe and it is accurate. I've used it for years. Click here I should note the Pardue spreadsheet is good for me because it allows for Jack Shaft gears. Most on line calculators do not, and quite frankly, it should never be about hitting top MPH, but attaining max. efficiency within the power band. I like lower gearing with two strokes. 7 or 8 to one. Four strokes, I go much higher.

You are going to want to check with Frank Moore to get a sense of where he is going to recommend you run it RPM-wise for max. power. You need engine RPM to determine speed, but one thing no calculator will give you is best torque range. You need a dyno for that, and "then" you'd mess with gearing. The kart racing versions did about 8K RPM, but you are not going to want to twist it that high.

Having said all of that, using a vintage bike and a vintage engine-in design if not age, so let me be blunt and say "archaic" is not what I would do with this bike. There are plenty of machines you can set up to beat around in the dirt that are not so valuable. I would not under any circumstances run any Taco at 45 MPH in the dirt or anywhere else. I had a 99 which is essentially the same bike, with a high performance flat head on it, and "Trail Tamer" (Earles) front end, and at about 40, it wobbled. I always had more throttle than I did "bike." They can be modified of course to run much faster, and it starts with the front end, then the front end geometry, and pretty soon they aren't mini bikes anymore.

I would not hesitate to build a Taco 44 with that engine and use it for occasional riding however. (My two strokes piss off the neighbors and we live in a hot rod town) Sorry to sound like a know it all ass here. There are many who have different opinions on things, and that's fine. I do hope you keep making plans and taking photos and sharing what you are doing. Mini bikes are cool. Dave

Thanks for the gear spreadsheet.

Well ... I already know I'm not going to be jumping the bike as I would not expect it to hold up to hard landings so I will just have to play it by ear as to how hard one can ride it.