Vintage 1970 Broncco tx2/tx1

1970 Broncco TX2/TX1

  • yes

    Votes: 2 33.3%
  • No

    Votes: 4 66.7%

  • Total voters
    6
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cfh

Well-Known Member
#62
As the prior post suggested, i bought a filler neck/cap on ebay and will weld it into the tank. Then i'll sandblast the whole tank inside and out, and weld a new bottom in place. Then weld a small square of steel, drilled and taped with 1/8" NPT female on the bottom, so i can install a petcock. If the tank leaks (and it may, depending on my welding), i will seal it with Pore20.
 

cfh

Well-Known Member
#65
Worked on the tank today. it was way worse than i thought. actually i was being dumb, i should have seen this coming...

Sand blasted the tank. It was filled with bondo. the gobbers on the inside of the tank was body filler. blasted that all out. and the outside of the tank had its share of bondo too. blasted that all out. And saw the reason this all happened... there were holes in the side of the tank, a lot of holes.

The metal where the holes resided was really thin. Made a stainless steel internal patch that covered the holes. it runs the entire length of one side of the tank, and wraps around the front and back. Tack welded that in place. metal too thin to do a continuous weld, so used many tack welds. This will allow the use of solder on the front of the tank. or even weld the holes shut.

Welded the new filler throat in place. that went pretty easy, though the metal was very thin there too.

Made a new metal bottom out of stainless steel. TIG welding that in place was a bit tricky. it was tedious. me and a couple friends took turns doing that TIG welding. it took a long time...

Then my buddy had this crazy idea of MIG welding the exterior side of the tank where the holes resided. Since there was new metal behind the holes, he felt he could lay a bunch of MIG weld in there. It looked messy but largely worked. Then used a TIG welded to finish plugging the holes on the outside.

What is left on the tank? Need to solder fill the sides and sand smooth. no body filler here...



 

cfh

Well-Known Member
#69
Did some more work to the orange Broncco. Now that the weather has gotten better, i have been riding it more. I'm not happy with the gearing. I used a 16t jackshaft sprocket to a 72t rear sprocket. Wheel size is about 14" diameter. That gives a 4.5 to 1 ratio. But with the series30 torque converter and HS50 with big cam/22mm carb, it just shifted wrong, and the engine could never gets above about 3500 rpm.

So i tried a Juggernaut torque converter drive unit. Holly crap, what a difference! Now the engine had no problem making 5000 rpm and it was just quicker off the line. The whole bike worked better. But there's one problem... The juggernaut drive unit is physically bigger than a comet, and it won't fit inside my custom torque converter cover. damn.

So i thought i would try tuning the comet series30 to see if i could get to what the Juggernaut was providing. I first tried a yellow torsion spring on the driven. This helped and kept it in low gear longer, but no where near enough. So next i tried modifying the drive comet with aluminum weights and black garter springs. Again it helped, but still not like the performance of the Juggernaut. With this set up the engine would go to slightly higher rpm, but it still seemed like it shifted to high gear too soon, and no big rpms are developed.

Next i tried changing the jackshaft gear from 16t to 15t. Again, it helped, but still not there... The rpms are a big higher, but still it shifts to high gear too soon, and the engine bogs. It's getting closer, but overall, the juggernaut really is the ticket. Just i didn't make the damn torque converter cover big enough to hold it!!
 

cfh

Well-Known Member
#70
Back to working on the green Tx1...

Originally the Tx1 had a jackshaft with two 13t sprockets. And a regular clutch on the motor. I'm changing this to a series30 torque converter. But the problem is, the driven torque converter (that mounts on the jackshaft) sits too low, and rubs on the lower frame tube. Ok so can space it out, but then the motor drive has to be spaced out also. This adds considerable width to the bike. And the PTO (at 3") is barely long enough on the motor to support this. The blue circle in the picture below shows where the 6" driven unit rubs on the frame. (the picture shows the jackshaft plate already modified into the new position).



To fix the problem, decided to raise the jackshaft upwards 3/8 of an inch. Don't want to raise it too much, because you don't want the chain to hit the pivot for the swing arm. 3/8" is just enough to clear the 6" drive unit. This allows the driven to be mounted nearly touching the jackshaft plate. And gives near perfect alignment with the motor drive unit.

So what's the easiest way to do this? Actually cut out a rectangle with the jackshaft bearing mount. And turn it 90 degrees. If done (measured) correctly, this can give the exact 3/8" rise to the jackshaft. Then some metal can be added to the side as a filler. The picture below shows how the newly mounted jackshaft just gives enough room for the driven unit, so it can be pushed up against the jackshaft plate. The blue arrow shows how the driven unit no longer touches the lower frame tube.



Now the jackshaft and the driven is perfectly placed. Notice how the motor drive unit lines up just right...



Last thing to do is to re-mount the footpegs. Have to do this because they were bolted to the jackshaft plate. With the TC driven unit blocking that mount, there was no choice but to move the footpegs. Used some Rupp footpeg mounts and welded them forward. Also moved the kickstand mount backwards (kickstand easier to access mounted back further.) Note the picture below shows the kickstand/foot peg mounts moved. In the picture above, there are no footpeg mounts, and the kickstand bracket is still in the forward position.

In addition welded a muffler mounting bracket on the rear seat mount. And welded the lower frame tube where it meets the neck (a known weak point on these frames.)

 
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cfh

Well-Known Member
#71
Did some engine work today for the green Tx1.
Using a late model HS50 with the smaller bore and smaller exhaust valve. Don't discount these motors! they are very plentiful and they work great. And since they are late model, they are generally in pretty nice condition. They are also CDI ignition so no points/condenser to worry about. I know a lot of people won't use these, but they are really awesome (and cheap!) You can bore them to .040 over if needed (but they don't seem to need that.) And i've used these before with a big cam/carb and they GO fast.

The HS50 motor i'm using here was off a snowblower. Check out the bore! i did run my hone in there for about 5 seconds. That's all it needed. Looks pretty awesome. This is typical for a late model snowblower engine.



Also installing one of my own custom cut high performance cams (basically similar to a dynocam 255). Since i'm doing that, need to use a billet Arc connecting rod. Governor has been removed too. Will use a 22mm carb and open exhaust. Because it's a late model HS50 engine, i can't use an aluminum flywheel. That's ok though! On the cast iron flywheel i cut off the electric start ring, so that helps decrease weight. Not to the level of an aluminum flywheel, but it helps. Don't let the steel flywheel scare you off. These engines still pull hard with that flywheel.

 
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cfh

Well-Known Member
#72
Finished up the engine. Lapped the valves too. The big cam really makes the compression pretty strong! I will use a slide carb and a custom exhaust and intake manifold. Will do that when the motor is on the bike. I know the engine isn't exactly the correct look (the blower housing is squared), but it will work just fine.



Next up was the rear wheel. Originally it had a combo rear sprocket and disc brake plate. I hate that look, it just gets so crappy from the disc brake rubbing on the sprocket. Also i'm not a fan of this old school disc brake - never seemed to worked well.

I went through my pile of 7" broncco wheels and found one with a brake drum. Easy to switch the center sections on these wheels. So I put the drum brake center on a rim set with a good tire. But the problem is the sprocket. That center drum brake assembly had a 32t sprocket and #41 chain! On this bike it needs a 72t sprocket (#35 chain.) So what do you do??? having a custom sprocket made is crazy expensive and just silly - i have enough damn money into this project! ha!

Looking on the web, Monster Scooter has a 60t and 72t sprocket #35 chain for $18.49. I bought that!
https://www.monsterscooterparts.com/35-chain-60-tooth-sprocket-for-go-karts.html
But the problem is, the center hole is 2" diameter. I need a center hole of 1.555" diameter. So how do you deal with that?

It's really pretty simple... back the hole with a thick piece of brass, and using the TIG welder, run a bead around the inside of the hole about 5 times. This will close the hole the approximate 1/2" that is needed. Also this sprocket was drilled with 8 holes (all in the wrong place!) So i fill welded four of the holes closed, because we'll have to drill new (proper position) mounting holes. Flip the sprocket over, and fill weld the other side (needs some touch up). After all the welding is done, used the flap grinder to make the welds smooth on both sides of the sprocket. Can barely tell it was welded. After it's painted/powder coated, won't be able to tell at all...

With this work done, brought the sprocket to the lathe. Reversed the jaws (so they could grab the sprocket), and re-cut the center hole to 1.555". That took all of about 5 minutes. Now the sprocket fits perfectly on the Broncco wheel! For the four mounting holes, used a transfer punch to center punch the new holes (using the old sprocket as a guide), and then drilled them onto the new sprocket. Bingo, a new sprocket that fits perfectly! Just have to paint or powder coat the sprocket silver (will probably use paint, as the powder coat guy is doing only critical work during the shut down).



While all this was going on, painted the frame metalic green. Can start assembling the bike!

 
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cfh

Well-Known Member
#73
Next up was to rebuild the Sebec rear shocks. There's a nice video on youtube about doing this, so i won't go into detail. i did make a spring compressor so assembly was a bit easier. It's a chalk gun with a small modification... the open side of the gun has to be widened just a bit to fit the shock body. I used the bench grinder to do this. Note after the mod the chalk gun is still good for use as a chalk gun!

One of my Sebec shock had a bent inside rod. It made the shock basically unusable because it would not compress. Taking the shock apart and using a mallet, as able to straighten the rod. I also used a very light coat of grease on the rods. Probably not a great idea because the grease attracts dirt. But for the most part, the rods are covered, so they don't have dirt sight to the element. Doing this made the shocks much nicer on both the compress and release side.



Started assembling the frame. The biggest obstacle is the jackshaft. The original was not keyed. Instead they used roll pins on the two 13 tooth jackshaft sprockets. For my build this won't work, because we are installing a torque converter, which requires a 3/16" key (to lock it to the jackshaft.) For this reason, i made a new jackshaft. I buy 5/8" keyed jackshaft rod in 3 foot lengths, and just cut it to length (as shown in the orange Tx1/Tx2 build.) But on this jackshaft one side i threaded the jackshaft rod 5/8-18, so a large locknut could be used. Why do that? It's just easier on this particular jackshaft set up. Normally i don't do this - just drill both ends of the jackshaft and thread it 5/16-24 and use a bolt. But in this situation, had to do it this way.



On the jackshaft going with a 14 tooth sprocket (instead of the stock 13 tooth.) Why? because i have a 14t sprocket handy! I went to 14t on the orange Tx1/Tx2 build, and it worked well, so why not do that here. Also on the front fender I didn't use the stock mounts. Instead of made an inverted V bracket, so the front fender could be mounted higher. This makes cleaning the bike a lot easier. I also like the look of this better. (Note I did this on the orange Tx1/Tx2 build too.)



Brakes are all mounted (but no cables just yet, because the handlebars aren't mounted.) Note the rear drum brake is used instead of the rear disc. Front still keeps it's original disc brake. Tomorrow I'll start working on the custom intake manifold (for the 22mm carb) and the custom stainless steel exhaust....
 

cfh

Well-Known Member
#77
The color is by Illusion from Prismatic and it's called 'money green'. it has a lot of metallic in it, sparkles a lot!
Did some more this afternoon. All the cabling is done now. just have to mount the gastank and seat.
On the torque converter, i will experiment with different drivers first, and then come up with a cover. Probably won't go to the extreme i did on making the orange Tx1/Tx2 bike's TC metal cover. that was a lot of work, and in the end, i could not use a Juggernaut. The TC cover is always the biggest issue. Do you just use the black plastic cover that is available everywhere? or something else? it's a tough call. Will probably just go with the standard black plastic cover, and doll it up with custom decals.

 

cfh

Well-Known Member
#78
Finished up the Green Tx1. Here's a couple things i found on this bike compared to the orange Tx2/Tx1 bike...

First those "wacky handlebars" as broncco called them on the green bike are indeed, wacky! it handles Ok with them, but man they are weird.

Second I am running a stock comet series30 torque converter on the green Tx1. It seems to work fine with that set up! Unlike the orange Tx2/Tx1 bike, where i just couldn't get the torque converter tuned right.

Third... to the above 2nd point... i installed a Juggernaut on the orange Tx1/Tx2. Because i can't used the custom torque converter cover i made with the juggernaut, moved that cover to the green Tx1 (which is running a stock comet series30 set up.) On the orange bike i installed the stock black plastic comet cover.

Fourth... both bikes have nearly the same engine. They are both Tecumseh HS50 with the same modified cam, same 22mm carb, same open exhaust. Both turn about 5000rpm. The only difference is the green bike has a newer HS50 with CDI ignition and a cast iron flywheel (the orange bike has a points HS50 with an hs40 aluminum flywheel and the smaller rounded blower housing). Which one runs better and pulls harder? The newer HS50 (and it also starts better.) I know this seems weird. But those newer HS50/HSSK50 engines really run well with a big cam/big carb and cast iron flywheel (though i do remove the electric start gear from the flywheel). I've had really good luck with that set up. They are little rockets, and the newer HS50 engines are cheap and easy to find!

Note both bikes have the same gearing (14t to 72t) and both have the exact same wheels/tires.

Yes i am using the original seat on the green bike. It's in decent enough condition, at least for now.

This completes my build off project. Thank you for reading all this...





 
#80
Finished up the Green Tx1. Here's a couple things i found on this bike compared to the orange Tx2/Tx1 bike...

First those "wacky handlebars" as broncco called them on the green bike are indeed, wacky! it handles Ok with them, but man they are weird.

Second I am running a stock comet series30 torque converter on the green Tx1. It seems to work fine with that set up! Unlike the orange Tx2/Tx1 bike, where i just couldn't get the torque converter tuned right.

Third... to the above 2nd point... i installed a Juggernaut on the orange Tx1/Tx2. Because i can't used the custom torque converter cover i made with the juggernaut, moved that cover to the green Tx1 (which is running a stock comet series30 set up.) On the orange bike i installed the stock black plastic comet cover.

Fourth... both bikes have nearly the same engine. They are both Tecumseh HS50 with the same modified cam, same 22mm carb, same open exhaust. Both turn about 5000rpm. The only difference is the green bike has a newer HS50 with CDI ignition and a cast iron flywheel (the orange bike has a points HS50 with an hs40 aluminum flywheel and the smaller rounded blower housing). Which one runs better and pulls harder? The newer HS50 (and it also starts better.) I know this seems weird. But those newer HS50/HSSK50 engines really run well with a big cam/big carb and cast iron flywheel (though i do remove the electric start gear from the flywheel). I've had really good luck with that set up. They are little rockets, and the newer HS50 engines are cheap and easy to find!

Note both bikes have the same gearing (14t to 72t) and both have the exact same wheels/tires.

Yes i am using the original seat on the green bike. It's in decent enough condition, at least for now.

This completes my build off project. Thank you for reading all this...





Wow you knocked that out fast...
Two more back to life, great work!
 

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