Purchased a lemon, repair not going so well

[DKM802]

For years i've been wanting to get my hands on some sort of off road vehicle. ATVs and side by sides are a little out of my price range so i settled with a bigger go kart. I found a used one in my price range and decided to go check it out. no issues in the ad and it was passed off as running well. The seller drove it out and went up and down the street a few times to demo it.



I found out pretty quickly that it didn't idle well but did fine under load. Rode it for about an hour and then the axle slid out of the diff. I changed the bearings and installed new lock collars and that solved that.

I changed out the spark plug, air filter, ran a new throttle cable, replaced the pullstart rope, replaced the oil, cleaned the tank and turned down the idle screw and it ran fine for about an hour.

Fuel line broke so i replaced that and went ahead and replaced all the other tubes before they cracked as well.

I took the engine off, pained the frame, reinstalled and when i got back from my first trip i noticed the head was leaking oil..

I replaced the gasket and torqued to spec.


My next trip out i was doing a speed test and hit 38 mph. i heard a rattle from the engine and the rear plate on the driver pulley had broken! this was the last straw i really didn't want to invest any more time into this engine.

I decided to purchase a 420cc predator engine and bolt up a decent 40 series torque converter. i spent about 250 on a kit and although it wasnt the nicest one it wasnt the cheapest option so i figured it would be decent quality. it also was marketed to work with the predator 420 so i figured it would work.


So the toque converter plate sticks out 3 inches where the driven pulley sits so the only way to line the pulleys up is to put it backwards on the shaft because the shaft is too short to just slide it out and run collars. i also can't get away with using a small piece of shaft because the driver pulley is only on by 1 cm when lined up correctly.


With the pulleys installed in opposite directions the belt becomes miss aligned and ends up slipping, getting stuck etc.

So i ordered a flat torque converter plate so that the driven pulley can come closer to the engine and i can install the driver correctly.

This is going to change the location of my sprocket which means i will need to move the engine over a few inches to make up for the difference.

There may not be enough space on my mounting plate to move it which means more welding before i drill.


Once i have this taken care of then i can move on to the breaks. The return spring isn't strong enough and the breaks don't grab enough but that seems realitively easy to fix in comparison to the previous issues.

This project has consumed far more time then i have been able to ride but it has forced me to learn new things such as flux welding.


Pics to come later thx for the read

 

[landuse]

Welcome to the forum!!

Post some pics of your setup, but right off the bat I can say that buying a series 40 that uses a backplate was a bad idea. They were never designed to be used with a backplate, but some bright spark thought it would be a good idea. You might need a reverse wound spring to get it working. The alignment issue is also due to the stupid backplate.

But we will be able to help you further once we see some pics

 

[DKM802]

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Replaced the torque converter plate with a flat one which brought the driven pulley 2.5 in closer to the engine; allowing me to reverse the driver pulley to the correct orientation.

Replaced the mechanical brake caliper as the old one wouldn't function correctly. the tension bolt would jump back a thread or two when the lever was engaged causing the pads not to grab. Rotor was rusted in place so i had to drop the axle. Actually went pretty smooth.

I added a spring to the throttle to increase the return to idle tension and added an additional spring to the brake rod so the pads wouldn't ride as much.



The last issue i need to solve has to do with the left rear wheel/hub/axle.

the wheel doesn't roll parallel with the kart, its slightly angled out. once you get up to half speed you can really feel it in your ride it sorta bounces the kart up and down.

The axle set up is differential so each axle is its own piece. the right side rolls fine.


I wouldn't be opposed to replacing the left section of the rear axle and getting a new hub for the end but i can't find it anywhere.

What makes it so difficult to find is that the end that slides into the diff is machined with gear like threads. not exactly something i can find on bmi/omb/gopowersports

 

[jonlasaga]

I really like the look of that frame. Did the previous owner weld this up themselves or is this a kit/full chassis you can buy? I dont have any suggestions for you unfortunately but I hope you can get it running well.

 

[DKM802]

I believe it is mostly original, it’s a Kenbar streaker performance DD9

Right now the only thing holding me back from riding is belt issues. When I try to move forward the driven pulley opens up and then when I let off the gas and the rpms drop the belt gets wedged in the driven pulley as it closes. It gets stuck frequently and I have to turn the engine off and pull the belt off the pulley to free it and then put it back on.

My kart weighs about 200 lbs. the engine is around 90. Rider 150 rounding to 450 total weight
The tire diameter is 22 inches
Sprocket on jackshaft has 12 teeth
Sprocket on axle has 60 teeth

Is a 1 to 5 ratio too high for the tire size and weight?
Or perhaps the spring tension is incorrect in the driven pulley?


If my gear ratio is ok would I need to increase or decrease the tension in the pulley?
I’m leaning towards less tension so it doesn’t snap back so fast catching the belt..


( my pulleys are fairly well aligned I have about a 3/8 offset )

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I changed the tension on the driven pulley so that it takes longer to engage. Not as much acceleration now but still plenty.

Right now im working on aligning the sprockets. i think i have a 1/8-1/4th offset and the chain doesn't like the angle. When i straighten the motor out i can't pull it back enough to create good tension on the chain. Probably take the engine off and drill out the mounting holes a bit more.

I also need to replace a bearing on the new TC. One went in fine the other i couldn't get it in all the way. Broke it trying to remove it. Ill probably freeze the bearing and sand the housing and that should do it.

Shaft clamps also aren't doing a great job at keeping the jackshaft in place. Gonna weld the rear clamp and maybe drill into the shaft a little on the other end so that the screw can bite harder.


I destroyed my belt before getting my tension and allignment correct so i have a new belt coming in with the replacement bearing tomorrow.

 

[DKM802]

Welded 1 of my shaft clamps for the jack shaft today
Waiting on replacement bearing before i reassemble.

I got my hands on a 10 tooth sprocket so i can try out a 6:1 ratio rather then the 5:1 i currently have.

New belt came in today as well.



Still trying to sort out the rear wheel that doesn't roll straight. a few variables come to mind when contemplating the root cause.

1) axle bearing 1 of 2 is a quarter inch too close to the sprocket but still in housing. Its just not centered and flush like the other bearing on the axle.

2) chain tightness was applying too much pressure on the sprocket which transferred to the axle/wheel.

3) rotor is significantly bent and could be throwing the weight of the tire off. This rotor doesn't have a caliper so it spins without resistance but its rusted to the shaft and beat up.

4) my shaft could be bent?
5)my hub could be misaligned/bent on the shaft end?
6)my rim could be bent?
7)other possibilities that don't come to mind

I decided to start with that i could/can do. I used my angle grinder with a metal blade and cut the rusted bent rotor in half and it fell off the shaft.

I also decided to remove and replace the bearing that wasn't aligned in the housing properly.

But now i can't get the new bearing onto the shaft. I used a wire brush to remove all the rust from the shaft and wiped the grime and debris off with blue towels and wd40.

I really don't want to drive the axle in with force i feel like its either going to jump out of the housing or damage the bearing.

my other option being temp it would be possible to freeze the axle and heat the bearing and let expansion and contrast aid me but i dont think i can fit the axle and hub in my freezer lol!

If i can get the TC bearing to cooperate and the rear axle bearing to cooperate it should at least be ride able.

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[jonlasaga]

I may be wrong about this but It looks like your axle is getting beat up because your tire isnt quite straight on the end of it. I cant tell because I cant figure out exactly what angle the camera was at when it was taken but it looks like your hub is slightly bent.

 

[DKM802]

the hub did appeared to be bent and the axle seems to be fairly straight.

ill go ahead and order a new hub and see how that works with the axle.

Anyone know how i could replace the axle? its 1 inch diameter 16 inches long, 2 inch step down to 3/4in threaded. im not sure how to classify the end that goes into the diff.

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[mckutzy]

The end as milled is called a spline. It will be probably diff specific as they are not all treated equally.

 

[DKM802]

what are the chances of me finding a axle shaft with the correct spline, diameter, length etc?

I couldn't find anything on the major kart supplier sites.

Nor could i find a replacement diff unit for the kart. I think i found links to two but they were no longer manufactured.

 

[BigWes]

Ken-Bar used the comet scd-1

I have several. You might be able to source parts other places but here is a link. It's a 1 inch shaft turned down at the end.

https://www.mfgsupply.com/gomini/gominiaxles/gominiaxlesdiff.html

 

[kencam]

The 40 series TC's pulleys are supposed to go in opposite directions.

https://www.bmikarts.com/PDF/Comet_40series.pdf

 

[DKM802]

bore'd the step down a .13in to allow the shaft through. tight fit as well needed a little convincing. New bearing slid on fine, same internal Diameter but different manufactures.

my flange bearing housing (triangular bolt pattern) isn't holding the bearing still enough. lots of play and the bearing can travel more then 1/8 in. The other one holds the bearing much more stiffer.

going to try to locate the correct housing and see if that fixes my bouncy ride!

 

[DKM802]

I tried the new bearing housing and swapping out the tires and rims and it still isn't spinning straight.

Converting to a live axle set up this week just waiting on the parts to arrive.

 

[DKM802]

First test run with the new axle went well. The only issue im really having right now is the driver pulley is getting stuck and wont retract all the way during idle so its grabbing onto the belt while im trying to apply the brakes. a small wack with a wrench will pop it back into its resting position but thats only a temp fix. I think its a cheap knockoff and thats why it wont function properly. Ordered a replacement 40 series driver pulley from gopowersports and i think it will operate much better. my pulley also didnt have the copper sheathe that helps the belt idle without taking off which was a little annoying, so im not sad to see it go.


I need to replace the driver pulley when it arrives
I also need to make a few more welds in my engine mount
I may also adjust the spring tension in the driven pulley.


Fairly easy tasks and then it should be fully restored!!

 

[DKM802]

This is what it looked like when i acquired it a couple months ago