having trouble with mini bike build

[johnnyp]

hi. i purchased a centrifugal clutch that was supposed to have 1/4-28 tapped holes for set screws. they are not as advertised. going through a lot to get the right set screw and decided to try to use a washer bolted to the drive shaft. its an old briggs and stratton engine, 3.5HP. anyone know what bolt i need for it?

 

[creia]

hi. i purchased a centrifugal clutch that was supposed to have 1/4-28 tapped holes for set screws. they are not as advertised. going through a lot to get the right set screw and decided to try to use a washer bolted to the drive shaft. its an old briggs and stratton engine, 3.5HP. anyone know what bolt i need for it?

It is always better to use a crank bolt, lock washer, and fender washer to retain your clutch on the crankshaft. Forget about those set screws!
Michael

 

[johnnyp]

i bought a tap and cleaned out the threads on the clutch (for the set screws). they were not 1/4-28. i will buy a few bolts to see if i can get one to fit the threaded portion of the crankshaft.

 

[Jim Donovan]

Creia -- is correct, bolt and washer only to hold a clutch in place. We no longer put set screw holes in our clutches for the 3/4" crankshaft. You want the clutch to be able to float on the crankshaft so it can self align with the rear sprocket that NEVER runs true. The Max-Torque clutch is .070 shorter than the crankshaft just so there is some built-in float. When you hold a clutch in place you want the pressure of the bolt on the crankshaft NOT on the clutch. 95% of crankshaft on the 3/4" are drilled and tapped. If you have an old American made engine that isn't drilled, then do it yourself and put a 1/4"-20 hole in it. Foreign engines you will have a problem drilling since for some reason they heat treat their cranks and since nothing spins free on them why heat treat them? One of those mysteries in life that we will never know the answer to.

 

[creia]

hi. i purchased a centrifugal clutch that was supposed to have 1/4-28 tapped holes for set screws. they are not as advertised. going through a lot to get the right set screw and decided to try to use a washer bolted to the drive shaft. its an old briggs and stratton engine, 3.5HP. anyone know what bolt i need for it?

If it is a 5/8" crank it is probably a 1/4"-28 bolt
If it is a 3/4" crank it is likely a 5/16"-24 bolt
This is what I have seen Briggs drill their cranks from the factory and what I drill and tap them for if they were not threaded from the factory.
Michael

 

[johnnyp]

creia...........thank you very much for your response. i will post a pic of the minibike when it is complete. will be my first minibike build.

 

[johnnyp]

After looking at the crank closer, the end that I thought was threaded is either not threaded or a bolt has been broken off in there. I have never drilled and tapped a crank before. Is there any way I can spot weld a washer on the end instead of drilling and tapping the crank?

And if I wind end up drilling and tapping the end of the crank, how deep (or how much thread engagement) is needed

 

[sparkwizard]

Do you have a wire fed welder?

 

[creia]

After looking at the crank closer, the end that I thought was threaded is either not threaded or a bolt has been broken off in there. I have never drilled and tapped a crank before. Is there any way I can spot weld a washer on the end instead of drilling and tapping the crank?

And if I wind end up drilling and tapping the end of the crank, how deep (or how much thread engagement) is needed

Let's see some good (clear) close up pics of that crank end.
Michael

 

[johnnyp]

Do you have a wire fed welder?

I need to purchase a home welder. I am looking at multi function so yes a wire feed is a possibility.

 

[Minimichael]

Is there any way I can spot weld a washer on the end instead of drilling and tapping the crank?

I'm not the smartest here but that sounds dum.

 

[johnnyp]

Let's see some good (clear) close up pics of that crank end.
Michael

Let's see some good (clear) close up pics of that crank end.
Michael

here are some pics

 

[johnnyp]

I'm not the smartest here but that sounds dum.

please give me your reasons why you think it is dumb

 

[Minimichael]

No way to open the case. Welding boogers onto a machined shaft. Tearing up your seal.

 

[johnnyp]

No way to open the case. Welding boogers onto a machined shaft. Tearing up your seal.

the spot weld would be in center of washer and center of crank.......the clutch wouldnt know the difference

 

[Skipp]

It takes 30 minutes to drill and tap
That crank….if it a broken bolt…

Drill Hog USA 6 Pc Square Easy Out Set Straight Screw Extractor….

I bought a set something very similar to this that the maintenance guys at the plant used….I have found nothing yet I can’t remove….

 

[creia]

As the photos clearly show there is no "bolt broken off" in that crank end. It has never been drilled and tapped. Take the time and effort to do the job right- drill and tap it then use a bolt, lock washer and fender washer as I have previously stated. Forget that (crappy) idea/solution of welding a washer on the end of the crank!
Michael

 

[johnnyp]

so my question is the following......not all cranks are drilled and tapped. so for years the minibikes worked well without a bolt and washer? i agree that its the best way to proceed but i am interested in the history and what the "older" guys did back in the day.

 

[nightgrider]

Not all small engines were intended for Mini Bike. So not all output shafts are tapped. But over the tears can find their way onto mini bikes. I would tap the outshaft. Harbor freight has cheap sets. I own an SAE and a Metric set. They are handy to have on hand.

https://www.harborfreight.com/carbon-steel-sae-tap-and-die-set-40-piece-62831.html

 

[sparkwizard]

I asked about a wire welder because that is how I remove broken bolts. I am one of the older guys and I have always used a bolt, fender washer and a lock washer to mount a clutch. It would make no sense to explain how I remove broken bolts because you don't have a welder, and there is no bolt in there.