4G T drive bearing conversion

Discussion in '4 Stroke Bicycle Engines & Kits' started by cobrafreak, Mar 3, 2012.

  1. cobrafreak

    cobrafreak New Member

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    I've done some playing around with my 4G T drive transmission. The biggest problem that I had was the blasted brass bushing in the clutch. Bad technology all around. I did a lot of research and did a sealed cartridge bearing conversion to the stock 4G T belt transmission. It is a great mod. Quiet, and smooth. It lowers the maintenance significantly. The conversion uses 6 13x20x4mm bearings. The stock engine output shaft is 15mm and requires the removal of 1mm of steel which is really 2mm or steel radially for the fitment of the 13mm bearings. Bushings suck big time. No more oiling, no more wear. It was night and day from the bushing to the bearings. So much nicer. The bearings only cost 99 cents each.
     
  2. The_Aleman

    The_Aleman New Member

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    #2 The_Aleman, Mar 3, 2012
    Last edited: Mar 14, 2015
  3. scotto-

    scotto- Custom 4-Stroke Bike Builder

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    That is a nice conversion but it's not the "end all". Those 99 cent bearings are after all......$0.99 bearings. Spend a few more dollars on some better quality bearings and you'll be a much happier camper in the long run. Those bearings are cheaper than you may think ;)

    dnut
     
  4. cobrafreak

    cobrafreak New Member

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    As a general rule, for every bearing added to a job it doubles the load rating. I use six. Whatever the load rating of these permanently sealed bearings were, they are many times more durable than the oil-lite bushing and are more than up to the task of smoothing out a clutch. They are also labeled "high speed bearings". The speed the clutch engages is hardly high speed. They won't break a sweat. Remember, the only time they really work is at idle when the clutch shoes are not engaged. These bearings may be 99 cents each but you wouldn't know it if you held them. Very smooth with no unwanted movement sideways. No noise. They will last a very long time. They fit the clutch perfectly. As I said before, you need to turn the engine output shaft down to 13mm from 15mm. Not the whole shaft, just the shaft after the clutch, so you are only dealing with a little more than a single inch. Very easy and quick. You can use a belt sander or grinder. I remove the three clutch shoes as they are in the way during the procedure. This is a good time to add washers to the springs to raise the rpm the clutch engages into so you can do smooth pedal free standing stop take-offs. I idle the engine while someone holds the bike and I remove a little amount of metal at a time until a single bearing slides all the way onto the shaft against the clutch. Since the shaft is spinning as you remove metal it will be perfectly true. This is an awesome mod.

    [​IMG][​IMG][​IMG]
     
    #4 cobrafreak, Mar 3, 2012
    Last edited: Mar 3, 2012
  5. hmiwb

    hmiwb New Member

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    That sounds like a great solution to the problem. I've just ordered the recommended replacement bushing from McMaster-Carr, but if that doesn't work out I may well try your solution. Thank you for sharing your idea!
     
  6. fredgold52

    fredgold52 New Member

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    I really like this idea. I think it has many advantages over the stock set up. My only concern is maintaining concentricity with the crank shaft. How do you make sure the clutch and the crank shaft have the same axis? Did you remove the stock with the engine stopped or running? That may seem like a stupid question, but with the engine running you could remove stock and be more assured the new circle was concentric with the old one. Like with an engine-lathe (sorry about the pun).
     
  7. hmiwb

    hmiwb New Member

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    Yes, he did mention in his write-up that he had the motor idling while he ground the shaft. It would still require a lot of measuring and care to keep from going too far or out of round. Still it sounds promising.
     
  8. cobrafreak

    cobrafreak New Member

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    Yes, it was running to maintain trueness. I've been riding mine around for a while and it's still not doing anything out of the ordinary. All's well. Let me play devil's advocate and say for example that I didn't get the crank true. Let's say it's crooked, what would I do now. (I was thinking of this just in case something went wrong). I came up with these back up plans:

    I could determine a potential low spot or high spot and re-weld that section back up to specs and regrind.

    I could braze a low spot and grind true.

    I could use JB weld or PC Putty and grind true. (don't laugh, I used JB Weld on my 5.0 Mustang throw-out bearing shaft because of deep grooves when I did a clutch rebuild 4 years ago and it's still going strong) If it lasts for a 350 hp motor it would last for a little 2hp motor.

    This is just theoretical exercise. I didn't need to do any of the above because I was careful. I'm sure they would have been effective though. There is always a work around.

    A perfect set-up to me would be to remove the engine from the bike, make a jig to bolt the engine into and a lathe cutting tool. I'm wonder if you could even take the whole engine to a machine shop and say "take this small section of shaft after the clutch down from 15mm to 13mm" they could probably do it. It would be worth it because the trade off is smoothness, quietness, no maintenance. Worth the effort.
     
  9. The_Aleman

    The_Aleman New Member

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    #9 The_Aleman, Mar 4, 2012
    Last edited: Mar 14, 2015
  10. cobrafreak

    cobrafreak New Member

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    I ordered them from VXB bearing. They are listed under the size, which is "13x20x4" sealed bearing.
     
  11. fredgold52

    fredgold52 New Member

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    I agree completely. And that's part of what makes these bikes so much fun. They are a great test of a person's shade tree engineering skills.

    This idea sounds great, I'm gonna try it.

    dance1
     
  12. hmiwb

    hmiwb New Member

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    Please keep us updated if you do try it Aleman. Cobrafreak may be onto something really good here.
     
  13. MotoMagz

    MotoMagz New Member

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    I've been thinking of adding a needle bearing and giving that a try.Either way I think most of us would feel better opening the clutch bell by a mm then dealing with the engine shaft.So maybe instead use a (6) 15x21x4 bearings or 16x21x4. I may try a sigle needle bearing which is 15x21x22mm.Just putting this out there.
     
  14. The_Aleman

    The_Aleman New Member

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    #14 The_Aleman, Mar 5, 2012
    Last edited: Mar 14, 2015
  15. cobrafreak

    cobrafreak New Member

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    To use needle bearings you need to weld up the woodruf key slot and grind or it will destroy the needle bearings. Unless you sleeve it, but it may be too large then.
     
  16. MotoMagz

    MotoMagz New Member

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  17. cobrafreak

    cobrafreak New Member

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    No, it's not sleeved. It has an outer race only, not an inner one. When the needle bearings spin around on the shaft they are going to get abused and the keyed shaft and fail unless you can fill the keyed groove for the woodruff key in solid with weld and grind it perfectly. The outside diameter of the bearing needs to be 20mm or you will need to make the hole larger in the clutch bell, and again, it will need to be precise. Personally I think needle bearings would be better in this application but they require perfect races, which is why I decided not to go this way. With the sealed cartridge bearings I chose they already have the inner and outer race. You just need to make a reasonable tight and strait fit and it will work a TON better than an oil-lite bushing. But alas, there are many ways to skin a pig. I just chose one way.
     
  18. The_Aleman

    The_Aleman New Member

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    #18 The_Aleman, Mar 5, 2012
    Last edited: Mar 14, 2015
  19. cobrafreak

    cobrafreak New Member

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    It's really quiet other than the engine idle. Not totally gone but 90% is.
     
  20. The_Aleman

    The_Aleman New Member

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    #20 The_Aleman, Mar 6, 2012
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