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4 Stroke Bicycle Engines & Kits 4 stroke engine kits are great if you want reliability or do not want to mix your oil and gas. Learn from each other how to get the most out of your 4 stroke bicycle engine

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Old 03-03-2012, 02:12 AM
cobrafreak cobrafreak is offline
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Default 4G T drive bearing conversion

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.
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Old 03-03-2012, 02:39 AM
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The_Aleman The_Aleman is offline
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Default Re: 4G T drive bearing conversion

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Old 03-03-2012, 03:27 AM
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Wink Re: 4G T drive bearing conversion

Quote:
Originally Posted by cobrafreak View Post
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.
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

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Old 03-03-2012, 11:49 AM
cobrafreak cobrafreak is offline
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Default Re: 4G T drive bearing conversion

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.


Last edited by cobrafreak; 03-03-2012 at 01:08 PM.
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Old 03-03-2012, 11:08 PM
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Default Re: 4G T drive bearing conversion

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!
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Old 03-04-2012, 10:35 AM
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Default Re: 4G T drive bearing conversion

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).
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Old 03-04-2012, 10:48 AM
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Default Re: 4G T drive bearing conversion

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.
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Old 03-04-2012, 01:15 PM
cobrafreak cobrafreak is offline
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Default Re: 4G T drive bearing conversion

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.
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Old 03-04-2012, 01:47 PM
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Default Re: 4G T drive bearing conversion

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Last edited by The_Aleman; 03-14-2015 at 08:43 AM.
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Old 03-04-2012, 03:24 PM
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Default Re: 4G T drive bearing conversion

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