T20 Fragged Output Sprocket

[jpswift1]

6x6World member Amphibiousdrew came up today so we could do some work on the T-20 out of his 1979 Attex Tomahawk. We also made a trip up to Recreatives for some parts and a BS session. We were trying to figure out why one side of the T-20 wasn't working, in reverse or forward. After a good bit of troubleshooting we found out that the previous owner that "rebuilt" the transmission put in the wrong main input shaft bearing. There was a good bit of slop in there because of it, and then recently all that slop caused the output sprocket to shark-fin over really badly AND completely snap off of the rest of the shaft. I'll be heading up to Recreatives for some new parts and Drew and his Tomahawk will be back on the trails next weekend.

[LarryW]

That sucks but sounds like fun! Im sure it will be up and running in no time!

[jpswift1]

That sucks but sounds like fun! Im sure it will be up and running in no time!

It'll certainly be up and running without any issues, Larry. It was a good day though. I think this needs to be a lesson to people that replace their main bearings on their T-20s. The T-20 will only accept bearings directly from Recreatives. There are NO other options. Many members, including Whipper-ag and myself have looked all over the place for replacements, but never found any. The bearings from Reacreatives are manufactured specifically for them, with a certain amount of material machined off of the bearing race so that they fit properly in the T-20. If you use the incorrect bearing to save a buck or two like whoever "rebuilt" this transmission did, this is what will eventually happen. Damn townies!

[LarryW]

Good to know JP, I will keep that in mind if I ever have to redo my t-20.

[jpswift1]

Glad to point that out. You can't see it as much in the pictures, but that output sprocket looks like a saw blade the teeth on it are so bent. Just looking at them you would have thought Drew was running some huge liquid cooled 80+HP triple behind that T-20 and dropping the laterals at 5000 RPMs. But nope, just a torquey Tecumseh (and some townie that owned it before him that rebuilt the transmission wrong).

[amphibious drew]

I hate townies that rebuild T20's wrong. Good thing I know people. Thanks JPswift.

[jpswift1]

I hate townies that rebuild T20's wrong. Good thing I know people. Thanks JPswift.

Me too, they're so worthless and they shouldn't be allowed around any kind of AATV. Glad I could help you out, Drew. At least all they did was rebuild the T-20 wrong......I'm just happy that they didn't paint that nice Tomahawk of yours camo and put an 8 track player in it. And thanks for the tracks, Drew! You'll most likely be back on the trails next weekend! Make sure you get some good video footage. I love those Tomahawks......so bulletproof, and the absolute best trail machine Attex ever built. I found this one on Youtube and just had to post it. I don't know whose it is but it's so cool. Just listen to that torquey thump coming from that machine. I want one!

[thebuggyman1]

Hey JP, What ae the dimensions on that bearing? I recently learned a trick from a buddy that builds 8-900 hp sprint car motors for a living. My jlo in the sears had a bad main on the flywheel side just before Ash. The case half came off without heat, typically meaning the motor was junk. My buddy gave me a loctite product that is supposed to displace up to ten thousandths (.010) of an inch. The drawback is it will not come back apart without heat. And I was up and running for ashtabula.

[Don]

There's a guy down in Florida that puts a slightly oversized (OD) bearing on a fine, water-cooled grinding wheel until the bearing will fit the case. I've always thought that it was easier just to bite my lip and buy a bearing from RI even though I consider them a bit overpriced. Has anyone ever bored out the side case a few thousandths in order to accept a standard bearing? That seems a little more logical to me.

[thebuggyman1]

You could always reinforce the case on the outside, but all that work.... How overpriced can R.I. be? What do they want $25 for a $12 bearing?.....sounds like its worh it to me.

[mark m.]

There's a guy down in Florida that puts a slightly oversized (OD) bearing on a fine, water-cooled grinding wheel until the bearing will fit the case. I've always thought that it was easier just to bite my lip and buy a bearing from RI even though I consider them a bit overpriced. Has anyone ever bored out the side case a few thousandths in order to accept a standard bearing? That seems a little more logical to me.

Don. It's not the O.D. that is the problem. It's the width. A very standard and cheap bearing with the correct I.D. and O.D. (35mm x 72mm) is a #6207. The problem is it is 17mm wide. the T20 bearings need a 15mm wide bearing. My local bearing supplier (Buffalo Bearings) tried to source those narrow bearings but to no avail.

I suppose you could buy the 6207 and surface grind 1mm of both sides but that is not practical. So we T20 owners are held hostage by RI

[Don]

Thanks, Mark; I learned something! I guess it's never too late.

He'd been working on T20s for a lot longer than me so I accepted the story as gospel. I wonder why the other bearings in the T20 are standard and they went out of their way to be the sole source for the mains? I've bought over-the-counter planetary gear bearings and old-style T20 bearings for the supported shaft, but always went to RI when I needed the output shaft bearings.

[lewis]

I have a rep that works for Applied Technology that is all over bearings. He has done special bearings for us at the plant before. Either Rec is having these 6207 bearings special made or they also are having them ground to match the case thus the higher cost for the bearing. I am now wondering which is the case. I will check with the bearing rep, but we would not want to put our only source of T-20 parts and bearings in a bind by outsourcing, this may not be good. Like Don said sometimes it is just better to bite your lip and pay the price because they are on the shelf.

[Mike]

... Either Rec is having these 6207 bearings special made or they also are having them ground to match the case thus the higher cost for the bearing. I am now wondering which is the case....

They are having them ground down. If you look at a new bearing from them you can tell where it has been modified. Here is a picture I stole from our How to rebuild your T20 article. You can see what appears to be scoring left from the grinder:

[thebuggyman1]

I think I would rather mill .080" off the case. Providing it wouldn't weaken it or ceate a clearance issue. I have never had one apart to see.