Tav30 backplate, broken weld, questions..

[MikeBear]

I have a Tav30 with the steel stamped backplate installed on my Kenbar MB-6 minibike. It has a Tecumseh 6hp OHV engine. #41 type chain, wheel sprocket is probably 72 tooth though I haven't counted it yet. Looks like the same one on the Manco Thunderbird. Almost the same size as my 480/400x8" rear tire.. Which probably isn't that good back on trails covered with branches, fallen trees, sticks, all sorts of crap. Easy for something to cause damage to it.

Anyway, I was back on the state land today, rode probably around 12 miles just fine, went up about 1/4 mile up a path I haven't gone on before, and threw the chain. It jammed TIGHT in between the sprocket and the frame. You couldn't even turn the wheel, and this bike weighs 175lbs, and I was 1 mile into the wilderness from the nearest paved road... NO TOOLS with me.. (Yeah, dumber all the time, right?) NO WAY was I going to leave my bike, and walk out! Maybe I couldn't pick it up and get it out, but I bet you a dollar, it wouldn't be there when I got back...

Anyway, thank God for deer hunters! I had gone by an old deer blind that was abandoned. In fact, the chain threw almost in front of it. First blind I've ever seen back there. I went to it, and looked inside to see if there was anything to help. Well, lookie here! 2 chunks of 2x4, and 2 chunks of 4x4 wood! Just the sort of things to help... I used the 4x4's under the bike, to prop the rear wheel off the ground. I was able to use the 2x4 pieces, to wedge the chain up a little bit, which allowed me to pull it back up on the sprocket, and feed it back around.

I think I drove over a small tree, which wedged in between the sprocket and chain, and that's what pulled it off. It is not really loose, but the chain might be damaged or stretched a little now. The previous owner said he replaced it this year with one from the local TSC store, so I don't know the original quality of the chain. Anyway, I slowly drove/limped back home, (2 miles, 1 mile to the paved road, and 1 mile to my house) Oh yeah, I put the wood pieces back in the blind before leaving, never know when they might come in handy again.....

Ok, after getting home and looking things over, I noticed that there is a cracked weld on the back of the tav plate, where the driven shaft runs on the bearings. So, I'm going to have to remove the plate, and get that re-welded. Since I have to do that anyway, can anybody tell me exactly what they have done to strengthen the stamped plate? I keep reading here and there about "welding some pieces of "L" metal" on it, but can't find a posting that explains exactly where and how they did this?

I did see a post where the person made a second plate, and mounted it to the engine cover bolts, to help support that bearing shaft that sticks out.

Anyway, I got out safe, and learned some lessons:

1: Carry some tools!
2: Lube your chain more frequently, and check for possible damage from previous riding!

Any advice on fixing this, and improving it, is welcome! I'm also going to replace this chain, as I won't trust it now.

 

[MikeBear]

I have a Tav30 with the steel stamped backplate installed on my Kenbar MB-6 minibike. It has a Tecumseh 6hp OHV engine. #41 type chain, wheel sprocket is probably 72 tooth though I haven't counted it yet. Looks like the same one on the Manco Thunderbird. Almost the same size as my 480/400x8" rear tire.. Which probably isn't that good back on trails covered with branches, fallen trees, sticks, all sorts of crap. Easy for something to cause damage to it.

Anyway, I was back on the state land today, rode probably around 12 miles just fine, went up about 1/4 mile up a path I haven't gone on before, and threw the chain. It jammed TIGHT in between the sprocket and the frame. You couldn't even turn the wheel, and this bike weighs 175lbs, and I was 1 mile into the wilderness from the nearest paved road... NO TOOLS with me.. (Yeah, dumber all the time, right?) NO WAY was I going to leave my bike, and walk out! Maybe I couldn't pick it up and get it out, but I bet you a dollar, it wouldn't be there when I got back...

Anyway, thank God for deer hunters! I had gone by an old deer blind that was abandoned. In fact, the chain threw almost in front of it. First blind I've ever seen back there. I went to it, and looked inside to see if there was anything to help. Well, lookie here! 2 chunks of 2x4, and 2 chunks of 4x4 wood! Just the sort of things to help... I used the 4x4's under the bike, to prop the rear wheel off the ground. I was able to use the 2x4 pieces, to wedge the chain up a little bit, which allowed me to pull it back up on the sprocket, and feed it back around.

I think I drove over a small tree, which wedged in between the sprocket and chain, and that's what pulled it off. It is not really loose, but the chain might be damaged or stretched a little now. The previous owner said he replaced it this year with one from the local TSC store, so I don't know the original quality of the chain. Anyway, I slowly drove/limped back home, (2 miles, 1 mile to the paved road, and 1 mile to my house) Oh yeah, I put the wood pieces back in the blind before leaving, never know when they might come in handy again.....

Ok, after getting home and looking things over, I noticed that there is a cracked weld on the back of the tav plate, where the driven shaft runs on the bearings. So, I'm going to have to remove the plate, and get that re-welded. Since I have to do that anyway, can anybody tell me exactly what they have done to strengthen the stamped plate? I keep reading here and there about "welding some pieces of "L" metal" on it, but can't find a posting that explains exactly where and how they did this?

I did see a post where the person made a second plate, and mounted it to the engine cover bolts, to help support that bearing shaft that sticks out.

Anyway, I got out safe, and learned some lessons:

1: Carry some tools!
2: Lube your chain more frequently, and check for possible damage from previous riding!

Any advice on fixing this, and improving it, is welcome! I'm also going to replace this chain, as I won't trust it now.

Ok, I removed the Tav 30 from the engine, to get it welded. There's 1 weld cracked for sure, and another one that looks "iffy". Oh, do the bearings have to be removed before welding? If so, how do you get them out?

I also counted the teeth on the rear sprocket: 80 teeth, not 72. It's a large one. I'm thinking about replacing this also, as it's worn. I'm not sure how much wear is safe. The chain is definitely stretched, and there's links here and there that want to "bunch up". So, bad or damaged chain for sure.

Anybody know the best #420 chain for purchasing, and a site I can buy it from? There's all sorts of it out there, and I don't want the junk Chinese stuff. It's 116 links, or just short of 5 ft. long.

 

[125ccCrazy]

not sure what you want to spend on chain but these are nice chains
DID 420V-120 O-RING CHAIN: eBay Motors (item 400111073107 end time Oct-19-10 14:23:30 PDT)

RENTHAL R1 R 1 420 Works Chain: 120 LINKS: eBay Motors (item 390246814944 end time Oct-30-10 13:24:56 PDT)

as far as the plate, if you cut some pieces of 1/8 or 3/16" plate in the shape of a triangle and weld them around the bearing tube that will stiffen it up alot...3 or 4 plates spaced evenly oround the tube will add alot of support...You can also make a bracket that will clamp around the tube and bolt to the engine somewhere will help keep the plate from flexing..

 

[jeep2003]

the bearings punch out. take a socket extention and go through each side to punch them out :thumbsup:

 

[george3]

best make sure its 420 not 40 chain. 420 wont fit on a 40 sprocket. sprocket is too fat. your chain should say on it the size.

 

[MikeBear]

best make sure its 420 not 40 chain. 420 wont fit on a 40 sprocket. sprocket is too fat. your chain should say on it the size.

The sprocket at the rear wheel is a 41, as it's too thin to be a 40, which 40 chain is much wider. The chain is a 420. I'm going to replace it with a good D.I.D. 420 chain. Previous owner used junky TSC Chinese crap chain. Also, 2 welds on the Tav cracked, and canted the driven pulley shaft slightly, and that contributed to the chain jumping off.

It's almost impossible to find a #41 80 tooth sprocket (at least, I haven't found a source as of yet) , so I'm not going to replace that right now. Since this is running a Tav 30, I'm not sure if it would be smart to downgrade the sprocket to say a 72 tooth, etc. I need torque and power for trail riding, more than I need to go faster than 36mph.

 

[Harleys Papa]

It's almost impossible to find a #41 80 tooth sprocket (at least, I haven't found a source as of yet) , so I'm not going to replace that right now. Since this is running a Tav 30, I'm not sure if it would be smart to downgrade the sprocket to say a 72 tooth, etc. I need torque and power for trail riding, more than I need to go faster than 36mph.

Here ya go Mike Motion Industries - Parametric Details - 41A80 PLATE SPROCKET 103245 You will have to open up the center bore and drill mounting holes

 

[fixit]

Let me know if there is something I can do to help. I'm in Highland Michigan and the garage is fairly well equiped, small lathe, mig & tig welder, chop saw etc.
Mike

 

[MikeBear]

Let me know if there is something I can do to help. I'm in Highland Michigan and the garage is fairly well equiped, small lathe, mig & tig welder, chop saw etc.
Mike

Thanks for the offer, I appreciate it! However, I'm about 106 miles north from you at present. I wish you lived down the road!! :laugh:

I hope to build a new triple-tree, and replace my front springer end, with hydraulic shocks from a Yamaha Pw80 this winter. Your garage would make it a little easier.

I found a local welder, and got my Tav 30, and a crack on my rear fender re-welded for $20 total. He did a fantastic job, and it looks really good. You should see his Miller Tig welder, looks like it's worth like $20,000. They do welding, and also build trailers for sale. I remounted it on my engine, and I'm waiting for my new chain to arrive. It's supposed to be here Friday.

 

[MikeBear]

Here ya go Mike Motion Industries - Parametric Details - 41A80 PLATE SPROCKET 103245 You will have to open up the center bore and drill mounting holes

Thanks for the link! I looked around their site, but it's really very confusing, and couldn't find this one.

I just placed the order. It's probably best I replace the sprocket, and even with shipping, this sprocket is cheaper than some of the others that weren't even 80 tooth like I need.

 

[hopper336]

Hey Mike,

I imagine you've long since had a new sprocket, being this is an older post. I changed out my sprocket years ago. I believe I'm running a 60 tooth now, but I'd have to count to assure myself. It still has plenty of low end power for climbing hills and trail riding. If you really like the 80 tooth sprocket, I'll sell you mine that I took off, if you'd like a backup. I believe I've still got it somewhere.

 

[MikeBear]

Hey Mike,

I imagine you've long since had a new sprocket, being this is an older post. I changed out my sprocket years ago. I believe I'm running a 60 tooth now, but I'd have to count to assure myself. It still has plenty of low end power for climbing hills and trail riding. If you really like the 80 tooth sprocket, I'll sell you mine that I took off, if you'd like a backup. I believe I've still got it somewhere.

Nope, I replaced it a long time ago. Thanks for the offer though!