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Post by 90GTVert on Jul 26, 2009 9:01:17 GMT -5
I have seen Enviromoto and others comment that the 80+cc kits cause reliability issues but I haven't seen people posting that their 80+cc kits are having problems. Is this just a theory that the additional stress of the 50+mm kits is too much for the bearings or is it a proven fact? Has anyone upgraded crankshaft bearings and then used one with proven better results?
It's a different setup, but my 2 strokes both use the same 6204 stock bearings (though I do have ceramics for the engine I'm building) and they are holding up fine with a 54mm piston. The 90cc came stock with the same bearings as the 49cc version but using a 52mm piston and a larger crank.
After seeing the power (or lack of) that these engines put out, even with a 72cc kit, I'm thinking an 80+cc kit may be somewhere in my future. Not right away though.
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Post by erictheviking666 on Jul 26, 2009 16:12:25 GMT -5
Yeah, I've always heard that too. But I don't know of anyone that I've heard of that has had a failure on a daily driven Scoot. You brought up a good question because I can't remember a thread on any other Forum about crankshaft bearing failure due too an 80+cc kit.
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Post by 90GTVert on Jul 27, 2009 4:49:41 GMT -5
There is a guy around me that rides a lot with one. He's supposed to talk to me about doing some work to it, so if I can't get an answer I suppose I'll see how many miles he's racked up so far.
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Post by erictheviking666 on Jul 27, 2009 12:35:16 GMT -5
Yeah cool. I've been thinking about an 80cc kit or just buying the complete engine with the 80cc kit already installed.
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Post by 2strokd on Jul 28, 2009 7:45:22 GMT -5
I guess its more job security just like you can build a 400HP Stang with the stock short block or go with a good balanced and forged bottom end, they both can blow but one is built for the abuse.
Good question, you thinking about it?
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Post by 90GTVert on Jul 28, 2009 8:23:19 GMT -5
Definitely considering it down the road a bit.
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Post by 2strokd on Jul 28, 2009 8:25:27 GMT -5
Good to ponder ahead thats fer sure.
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Post by 90GTVert on Jul 28, 2009 8:37:40 GMT -5
As long as I've been around a few forums, I really haven't seen anyone give any evidence that 50+mm bore kits are killing bearings (mind you I have never spent tons of time in the 4 strke sections). That's why I'm posing my question early. I do think the greater mass of the piston and the additional force applied with have to reduce longevity, but how much. Are we talking about issues in 2,000 miles or 10,000 miles? I know you can't always predict this stuff, but I would think someone should have some idea. If it's really that bad, there should be a lot of people on ScootDawg or other forums asking how to replace bearings or why their 85cc blew up. I tried doing a little Google searching and searching on a few forums, but I've came up with nothing so far.
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Post by Enviromoto on Jul 28, 2009 15:19:07 GMT -5
I have a couple on the shelf that have failed due to 82cc kits. One was Indy50 from scootdawg his bearings are shot after 1500 miles.
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Post by 90GTVert on Jul 28, 2009 15:57:24 GMT -5
Is that 1500 miles of total engine life or 1500 miles of the big bore? Obviously if the engine had _,000 miles on it prior to the 82cc kit the results are only worth so much. What type of failures are we talking about here BTW? Meaning, are the bearings out of spec now and getting bad vibrations so they need to be replaced, or is it goodbye engine type of stuff that's happening? Since you've been around a lot fo 72cc kits, any clue how much they reduce bearing life on the little GY6?
I don't even know what type of power they really make to know how much risk it's worth either. The 80+cc that was in the group of scooters I raced with my Triton made nice low end torque for taking off and kept with the stock 2 strokes O.K. but he was nowhere near the 70cc 2 stroke and I. He had the BBK, 150cc carb, 150cc intake, cam, air filter, and exhaust. Not sure exactly what's done to the transmission. Changing bearings every 2,000 miles for mild 70cc 2 stroke power doesn't sound like the best idea.
It's just so tempting since so far I've managed 39MPH. I'm sure it's got 40 MPH in it with more tuning and ideal conditions, but that's still well shy of stock for my 49cc Triton. Seems like there's gear left, but not power.
While you're here, are there upgear kits available for the 139QMB?
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Post by 2strokd on Jul 28, 2009 20:14:00 GMT -5
Almost 40, holy wow, hold on tight! lol j/k man...
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Post by 90GTVert on Jul 28, 2009 20:22:32 GMT -5
If I was about 100lbs lighter it might be more impressive. Then again, I was the same weight with my stock 2 stroke.
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Post by Enviromoto on Jul 29, 2009 7:34:34 GMT -5
That was total engine life and the crank is just flopping around in the case. I have seen it happen on the 72cc kits as well but Troll beats the dog snot out of them so thats why. I do not have any sources for up gears for the QMB at this time or know of anyone that makes them. My whole thought process on the 72cc stuff is, keep it safe and dependable while offering a mild performance boost. I could easily sell a 85cc kit with all the fixins but that leaves me open to a lot of liability.
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Post by 2strokd on Jul 29, 2009 8:20:17 GMT -5
Not if you keep that one for certain "special" customers, but you probably couldnt make a whole lot that way.?.
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Post by 90GTVert on Jul 29, 2009 9:05:53 GMT -5
Why couldn't you sell 85cc kits with a disclaimer... no warranty, recommended for racing only, etc... ? It doesn't sound like I'll be adding one just yet, so it doesn't matter much to me. People are buying them though, whether it's from you or eBay or whatever.
Next question, has anyone actually upgraded bearings to see if they'll hold up or is that just a theory? I would imagine quality bearings would last longer, but if it's say 2,000 miles instead of 1,500 miles it would still really have to be worth it to someone to go fast (relatively) with a 139QMB.
Another question : Has anyone tried balancing a 139QMB's crank to the weight of the larger piston?
I think it's possible to have an 80+cc engine that can be reliable for much longer than 1,500 miles. At this point I'm just pondering out of curiousity though. It would take a pretty good budget to go ceramic bearings, balanced rotating assembly, etc... and once you do all of that you probably need to spend plenty of time and/or money on the top end to really make it pay off.
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