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Post by crackmastick on Feb 28, 2021 11:27:10 GMT -5
What's an acceptable amount of pressure venting from the crank case? I've got a 50cc tao tao that seems a little sluggish and weak in acceleration. I went to a cone airfilter and ran the breather line to a small filter to vent. It feels like a pretty steady and strong flow at idle. I'm wondering if the piston rings are failing.
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Post by jbjhillbilly on Feb 28, 2021 12:03:35 GMT -5
Have you check your valve lash?
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Post by mikehailwood on Feb 28, 2021 12:50:33 GMT -5
And have you checked your compression?
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Post by crackmastick on Feb 28, 2021 13:16:36 GMT -5
Valves are set to .004 haven't checked compression yet. I don't have a tester yet.
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Post by crackmastick on Feb 28, 2021 13:19:23 GMT -5
I know a compression check will tell the story. I was just wondering if there is always alot of venting going on from the crankcase and why?
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Post by mikehailwood on Feb 28, 2021 18:04:06 GMT -5
I'm hoping a real mechanic will chime in because I am not one. However, I can tell you an experience I had a long time ago. I decided to install new rings in a 1-cyl motor but I did not hone the cylinder walls. All kinds of oil would blow back out of the crankcase. Rings couldn't seat properly whether the piston was going up or down. I didn't check compression but with the rings not seating I expect compression would have been bad. And I would expect that with really worn out rings the same thing could happen. But again, I'm no mechanic and I hope a real mechanic responds.
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Post by GrumpyUnk on Mar 1, 2021 11:58:58 GMT -5
The pressure in the crankcase should actually fluctuate as the piston moves up and down.... displacing ~50cc on each stroke.... in BOTH directions. That's a bit of pumping. You should feel a 'flutter' at the vent tube on the cam/rocker cover. If you have a catch can or feed the tube output to the air cleaner, you may likely find a slight film of oil. It should not really squirt droplets. If you fit a loooonnnngggg bit of tubing, it can act as a 'buffer' accepting 50cc of air, and giving it back to the crankcase as it desires. It would then not vent anything unless it is pumping stuff out. tom
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Post by crackmastick on Mar 2, 2021 22:17:57 GMT -5
120 psi on the compression test. Checked the valve lash again at .004. got the idle screw 3 1/2 turns out. 85 main jet with the needle set at halfway notch. Cone Intake and "performance" exhaust. The jet and intake/exhaust are newer mods with unnoticeable performance gains. The scoot just doesn't seem to have any "umphf" when it's going uphill or into the wind. With a tailwind it'll rev out and do 45 to 50.
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Post by crackmastick on Mar 2, 2021 22:20:48 GMT -5
Recently opened up the variator and found some flat spots on the rollers. Also some metal wearing out on the edge of the roller ramps on 3 of the ramos in alternating position. The ramp edge going to the center was shaved down to a sharp edge. I replaced the rollers with some Dr.pulley 5g sliders.
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Post by FrankenMech on Mar 3, 2021 0:21:20 GMT -5
There is always leakage past the rings and through the ring gaps. If the crankcase is not vented it will blow the seals. There is no acceptable pressure, the vent should be clear and unobstructed. Sounds like a new variator is in order along with general maintenance of the CVT system. Find a service manual for your scoot.
A 50cc 4T will always be sluggish. When you changed to a cone filter did you re-jet the carb?
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Post by crackmastick on Mar 3, 2021 1:02:47 GMT -5
Yes went up to a 85 jet from a 78. I did order a new variator today. I'll get some pics of the old one when I open it back up for the swap.
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Post by GrumpyUnk on Mar 3, 2021 8:35:24 GMT -5
If you are getting 45-50 with a slight tailwind, you are doing better than a lot. Expecting more of such a tiny engine is asking a lot. IMO. I have a weed eater(string trimmer)that is a 30cc 2T. It may develop more hp... It may have a bit more displacement as I replaced the original piston/cylinder with new, and the factory part was larger. You can trade hill climbing for top speed. Or trade top speed for hill climbing. Which do you prefer? You can watch videos about tuning the CVT, including weights, belt size, clutch springs, variator shimming, and more to gain a smidge on acceleration or top speed. I am lazy, and will accept decent performance, realizing the limits imposed by the base machine. Actually, I have gone faster on one of these than I felt comfortable. Doing 45-50 is a bit more than I will feel comfortable with. The dynamics of handling and braking are somewhat 'Iffy' at those speeds in my opinion. I have other bikes that can easily surpass that, but they were designed for higher speeds and their handling and braking are superior. Know your limits... tom
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Post by crackmastick on Mar 3, 2021 23:34:38 GMT -5
Ho lee schit!.... Ok so I just test drove after installing a new variator and new belt. And OMG this scooter was ripping. Forgive my excitement. The sluggish acceleration is a thing of the past. Holy cow this was an improvement.
After inspecting things I found the old belt to be worn down to a smaller speck than stock (.767 inches) compared to the new belt (.800 inches). After that the variator ramos had some wear marks on the edges suggesting the cover plate was over locking and rubbing against the metal. The poles the slider plate rides up and down had some banana shape wear. I believe this was causing my mid grade sluggish acceleration. The plate was meeting resistance as it tried to slide past midway to max extension.
I've included some pictures worth reviewing. I am super pleased with the performance I got out of replacing these worn out parts. The RPMs instantly sound drastically higher and I think I'm finally feeling the intake/exhaust/jet upgrades.
I can now accelerate strongly through 35mph-40mph indicated. And tucking in the scoot allowed 50mph indicated. (There may be some error in the indicated speed) but that's what I see on the guage. I'll test that next with my phone.
I did like hearing what I read in the last post about knowing limits and the handling / braking limits of a small scooter like this. Made me think a bit. I'll remember these words. For now I'm happy with the results of a simple part swap. Looking forward to a good ride tomorrow. No longer lagging behind my scooter crew.
*** Maybe I won't have pictures, how do we add pictures? Haven't figured that out yet 😂
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Post by crackmastick on Mar 4, 2021 1:02:10 GMT -5
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Post by FrankenMech on Mar 4, 2021 1:20:38 GMT -5
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