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Gas Yamaha Gas Yamaha Golf Cars; G1 through "The Drive" and U-Max Utility Vehicles



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Old 05-08-2016, 04:06 PM   #1
twobore
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Location: central California
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Default G1 exhaust roar - how I reduced mine

My G1 engine had an ear splitting exhaust noise. I took a length of vinyl tubing and, using it like a stethoscope, listened around all the exhaust joints, muffler seams, etc I could reach. When I stuck it under the Exhaust flange between the engine and muffler (the exhaust pipe that contains the butterfly valve - Yamaha parts listís call this a Nut, Ring) - I not only found the source of my noisy exhaust but got hit with a blast of air from the hose to confirm it. I removed this part and discovered a sheet metal cup that is a press fit onto a cast stud on the exhaust flange (see arrow in Pic 1). The cup had vibrated loose and was allowing significant exhaust leakage , causing my Harley like exhaust roar. Inside the exhaust flange there is a circlip at the bottom of the shaft that rides on the seal held in place by the sheet metal cup (itís on top of the washer in Pic 2 - I added the bottom, larger washer). Unfortunately the circlip is smaller than the inner diameter of the shaft so when the cup loosened, it allowed the whole works (cup, seal, circlip) to drop until the butterfly valve bottomed out allowing massive exhaust leakage.

To solve this problem, I added the larger washer inside with the circlip riding on top of it (Pic 2). Now the assembly canít drop down even if the cup should loosen. But to make sure the cup doesínt drop, I added the two small washers at the bottom of the shaft (Pic 1 & 2).

I kept trying different washer combinations until everything fit snuggly without binding. I also replaced the two original M3 x .5 phillips head screws with stainless steel cap head (allen style) screws and locktited them in place.

This solution cut my exhaust noise in half. Iím a much happier camper.
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Old 05-09-2016, 07:18 AM   #2
Spicyunicorn
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Default Re: G1 exhaust roar - how I reduced mine

sounds like it would have been easier to just pull the valve out and weld the hole shut
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Old 05-09-2016, 11:55 AM   #3
twobore
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Default Re: G1 exhaust roar - how I reduced mine

Probably. But Iím trying to get everything back to factory spec before I diddle with any modifications. Essentially create a baseline to measure mods against.

The reason I posted this is because so many people have complained on these forums about their noisy G1 engine exhaust and I think, in some cases, their noise could be caused by this same problem.

The sheet metal cup, pressed onto the stud, in a high heat, high pressure, high vibration environment with the shaft in constant motion is a very poor design. It is practically designed to fail. When it vibrates loose, gravity drops the cup and the seal a quarter inch or so allowing a massive exhaust leak.

At any rate, itís simple to check this point with a length of tubing and then either eliminate it as a source of the loud exhaust, or, if it is leaking decide whether to fix it, as I did, weld it up as you suggest, tap it and plug it with a bolt, or use some other solution.
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Old 05-10-2016, 07:52 AM   #4
slonomo
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Default Re: G1 exhaust roar - how I reduced mine

Quote:
Originally Posted by twobore View Post

The sheet metal cup, pressed onto the stud, in a high heat, high pressure, high vibration environment with the shaft in constant motion is a very poor design. It is practically designed to fail.
It's good enough to last 20+ years! That part prob hasn't been touched since it was originally assembled in the 80's, not sure what year your cart is. Nice write up though. Yeah most of us remove that butterfly and weld it up. I think that valve didn't do anything but act like an exhaust brake when decelerating.
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Old 05-10-2016, 12:28 PM   #5
twobore
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Default Re: G1 exhaust roar - how I reduced mine

Actually, the butterfly valve is crucial to the G1ís oil delivery system (for those that are still using it). It modulates the intensity of the exhaust ďpuffsĒ that are fed back from the exhaust jet sensor to the oil pump diaphragm and is the reason the pump delivers 300:1 oil/gas ratio at low rpm increasing to 150:1 at high rpm.

Iíll probably remove mine eventually but Iím just anal retentive enough to enjoy the challenge of trying to get everything working first and go from there. Hey, itís a hobby, sort of.

Right now,as I mentioned on another post elsewhere in this forum, Iím running on a premix while directing my oil pump output into a container. Iíll compare this against the measured amount of fuel Iíve consumed and it should give me an average (somewhere around 200:1+, Iím guessing, since Iím usually running flat out). Iíll let the forum know how this works out.

BTW, my G1 is a 1983 model year.
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Old 05-12-2016, 04:27 PM   #6
slonomo
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Default Re: G1 exhaust roar - how I reduced mine

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Old 10-07-2018, 01:09 PM   #7
murrman26
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Default Re: G1 exhaust roar - how I reduced mine

Did the 79 motors come with exaust valve ?

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