Author Topic: Reduction unit question  (Read 5930 times)

BuggeredBuggy

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Reduction unit question
« on: June 03, 2012, 04:07:39 PM »
Hi everyone,
I just bought an old Odyssey that was not running. I managed to get the engine running, but the clutch grenaded and took the crankshaft with it (no belt was on at the time). I bought a new 4 stroke 390cc motor to swap in ($100 brand new, could not go wrong!), and I was planning to convert it to a chain/sproket. While trying to figure out the optimal gear ratio, the first thing I had to do was check the reduction unit gear ratio. I put it on jack stands and turned the wheels to count the revolutions of the input shaft. Here were my (non-scientific) results:
For every 1 turn of the input shaft, the tires will spin approx. 9.25 times.
This seems backwards to me - I thought it was supposed to reduce it by 9.5, not increase it. Am I mistaken?
Thanks!

LiveWire

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Re: Reduction unit question
« Reply #1 on: June 03, 2012, 04:47:11 PM »
You are not supposed to rev the engine without the belt on as it can cause the clutch to explode.

I would get a clutch to fit the crank shaft of the engine you bought and leave everything else intact.

As far as your specific question, can you clarify how you counted? You said you turned the tires and counted the input shaft turning. One turn of the tires should have turned the input shaft the 9+ times.

BuggeredBuggy

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Re: Reduction unit question
« Reply #2 on: June 03, 2012, 05:11:45 PM »
Hi LiveWire,
Thanks for the help!
I would look at getting a replacement clutch, but the crankshaft had gone with it as well. I would have to rebuild the engine and that will cost alot of money for a little toy. I did not intend to rev the engine, it decided to do that on it's own (or as a result of my ignorance to check if the throttle was working correctly!)
To check the ratio, I put the buggy up on jack stands and rotated the tire. I had to turn the tire a total of 9.25 times in order to get 1 complete rotation of the input shaft on the gear reduction unit. I think I calculated a top speed of 200 MPH plus if I used the biggest sproket available to me (60 tooth from a 14 tooth sproket on the clutch). Of course I would have to be at the top of a big hill before I ever got it moving at all.
So I can deduce from your reply that something is very backwards with my unit. The next question I guess, is whether someone can put the gears in the wrong way? Judging by the quality of work that was already performed on the unit, if it was possible then they probably did.
Thanks!

BuggeredBuggy

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Re: Reduction unit question
« Reply #3 on: June 03, 2012, 05:13:36 PM »
LiveWire,
Sorry, I misread a bit - I have my eyes open for a clutch to fit the engine I bought. I thoguth you meant put a new clutch on the old engine, as technically I just bought that one too!

Regardless, sounds like the reduction unit is now and increaser unit?

LiveWire

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Re: Reduction unit question
« Reply #4 on: June 03, 2012, 07:49:00 PM »
Yes, something is wrong. Most of my knowledge is with the 350s. I have only seen the exploded view of the 250 box. You might as well pull it apart if you were already looking to not use it. i should be able to get you a clutch. I am guessing it is a 1" keyed shaft.

BuggeredBuggy

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Re: Reduction unit question
« Reply #5 on: June 04, 2012, 06:04:01 AM »
Yes, 1" keyed shaft. This is the engine: http://www.princessauto.com/pal/product/8129553/Horizontal/13-HP-389cc-Horizontal-Gas-Engine-with-Electric-Start

One thing I like about the idea of going to a sprocket - all of the parts I will need to replace sprockets, chains, engine parts, clutch, ect. will all be at this Princess Auto store. Trade off is dealing with a fixed gear ratio, but this is more for the GF anyways, and she doesn't plan on really tearing it up.
Also, the driven clutch looks funny to me - the spring looks all bound up or something, I would have expected it to sit in there like a nice even coil, but it looks like it is pushed off to one side. I will have to take a closer look at that as well before I chew through 8 belts. I would be interested to know what a clutch will run me regardless!

BuggeredBuggy

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Re: Reduction unit question
« Reply #6 on: June 04, 2012, 06:21:25 AM »
I certainly plan on using the reducer, as it will increase my clearance over a chain directly to the axle. Plus, it is easier to put the sprocket onto the reducer shaft than try to make one fit in the splines on the axle. I will have to pull it apart anyways and put it back the way it should be, that will allow me to inspect it and replace the chain if necessary.

LiveWire

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Re: Reduction unit question
« Reply #7 on: June 04, 2012, 08:35:06 AM »
I'll look up a clutch for it.

BuggeredBuggy

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Re: Reduction unit question
« Reply #8 on: June 05, 2012, 07:34:54 AM »

LiveWire

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Re: Reduction unit question
« Reply #9 on: June 06, 2012, 04:47:49 AM »
Personally, I would use an actual Comet and not the Chinese knock off.

whammo77

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Re: Reduction unit question
« Reply #10 on: June 06, 2012, 04:17:18 PM »
You are not supposed to rev the engine without the belt on as it can cause the clutch to explode.

I would get a clutch to fit the crank shaft of the engine you bought and leave everything else intact.


I would have to agree... I would rather keep the original motor. The clutch isn't THAT expensive, and if you already got the engine running anyway.........

Just sayin.....

BUT, if you insist on going ahead with the swap, I might be interested in your old engine and parts  ;)