Idler Pulley

[Mike Sal]

I pulled the idler pully & bracket from the box-o-parts to clean & re-paint (forgot to send the bracket to the powdercoater), & when taking the pulley off, I noticed that something foul was afoot.  Half of the original mounting bolt has been turned down to 3/8 diameter & then threaded again to accept a pulley with a 3/8 hole thru it.  The pulley is the 2pc sheetmetal type & is 2.75 diameter.  Is this the right size pulley, or somthing the previous owner cobbled on?
Mike Sal

[Ricks]

Mike, here is a couple of pictures of what the mounting bolt and spacer looks like.  The bearing has a 3/8" hole.  The bolt is 5/16" x 2".  The spacer is 1/2" x 15/16", then necks down to 3/8" x 3/8", for a total overall length of 1 5/16".  

Rick

[Mike Sal]

Ya, that hardware is nothing like mine.  I think the guy got a pulley from a lawnmower & adapted the bolt for it to fit.  You can tell the bolt was turned down on a lathe & when he tapped the new smaller threads, his tap was a little crooked.

I guess I'll call way tomorrow to see what's up.
Mike Sal

[Ricks]

That doesn't look like any pulley that I have seen.  I think you are right, a previous owner cobbled something together.

Here is a picture of one installed on my truck.  It is the same as the 2 wheel bikes except I made the spacer a little shorter to fit.

Rick

[Mike Sal]

The construction of my pulley is the same as the late model pulley shown in the catalog (p/n 2242), but I think the correct one should have a larger bearing & I don't know what the correct diameter is supposed to be.  The hardware shown in your first pic's are trhe earlier style parts.
Mike Sal 

[bill marcum]

Hey guys,
I need a little in put. My bike will have a GC 160 honda engine. I am planing the drive train. I was going to use a 1 to 1 ratio from the engine to the jackshaft. what I would like to know is what size pullie to use to drive the back wheel from the jackshaft. I would like to be able to do 45 mph every once in a while. most of the time 35 around town. Bill Marcum

[Ricks]

That's a good question. I wish BJM would get on here and answer that for us.  Looking at his setup, it appears he is running about 1-1 to the jack shaft, and around a 3" pulley.  Are you going to use a chain clutch like BJM or a pulley clutch?

Rick

[bill marcum]

Rick , I already had a centrifical clutch for when my boys were into mini bikes that I am going to use. got the jack shaft and the chain gear and the adjustable bearing mounts and bearing from a local gocart dealer. He said that I need to use racing chain because the regular chain might kink? Will buy the chain later. Wating for Wayne to answer the phone, need to order some parts from him. I got to lean how to have patience. Bill Marcum

[kartjockey]

Let's try this Bill. Let's assume your engine will hit max RPM at 3600. Now take the jack shaft pulley and divide it into the wheel pulley. For easy math purposes lets say the wheel pulley is 18" and the jackshaft pulley is 3". 18/3=6.  This puts you at a 6:1 ratio to the wheel assuming you stick with a 1:1 ratio from the engine to the jackshaft. With this in mind your wheel will now turn 1/6 the rpm of the engine. That being 3600/6=600. So your wheel turns 600 revs per minute. Now we need to know the circumference of your rear wheel. I measured my Servi to be about 27"(you will want to be accurate at this)  Circumference is 3.1415 X the dia. So 3.1415 X 27= 84.8". So each time the wheel goes around the bike moves 84.8" down the road. And we know that at full throttle your wheel will turn 600 times around per minute. So take 600 X 84.8" which = 50880". Convert this to feet now. 50880/12= 4240ft. We know a mile a minute is 60mph. So we are traveling less than that because there are 5280 feet in a mile. If we take 4240 and divide it into 5280 it will give us a percentage. 4240/5280= 80% now just times 80% by 60(mph).  .80 X 60= 48.  So, mathematically, you will be going 48 mph at full throttle. Plug in your own numbers and give it a try.

[bill marcum]

Kartjockey,
Sounds correct I will have to sit down and get the numbers together and figure it out. Are you a math teacher or an enginer. Sounds like a home work problem from high school 43 years ago. Wish me luck . Hope I get an A. Thanks for the input. Bill Marcum

[Mike Sal]

This is the same way the model T guys figure their speed.  They only rev to about 800 or so rpm.

I read somewhere what the ratio's were between "low" gear & "hi" gear on a simplex, but can't find it now.  I thought they even mentioned what rpm the engine topped out at, but again, can't remember where I read it.

I think 1 to 1 may be too tall, but don't know what torque your engine is rated at.
Mike Sal

[Ricks]

The reason I used a Torque Convertor on my 3 wheel truck instead of a clutch is you have gearing to help get you going.  Low gear on a convertor is 3-1, and can get to about .90-1 in high gear. My outside clutches have 3.2" pulleys on them, so this should see a speed of 45 mph without much problem. 

BJM told me he has hit 55 mph on his GC160 conversion. I wonder what the acceleration was like.  I remember when we converted a kart from clutch to torque convertor, it was like night and day.

Rick

[bill marcum]

Rick
I might try a torque converter after I get it all together and see how it runs. This year just get it running and next winter try some up grades and fine tuning. Bill Marcum

[mywaymfg]

When I was a kid I had a mini bike named a buffalo had a 5hp tecumsa comet torque converter and tires like a 3wheeler  trail rode pretty rough terrain plenty of torque not very fast though never seen another buffalo.

[Mike Sal]

Talked to Wayne again this morning & he said he doesn't have the exact late model pulleys either, he gets some from lawnmower shops & modifies them by adding spacers & bushings.  He agreed with me that the bearing in mine was marginal in size for long term riding.   I'll check the local farm supply place tomorrow.
Mike Sal