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Old 07-15-2019, 02:21 AM
Mrmonk7663 Mrmonk7663 is offline
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Default 40 series for predator?

I am in need of a 40 series for a predator. The 44c Magnum comes in 3/4 but it is reccomended for 5k max rpm. That will not work. Since that is off the table I need a Comet 40. They only come in 1. The predator has a 3/4 shaft.

How are yall running these on the predator? Are you using the adapter sleeves that are available on Amazon that change the 3/4 to 1 and the 3/16 keyway to 1/4?

This is the only thing I can see working, and is an easy enough solution, but I want to make sure Im not misinformed or missing anything.

2nd question...the 40 driven is 7.5 correct? The 44 driven is 8.5 and can be mixed with a 40 driver? The bigger the driven the more torque?

I guess Im not seeing the point of the 44 Driver. Its the same price as a 40 driver, but other than having a 3/4 diameter option it seems to be inferior to the 40 Driver.

Thanks!
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Old 07-15-2019, 03:01 AM
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Doesn't the 40 series also come in 3/4"?

Here is just one link I found .There are many

https://cometkartsales.com/209133A-C...-3-4-Bore.html
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Old 07-15-2019, 03:27 AM
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Driver Paul, not driven.

The 44C Driver is superior to the series 40 in that can be tuned in a much wider range for engagement speeds.
namely to fit onto two stroke engines as well as four strokes (with much higher engagement speeds usually)

So frankly... I doubt it's limited to 5k considering one of the intended and valid setups make it engage at 4k

Anyways, maybe what you're really wanting is a 500 series TC instead (a salsbury)
it's certainly available as a 3/4" driver, can handle 18 horses AND has 19% overdrive with the 7.5" driven.
No you won't find a chinese copy of that, and yes it's one of the more expensive TCs
Comet has (since it's not exactly as common as the series 20,30 or 40).

'sid
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Old 07-15-2019, 03:34 AM
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Not that I am aware of. The link you provided is for the Driven. The driven is available in 5/8, 3/4 or 1”. The Driver (the part that goes on the crankshaft) is only 1”.

Edit...posted this same time as Sid.

---------- Post added at 04:34 AM ---------- Previous post was at 04:28 AM ----------

Sid...maybe I misread. I thought max engine rpm was 5000, but it is the max engagement rpm. So I guess that is now a viable option. I’m looking for a setup for my stage 2 predator with headwork and higher compression. The 500 is overkill. I do not understand if the Driver effects top speed and torque or only the driven. Your calculator for instance when using the 40/40 has a huge difference in speed vs using the 40/44 option.

I will be using 16” tires. 54 tooth sprocket. 9 tooth jackshaft. Kart goal is 50-60 mph on pavement.
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Old 07-15-2019, 03:43 AM
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the difference you see is the driven the 40 driven is 7.5" the 44 is 8.5"
and yes you can use both on both I know..

Since that additional inch in diameter changes the gear ratio (on both ends)

run the calculator again and see what min and max ratio you'll get and how it changes when swapping the 7.5 to a 8.5

'sid

PS but you're right that should've been named differently... I'm going to change that someday I guess
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Old 07-15-2019, 03:47 AM
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Tha is for the clarification. I appreciate it.

So basically I can use a 44C Driver with the 40 Driven (7.5”) which will give me the speed.

Engagement speed. What is the role it plays in acceleration? Why would you want a later engagement speed and how do I determine that engagement speed based on my build

Finally, does the Drive unit have any effect on the gear ratio or is it only the driven?
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Old 07-15-2019, 04:11 AM
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What are you putting it on? If you want to save some money you could use an adapter with the 40 series driver. The driver engagement speed will affect how your kart takes off. The higher the engagement speed will give you faster acceleration when it grabs the belt for takeoff. That may or may not be good depending on the weight of your kart and the type of riding your doing. The only thing that will change the gear ratio is by using the larger driven pulley. You will get more torque if you have a heavy kart and are trying to get up steep hills but most likely you won't need that.
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Old 07-15-2019, 04:45 AM
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Ok. So my original idea of the sleeve is valid too. Good to know. Alright, here is the deal.

Stage 2 predator
Billet flywheel and rod
Compression around 10.8:1
Mod 2 camshaft
Professionally Ported Head intake and exhaust
Stock 27/25mm valves
22lb valve springs
Genuine Mikuni 22mm carb

Sprocket-54t
Jackshaft-9t

The Kart is the Baja from Bird Engineering. It is a small kart and is relatively light. The bare frame is probably 60-70 pounds. So with wheels and engine let’s call it 150 pounds max....probably a bit lighter.

Riding will be pavement and occasional flat grassy area. No hills or mud. I am looking for acceleration and speed. It is geared (assuming a 7.5” driven is used) to top out at around 51mph.

The only possible change could be a 10tooth jackshaft sprocket, but initially it will have a 9.

I weigh 160 lbs dressed.
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Old 07-15-2019, 07:11 AM
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except that you are likely overestimating the power of your engine ...
we'll see

Oh and to get the takeoff torque a higher engagement speed will COST you top speed!
since you cannot take off at 20mph of course soooo a belt will get burned in trying
which means you will have to gear lower to compensate

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Old 07-15-2019, 12:18 PM
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I might be overestimating at 15, but if I am not by much. Either way, there are no hills in this kart’s future.

Engagement speed-This is the rpm at which the kart begins to move from, when the belt just begins to rise on the Drive correct? So a higher engagement speed is like dumping the clutch in a car? The goal is to engage when you are coming in to the powerband instead of before?
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Old 07-15-2019, 02:27 PM
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Ive always wondered about those shaft adapters. You talking about the one with the stepped key?
My 40 series driven unit has the key built in, so I guess youd have to grind part of the built in key away to make it work with the adapter.
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Old 07-15-2019, 02:33 PM
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Yes that’s the adapter I’m talking about, but it doesn’t apply to the driven unit in this application. It is for the crankshaft. The Driver unit. A built in keyway on the driven will be fine for me. I haven’t seen any drivers with built in keyway so that’s a non issue. Hope that makes sense.

What knockoff did you buy?
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Old 07-15-2019, 04:49 PM
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I meant driver unit.
All of the knockoff 40 series drivers have the key built it.
Not sure about genuine comet.

I got mine from eBay for $98, but it looks like they are $82 now.
https://rover.ebay.com/rover/0/0/0?m...2F361206465290

Or better yet, $68
https://rover.ebay.com/rover/0/0/0?m...2F371669018054

You can see the key in this picture...
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F39E7958-97A2-4FA0-818B-9C5367308777.jpg   975C2BBC-A84E-41E3-80F1-79F9BF50BD4A.jpg  

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Last edited by itsid; 07-15-2019 at 06:47 PM.
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Old 07-15-2019, 05:52 PM
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Quote:
Originally Posted by bob58o View Post
You can see the key in this picture...
Good catch Bob that is a problem.
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Old 07-15-2019, 06:55 PM
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Quote:
Originally Posted by bob58o View Post
Ive always wondered about those shaft adapters. You talking about the one with the stepped key?
My 40 series driven unit has the key built in, so I guess youd have to grind part of the built in key away to make it work with the adapter.
I haven't seen any premade yet..
show me and I can tell you if it's what I had in mind

But in essence it's easier to cut a keyway in an already 1" shaft
than to have a protruding key machined from 1.25" stock, right?
So it doesn't matter if the driver has a key cast in or seperated.
What matters is the key that spans over the original PTO and the shaft extension, too long and it won't fit with the key of the driver,
too short and it might slip during installation and not rotationally lock the extension;
and that extension might then not drive the clutch reliably..

A cast driver key on an inboard mounted clutch actually works in our favour,
since it prevents the key from falling out at the front
(a washer would too.. but you know what I'm saying, right?)

'sid
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Old 07-15-2019, 11:11 PM
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This is what I was talking about...
If you cut this stepped key shorter and keep it close to the engine on the PTO, you still might have to grind away some of the key cast into the driver.
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Old 07-15-2019, 11:57 PM
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Nice catch indeed. I was able to cancel an order for the 40 series. I guess the only option truly is the 44c (or 500 as Sid mentioned) the adapter sleeve won’t work. The 40 series with built in key would fit the sleeve but the key wouldn’t fit the crank. It would need to be stepped like the adapter key is. I guess no real way to save money in the driver. An aftermarket 44c is like $130 and a genuine is around 150-160. The driven I can still save some money. Looks like it’s $225 minimum for genuine driver, aftermarket driven, and a comet belt. I’m surprised no one has made an adapter kit. Seems like it would be profitable for the Chinese manufacturing.

Edit-Bob yes that is the sleeve I had ordered. I would have to grind 1/2 of the 1/4” portion, then tri to grind the hub keyway an equal amount. No way I could file the hub keyway straight. I’ll just pony up the mint for the 44c.
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Old 07-16-2019, 12:05 AM
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By the way, I run a $50 eBay 30 series on my minibike that turns over 8k rpm. I did replace the the 6 driven with a 7 driven unit.

Cam has 0.285 lift and 250 degree duration.
28.5mm / 25mm valves
3 angle valve job
Ported Head
~11 :1 compression ratio
24mm flatside carb
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Old 07-16-2019, 01:29 AM
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Really? And your belts are ok? How long do they last? I am confused because 1/2 the people here will say the 30 series on something like your engine or the one I built will not work and will simply tear up belts rapidly. Then the other half will say it works fine despite it being rated at way less power.

---------- Post added at 02:29 AM ---------- Previous post was at 01:37 AM ----------

Screw it. I ordered the Genuine 44c magnum with the 3/4 bore. Price was 119.95 shipped. I used a google express coupon. Price before coupon was 139.95.
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Old 07-16-2019, 01:41 AM
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I’m still on the original belt, but I don’t have more than a few hours on it (<5 hours probably). I moved and don’t really have the real estate to ride it, plus my drivers license is suspended at the moment and can’t risk getting slapped with a driving on a suspended.

I always use genuine comet belts and it’s geared really low. It’ll toss me off the back like nothing if I’m not careful with the throttle.

The combination of gearing, 7” driven unit, comet belt, and the light weight minibike seems to be working fine for me. I’m not the least bit concerned about my TC choice.

Are you a member of any Facebook groups? Ask around on there. You are using a mod 2 cam on a relatively mild build, right. See if others had issues. Some will say you need a “lockout” washer/bushing to stay out of overdrive if you want to achieve the RPMs that cam is capable of (if using the 6” driven). That’s a new craze all over FB. I don’t really buy into it. If geared correctly, it should still rev out.

With a heavier kart/buggy, you might experience more issues. I had another 212/30 series on my buggy with 16” tires. Black mamba jr cam, 11 :1 CR, gx390 carb.... I beat the dog sheet out of that. I had that geared 60 :8 with the 6” driven unit. I did have to replace the cheap Chinese belt that originally came with the unit. And eventually the driver unit started failing to close. It would get super hot and I had to manually close it. I replaced the springs and cleaned up the weight pack and it started functioning normal again. Eventually I swapped in the 420/ 40 series and put that 212 on a minibike.
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