Sprocket Help Please !

[KOUP]

Hi All,
I have a buggy that I'm going to use a 390 clone engine with a torque
converter . The torque converter has a 10t 420 sprocket and my rear wheel diameter is 18". Could someone advise on the best rear sprocket size for being practical and reliable please ?
Any help greatly appreciated.

 

[Mrmonk7663]

You need to provide torque converter information. Specifically the driven size (6”, 7”, 7.5”, 8.5”) if this is on a live axle and you want a steel sprocket, the only “off the shelf” option will be a 60 tooth. Bigger than that will require a bigger investment and welding. Aluminum there are more options but on a buggy I am opposed to aluminum.

 

[itsid]

Sorry Mrmonk but you are incorrect in every point

What he needs to provide is a good estimation of the WEIGHT of the vehicle first.
knowing what exact tc we're dealing with surely helps though.. but if we assume a 40/40D
as per usual for a gx390 engine, a 40/44D would work as well in the end.. so it's no critical info at all!)

Also: 420 sprockets (aka #41 sprockets since they're exact the same in profile)
are available up to 80 teeth off the shelf and up to 124 teeth (20" in diameter) on a custom order from Azusa

And aluminium sprockets are perfectly fine for a gx390 clone engine
it's the engine torque that could destroy the sprocket, not the vehicle!

And with a rubber belt in between, the bottle neck will be belt slip anyways

'sid

 

[KOUP]

Sorry Mrmonk but you are incorrect in every point

What he needs to provide is a good estimation of the WEIGHT of the vehicle first.
knowing what exact tc we're dealing with surely helps though.. but if we assume a 40/40D
as per usual for a gx390 engine, a 40/44D would work as well in the end.. so it's no critical info at all!)

Also: 420 sprockets (aka #41 sprockets since they're exact the same in profile)
are available up to 80 teeth off the shelf and up to 124 teeth (20" in diameter) on a custom order from Azusa

And aluminium sprockets are perfectly fine for a gx390 clone engine
it's the engine torque that could destroy the sprocket, not the vehicle!

And with a rubber belt in between, the bottle neck will be belt slip anyways

'sid

Hi, thanks for quick reply.
Think I may be kicking myself here, just thought torque converter would be ideal as it had a 1" bore but would really appreciate whether you think I could get away with using it due to 8hp rating if using the correct rear sprocket size please as I believe it is a 30 series. Buggy is old honda pacer sort of size 10t 420 drive sprocket ,solid rear axle. Thanks in advance.

 

[420Racer]

So do you have the engine and torque converter already?

 

[mckutzy]

Lets see some pics...

 

[itsid]

Hi, thanks for quick reply.
Think I may be kicking myself here, just thought torque converter would be ideal as it had a 1" bore but would really appreciate whether you think I could get away with using it due to 8hp rating if using the correct rear sprocket size please as I believe it is a 30 series. Buggy is old honda pacer sort of size 10t 420 drive sprocket ,solid rear axle. Thanks in advance.

A series 30 (TAV2 Kit usually sold as a cheap chnese copy complete kit on ebay)
is not going to serve you very well if at all.
the belt for a series 30 is smaller than for a series 40
(no they're not interchangeable between series)

and the small belt just cannot transmit enough engine torque for you reliably.

A series 40 (also sold as a chinese well made copy 'semi' kit for relatively cheap on ebay [both pulleys sometimes with a belt sometimes w/o]) is what you need to pick for an engine like yours

All you need to complete is a jackshaft kit
and a belt that matches your center to center distance.

Stay clear of the sets that come with a backplate!
They do not serve you well in the end.

'sid

 

[bthompson224]

Stay clear of the sets that come with a backplate!
They do not serve you well in the end.

'sid

I'm curious, why?

 

[itsid]

I'm curious, why?

series 30 kits are not suited for the engine as mentioned.

and the series 40 kits are a bad idea in the first place;
there is very good reason why Comet never made a backplate for the series 40 TC.. it's a stupid!

First ideally you want the series 40 running inboard not outboard (as a series 30 runs)
that way the moveable sheaves of driver and driven run in unison and belt alignment is always as set in rest.

Running the driven outboard (as needed on the backplate) would require the driven to float ~7/8" inboard to compensate for belt offset during shifting phases.
that is simply IMPOSSIBLE and thus the belt runs crooked either in low or in high gear (or in both)
With an outboard driven and outboard clutch.
dramatically reducing belt life in the process stealing another significant portion of your power.

So while I generally like GPS.. that is a brain fart
(one GTC had before them but they scrapped the idea before they ever sold a set... they even removed the announcement of it's developement from their website)

NOW a few months ago (to my best knowledge) there's this kit on ebay showing up with an inboard running clutch ...
and while that could solve the belt alignment issue for some,
it requires a looong engine shaft that is nowhere to be seen on current industrial engines ..
I haven't seen one installed so far, and I haven't heard any reports on that being a viable alternative so far.

Chances are you need to fab your own shaft extension (keyed 1" shaft ~1.5" long center drilled and properly keyed to the existing PTO)
and then hope for the best the keys don't move..

IDK but IYAM that's way more trouble than installing a proper Jackshaft plate or two pillow blocks.

Sure, you can install that stupid backplate thing, and run your 13horse engine with only 8horses at the wheels.. but WHY?!
especially since it'll cost you not only a rather expensive back plate but also a rather expensive belt every other month that you wouldn't need without that idiotic contraption.

Or short: laziness comes at a high price (in hard earned dollars this time)

'sid

PS and until I've seen a inboard running clutch working reliably without any additional fabwork.... I remain with
"Comet would have made one if it'd work as it should" so it doesn't work too well either.

 

[bthompson224]

Thanks. Would you say the same thing about a series 30 on a smallblock?

 

[Mrmonk7663]

The torque converter selection plays a huge role in speed and torque. Weight is important for gearing choice...but so is gearing and we both know the driven influences the gearing and top speed. We have been discussing this in other threads. If off the shelf 1” bore sprockets are available that do not require an additional hub and are made in steel please tell me where...I have looked extensively. Even sprockets that work with a hub I can’t find in steel higher than 60t. They are either aluminum or are for #35 chain.

Speaking of chain the #41 is weaker than the #40. This is important especially for a buggy.

He is building a buggy, which would lead you to believe it is an off-road build. Sure aluminum will work but for how long? Dirt and other particulate will get on the sprocket between the chain and it will wear considerably faster than steel, and if it is not perfectly aligned again it will rear much more rapidly.

I’m far from an expert so take my info with a grain of salt.

 

[itsid]

Speaking of chain the #41 is weaker than the #40. This is important especially for a buggy.

True but he's talking about 420, not #41
And while 420 has the exact smae outer dimensions as #41 it's stronger than #40 (by ALOT!)
most of the magic is pin diameter btw..

The TC plays 100% NO ROLE in torque nor speed..
in fact you can have more of either without one
(about 20% more at least)

A TC just is the best compromise we can make if we want both torque AND speed;
But a TC is no magic spell it toohas to rely on correct gearing.
And that gearing decides if you have enough torque and/or enough speed.

And again: if we dial in for the smaller of the two options (a 7.5" driven on a series 40)
we are still gearing great for the larger 8.5" driven
producing less top speed at worst..
but as you know.. getting a smaller sprocket than anticipated is always the easier task, than the other wy around

Your wish for steel is bs.. but if you so please just look for industrial sprockets rather than hobbyist ones and you'll find plenty.
grainger for example..
usarollerchain has some Btype (hub section) in 80 and 112 T for all I know on their shelves as well...
A B type 112 T is ~18" in diameter that afixed by nothing but the B-type hub is -mildly said- a 'brave' idea
That only really works on static appliances, certainly not on karts..

You want a RIGID base (hence karting hubs are usually large in diameter themselves for bigger sprockets... to prevent lateral play and jumping chains)
especially for off roading (buggy, huh?)


'sid

 

[950speed]

Thanks sid that helps a lot for he future on other projects

 

[itsid]

Oh.. I was mistaking.. it's not grainger;
it was Linngear that had the vast selection of sprockets
(#40 steel 120 teeth 19" 23lbs.. have fun )

'sid

 

[Mrmonk7663]

Through my lack of knowledge we have received an education . Thanks for the detailed response sid