Murray Hard Drive 420cc 40 Series TC gearing

[Dewindoeth]

Hi, new to the group.
Just acquired a Murray hard drive without an engine. So have ordered a 420cc Loncin engine (Predator not available here in the UK).
I’ve also ordered a 40 series torque converter.
Now my plan is to run the kart with stock sprockets (26t & 10t on jackshaft and 36t on axle). I believe it’s a 10t sprocket off the TC as well. Anyone have experience on this set up? Thanks

 

[Hellion]

Hello. Tons of material on this site. For example:
https://www.diygokarts.com/community/threads/murray-hard-drive-question.41686/

This manual may be of some use:
https://www.lawnmowerpros.com/pdfs/murray/gt60401x92a.pdf

 

[Denny]

60 tooth axle 10 tooth jackshaft. 6:1 the Goldie Locks ratio!

 

[Dewindoeth]

60 tooth axle 10 tooth jackshaft. 6:1 the Goldie Locks ratio!

Thanks. From what I’ve read on here, this seems to be the best combo. Unfortunately, I doubt I will be able to fit anything much bigger than the current 36t on axle due to clearance. Unless I cut and re fab the frame, which I don’t really want to do. Hence thinking of keeping the original jackshaft with the 26t to 10t reducer. So would be 40 series TC with 10t sprocket to 26t to 10t jackshaft to 36t axle. If that makes sense!

 

[Denny]

Thanks. From what I’ve read on here, this seems to be the best combo. Unfortunately, I doubt I will be able to fit anything much bigger than the current 36t on axle due to clearance. Unless I cut and re fab the frame, which I don’t really want to do. Hence thinking of keeping the original jackshaft with the 26t to 10t reducer. So would be 40 series TC with 10t sprocket to 26t to 10t jackshaft to 36t axle. If that makes sense!

Maybe, I suck at math and I’m old and don’t like to think too much. Just yell at kids to get off my lawn. Darn their back. Hey , you kids get off my lawn! Got to go now.

 

[Edwin Spangler]

Theyre


Sry

 

[bob58o]

(26 / 10) x (36 /10) =
2.6 x 3.6 =
9.36

Sprocket Ratio is using 10 -> 26, 10 -> 36 is 9.36 to 1.

With a 40 series TAV, lowest gear is 2.43 :1 and highest gear is 1:1. This gives a total reduction of 22.75 : 1 at engagement and 9.36 : 1 when fully shifted out into highest gear.

Gearing is probably alright if you want all the torques. Might not obtain frightening top speeds. How big are the rear tires? The diameter? In inches?

With 18” tires, you might get about 20mph at 3600 RPM.

you might want to swap one of those 10T sprockets to something larger like 14T (depending on the tire size).

14 -> 26, 10 -> 36 with 18” tires would be about 29 mph at 3600 RPM.

 

[Whitetrashrocker]

1.24:1 if using a 7" driven over the 1:1 on the 6" IIRC.

 

[Dewindoeth]

(26 / 10) x (36 /10) =
2.6 x 3.6 =
9.36

Sprocket Ratio is using 10 -> 26, 10 -> 36 is 9.36 to 1.

With a 40 series TAV, lowest gear is 2.43 :1 and highest gear is 1:1. This gives a total reduction of 22.75 : 1 at engagement and 9.36 : 1 when fully shifted out into highest gear.

Gearing is probably alright if you want all the torques. Might not obtain frightening top speeds. How big are the rear tires? The diameter? In inches?

With 18” tires, you might get about 20mph at 3600 RPM.

you might want to swap one of those 10T sprockets to something larger like 14T (depending on the tire size).

14 -> 26, 10 -> 36 with 18” tires would be about 29 mph at 3600 RPM.

That’s great, thank you. Rear tires are standard 16”.

 

[bob58o]

That’s great, thank you. Rear tires are standard 16”.

1.24:1 if using a 7" driven over the 1:1 on the 6" IIRC

7” Driven is 1:1 in high. 8.5” Driven is 1.24:1 in high.

With 16” tires, I might go with a 16T instead of 14T.

16” Tires, 16T -> 26T, 10T -> 36T, 1.0 : 1 TAV ratio in high gear…

5.85 : 1 overall ratio in high gear.
3600 RPM
29 mph at 3600 RPM.

But it depends on what you want to do and where you plan on driving it. If climbing hills and on rough terrain, you might want more torque. If on flat paved open road you might want more top speed. If you want more speed, you could use a 19T sprocket and gear for 35 mph at 3600 RPM.

 

[Dewindoeth]

View attachment 152019
7” Driven is 1:1 in high. 8.5” Driven is 1.24:1 in high.

With 16” tires, I might go with a 16T instead of 14T.

16” Tires, 16T -> 26T, 10T -> 36T, 1.0 : 1 TAV ratio in high gear…

5.85 : 1 overall ratio in high gear.
3600 RPM
29 mph at 3600 RPM.

But it depends on what you want to do and where you plan on driving it. If climbing hills and on rough terrain, you might want more torque. If on flat paved open road you might want more top speed. If you want more speed, you could use a 19T sprocket and gear for 35 mph at 3600 RPM.

Thank you, this is really helpfull. I will be using it in our field with the kids. The field does have a slight slope so torque will be favoured over speed. I have ordered a 14t sprocket after reading your previous post (before I seen this). So will give it a try and order another (maybe 16t) if it does feel too slow.