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ST824 Tecumseh-to-Predator Engine Swap

23K views 76 replies 17 participants last post by  Russell Stephan  
#1 ·
A one-take video overview presentation of the effort:

 
#36 ·
Well.
I had a brilliant idea for a few minutes of converting the impeller/auger to a chain drive with an adjustable clutch to limit torque.

Then I realized there would be no way to stop it under normal conditions. :rolleyes:
 
#37 ·
I had a brilliant idea for a few minutes of converting the impeller/auger
to a chain drive with an adjustable clutch to limit torque.
Have a gander earlier in the thread where I link to a YouTube video about installing a charging coil and starter on a 301cc Predator engine... Just before that I provide a link to a electro-mechanical clutch used in commercial lawn mowers.

Although, I would doubt charging coils would be enough to lock up the clutch. But an alternator... ;-)
 
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#38 ·
For what it's worth I noticed there's also a Predator 5500W generator that uses the 301 engine.
The general rule is 2HP per KW and the Tecumseh 10HP was used on some 5000W generators. Also, from what I've found the Tecumseh HM100/HMSK100 was rated something like 15.5ftlb @ 2600 while the Predator 301 is rated 14.9ftlb but they didn't specify an RPM but I would assume 2500RPM.

Very strange that a Harbor Freight engine would perform better than the claims. Isn't it?

Meanwhile we've got shop vacuums that claim to be 6HP when they're lucky to be a sixth of that.
 
#39 ·
Interesting info I’m a follower.
Mounting a larger motor isn’t the hard part- a simple motor mount plate would solve that issue. You could either weld the plate or bolt it to the tractor. It seems that most of the issue is finding a belt the proper size. I do remember a thread on here that the belt was 1/2” too long why not just mount the motor 1/2” higher then finding a belt isn’t the issue. I get the belt guard will need modified, but that too isn’t a very hard thing to do.
 
#40 ·
Interesting info I’m a follower.
Mounting a larger motor isn’t the hard part- a simple motor mount plate would solve that issue. You could either weld the plate or bolt it to the tractor. It seems that most of the issue is finding a belt the proper size. I do remember a thread on here that the belt was 1/2” too long why not just mount the motor 1/2” higher then finding a belt isn’t the issue. I get the belt guard will need modified, but that too isn’t a very hard thing to do.
They sell a riser kit for the belt guard so that isn't an issue.
 
#41 ·
For those attempting to fine-tune belt lengths for the absolute minimum amount of slippage, McMaster-Carr offers custom-lengthed belt building:

McMaster-Carr
 
#42 ·
For those attempting to fine-tune belt lengths for the absolute minimum amount of slippage, McMaster-Carr offers custom-lengthed belt building:

McMaster-Carr
But still no raw edge selection, no?

Can an idler on the opposite side be used to take up some slack?
 
#43 ·
But still no raw edge selection, no?

Can an idler on the opposite side be used to take up some slack?
My standard lengthed raw-edge belt should be arriving today or tomorrow. Although, it does look like our weather has moved out of the standard winter pattern. The snow may be over until next year...

My plan of attack for tightening up the drive system involve:

1) Attempting to "push in" the reach of the idler pulley when engaged. I should be able to gain 1/4" with a minimum of fabrication/modification.

2) After #1 is completed, bump up the spring tension in the idler mechanical circuit with a stiffer spring.

3) Try a slightly larger diameter idler pulley.

------

And if those don't work out, upgrade to a slightly larger diameter 5L belt width impeller pulley and driven wheel.
 
#45 ·
Do you recall what size the idler is?
I'm guessing 1.75 - 2"?

Odd question.....but I have a reason for asking.
It's a 2" diameter with a 3/4" running channel width.
 
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#46 · (Edited)
And, the education continues...

My raw-edge belt has arrived. I have yet to install it. It looks like our snow season is over for 2021. But, my research on V-belts has not let up.

From all I've read, the typical 4l and 5l belts are fractional HP belts for extremely light-duty applications under or around 1HP. Hmmmmm. An eight HP engine throwing snow? The belt certainly has to be rated for more than a fraction of 1HP. It seems there are light-duty belts (2L, 3L, 4L, 5L). Then, there are the conventional higher HP-rated belts of A, B, C, D, and E designations. And a third category called "narrow" or "wedge" belts which have greater side surface area for more power transmission capabilities.

Here is an informative chart with recommended HP ratings for various belt designations:


So, how to proceed? I've done a bit of research and can't seem to find a cross-reference guide which explicitly states the type of belt the OEMs use. I'm guessing, however, it's most likely the "narrow" or "wedge" belts. It's the only type which appears to match up with eyeballed width and depth guesses on my part along with the engine's HP rating. However, I hate guessing...

Given the various types of belt profiles and such, I figured there had to be a set of gauges for determining exactly what type of belt is used in a given sheave/pulley. And yes! There are gauges. So, to avoid guessing, I ordered a set off eBay. The gauges will come in handy for other belt applications in the shop too, like the air compressor which recently decided to eat a 4l linked belt after more than a decade.

Now we wait on the arrival of the gauge set in hopes of coming up with the proper belt to get all that engine power into throwing snow.
 
#47 ·
Yes they're rated as fractional belts but I believe that's under continuous use. It doesn't mean it can only handle that much without breaking etc.

I believe my dad's tractor used a 5L for 12hp.
But, the pulleys were larger than 2.75" and it had a much stronger spring on the idler.

Im having issues too because it appears choosing belts isn't simple at all.

On a similar subject. It looks like the Predator 301 and 420 are almost identical as far as shaft hight.
 
#48 ·
Russell, you are reading too much in to this. For a drive belt, they generally are 3L, auger belts generally are 4L. My preferred belts are D&D Power, Pix, A.I. Sports, for their durability and their accurate length.
 
#49 ·
Russell, you are reading too much in to this.
If that were indeed the only issue...

As mentioned numerous times throughout the whole thread and repeated again here, the ST824 with the Predator engine suffers from belt slippage. Hitting deep snow does not bog the engine down. Rather, it just brings the thrown snow to a dribble.

I'm in the process of attempting to get all that engine power into thrown snow.
 
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#52 ·
You kept the stock pulley sizes right?

How much bigger one an impeller pulley do you think it would need to
make the new belt the correct length?
The current drive and driven pulleys/sheaves are stock. The current 4L belt (420) is as close to perfect in terms of length that can be applied without going off into the weeds of quarters or eighths of inches. The only reason I mentioned a drive pulley diameter increase is because this is an easy way to gain sheave/belt surface area contact.

Tinkering with the belt/sheave setup will be on-hold until the belt profile gauges show up so as to remove any and all doubt concerning the absolute correct application.
 
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#53 · (Edited)
The reason I'm asking is I'm still feeling out how difficult the 13HP / 420 would be to get to work decently. I believe the 301 and 420's shaft height is almost identical.
I recall you buying a belt that seemed too long unless that's what you ended up with?

I had planned on making a new sheath from scratch that could use a 5L belt for the impeller, so any size is possible within reason. With the 13Hp i'd want something closer to 3" or 3.25" though to get the speed up some. But literally anything in between is possible. If I go through with it I'd like it to run stock impeller speeds at around 3000- 3300 rpm.
 
#54 ·
The reason I'm asking is I'm still feeling out how difficult the 13HP / 420 would be
to get to work decently. I believe the 301 and 420's shaft height is almost identical.
I recall you buying a belt that seemed too long unless that's what you ended up with?
See the YouTube video description of the post starting this whole thread concerning the trials and tribulations with belt lengths.

I had planned on making a new sheath from scratch that could use a 5L belt for the
impeller, so any size is possible within reason. With the 13Hp i'd want something
closer to 3" or 3.25" though to get the speed up some. But literally anything in
between is possible. If I go through with it I'd like it to run stock impeller speeds at
around 3000- 3300 rpm.
A custom sheave setup certainly opens a world of possibilities. I did find a couple of machine shops on-line that specialize in making custom sheaves. I really do need a fully-equipped industrial-sized fabrication shop available for my personal use!

If I were going with a custom belt/sheave modification, I'd skip the fractional horsepower belt profiles and go directly to the industrial grades I mentioned a few recent posts ago.

Be sure to check if the Ariens dual pulley upgrade kit would possibly work for your setup, though.
 
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#55 ·
See the YouTube video description of the post starting this whole thread concerning the trials and tribulations with belt lengths.


A custom sheave setup certainly opens a world of possibilities. I did find a couple of machine shops on-line that specialize in making custom sheaves. I really do need a fully-equipped industrial-sized fabrication shop available for my personal use!

If I were going with a custom belt/sheave modification, I'd skip the fractional horsepower belt profiles and go directly to the industrial grades I mentioned a few recent posts ago.

Be sure to check if the Ariens dual pulley upgrade kit would possibly work for your setup, though.

It is nice but the problem I always have is never enough time.
I'm currently modeling new hinges for my antique refrigerators so I can machine new ones but again, never enough time to finish.

The reason I was thinking a 5L belt is it seemed typical to use such for these applications. I had a very hard time figuring out minimum pulley diameter for belts as well as which allowed a back idler. It's certainly far from my area of expertise.
 
#56 ·
I took the gas tank off the old blown Tecumseh engine today. Nice little crack in the block...
177401
 
#58 ·
That’ll buff right out.
After a bunch of TIG work and/or aluminum brazing rod... But, with the time/money curve, a whole new engine for the win! ;-)
 
#59 ·
The roached 8HP Tecumseh internals.

The galled crank connecting rod journal. What's left of the piston connecting rod. The engine case from the inside with a yellow trouble light revealing the big crack.


177422
177423
177424
 
#60 ·
I've got the engine fully disassembled. If there's any parts required, give me a shout!

Magneto, muffler, engine side cover, head, flywheel with starter gearing, cam, pull cord mechanism and shroud.

177425
 
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#62 ·
I would have just thrown a Predator 212 on, its a direct bolt on without modifications and is already far more powerful than the original 8hp Tecumseh and 10hp for that matter. I'm running one on my 1971 32" wide Predator and that things a beast. I just picked up that ST824 last week and if I keep it, that's probably exactly what I'm gonna do drop a 212 on it and retire my 24" from 1971 keep the 87 ST824 znd the 71, 32". Being a 24" its all it really needs, the 32" has plenty of power as well, but thats the one that could really use the jump if any.
 

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#67 ·
Would a small shim or plate under the motor work? Might work if
there is a little play or adjustment on the drive belt?
This is certainly a solution for fine-tuning the PTO height.

However, simple washers used as spacers between the engine deck and the motor would be far cheaper in addition to allowing fine-fine tuning.

Thanks for the suggestion!
 
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#71 · (Edited)
That snow is not nearly as wet and heavy compared to the stuff I get near the coast.

That machine does a decent job with the 212, though.

I'm thinking I would need a 301cc or larger engine on my 30" Husqvarna that currently has a HMSK100. But, I am thinking of changing the impeller drive pulley from 2.75" to 3". If that gets me 10-15' more throwing distance, then no need to upgrade the engine.

BTW, when Husqvarna changed over from Tecumseh engines to LCT they started using an engine mounting plate for the larger engines. That would work for me because the chassis already has the holes on the sides to bolt the engine plate in the correct location.

PartsTree - Home of OEM Parts for Outdoor Power Equipment
 
#73 ·
A long overdue update... The use of an AX40 V-belt for the impeller seems to have banished the belt slipping when the nose of the machine is stuffed into a pile of end-of-driveway city plow cast-off.

At the start of the 2022 season, the hour meter on the Predator 301cc engine married to the ST824 chassis reads 23.2 hours.
 
#74 ·
Thanks for the video, well done, waiting to see your modified/new belt cover.
See the current "Short & Stubby" thread. I fabbed up a make-do cover recently in that thread.
 
#75 ·
Central Ohio received 4" of wet heavy snow on January 22, 2023. The Predator 301cc (8HP) engine and the Ariens ST824 chassis functioned beautifully. The engine worked through the slop without so much as a complaint.

A couple of time, though, the chute did clog due to a front-covering guard/skirt (removed later in the day). The squealing of a slipping belt (AX40) was obvious.

So, the Predator 301cc engine will handle all that the Ariens chassis can shovel in its mouth.
 
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#77 ·
I plan to get a video one of these times when conditions allow for good filming.
 
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