Poor decisions.

Soooooooooo...... I just ordered a seized up Tecumseh HM100. Why, I do not know. I have an HM80 with a cool inspection window in the block, and it has a lot of good parts on it. I want to build an engine for my big Ariens rear tire tiller (thing is huge). The HM80 was its original engine. Any pointers on optimizing one of these flatheads for maximum low end torque? I have a Briggs 825 on it now, and though it's a great engine, it doesn't have enough power to drive the tines and keep the tiller moving slow. I have to run it wide open to drive the tines with enough force, but then it moves too fast, and bounces across the ground. The wheels and tines are geared together, so no options there. I know there are better options out there, but this is what I have to work with. I also just love building engines, and jump at every chance I get.

Best you can do is make it flow better, really. Open up and smooth out the ports, there’s almost always room to improve flow on a small engine

RichieRichOverdrive wrote:

Best you can do is make it flow better, really. Open up and smooth out the ports, there’s almost always room to improve flow on a small engine

I know I'm not very good about it, but I'll try to chronicle this adventure with pics.

Engine came in today, and I'm am pleased to report that it was NOT locked up as the seller stated. There was a large dried wad of plant matter between the flywheel and coil. Removed that, and the engine turned over fine. No compression, and the oil looked like chocolate milk, but I think it's worth a shot! About to order gaskets and rings.

> but then it moves too fast, and bounces across the ground.

Maybe some weight to help itt dig in?

On my tiller, the wheels move it forward as the tines try to drag it back, so, it basically sits and digs.

JB_4x4 wrote:

> but then it moves too fast, and bounces across the ground.

Maybe some weight to help itt dig in?

On my tiller, the wheels move it forward as the tines try to drag it back, so, it basically sits and digs.

I just came up with an insane idea to make a reverse rotation gearbox out of a blown up diff I have. It would go between the "transmission" and time drive. I'm brainstorming furiously.

@Ifitaintbroke I don't mean to be stupid but how would that engage the ground properly if it's spinning backwards?

ranch king pro 08 wrote:

@Ifitaintbroke I don't mean to be stupid but how would that engage the ground properly if it's spinning backwards?

Because it's being dragged forwards by the wheels. The tines dig into the ground better.

@Ifitaintbroke ok that makes much more sense Lol.

make and model or a picture would be nice ...

> but then it moves too fast, and bounces across the ground.

FWIW: Is the depth gauge in place? Upon further thinking it sounds as if the tiller is in transport mode. There should be a handle that raises and lowers a vertical metal rod. That rod determines how well and deep the tines dig.

It raises the tines about the surface so just the wheels have traction. Tilling forward (lift slightly up) when going across cement prevents the tines from hitting pavement.

Skipping is transport mode so you do not have to roll it. Once you get it where you want you raise that rod about an inch, do a pass. Then raise it again to go deeper. Once you get to about 3-4" inches deep, you can try the full 6-8" deep in one pass, if you need it that deep..

JB_4x4 wrote:

make and model or a picture would be nice  ...

>  but then it moves too fast, and bounces across the ground.

FWIW:  Is the depth gauge in place?  Upon further thinking it sounds as if the tiller is in transport mode.  There should be a handle that raises and lowers a vertical metal rod.  That rod determines how well and deep the tines dig.

It raises the tines about the surface so just the wheels have traction.  Tilling forward (lift slightly up) when going across cement prevents the  tines from hitting pavement.

Skipping is transport mode so you do not have to roll it.  Once you get it where you want you raise that rod about an inch, do a pass.  Then raise it again to go deeper.  Once you get to about 3-4" inches deep, you can try the full 6-8" deep in one pass, if you need it that deep..

Yes, I use the bar. The problem is that the tines are very, and I mean VERY worn down. They don't cut well. But the backsides of them would. Model is an 80ish Ariens RT7020, commonly referred to as a "Rocket". Sure ain't no rocket.

If your tiller is gear driven, you might have a system where the tines slide off a keyed shaft and you might be able to replace them either with the same or from another OEM.

JB_4x4 wrote:

If your tiller is gear driven, you might have a system where the tines slide off a keyed shaft and you might be able to replace them either with the same or from another OEM.

That should be the case, and I tried and got all but the inner on one side. It wouldn't come off, and I gave up. Counter rotation, is so much better, plus I want something to mess with.

> got all but the inner on one side

It might be staked with a roll pin to prevent it from pushing inward, if a collar/stop is not molded into the shaft. I think I encountered that on a front tine Craftsman.

> plus I want something to mess with

That is how I get something I really wanted :-)

JB_4x4 wrote:

That is how I get something I really wanted :-)

Exactly. I want one with counter rotating tines, SO I'M GONNA GET ONE!

Rebuild kit is ordered. Carb will be soon.

Carb is on the way. Got one for $12.

Got the engine torn down completely. Bore looks good, and ready to hone. Started porting, and things got a little crazy. 

Prolly took too much out on the intake, but i couldn't help myself.

Looks fine, hard to make it worse than stock. What’s the head look like?

You might try “unshrouding” where the valves pop up in the head, so that air has more room to flow out around the valves instead of just one direction towards the piston. Did that on my oppy heads.

@Wheelinhorse mentions it in this video at about 9:30. This video series is a must watch for anybody messing with these old flatheads.

RichieRichOverdrive wrote:

You might try “unshrouding” where the valves pop up in the head, so that air has more room to flow out around the valves instead of just one direction towards the piston. Did that on my oppy heads.

@Wheelinhorse mentions it in this video at about 9:30. This video series is a must watch for anybody messing with these old flatheads.

Pretty good stuff there. Can wrap my gulliver round most of it. Hard to judge what to remove without viddying what it looks like

Decided to wing it, and figured the best I could do is match it to the gasket. Here's what I came up with:

Ended up removing more on the exhaust side, as there was more to work with. Mainly just cleaned up the intake side and smoothed the transition to the piston side.

Not bad, almost guaranteed to help, theres almost no way to make these flow worse than factory without doing something really crazy. It’s hard to offer advice on whether to cut more or not, it’s the kind of thing you gotta see in person. Looking forward to seeing it run!