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Mf-7 Repower

h70 tecumsey mf-7 ohm90

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#1 Utah Smitty OFFLINE  

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Posted June 22, 2012 - 11:40 PM

I bought a couple MF-7s last fall. One ran, one didn't. The running tractor had been repowered to a larger Tecumseh flat head engine--they had to cut out the hood on the left side to do it, but I couldn't find a model number.

I changed the oil and put fresh gas in the repowered tractor and let my mom use it to mow her lawn around the house. She really likes it, it's small and has a sharp turning radius, and she can get to places on her lawn that her big GT18 can't. But the engine is tired--after running for about 30 minutes it doesn't want to run anymore. It also had a crack in the gas tank that left a mess on the ground whenever we parked it...

I could never get the other MF-7 to start--it gets spark, but when it's turning with the plug in it pauses for a moment every second turn--I tried all the usual things--cleaned the carb, put carb cleaner down the spark plug hole, etc. but no go... I even pulled the flywheel and cleaned and set the points.

Tecumseh H70.jpg

So, I finally decided to repower at least one of them.

I considered using one of the Chinese Clones, but I thought the 6.5 hp might not have enough torque, and the 9 hp models at HF didn't have electric start. Home Depot sells some Chinese closes as well as eBay, but I was generally looking at over $350 by the time I paid for freight, etc.

I finally found a brand new, never used Tecumseh OHM-9 OHV engine on a local classifieds. The guy wanted $200--a reasonable price I felt. I went over to look at it and took measurements--crankshaft diameter was correct (1"), mounting holes in the same place; heigth and width were okay... so I bought it.

I got it home, and discovered a few things..

1. The big wrap around gas tank stuck out too far on the left side; ditto for the square plastic air cleaner. The exhaust was okay as far as size, but it would have exited under the hood... not a good idea.
MF7 Engine Swap LH Frt.jpg
2012-06-09_15-16-29_233.jpg


2. The battery can be put back in it's original place, but there's no place for a fuel tank. One option for the battery would be to put it at the front of the engine below the carburetor. I know batteries give off explosive hydrogen gas when charging... does anyone know if this location would be a problem?

3. If I can't put the battery in front of the engine, it will have to share space with the fuel tank... The little red half gallon tank I used to break in the engine will just barely fit under the hood, leaving about 4 inches to one side--maybe enough room to put in a motorcycle-sized battery... whaddya think??

MF7 Engine Swap RH Close.jpg MF 7 Engine Space 2.jpg

Regards,

Utah Smitty

Edited by Utah Smitty, June 22, 2012 - 11:42 PM.


#2 MH81 ONLINE  

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Posted June 23, 2012 - 12:54 AM

Smitty, I think the best place for the battery would be up by the tank. Less because of gasses, and more because of heat buildup right in against the block like it would have to be if it was up front.

As for capacity, a mc battery should have more umph than needed, the Tecumseh should have compression release anyways.

The exhaust reroute should be pretty easy... If the block is threaded. If not, you'll need to make an adapter to get to standard pipe.

Good find on the engine, I'm sure it'll do Mom a good job.
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#3 JDBrian OFFLINE  

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Posted June 23, 2012 - 06:12 AM

Nice find on the engine Smitty. It's hard to find good vertical cylinder horizontal shaft engines these days. The new ones tend to be the Honda style slant cylinder arrangement which is a totally different shape than what is needed. I have an MF8 that need an engine as well. There are a lot of cheap snowblowers around this time of year that are a good source of 8 and 10hp Tec hm engines. I bought one the other day for 100$ with a nice non smoking hm80 on it. Good luck on the re power.

#4 Utah Smitty OFFLINE  

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Posted June 24, 2012 - 09:09 AM

Well, I got the exhaust adapter made and put a can-type muffler on it. Here's how it looked before:

MF7 Engine Swap RH Close.jpg

The original muffler openings were toward the grill and I didn't like the exhaust exiting under the hood. I decided to make an adapter and put a 1" screw on muffler out the side.

I started by making a flange for the exhaust port out of 1/4" HR plate. I have a 1" metal hole saw, so it was faster than drilling a bunch of holes in a circle, breaking out the middle, then filing it smooth (which is what I did on my first attempt before I remembered the hole saw!!)

I laid out all the holes first, then drilled pilot holes for the hole saw drill bit, and the two bolt holes.

MF7 Exhaust Flange Setup.jpg

I also had originally planned to use just a 1" nipple cut off at one end so it was only about 1/2" long, but it was too short and didn't leave enough room to put the bolts in.

2012-06-16_10-12-08_245.jpg

I beveled the the hole so that it lined up exactly with the 1" pipe, then tacked it on the inside to hold it while I welded the outside.

MF7 Exhaust Tack.jpg

As you can see, my welds are always neat and tidy... NOT!!
2012-06-22_15-07-08_726.jpg

The bolt holes are pretty close to the port opening, so I ended up having to use socket head screws on them.
2012-06-22_14-55-10_356.jpg

Here's the end result:

MF7 New exhaust.jpg



I used copper-based anti-seize on all the threaded parts as it's good to 1800 degrees. As you can see, it clears the lower edge of the hood, but doesn't project too far out and risk burning someone.

Now I have to figure out how to adapt the air cleaner. The factory model juts out to far on the side and keeps the grill from being installed... Even with it off, the bore to the carb is pretty close to the inside of the grill--there's a couple screws sticking through the grill that make it more challenging as well. I thought of making another adapter and putting a round air filter on it in front of the engine, but things are a bit tight and I'd have to put a 90 degree bend...

2012-06-22_15-47-35_78.jpg

Anyway, any suggestions are sincerely appreciated...

Utah Smitty

Attached Thumbnails

  • 2012-06-22_15-47-14_580.jpg
  • 2012-06-22_14-47-32_229.jpg
  • 2012-06-22_14-47-41_474.jpg
  • MF 7 Engine Space.JPG

Edited by Utah Smitty, June 24, 2012 - 09:20 AM.


#5 redcarkids OFFLINE  

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Posted June 27, 2012 - 02:46 PM

What are you going to do with the old engine Utah? I need the bracket on the the top that holds the throttle cable all the carb linkage, rods and govener rod ect. May be interested in the shroud also. If you want to part out some of the old engine give me a shout thru e-mail here on the sight.

#6 xrman2 OFFLINE  

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Posted July 04, 2012 - 10:37 PM

Looks like you did good job on exhaust...Gives me some ideas. Thanks

#7 Tencubed OFFLINE  

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Posted July 05, 2012 - 02:36 PM

What are you going to do with the old engine Utah? I need the bracket on the the top that holds the throttle cable all the carb linkage, rods and govener rod ect. May be interested in the shroud also. If you want to part out some of the old engine give me a shout thru e-mail here on the sight.


I'm in need of the linkage from the governor arm to the carb if you're interested in parting this engine out. I need everything but the bracket that's welded to the tinwork. Screws, brackets, linkage, springs and all.

New member here, great place from what I've seen so far.

Thanks

Mike

#8 Utah Smitty OFFLINE  

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Posted July 15, 2012 - 04:02 PM

Well, I've moved along on the repower... finally got the airfilter situation solved by making an adapter flange for the carb with a piece of 1" ID pipe welded to it, then used an elbow on a 1" Diam. radiator hose to mount the aircleaner up above the carburetor.

Now my problem is hooking up the electrical. The new engine is an OHM 90 with electric (12V) start. There is a kill switch on the fan shroud, and a 4 position spade-type connector with two wires--red and green, running from the back of the shroud by the starter. I started the engine and tried to measure the voltage from the wires but only got a couple volts when measuring DC, and about 26 volts measuring AC.

Does anyone know what the voltage output on this engine is and how I would adapt it to the MF7 wiring harness? The engine is a Tecumseh OHM 90 222302A--I'm kinda stuck...

Thanks,

US

Edited by Utah Smitty, July 15, 2012 - 04:04 PM.


#9 KennyP ONLINE  

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Posted July 15, 2012 - 04:21 PM

Ask Pat (Amigatec)! He helped Ray with his Cummins thread! :bigrofl:
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#10 HowardsMF155 OFFLINE  

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Posted July 15, 2012 - 04:53 PM

On my Tecumseh "Formula" engine, the two wires appear to be for a remote kill switch. I think I used the green wire to go to the ignition switch which grounds out to the frame to kill the ignition. It also appears that if the red and green wires are shorted, then it also kills the engine. I THINK that if there is any charging coil it outputs to where the battery cable wires onto the engine. I do remember making the same tests you did because those wires appear to match the the original engine wiring harness. I got pretty much the results you did, and when I hooked those wires to my voltage regulator, the engine ran VERY rough, which it had not before.
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#11 Utah Smitty OFFLINE  

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Posted July 21, 2012 - 04:40 PM

On my Tecumseh "Formula" engine, the two wires appear to be for a remote kill switch. I think I used the green wire to go to the ignition switch which grounds out to the frame to kill the ignition. It also appears that if the red and green wires are shorted, then it also kills the engine. I THINK that if there is any charging coil it outputs to where the battery cable wires onto the engine. I do remember making the same tests you did because those wires appear to match the the original engine wiring harness. I got pretty much the results you did, and when I hooked those wires to my voltage regulator, the engine ran VERY rough, which it had not before.


I think I got it figured out...

The green wire is to kill the magneto like you said, the other wire goes to the battery post on the solenoid to charge the battery, etc. According to the Tecumseh Service Manual (which I found under the Manuals Section) the alternator has to have battery voltage to work.

I removed the fan housing, and discovered that there are also 2 yellow wires that go to a rectifier-- only the red wire comes out. I figure if I hook the green up to the "D" Terminal and the Red to the Battery side of the starter solenoid, I can probably bypass the Voltage regulator altogether... we'll see.

#12 Utah Smitty OFFLINE  

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Posted July 21, 2012 - 04:43 PM

Another question, which actually applies to all belt drive situations. There are a number of metal "fingers" approx. 3/16" diameter that are placed over a pulley, etc. Are these just to keep the belt from slipping off?

Also, when I ran the engine on the other frame I had, it took a long time for the transaxle pulley to quit spinning after I put the clutch in... is there something that helps to slow this down, or is it just because the tranny is worn and everything's loose?

Thanks in advance...

#13 HowardsMF155 OFFLINE  

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Posted July 21, 2012 - 05:12 PM

Hi Smitty,
On my MF 8, the fingers seem to serve two functions. One is to help hold the belt in place, but the other is to help stop the belt. I found that if I tweaked the guide finger on my idler/clutch pulley so that it engaged the belt when the idler wheel loosens the belt, then the whole assembly stopped much faster.
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#14 Utah Smitty OFFLINE  

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Posted July 21, 2012 - 06:35 PM

Thanks, Howard... I wondered if they worked like that--I'll have to finesse the one on the idler clutch pulley. It looks like if it was a little to the rear, it wouldn't drag when the transaxle was engaged, but would tend to snub the belt when the clutch was pushed in.

Regards,

Steve

#15 Utah Smitty OFFLINE  

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Posted August 08, 2012 - 01:21 PM

Well, I hooked up the wires from the engine to the harness and everything works fine. I hooked the green wire to the "S" on the key switch. It connects to ground when the key is off, which grounds the magneto and stops the engine. I hooked the red wire to the battery side of the solenoid, which supplies nominal 12V to charge the battery.

2012-07-28_10-40-09_747.jpg

The magneto on the engine had to have current from a battery, etc., before it would generate power.

Thanks for all the input on this...

I've continued to work on the tractor and will post pics shortly.

Edited by Utah Smitty, August 14, 2012 - 09:41 PM.





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