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Tecumseh HM80 vs HM100


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#1 EricFromPa ONLINE  

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Posted February 11, 2020 - 07:32 PM

Pondering on taking apart 2 running engines to swap out the side cover,cam and crank.

 

I have a HM80 on my MTD built 8/24 snowblower with 11" impeller that runs fine but has a worn valve guide. It uses oil, not horribly much but I do have to keep an eye on it and add some once in a while. It blows wet snow,dry snow,slush and doesn't clog up. It's smaller size makes it more maneuverable and being built by MTD parts are plentiful and cheap.  

 

I have a larger Noma (Murray built) 10/29 snowblower with HM100 engine. The engine runs smooth and strong.  It's a horribly designed blower IMO. The hole for the chute is just slightly larger than a 2x4 and it has a smaller 8" impeller. It clogs up constantly and the gear box has quite a bit of slop in it. It's a big heavy worthless turd because we get nothing BUT wet sticky snow and lots of slush. Parts for it are pretty hard to find and quite expencive.

 

I would like to put the HM100 on the MTD built blower.

 

The HM80 has 2 output shafts and 3 belts. 2 belts run off of the crank and 1 off of the Camshaft. The HM100 just has 2 belts that run off of the crank.

 

The outside crank diameters are different as well.

 

 

My question is, will the HM80 Crankshaft,Camshaft and timing cover work in/on the HM100 block? The blocks look identical on the outside. I know that both engines use a bunch of the same parts on them.Carbs,flywheel,coil,Blower housing ect.  Is the bore size the only difference between the 2? Or are the crankshafts also different? 

 

I would like to put the better of the 2 engines on the better blower and use the 8hp on my big belt drive pressure washer that currently has an old 5hp briggs powering it. Then I can finally turn the pressure up a bit. The pump is rated @ 4,500 PSI but I can only run it around 1800psi with the old smokey but usually very reliable 5hp Briggs flat head without stalling it.


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#2 4getgto ONLINE  

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Posted February 11, 2020 - 07:59 PM

I believe you're going to find extra bearing journals inside the HM80 block which the 10 won't have because it doesn't have the auxiliary shaft.
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#3 EricFromPa ONLINE  

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Posted February 11, 2020 - 11:47 PM

Did a bunch of digging.

 

Looks like the sump is just drilled the rest of the way through and a seal installed. Found 1 on Ebay with pics.

 

https://www.ebay.com...ity!15554!US!-1

 

I went up to the shed and wrote down the model number off of the HM80. Looked it up on parts tree and found the crankshaft part number. Tecumseh crankshaft part number 36245. Then looked up that part number and came up with it being used in the HM80 HMSK90 and HM100.  

 

Then I found these.

HM80   https://www.smalleng...atures/hm80.jpg

HMsk90   https://www.smalleng...ures/hmsk90.jpg

HM100 https://www.smalleng...tures/hm100.jpg

 

Crankshafts look to be the same. They have the same stroke. Only difference that I'm seeing is the bore size.  

HM80           Bore 3 1/8"         Stroke 2 17/32"

HMSK90       Bore 3 1/8"         Stroke 2 17/32"

HM100         Bore 3 5/16"       Stroke 2 17/32" 

 

I'll pull the HM80 sump off and have a look at the cam bearing/bushings before I go tearing both engines off and completely apart just to find out that it won't work. If it's just drilled for the extended shaft like the 1 I found on Ebay I'll proceed into tearing them both apart. 

 

10hp on a 24" blower with 11" impeller should make a heck of a good machine.


Edited by EricFromPa, February 11, 2020 - 11:48 PM.

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#4 oldironmm OFFLINE  

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Posted February 12, 2020 - 12:32 AM

Keep us informed please on how it goes. Sounds interesting.
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#5 dodge trucker OFFLINE  

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Posted February 12, 2020 - 11:09 AM

been there done that.... bought a Sears blower with a worn out basketcase engine, and had an 11hp OHV Tecumseh with the wrong crank, the crank was spared in the 8hp, so I swapped it right over. Some versions of the 11 hp actually called for the same crank PN as the 8hp did, they took the same rod, and more... 

go to a place like Pat's small engine parts or Jack's and play with their parts lookup pages, click on various 8 and 10hp versions of this engine. Youll find out they are more alike than you now realize.... 


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#6 dodge trucker OFFLINE  

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Posted February 12, 2020 - 03:26 PM

If the crank on the 10hp is "too big" I have also tak en them to the machine shop and have the PTO end cut down to match what I'm needing. Take both cranks so the machine shop knows what they have to match up to. If replacement is too small sometimes a spacer can be fabbed.
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#7 EricFromPa ONLINE  

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Posted February 16, 2020 - 04:02 PM

OK Update.

 

The Cranks are identical except for the PTO end being longer and larger diameter. One steps down to 5/8" and one and 3/4". 1 is also 1" longer than the other. Which is why I have to swap the cranks over.  

 

Camshafts are identical other that the auxiliary shaft that sticks through the cam cover. Found something a bit funny. The short cam on the 10hp looks like it was cut to length with a band saw and chamferd. There are clear saw marks on the outer end that are not on the other end. I bought this from the original owner and I am the only one that has ever worked on it.

 

I bet ya they make them much longer and then cut them to length as needed. It kinda makes sense that they would do it that way instead of having to make a bunch of different length cams.

 

Other than being longer the lobs and everything measures out to be identical. I measured with my little 2" Mitutoyo micrometer.

 

I made a mistake once with a crank journal. Don't measure a journal with a cheap Chinese digital Caliper. They can be off by as much as .005"-.008" which on most engines is going to be way out of spec. Either use a Micrometer or a Good brand name 5+ number Caliper. Most decent calipers will have a +/-0.001" Accuracy. 


Edited by EricFromPa, February 16, 2020 - 04:08 PM.


#8 EricFromPa ONLINE  

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Posted February 16, 2020 - 04:15 PM

I'll take a pic or 2 of the cams when I get back up there. It's clear that the 1 cam was cut to length.

 

Hope I don't need it for a couple of days lol. I pulled them off and took them apart. Then it started getting cold in my little work shop so I quit for the day. My darn fingers don't work well in the cold. They quickly get stuff and numb especially while handling cold tools.  


Edited by EricFromPa, February 16, 2020 - 04:17 PM.


#9 EricFromPa ONLINE  

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Posted February 17, 2020 - 03:33 PM

Got the 10hp back together. Would of had it together hours ago but I Had to go buy new gaskets. They were cheap. These smaller aluminum block Tecumseh engines use the gasket to shim crank end-play. So if you remove the gasket and just use gasket maker it might make it a bit to tight. I did not want to chance hurting something and I plan on keeping this blower going for a long time.    

 

Started 1st pull and runs fantastic. No knocking, valves are quiet and best of all no smoking. Ran it for 20 minutes varying the throttle and changed the oil. It's Good to go. I'll put it on the blower once I throw the other engine together. I'm out of room in the shed again. Barely enough room to turn around.

 

So it is confirmed. 8hp, 9hp and 10hp Tecumseh (snow king) flat heads are identical other than the 10hp having a larger bore.

 

The blower says 7.5hp on the plastic cover but if you look at the engine id tag it said HM80 which is an 8hp. Guessing that was a marketing thing from the blower manufacturer. Now it's gona have a 10hp on it. More power is always better lol.      


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