tecumseh crank swap?

Don B.

Member
I just brought home a 2 stage walk behind snowblower with a bad engine, and have a hopeful replacement on hand. Having a 2:1 extended cam is tough to find when you need one. my replacement happens to also have the same. problem being, the crank PTO's are different between them.
the 2 engines are an HM80 8HP Tecumseh (bad engine, cam and bearing surface for it, in the block side cover are scored beyond hope) crank unhurt, mikes out as new.
I have been scouting the auctions and Craigslist recently looking for something worthy of this engine as I'm tired of watching it sit here. and adapting this one to work would be faster, easier and cheaper than any other way.. buying the parts for the original engine or seeking out another extended camshaft engine that would work on this machine. besides I'm itching to see if this "11HP" OHV really does seem more powerful than the 8HP snow king on my other blower with same cc/cid displacement.

the hopeful replacement is an OHV 11 HP Tec, model HMSK110.
both have same bore X stroke, also same crank and rod bearing journal diameter.
differences; PTO end configuration (reason for swap), dia of hole through crankpin in crank casting, thickness of counterweights; in this area the OHV engine has thicker counterweights and smaller hole thru crankpin... if I throw the lighter crank into the OHV block, will it vibrate my teeth loose from unbalance?
Plan B is to take the crank from the OHV engine and have its PTO end machined down to match the dimensions of the original engine's crankshaft so all the original pulleys and such still fit as originally set up. either way I am going to have to have a keyway cut into the end of the cam, the portion that protrudes thru the block... I have someone that can do that for me and "owes me a favor"...
being able to put the original engine's crank into the OHV engine would certainly allow me to get the machine back to blowing snow sooner.
 

If I understand it the 8 HP crank will fit into the 11 HP block, however, the crankshaft counter weights are different. Since it has the same bore and stroke I would compare the piston and rod weights between the two engines. If the reciprocating parts are of the same weight or close I would think the balance would be acceptable. Also, check the rod lengths, a longer rod tends to shake less.

Note: You state the OHV engine has thicker counter weights - this does have to mean it has a different balance than the 8 HP. The 8 HP could have thinner counter weights, but a larger diameter and actually balance the same.
 
It would seem to me that buying another engine would be a lot simpler, what your asking about is a lot of work for maybe a workable out come, if the 11 hp is a running engine why not just install it?
GB in MN
 
that is exactly the plan but the 11 HP crank is way different.
The 11 hp is just an engine I have had laying around for a while, good running low hour.

and like the dead 8hp, this 11hp has the extended camshaft, something very hard to find. I have this 11hp collecting dust and want to use it.
Plan B is to take the 11hp crank and have the pto end machined to match the one that was in the 8. Just thought that since these engines share bore and stroke, also main and crankpin bearing diameters, that if I could just swap them it would be easier.
 
So if I understand it the crankshaft on the 11 hp has a larger diameter, or is the length wrong, or is it a tapered shaft? I'm still thinking you would be far better off using the 11 hp engine. Have you checked CL for engines here in MN there are 4 /5 8 hp Tec snowblower engines for sale.
GB in MN
 
both larger diameter and too long. and stepped at the end though the step is not far enough to get the pulley to slide back to meet the machine's pulleys. yeah I have checked CL, but none available say anything about having an extended camshaft (which the 11hp also has) and I've had teh 11hp sitting collecting dust for too long now already. so I want to be able to use it.
 
How about going to a bearing store and getting a pulley with the larger diameter hub that would fit the 11 hp Tec. as for the for the camshaft extension shaft if you found another 8 hp Tec without it you could take the one from your bad engine and put it in the replacement engine the cover are very easy to convert, they are all the same just need to install a seal for the shaft.
GB in MN
 
not quite. The extended cam IS the problem with the 8hp, the shaft is chewed up at the bearing surface where it goes thru the cover. and with the stepped crank that is in the 11, simply finding an alternative pulley is out of the question.
good ideas though.
and as far as finding another engine, that kinda defeats the purpose here, I looked for a machine in otherwise good condition with a bad engine so that I could find a home for this good running 11hp that has served as a tripping hazard in my garage for a couple years now....
 
well an update. I just looked up both engines' model and spec numbers on parts tree, and found some interesting things.
Piston.... PN on 8hp, supersedes to same PN as 11hp takes.
Rod....... same story as the piston.
Flywheel.. same PN for both engines. (no I do not need a flywheel here, just another source of verification)

end play spec; 8hp 0.005-0.027 11hp 0.002-0.042 I dry fit the 8hp crank into the 11hp block and endplay definitely falls within acceptable range.
I think that it is going to work! great, that will save me a trip to the machine shop to have the crank from the 11hp turned down to match the pto end specs of the 8hp.
the OHV Tecumseh service manual I have, lumps 8-11hp OHV engines together in same column for internal engine specs
the 11hp is a 1998 motor, right smack dab in the middle of the time when they were increasing HP by virtue of a sticker... remember the lawsuits a few years back about overrated engine outputs?
 
Hi Don, now I understand, and looks like your making headway with your research, I'm thinking you'll get it figured out, and I fully understand about finding a use for the trip hazard. That's one think about Tec that can drive you up a wall they built so many engien of the same hp physical size etc and all different, B&S seems that their engines are a lot easier to interchange cranks fairly standard etc. Good luck hope you get it going, here in WC MN so far the need hasn't been to great but we still have a lot of winter to go.
GB in MN
 
had same here i just stuck another new engine on it for less than what you are trying to accomplish sure looks to me like.
 
So you have replaced an engine for less than the cost of 2 oil seals and a side cover gasket??? I have this 11 hp motor here already and it is a good runner currently just collecting dust.

I don't see them with extended camshaft like this come up very often, but I have one so why not put it to use???
 

Sounds like a plan is coming together. It is curious that the rods and pistons share P/Ns and the crankshaft is different. I assume the 8HP was a flat head with the cylinder straight up and the 11HP is an OHV with the cylinder off at an angle. This could account for the different looking counter weights - perhaps they wanted a sightly different balance factor - don't know. However, I still believe the balance will be acceptable. Good luck.

Note, there is an error in my original post - the word "not" is missing: The sentence should read, "...this does not have to mean it has a different balance...". I suspect you figured out what I meant.
 
I have never swapped parts on a Tecumseh, so can't say for sure, but I tried something similar with a Briggs engine once where the crank "appeared" to be the same and ended up with an engine that vibrated like crazy. I personally would not spend anymore time on a Tec than it took to remove it and throw away. Had one on a snowblower once, ran awesome, when it was 80 out. It was a great day when it exploded and I swapped to a Briggs. Dad still uses that blowers, thanks me for swapping out the Tec every winter.
 
I hear that all the time about scrapping an engine just because it's a Tecumseh. Well I don't know why but I tend to have better luck with them than Briggs. I will say that I liked the carbs on the older ones better than the newer ones.
But you're probably a Chevy guy ?nyhow, I have always been a diehard Mopar guy....
 
you were talking about switching cranks and everything else in the reply. now its just seal. what ever works for ya fine.
 
I don't really have any vehicle loyalty, lol. My family does have an aversion to Tecumseh engines, though. Never had one that ran great and/or was dependable.
 
no not quite. I am replacing the seals and side gasket in addition to the crank, so I do not end up with an oil leak when back together.
I have an 8hp that is bad, but the crank isnt damaged, and happens to fit with what the machine itself needs.
I also have this 11hp just sitting here not being used at the time.
did not have to go out and buy that.
I also do not have to go out and buy the good crank because I already have that in this junked 8hp.
so all that I have to go out and get, is the gasket and seals.
I cannot go out and buy an engine for the cost of a gasket and a couple seals and an hour or so of my time (I do not charge myself for my own labor LOL)
 
Over the years I have found that if someone buys a piece of equipment that does not give satisfactory service, they badmouth that brand from then to eternity. I worked on Sears lawn and garden equipment for 22 years and saw a lot of Briggs engines give major trouble as well as Tecumseh. I never worry about what engine something has on it, as long as it is properly cared for, it will give good service. If you have and/or can find everything you need to repair it, then go for it!
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top