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Discussion Starter #1
I have a Tecumseh HM80 sno-king from 1977 and would like to see if there is any preventative maintenance I can do on it this summer/fall to ensure it delivers maximum power. My first thought was to test for compression and then if low look into the head gasket, valves, and rings.

Are there other things I should check so that when we get snow, it can muscle through it?

Thanks.

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You probably have less power than before, yes. Likely due to reduced compression.



I had an HMSK80, I found the valve clearances were a little too large, due to the valves wearing over time. This can prevent them from sealing fully. I had to remove one valve down carefully grind down the length by a few thousandths of an inch.


Checking valve clearances is pretty easy. On my engine there was a small rectangular cover on the side, you'd remove that and use feeler gauges to check clearances. *Changing* the clearance is a pain, unfortunately.



But unless there's something severe (a blown head gasket, leaking valve that could manifest itself as a glowing muffler, or backfiring out the carb, etc), I'm not sure you're going to find a silver bullet that's going to make a big noticeable difference.



A more powerful engine is one option, of course, but that's somewhat involved. So you'd have to make take a look at your engine, see what you find, and then decide how much of an improvement you're looking for.



If your valves are good, head gasket is intact, etc, and you're looking for 20% more power, I think you're going to have a hard time getting that from your engine.
 

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That's a good point. On a related note, if you can remove the carburator's heat box (air shroud) you might be able to see the governor linkage, while running.



If, while blowing heavy snow (very difficult to simulate in summer, unfortunately), the RPM sags by more than maybe 100-200 RPM, and the governor hasn't opened the throttle plate fully, then the governor may not be giving you your full effective power. I re-adjusted my governor a few times on a newer Tecumseh (OHSK100), then also replaced the governor spring, and that helped. It reduced the RPM sag under a load, the governor seems to do a better job now.



I've considered temporarily putting a string to the throttle plate directly. So that, while blowing heavy stuff, I could briefly give the string a tug to open the throttle plate fully. This would let me see if the engine actually has more power to give (and the governor is letting me down), or if I'm truly out of power.


But adding a string to the throttle plate needs to be done a bit carefully. If something caught on the string and kept it yanked, with no load on the engine, the engine RPMs would climb too high, and you could break the engine's connecting rod. Then at least you'd get to upgrade your engine :)
 

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adding a cheap ebay digital tach would at least help in determining what rpms its running at idle and/or load, if rpms are low at wot but with no load you will loose hp, should be ~3600rpm at wot, governors job is to try to maintain that rpm under load for max hp

 

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Predator swap, impeller kit, better tires, auger bearing, etc, etc. She is 40+ years old. Maybe something a bit nicer\newer off craigslist? great time to buy....
 

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For better understanding your current engine, the cheap digital tachometer is a great idea. You can at least be sure the RPMs are set correctly, and see how much they're falling during use.



Other hardware ideas from gibbs296 are good suggestions. The impeller kit will help you throw further, by making the impeller pump more effective.



Also a good point about shopping for good deals on more-capable machines during the off-season, if that's of interest! I wouldn't go with just some cheap brand that's got flashy features but limited substance. But a nice newer Ariens, Toro, etc, could be a nice upgrade.
 

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Discussion Starter #10
Thanks all.

I'll take a look at a digital tach that doesn't need a 12v power source.

I might also pull the head and clean any carbon, inspect the valve seats, and the cylinder wall.

Also, I plan on looking at the valve/tappet clearance. My dad has a spring compressor tool that will come in handy. I have a Tecumseh shop manual with the tolerances.

As far as compression, I've never tested it, and I don't know anything about this subject. Is this the type of tool I'd be looking at? https://www.amazon.com/Innova-3612-Compression-Tester-Piece/dp/B000EVU89I/ref=sr_1_5?ie=UTF8&qid=1531152652&sr=8-5&keywords=small+engine+compression+tester
 

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if it aint broke dont fixit.
remove spark plug and look into head or use a cheap camera scope attached to a mobile phone.
tach will tell u if its running at spec rpm at wot.
tach is hooked up to spark plug wire and runs off internal watch battery type that last a long time.
best investment without breaking something is impeller mod bar none. engine teardown for the sake of doing it is wasted time, prone to user error on teardown/reassembly.
imo, ymmv
 

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I think vinnycom makes some good points.



Extra carbon in the head will actually increase your compression ratio a bit, theoretically increasing power by a touch :)



You don't need a spring compressor to check valve clearances. Just remove that little side cover (assuming it's like my engine), as well as the spark plug, and follow instructions for checking clearance, comparing the results vs the specs.



Yes, that sort of compression tester will do what you want. Compression tests can be a bit tricky to interpret, however. There is an automatic compression-release on most engines, which will give "artificially-low" results. It props one valve open just slightly during the compression stroke at low RPMs (like when starting it), to make it easier to pull. This bleeds off some pressure. The amount of compression reduction is based, in part, on the current valve clearances.



If you *really* want a reading subject, you could look into leakdown testing. Leakdown test are done with the engine not spinning, so it's kind of a more controlled test. You then add your own controlled air pressure source *to* the cylinder, then you listen for where the air is leaking out of the engine.



Air is leaking out the crankcase, through the oil filler tube? Leaking piston rings. It's coming from the intake? Leaking intake valve. It's coming out the exhaust? Leaking exhaust valve. Coming from around the head? Leaking head gasket.



To do a leakdown test, you might position the piston a little past top-dead-center (like when checking valve clearances), so that both valves are fully closed. This is unlike when using a compression tester, which, again, has the valve pop open slightly during the test, due to the compression release while the engine is turning. With the engine in this "tight" position, you can better evaluate what's sealed, and what isn't.



Some info here about how to make your own, simple leakdown tester, if you were really inclined:

https://www.mytractorforum.com/44-small-engines-repair/1279105-low-compression-lawn-mowers-advice-needed.html
Or, frankly, the proper fittings, along with the compression tester adapters, might do it.


After reading about the DIY leakdown tester, I may try making my own, just to have it available. Ripping a spark plug apart sounds like a bit of a pain. But I have a welder, so I could attach a steel air fitting to the core of the plug. But if you had a compression tester, that gives you an interface to the spark plug hole, and you might just need to come with a way to connect your air compressor to that.



I haven't done a leakdown test, but I'd be leery of using much pressure for a test, at least initially. I'd start with maybe 5-10 psi, 20 tops. With a 3.3" bore, 20 psi is putting 170 lbs of force onto the piston. I think you don't want the piston exactly at top-dead-center. Which means that your air pressure is trying to make the engine spin, so the piston can go to the bottom. So don't touch anything on the engine or machine that could potentially turn, while pressuring the engine. Safety first! Locking the flywheel in-place (maybe with a ratchet strap wrapped around?) might be good for safety and consistency.
 

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IF . . . you really wanted to boost the power you might want to check around your area for someone who modifys engines for go carts. It's not a DIY but they can do things you can't and pull more than 8hp from the engine.

It's summer so you have time to check things over and see if anything is out of specs, if not but just a little worn than it's a matter of are you good with how it's performing or do you need/want more power. If it's the need/want then either modifying your engine or going with something bigger is the next step.

.
 

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And quite frankly, I wouldn't try to make any performance mods, personally.

If you definitely need more power in this particular machine, swap in a more powerful engine. Don't start changing cams, finding forged connecting rods, etc :) This is isn't a go-kart, there are no displacement restrictions, and power-to-weight doesn't matter.

But it's summer, so a good time to shop for a different, more capable machine. Which is the simple approach, at least, and newer machines have some advantages for ergonomics & safety. .

Sorry, you're getting a bunch of discussion on this, there's not a whole lot else to talk about at the moment :)
 

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I replaced an older Tecumseh HM80 on an Ariens 10,000 series with a Predator 212 CC from Harbor Freight. $99.00. This engine performed great this past winter, handled all snowstorms with ease. (Vermont) and has more power than the Tec. I had thought about upgrading the Tec., but with the cost of parts, and my labor time, it just isn't worth it IMHO.
 

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Modify the impeller works great, light snow or heavy... I do it a lot... 8 hp motor will throw about 25 to 30 feet... Some times there is a large gap between impeller and the housing, you close that gap up to the thickness of a paint stirrer you'll notice a big difference, drilling hole might be a pain, I use light rubber mud flap... 1/4" bolts 1" long with flat washers and nyloc nuts....
 

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Discussion Starter #17
Thanks, impeller mod is on my radar. I just ordered a tachometer so I can make sure WOT is where it should be, and also check how well it maintains RPM under load once we get some snow. Just for grins, I'd like to check the compression and see how it compares against what the shop manual says it should be.

It's a great engine and I love using it, I just want to keep it healthy and safe as it enters Senior Life! :nerd:
 

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I replaced an older Tecumseh HM80 on an Ariens 10,000 series with a Predator 212 CC from Harbor Freight. $99.00. This engine performed great this past winter, handled all snowstorms with ease. (Vermont) and has more power than the Tec. I had thought about upgrading the Tec., but with the cost of parts, and my labor time, it just isn't worth it IMHO.

It does not have more power then the tech
It turns higher rpms which makes the impeller spin faster
So it appears to have more power
 

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It does not have more power then the tech
It turns higher rpms which makes the impeller spin faster
So it appears to have more power
But the Tec was a bit over rated on HP, the predator is a bit under rated on hp and the Tec is 40 years old. So pretty much same hp and the Pred is new and spinning at higher rpms. I think I see which one is likely to provide a better experience.
 

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But the Tec was a bit over rated on HP, the predator is a bit under rated on hp and the Tec is 40 years old. So pretty much same hp and the Pred is new and spinning at higher rpms. I think I see which one is likely to provide a better experience.

All the motors were over rated then
the tec has more torque by alot thats what counts
my over rated 8hp tec blows snow 35 to 40 feet... farther then the vid of the guy on here with a predator
also has electric start
and its a winter engine
pred needs a carb box made


Bottom line the impeller kit is what he needs not a motor
 
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