What can I do to get more power from my Tec HM80? - Snowblower Forum : Snow Blower Forums
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post #1 of 24 Old 07-07-2018, 08:53 PM Thread Starter
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What can I do to get more power from my Tec HM80?

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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post #2 of 24 Old 07-07-2018, 09:13 PM
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post #3 of 24 Old 07-08-2018, 08:13 AM Thread Starter
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Thanks, but I am looking for advice on power. My question is: do I have less power now than I did 15 years ago? Being gradual, it might be hard to notice.

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post #4 of 24 Old 07-08-2018, 08:47 AM
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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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post #5 of 24 Old 07-08-2018, 10:31 AM
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Frankly, if the RPM does not sag under load, you've lost nothing . . . If it does, it could either be a loss of power, or impatience :-) :-)
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post #6 of 24 Old 07-08-2018, 10:46 AM
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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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post #7 of 24 Old 07-08-2018, 11:25 AM
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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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post #8 of 24 Old 07-08-2018, 01:58 PM
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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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post #9 of 24 Old 07-08-2018, 02:06 PM
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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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post #10 of 24 Old 07-09-2018, 12:17 PM Thread Starter
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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?


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