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Tecumseh: HM80 (circa '79)


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  #1  
Old 04-07-2007, 04:33 PM
Thierry M. Petersen Thierry M. Petersen is offline
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Default Tecumseh: HM80 (circa '79)

Hi All:

I am rebuilding my Ariens Snowblower engine (a Tecumseh HM 80, 8hp). I bought it used two years ago. It worked well for one year. It is now in tough shape: blows smoke, compression is low, has no spark, and it knocked like hell the last time it ran). The Carburator is a mess too - dirty & runs too lean (I think).

Anyway, two questions:

1) One of the flywheel magnets came off (see picture). How do I reconnect
it? I don't have a lot of experience but the construction seems
cheap.

2) What are your opinions of Tecumseh's from this vintage? The magnets
problem makes me think this is an "el cheapo" brand and my time might
be better spent getting a used engine of a different make, or rebuilding
another an engine of a different make. As I see it, there don't seem to
be too many guys collecting Tecumsehs. Makes me wonder.

The bottom line is: I need a low cost solution to get this thing running.

Thanks,
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  #2  
Old 04-07-2007, 05:16 PM
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Bill Geyer Bill Geyer is offline
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Default Re: Tecumseh: HM80 (circa '79)

The magnet can be re-installed with JB Weld or a good 2 part epoxy. Polarity must be correct, and I don't know an easy way to tell. I epoxied the magnets back in a Kohler alternator flywheel, but had other flywheels to copy, using a compass. Rust, debris, or hitting on the flywheel will make the magnets come unglued. Perhaps another Staker can instruct how the magnet goes.
Techunseh engines are ok but not one of my favorites
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Old 04-07-2007, 06:03 PM
Sky
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Default Re: Tecumseh: HM80 (circa '79)

i would do just like Bill said on the magnet(s) J&B weld works really good for glueing the magnet(s) back on. just make sure you have a clean surface there for the J&B welds to stick to. rust and any debree will make the epoxy come loose again. i've used J&B MANY times on tecumsehs with loose magnet(s) to answer you question, the magnets aren't really a cheap thing, thats just the way the tecumsehs were, they eaither had there magnets internal (underneeth the flywheel) or external (molded, or riveted into the side of the flywheel for the external magneto. dont really know why there's any collecting of tecumsehs going on, oh there might be a few people or so that collect tecumsehs but there just not like the other engines, thats all, a tecumseh was eaither a vertical shaft or a horizontal shaft, with nothing particularly fancy with any such features...they are pretty much just an engine...nothing special....that and there a pain in the A$$ to work on sometimes. Thats probably why. generally, tecumsehs are VERY picky engines, the old ones had to be timed2 or 3 ways, cam, points, and if the engine had an internal stater, that aswell had to be timed. if ANY 2 of the 3 was off just a smigen or if the valves weren't seating right, or wasn't set right, there was no way in H*ll that carburator and engine would tune in right and run. i've had my share of those. not fun and a rather headach to put it mildly. now todays tecumsehs are a little bit diferent now but there to new and cheap to be any kind of intresting. Briggs was always the best engine, and for numourus reasons i could set here an explain of all day but if you seen old pictures of the old briggs engines before and old lausons and kohlers and what not, you see why.
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Old 04-07-2007, 11:52 PM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Tecumseh: HM80 (circa '79)

Techempseh engines deliver more power to weight than B&S. The later ones are cheaper built, especially those built for sears (Read Programmed Obsolescence - built but to last just so long). Tech's do develop more power, BUT 1) they need clean fresh fuel, 2)they need regular oil changes, 3)READ - OIL LEVEL MUST BE MAINTAINED - READ - They WILL NOT tolerate a low oil condition. A Techempseh will nearly instantly throw a rod, or burn out a cylinder, if the oil is let too low., 3)They need clean air, 4They need a good muffler (factory or not) Running straight pipe will tend to burn out the exhaust valve.

I would NOT re-attach a dismounted magnet. Flywheels for these engines are cheap enough, not to have to worry if that de-stabilized magnet will come off at 3600 RPM. Besides, anything used to re-mount the magnet, will unbalance the flywheel. What made the original come loose?

If the engine was smoking - what kind? Blue/white - oil. Check valve guides (wobley valves in guides), damage to cylinder wall - if the walls are scuffed or heavily scored, go no further. The aluminum under the original wear surface is softer, and will wear out quickly. A short block is recommended (block,crank piston,rings, rod, valves and springs, lifters, etc). All you need to transfer is the mag, flywheel, sheet metal, head, and add a new plug., stuck rings, heavy carbon build-up on piston and head. Black smoke - carb float/fuel needle and seat bad - replace. Poor idle/transition - check throttle shaft for wear. These engines see a lot of throttle movement, due to load changes. The throttle tends to wear out. If you can move the throttle shaft more than .015, in any direction, replace the carb. New carbs are a lot cheaper than when this engine was built - $75-80 tops (I got one foe a HS60, cost me 45 + tax)
Poor compression, check valve stem clearances .008 intake, .010 exhaust, if the guides are OK. Bad valve clearances will cause engine overheating, which can lead to all your other problems! The H-80 is a good engine, and Techempseh makes a decent unit. Don't sell it short. Maintainance is the key, especially to this brand of engine.
Andrew
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Old 04-08-2007, 10:07 AM
Thierry M. Petersen Thierry M. Petersen is offline
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Default Re: Tecumseh: HM80 (circa '79)

Thanks all.

Andrew, to answer your questions:

1) It looks like some minor rust developed under the magnet's seat (not a lot, but some). It may have been weak and as I tapped to get the flywheel off (I was trying to be gentle) that must have been just enough to losen. Either that, or I hit it just right to cause my own problem.

2)The smoke is mostly blue. As I said, I only had this engine for two years. The guy that sold me the snowblower said it burned oil, so I took extra care and made sure it was always full. I had some carb trouble towards the end of that first winter and then I let the engine sit till late this winter.

I'll finish tearing it down this week and see what's going on. From everyone's responses, a Tecumseh isn't a lost cause. Any idea how much a short block runs?

Thanks again
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Old 04-08-2007, 12:34 PM
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Default Re: Tecumseh: HM80 (circa '79)

Dont really know how much a short block runs but chances are it would be cheaper just to rebuild the engine, but that also depends if there is any problems with the block, worn or just plain wore out main bearings, worn or scored cylinder..ect. sometimes your main bearings are the engine block, in that case it would have no press in type babbit type bearings to just push the old bearings out and press new ones in and them have them reamed to the crankshaft size, you would have to take the block to a machine shop or if you already have a machine shop and simply MAKE babbit type main bearings for the engine block if need be but if your main bearings are ok then i wouldnt worry about it. and if you have a scored cylender thats REALLY bad you can get 10 20 or 30 thousands oversize pistons for that engine and simply oversize the bore, reason for this is not particularly so the engine can become a hotrod, oversize is to attempt to remove the deep scaring of the cylinder with boring and honing the cylender to a specific oversize hoping at the same time that the scaring of the cylender goes away. if it's just your average scratch or scar in the cylender and you feel uncomfortable with it, 10 over usualy does the trick, if the scar is deeper, it usually takes a 20 over piston or so to clean the cylender up but if your cylender is ok then again, i wouldnt worry about it. as i said earlyer, if your engine block is in otherwise, good shape, it would probably be cheaper just to rebuild the engine other then buying a new short block. on the magnets of the flywheel, you'll be perfectly fine using J&B welds to stick the magnets back on, just make sure the magnets are stuck back to were they came from, as i said i have done that before, MANY times, i still have an engine the magnets came off of a few years back and i stuck them back on with J&B welds, there still stuck on.
if using J&B welds sticking the magnets back onto the flywheel causes an unbalance in the flywheel, it is very if not, extreemly minute and definitly not noticable, if so. using J&B for the magnets is probably stronger then what they stuck them on at the factory with anyway so... cause i've had the magnets come off for no reason...no banging on the flywheel or nothing, they just came off. and another thing, if you do indeed wish to rebuild this engine, i can help you with parts, i can get parts fairly cheap, there not cheap fall apart parts eaither, there aftermarket but definitly NOT cheap...if they were, i wouldnt suggest such a thing. i also have a parts HM80 tecumseh engine that ran at one time...i just set it in the corner, it needs a valve job, it pops and crackles when it runs and i did rebuild the carb but no change so i just set the engine in the corner. if there's anything wrong with your HM80 if you find anything worng like a bad block or something, i could let you have mine fairly cheap. it's a good block. just needs a valve job, i'll even do the valve job for you if you want it. engine dont smoke or nothing.
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Old 04-08-2007, 02:56 PM
Thierry M. Petersen Thierry M. Petersen is offline
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Default Re: Tecumseh: HM80 (circa '79)

Sky and all:

Thanks for the offer and info. I'll get back to you on both. The engine is off the snowblower and on the workbench right now. I will do some more exploring tonight (through this week).

Thanks again,

Thierry,

(aka: the only guy working on a snowblower in early April )
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Old 04-08-2007, 03:25 PM
Sky
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Default Re: Tecumseh: HM80 (circa '79)

oops, i goofed, actually i have a VM80 not a HM80...V and H...i cant remember to well so i guess my engine wouldnt work...

I CAN however, still help you with parts.
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Old 04-08-2007, 04:13 PM
Bill Sherlock Bill Sherlock is offline
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Default Re: Tecumseh: HM80 (circa '79)

I've had good luck with Tecumseh engines, including ones built for Sears, and at one time even preferred them to Briggs. My snowthrower is sitting in the yard as still might have to use it this spring. It's a 1973 vintage Toro Snow Hound with a 3 1/2 HP Tecumseh that I resurrected from a disposal site last fall. Used it a few times but really too small and only single stage but price was right!! (free)

Bill
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Old 04-09-2007, 09:28 AM
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Randy Hart Randy Hart is offline
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Default Re: Tecumseh: HM80 (circa '79)

The only problem I held against the Tec. engines was it seems the throttle shafts and their bore would wobble out long before it should have.. In the dealorship it was a costly phone call to inform the owner about a new carb.. Due to shop labor costs any bushings and shaft kits were out of the question.. I'm going on the hill to the scrap pile this morning to haul out a load.. I'll check and see if I have an 80 with a good flywheel for you..
Randy Hart Ohio
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Old 04-09-2007, 09:00 PM
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Default Re: Tecumseh: HM80 (circa '79)

Thierry, I looked today and all I find is an H 60, I thouht it was a much larger engine but it is what it is.. sorry..
Randy
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Old 04-09-2007, 09:12 PM
Thierry M. Petersen Thierry M. Petersen is offline
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Default Re: Tecumseh: HM80 (circa '79)

Hi All:

I took the head off and looked inside. The cylinder walls were surprisingly smooth - no pits or wear groves. The astonishing thing was that it looked like they were honed - I saw a uniform cross pattern on the walls - very light but there. Odd for an engine that is 25+ years old? It is aluminum so perhaps that is how it ages? I didn't see such a pattern on my 5s when I worked on that. To be honest, I can't be sure if this is not a problem. I have never honed a cylinder and am taking and educated guess.

I also put my feeler guage around the cylinder in hopes to check the rings: a .004 guage did not seem to go past the first ring. Is this a good test? I was stupid when I did the compression test and only tested it dry (i.e. without oil). It registered about 50-55. Fairly low, I think.

I also checked the valves - intake looks fine, but the exhaust valve has no gap between valve stem and lifter (but the both guides seem OK). So it looks like I have valve work to do. Any tips?

thanks again,
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Old 04-09-2007, 11:09 PM
Sky
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Default Re: Tecumseh: HM80 (circa '79)

...guess i could throw my 2 cents in again...as usual lol

ANYWAY, if you can still see a cross hatch pattern in the cylinder...i'd say you still have a very good engine block to work with yet...it probably hasn't been worked in extreemly hard conditions and musta been really taken care of good...as far as oil and filters goes..oil is the life of an engine..and filters.
on aluminum blocks with a cool bore, they sometimes call an engine a cool bore becouse it has no steel or iron sleeve pressed into the cylender like an I/C engine does (industrial commercial) since you have a cool bore, you dont have to hone the cylender, in fact, it's a nono acording to the engine books. i dont know exactly WHY but your not suppose to hone a cool bore (aluminum cylinder) but yet they supply oversize pistons for the engines to be bored out oversize so i dont know whats going on there but if your cylinder is good like you say it is, there is no need to hone it. you can however hone a steel sleeve engine or an iron bore, providing you know the rules to operating a hone and what to do and what to look for. on an aluminum (cool bore) your more likely of removing very useful metel from the cylender very rapidly THAN honing on an iron bore or steel sleeve bore.


now on ring end gap, the book says you should first have new piston rings on hand before you check your ring end gap inside the cylender. acording to the book, new ring end gap clearance should be a minumum of .010 thousands clearance to .020 thousands clearance so anything inbetween and you'll be fine. thats on all 3 rings. now on your ring side clearance (rings installed on the piston) the first ring (the compression ring) and the second ring (the scraper ring) side play should be very minumum of .002 thousands side play to a MAX. of .005 thousands. anything over .005 is definitly unsafe and is definitly prone to (as they say) busting or popping a ring. anything even below .001 thousand to a max. of .003 is REALLY safe and by rights, thats the way it should be...some pistons you cant even get a .001 thousand guage inbetween the rings and ring lands. so you should be ok if you see that everything is well within specs. they say a side play FOR THE OIL RING should be a minimum of .001 to a maximum of .004 thousands but the clearances i gave above pretty much takes care of it all. on compression, 50 to 55 is a little bit on the weak side and the engine is really due for new piston rings. now when you do the valve job, im sure you know what compounds to use for that, dont you? cource compound for the initial valve grind and fine compound to seat the valves in. by the time your done with a valve job, you should see a nice solid grey line around the valve face and around the valve seats. when your done, and with the engine internals assyembled back into the engine and the crank case sealed back up, then you gatta check your valve clearance by grinding VERY slowly and carfully or fileling the end of the the valve stem down a little at a time and check your clearance gradually between your intake and exaust valve stems and between the tappets. the clearnace on the intake should be .008 thousands and the exaust clearance should be .012 thousands. the clearances should be check only when the piston is (TDC) top dead center on your COMPRESSION stroke.

Last edited by Sky; 04-09-2007 at 11:16 PM. Reason: forgot to add a sentence.
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Old 04-10-2007, 12:26 AM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Tecumseh: HM80 (circa '79)

Check for valve guide wear. If you can move the valve more than about .005, you will probably need guides. Your compression will probably get better, when you re-clearance the valves. The reason you do not hone the Aluminum Cylinder, is as i stated above - the underlying material is not as hard as that of the surface of the original bore. It will wear more quickly than the original surface. In view of the compression, I would replace the rings only, clearance the valves, and put it back together!. By the way, the surfaces of the new rings are treated to wear more quickly than the underlaying material. Soft rings, hard cylinder, and they all wear in together. Weird science huh! break in the new rings with 10-30 oil.
Andrew
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