Want rebuild my HM80

[mml4]

Tecumseh HM80 15521X,Family 4TPXS3182BA,DOM 04302CB0041. This engine powers a MacKissic self Propelled Vacuum-Chipper Shredder. It has pulleys on both the crank shaft and the camshaft. The engine starts easily on full choke and runs with sufficient power. It smokes and uses oil. The compression tester says 67psi but I don't know if it has an automatic compression release. It pulls through very easily and feels like it has little compression. The shredder wheel is a large heavy welded assembly bolted directly to the crank. If I turn that by hand the engine feels like it has no compression! It hot starts only under full choke but does so on the first pull as it does when it is cold.When you shut it down it keeps turning over for several revolutions due to inertia and what i feel is a lack of compression. I am going to rebuild this winter as the duel pulley block is impossible to find and the replacement Briggs that MacKissic uses now is only 6hp and a small fortune.
OK-Thats' my tale of woe! Now some questions-
1)Am I correct in assuming the crank is ok as the engine has never seized?
2)How do you check if the valve guides are ok? Can they be replaced if they are worn? The last time I rebuilt an engine I just cleaned up the carbon and reused the old valves after hand lapping them. I didn't pay any attention to the guides because I didn't know better. I got lucky as it worked but am concerned this time.(Ignorance is bliss).
3)I have a new set of stock oem valves. Should I use them?
4) New piston,rod and wrist pin are available from Stens or OEM if I hunt around. Are the Stens parts acceptable?

I hesitate to say money is not an issue because it always is but this a VERY important machine to me! I am resigned to spending some money. I went to many of the local shops thinking I would have them perform the rebuild but after discussing it with them I have no confidence in their abilities or desire to do the work.
All advice,answers to my above questions and tips will be greatly appreciated. If anybody knows of a reputable COMPETENT rebuilder on Long Island New York please let me know.
Thanks,
Marc

[bgsengine]

Tecumseh HM80 15521X,Family 4TPXS3182BA,DOM 04302CB0041. This engine powers a MacKissic self Propelled Vacuum-Chipper Shredder. It has pulleys on both the crank shaft and the camshaft. The engine starts easily on full choke and runs with sufficient power. It smokes and uses oil.

That does not necessarily mean the problem is rings or valves - Check your breather tube (unhook it a few minutes and let engine run in a fairly clean environment) and see if it is blowing any oil out - if the breather is bad or oil drain in the breather gets plugged it can pass oil into the air intake and burn off in the engine.

The compression tester says 67psi but I don't know if it has an automatic compression release.

Most recoil start engines will have a bit of compression release. 67 PSI is not bad - not "like new" either though. Accuracy depends on how good the gauge is, and how the test is done, hot or cold (preferably both for comparison)

1)Am I correct in assuming the crank is ok as the engine has never seized?

never assume. You'll need a micrometer - crank can wear without seizing. as long as it is within wear limits, it'd be OK.

2)How do you check if the valve guides are ok?

Measure them. a "SWAG" method would be to see if a new valve has side play in the guide - a little is OK, a lot (such that when valve closes it can hang on the seat on one side) is not.

Can they be replaced if they are worn?

Usually need special tools - reamer and finish reamer to either replace or re-bush (new bushings) - very expensive tool sets.

3)I have a new set of stock oem valves. Should I use them?

If you got 'em and they are correct for the engine, I'd say yes, otherwise they just sit on the shelf unused... Might as well use 'em.

4) New piston,rod and wrist pin are available from Stens or OEM if I hunt around. Are the Stens parts acceptable?

Nothing like O.E.M. parts - if you want reliability and "fix it right the first time" , OE is recommended. With aftermarket parts you take a risk that their quality control is not up to the standards of the O.E.M. - Even though they give a warranty on their parts, what happens if a rod breaks and blows a hole in the side of the block? Will Stens get you a new engine?

I went to many of the local shops thinking I would have them perform the rebuild but after discussing it with them I have no confidence in their abilities or desire to do the work.

Many shops have little to no experience these days in rebuilding. Most times the cost to rebuild is more than a short block or replacement engine. Rebuild is usually only an option if there's no other service options available.

All advice,answers to my above questions and tips will be greatly appreciated. If anybody knows of a reputable COMPETENT rebuilder on Long Island New York please let me know.
Thanks,
Marc

Hard to find a competent rebuilder, but if you know a shop or a retired tech that has been in the business 30+ years, you will probably find a competent rebuilder. Engines kind of stopped being worth rebuilding something like 10 - 15 years ago.. overhaul parts plus labor became a bigger expense than a short block or replacement engine, as shop labor rates increased, and manufacturers (and shops) started jacking up prices on rebuild parts, to justify selling short blocks or new engines. I can remember when I could rebuild a 3.5 HP Briggs Pushmower engine for less than $50 and still make a great profit.. these days, same job would run to $300+ , while a replacement engine would run $185-$200

[mml4]

BGSENGINE=
"That does not necessarily mean the problem is rings or valves - Check your breather tube (unhook it a few minutes and let engine run in a fairly clean environment) and see if it is blowing any oil out - if the breather is bad or oil drain in the breather gets plugged it can pass oil into the air intake and burn off in the engine".

Interesting in that I checked the air filter today and the housing had oil in the bottom. The breather tube runs to a tubing adapter on the carburetor and is held in by a clamp. I changed the breather filter in the spring after I did the clean up in the yard from the winter. I will test it as you suggest. Wouldn't it be wonderful if that was the problem!!!
Thanks,
Marc

[bgsengine]

If you changed the breather filter (the one I am thinking of) you would have had to remove the breather from the engine.. If that is the case, it is *very easy* to put breather back in upside down with drain hole pointing up and it fills with oil, with the very result you describe.

Also have to check that drain hole (It will be just a very small , "wire size" hole in the bottom corner, usually) is not plugged - simple check- poke some tag wire (bread bag tie?) through the hole and make sure it isn't plugged from sludge or carbon (from cooked oil) - new breather is much cheaper than engine rebuild, if it comes to that. Just make sure drain hole is pointing down when re-installing

[mml4]

If you changed the breather filter (the one I am thinking of) you would have had to remove the breather from the engine.. If that is the case, it is *very easy* to put breather back in upside down with drain hole pointing up and it fills with oil, with the very result you describe.

Also have to check that drain hole (It will be just a very small , "wire size" hole in the bottom corner, usually) is not plugged - simple check- poke some tag wire (bread bag tie?) through the hole and make sure it isn't plugged from sludge or carbon (from cooked oil) - new breather is much cheaper than engine rebuild, if it comes to that. Just make sure drain hole is pointing down when re-installing

I will check it first thing on Friday after Thanksgiving! I will let you know what happened!!
Thanks,
Marc