Mighty Mac Tires

adielFebruary 5, 2011

I recently purchased a Mighty Mac 12P Shredder with the 8hp engine. The engine does not start and it needs new tires. I hope $120 was not too much. What do you guys think? Does anyone know which tire and the cheapest place to get them online is? I need all four tires.



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Well, 120 bucks good price if in good condition. IF you have to replace the engine, cutting blades, ect... it may not be. Inspections and condition only clue you may have if it's able to the put back in service if the owner has no clue, which maybe an indicator right there. But. most equipment as this just sets around and gets minimum use and the carb. plugs up. Most owners don't know how to fix it and don't want to pay 75 dollars hour Plus parts to have it repaired. Plus the brought it for couple jobs and then it just sets. So your questioning at the time you buy it will tell you alot?

you need to google the tires size, Locally you can check out harbor Freight, Attwoods, TSC, and any other farms type store you may have or may not have in the area. Best to shop around both online and locally.

as for the engine doesn't start not alot go on? You need to do the basics first. Remove the air cleaner, spark plug, look at the condition of the oil. The oil can tell you alot? is the oil level low? sticky black color indicate the oil wasn't changed regularly and low oil means either it's and oil burner (possible worn out) or the owner didn't even have the since to keep oil in it? either one would be not good, but don't render the engine done for.

Next spark plug, Inspect it, is there black build up on the sparking end? spray carb. cleaner on it and scrub with wire bush. check gap. Now pull the rope, does the engine turn over easily with no clanking noise? if so now spray carb. cleaner down the spark plug hole and pull the rope. this will lubricate the combustion chamber and prime it for starting.

Now put the spark plug on the spark plug wire lay it against the metal part of the head raise the throttle, pull the rope looking for spark at the spark plug end. Now if the oil is in the XXXXX/s on the dip stick, install the spark plug, spray some carb. cleaner down the spark plug hole and pull the rope. Should fire within three or four pulls. If it wants to fire, you now have to check condition of the gas tank. IF it's dirty or got old gummed up fuel you need to take the gas tank off and clean it out. using fresh gas by shaking it. sometimes you have to get a bottle brush and scrub the inside of the tank or use a pressure washer to get it clean. If you use a pressure washer you have to rinse all the water out with gas or alcohol.

If the engine wasn't totally neglected or broke this should get it to start. after starting let it warm up then change the oil and put new air filter in if the old one was dirty.

    Bookmark   February 5, 2011 at 7:50AM
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Does your 12P have two wheels or four? And do you need just new tires, or the entire wheel/tire assembly. I left my 12PT9 parked outdoors (under a cover) at a worksite a few years ago, and the rear tires went completely flat during the winter and I was unable to re-inflate them. I didn't try too hard, because the rubber had become somewhat rotten and was cracked. I jacked it up and swapped a couple of wheels from a utility wagon that I had. They were slightly larger than the tire/wheels that were on it, but that just gave my shredder-chipper a little more ground clearance, which came in handy. The size of your tires should be molded into the tires themselves. The 12P/12PT/12PTE PARTS LIST lists the tires as part 18, "4.10/3.50 X 4" PNEUMATIC WHEEL". If your metal wheels are still intact, it is possible to buy and install new tires, but inflating them is kind of tricky, because the original equipment tires are tubeless. Rather than try to inflate them myself, I would just take the wheels and new tires to a tire place.

Inspect your swinging hammers to get an idea of how many hours of actual use were put on your machine. If their corners are relatively square, it wasn't used much. But if it was used a lot, the corners will be rounded. If at least one of the hammer corners is square, you can swap ends and or sides to use a fresh set of hammer corners. A good feature of this shredder-chipper is that you can get four times the use out of the hammers by using all four corners of the swinging hammers. It explains that in the manual. There is a separate manual for the shredder chipper and for the engine.

If you don't have the manuals for your 12P, contact MacKissic Tech Support to see if they can provide you with a copy of each. They might be able to make a Xerox copy of their file copies.

My 9hp 12PT9 is pretty old, and your 8hp model is probably older still, so you may be faced with needing to sharpen or replace the chipper blade (I replaced mine), replace the V-belt (I am on my third V-belt and I have a new spare hanging in the garage), and possibly the centrifugal clutch. The main bearing needs to be greased every 10 hours of use, and if that wasn't done, it may need replacement as well.


    Bookmark   February 6, 2011 at 3:39AM
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I am not too sure on how to tell the quality of the blades or hammer. I am going to post some pictures:

Thank You,

    Bookmark   February 6, 2011 at 9:18AM
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Those flat head engines usually run for ever. all you probably need to do depending on how long it has set is clean the carb., gas tank, spark plug, rinse out the comb chamber with carb. cleaner very basic stuff and routine maintenance. Even if you have to remove the head and decarbonize the comb. chamber you can clean the head gasket up and reuse it, done that several times never brought new head gasket, they are thick multply metal. As for the tires just put tubes in them, once the come off the rims very hard to get them back on and when the go flat you'll have same problem, try to lub the end bearings on cutter shafts and maybe sharpen the blades if it don't chip good. You stole that one IMO.

    Bookmark   February 6, 2011 at 10:00AM
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Those pictures are very helpful, and you are a capable photographer. I agree with RC that you got your money's worth on that deal. If you bought this machine new it would cost you over a thousand dollars. Your 5th picture shows that the hammers have had very little wear, with nice square "sharp" corners. (The corners on my hammers have worn to about a one-quarter-inch radius, so I am overdue to "flip" my hammers.)

Those tires have plenty of tread (actually pulling one of these "wagons" around your property puts very little wear on the tires.) If the valve stems are in good shape, you could just put this thing up on blocks and take the wheels and tires to a tire place where they can use their high-volume air supply to "blast" the tires into a tight fit on the rims. Some places use a little acetylene or ether to "explode" the tires onto the rims, but I wouldn't recommend that it. I think they are just showing off when they use that reckless technique. This situation is very common with tubeless tires on outdoor power equipment, so a tire place should be able to get them seated and aired to the pressure indicated on the tire.

Your last picture shows the chipper blade and the throat of the chipper chute, and the fact that most of the paint is still on the chute confirms that this machine has had very little actual usage. When it comes time to remove this blade to sharpen it, you will access it through the swinging "door" shown in your first picture. The grease Zerk for the main bearing is close to that door. It originally had a plastic or rubber cover on it, but those things get lost easily. I accidentally damaged my Zerk cover with a MAPP torch flame when I was heating my blade retainer bolts to remove them. My Zerk cover is still there, but its retainer loop is fried. Those retainer bolts are factory installed with the Red grade of Loctite to absolutely lock those threads despite millions of impacts. That is vital, because that chipper blade takes thousands of impacts per minute when you are chipping. It could be catastrophic if those bolts loosened in use, so you shouldn't be able to remove those bolts without heating them very hot. After they have been heated to burn out the Loctite, they come right out. But you should use Loctite Threadlocker Red 271 when you reinstall them. Absolutely don't use the blue or the green grade of Loctite for those blade bolts.

The blade is high grade tool steel, and probably should be sharpened by a professional with a wet sharpening stone. You don't want to dry sharpen it, because the heat generated by the sharpening process could de-temper the edge. Ideally this tool steel blade could remain surgically sharp for years while cutting plain wood, but in reality wood contains some silica and your branches will have some grit and dirt on them and the blade will lose some of its sharpness over time.

This is a picture of my 12PT9 at a worksite this fall after I had just "polished off" a large brush pile to make a space for a flower bed next Spring.

You can see those oversize back wheels in that picture. The brush pile was large and an eyesore, and it yielded many wheelbarrow loads of wood chips for path material in my backyard garden.

(not associated with any product or vendor mentioned)

    Bookmark   February 6, 2011 at 2:18PM
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Thanks guys, I feel a little better now! I took out the carb and am thinking of ordering an overhaul kit for it. I found the kit number on Briggs website for my engine. I then found a cheaper version of it on ebay. Not sure of the difference between Briggs branded and this one but its cheaper:


The overhaul kit also contains a lot of extra things I think I don't need to change, what do you guys think? In reality I think I just need to change the Gasket for the float bowl and the Gasket from the intake to the carb.

So basically so far, I placed the carb in the carb cleaner gallon for 20 minutes. This is the second carb I attempt to fix so let's see what happens. The air filter was pretty dirty and I got a new one. I can see why they didn't change the air filter since you have to remove that bracket in front first. I also took out the spark plug, poured some sea-foam into the spark plug hole and then put in a new spark plug.


    Bookmark   February 6, 2011 at 8:09PM
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I would of just use spary carb. cleaner and blow out all the small passages of the carb. and needle and seat, but thats me. for one it cheaper than can of liquid cleaner and you will have other uses in the spray can. Then if that didn't work try to replace needle and seat and gaskets, putting kit in only helps if the needle and seat are worn out or a gasket is torn and leaking. Most of the time all it needs is blew out.

same thing down the spark plug hole. You can't hardly hydro lock the piston with spray carb. cleaner unless you set there and spray for 5 mins. pouring down the spark plug hole will usually put too much fluid inside the combustion chamber. You should of atleast pulled the rope couple of times to blow some of the liquid out the spark plug hole. All that liquid has to go some where? either down in the crank or out the muffler. I just pull the rope and blow most of it back out the spark plug hole.

Engine will fire off carb. cleaner alot easier that seafoam, so I would still spray a 4 second blast of cleaner down the spark plug hole and pull the rope before attempting to start the engine. You didn't mention what condition the oil was in or the level?

    Bookmark   February 7, 2011 at 5:57AM
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A couple of things I forgot to mention. First thing I did was to put in a new air filter. (The old one was dark and had a little bit of grass on the outside part of the filter. The inside of the filter was clean with no contamination getting through.) The reason the engine never turned on was that the valve under the gas tank was off! When I turned on the gas valve, the engine still did not start. I took off the spark plug, put some starter fluid down the spark plug hole mixed in with the sea-foam, put in a new NGK spark plug and it still did not start. I then noticed the new air filter was filled with gasoline. I then proceeded to remove the carb. The float bowl was very nasty with a crud of black stuff. I cleaned everything out, soaked the carb in the carb cleaner gallon for 20 minutes and then could not assemble it because the intake gasket was destroyed. As you see in the ebay link above, the gasket also contains a heat barrier. That is when I thought of getting the overhaul kit for the carb. As far as the oil goes, it was missing some oil so I topped it off. The oil did not have metal in it, it was dark. I plan on doing an entire oil change also once the engine starts. So that is basically where I am at now...


    Bookmark   February 7, 2011 at 7:53AM
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Hey Ariel,

Very nice purchase!

It seems you're pretty capable around equipment. If you're up for it and have an air compressor, you can do those tires yourself without much trouble. I've done it many times.

1. Take the wheel off the axle or get it off the ground somehow (I prefer to take it off so I can work on a bench).

2. Get the beads (that's what contacts the rim) close to the rim. You can add tire sealant to prevent leaks while you have it off the rim, if you so choose.

3. Wrap a light duty ratchet strap around the circumference of the tire to put pressure on the beads. You need to make sure you have a good seal around the circumference of both the inside and outside bead. Sometimes you need to wiggle the tire back and forth as your adding air to get the seal.

4. Add air.

5. Once you get a seal, stop airing it up and take the strap off.

6.Complete airing it up

I got to thinking there must be a youtube video that shows this and I found one of many - http://www.youtube.com/watch?v=QiojD1FoZJA He uses a short length of rope, but I've had better luck with a ratchet strap.

Good Luck!

    Bookmark   February 7, 2011 at 1:05PM
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Keep us posted on your progress. I can't profess any engine expertise, because I have never had any trouble with mine. I have replaced the air cleaner and I try to keep it clean. I am very careful to keep the oil topped off, and I change it as frequently as the engine manual recommends, even if it isn't very discolored. I drain the oil when the engine is hot, and tilt my 12PT9 enough to get a good drain-down. A brick under the "away" wheels is usually sufficient. I have used mostly Mobile One with a heavier weight range during warm weather and a lighter weight range in cold weather. I suppose I should check my spark plug gap, because I think it has been a while since I did that. Obviously I set the choke for starting the engine, unless it has been only a few minutes since I shut it off. It usually starts on the second pull when cold and on the first pull when warm.

If you should pull the engine cord several times with the choke set, you may have gotten into a flooded mode. Sniff the muffler to see if you smell gas. I use the highest grade of gasoline available, which nowadays seems to be only 91 octane in this area. I used to use 93 octane when it was available. I think it is a good idea to add some Sta-Bil fuel stabilizer to the gasoline because sometimes you don't use your outdoor power equipment for an extended time. I also use fuel stabilizer for my chainsaw, tiller, snow blower, and lawn mower for the same reason. Except, during the Summer, I skip the stabilizer in my lawn mower because I know I am going to be using it every few days.

(not associated with any product or vendor mentioned)

    Bookmark   February 7, 2011 at 1:34PM
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dmullen(Southern CA)

I agree that these small tires are hard to inflate. Something that worked well for me last time was removing the valve stem core before inflating. That made the beads pop right up and in place.

    Bookmark   February 7, 2011 at 5:51PM
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OK, first off do you know if you getting spark? Second was the gas tank dirty? is so when you turned the valve on all the contaminates went right into the carb. Next you can't have bunch of fluids inside the comb. chamber and expect it to start. This is why you pull rope with the spark plug out to to blow out the excess. Starting fluid not my choice for attempting to start and engine. IMO it evaporates too quickly unless you are spraying directly down the carb. while you cranking it over (pulling the rope with one hand and spraying with the other)

Consentrate Sea foam directly into the combustion chamber will coat every thing and IMO inhibit the ignition spark to egnite what little starting fluid you sprayed in do to the evaporation rate by the time you got you spark plug back in. this IMO why carb. cleaner is much better, it also has some lubricant and fires much like gasoline and evaporation rate is much lower than starting fluid.

IMO hears what I would do. First find out it you getting spark? is so remove the plug )buy a can of spray carb. cleaner not starting fluid) spray 5 second blast into the spark plug hole, pull the rope several times, this will wash out all the solvent coated parts and prime the comb chamber for starting. Spray the spark plug, scrub with wire brush and make sure you got gap, install the plug, connect the spark plug wire. Now remove the air cleaner, spray a 2 to 3 second blast of carb. cleaner directly into the carb. venturi. Choke it and pull the rope, should fire within 3 or 4 pulls. If not remove the plug and see if it's wet? if dry do the process over and try again. If wet pull the rope to clean any liquid inside the comb chamber.

Now this is just to get it to fire, once you got it to fire, you need to do fuel systm clean up/inspection, this may include replacing the rubber hose from the tank to the carb if its cracked, bulging or hard, scrubbing out the gas tank and rinsing, removing the carb. bowl and spraying out all the little passages, needle and seat area.

With the carb. off flip it upside down so the float closes off the needle valve, connect hose to it and apply mouth air pressure to see it the float is pressing on the needle and seating it against the seat and closing the air pressure off that you applying. Usually this will ensure the needle is seating preventing carb. flooding.

Fuel system cleanup will ensure any trash inside the gas tank will not end up back in the carb. and you maybe back where you started. plugged up carb. If you don't really understand how carb. works or have the basic knowledge to dissassemble for clean up seek help. that's it for me I'm tired of typing.

    Bookmark   February 7, 2011 at 6:43PM
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Thanks everyone and thank you rcmoser. I will try your suggestions and let you know how it goes next Saturday when I start working on the engine again.


    Bookmark   February 7, 2011 at 11:12PM
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Good news, the machine is working great! Here is a recap of what we did this weekend with the help of my Father:

-Fixed all four tires using the "ratchet" technique explained above. Awesome!! thanks..
-Cleaned out gas tank
-Put in a new gas hose from tank to carb
-Bought the overhaul kit mentioned above and a head gasket
-Removed cylinder head, cleaned out combustion chamber and valves, installed new head gasket
-Put carb in another 20 minutes in cleaner, main jet was still clogged, put in new main jet that came in kit, new needle from kit and new gaskets
-Took out the tiny round "cap" from the carb, sprayed carb cleaner in there and put in new cap that came with kit.
-Put in new air filter, new ngk spark plug
-Assembled everything

It started right up! It was great to try this machine for the first time and seeing how good it shreds wood. I had also put some seafoam in the old oil to clean out the camshaft etc. I then took out the old oil, put in some brand new amsoil synthetic small engine oil. Again thanks everyone who commented on this post.


    Bookmark   February 14, 2011 at 8:56AM
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