Lawn-Boy Commercial push mower

algraySeptember 8, 2010

I have a 1981 C21ZPRA w/o self-propel. It has a magnesium deck w/rear discharge. I bought it with the rear bag (standard); later I bought a side discharge chute. I don't have the mulching plate, but I never have cared for mulching anyway.

The Mg deck is prone to cracking from rocks and having sticks jam between the blade and deck. The lower chute plate is plastic and after going thru 2 of them I do without. It doesn't make any difference as far as I can tell anyway.

The parts are REALLY expensive, that is, the ones that are still available. I wouldn't give much for one of these mowers even if it runs well and is in good shape (no cracks or significant corrosion of the deck).

When it was new the fuel tank leaked and was replaced under warranty with a revised design.

The CD ignition module failed and was replaced under warranty.

The recoil spring broke and was replaced under warranty.

The rear bag frame broke at a weld and was repaired under warranty.

I bought this mower from Green Hills Lawn Mower in Nashville, Tn. on a discontinued closeout for $300. In 1981 or 2 it listed for over $600. I have definitely gotten my money's worth out of this mower even if it died today. It has outlasted many El Cheapo mowers. It has led a hard life, mowing rental property yards, neighbors' yards in addition to my own yard. Other people's yards are rough on mowers as you aren't familiar with obstacles hidden in high grass & weeds - sticks, rocks, chunks of brick & conc block, pieces of pipe, etc. I have replaced the blade at least 3 times that I can recall. As I don't mulch I choose a hi-lift non-mulching blade for better ejection.

GH did manage to lose the bag one time when I took the mower in for warranty repair. They would not admit that the bag was on the mower when I brought it in, so I had to buy another bag for $50 (now $180.78 frame + $86.99 bag!!), which they said was their cost (they had it in stock and were unlikely to sell it to anyone else - same for the $25 side discharge chute).

The crankshaft has withstood abuse that would have bent lesser mowers' shafts. I have bent blades so badly that I couldn't get them really straight again with bench vise, hand sledge, crescent wrench. The drive bosses on the blade mount plate sheared off, so the blade is strictly friction drive now. Still the c/shaft runs true. A straight blade is true within 1/32" at its tips at any position relative to the drive plate.

Most of the plastic trim crap has fallen off. These bits don't do anything anyway.

When this mower dies I will make sure to hang onto the wheels. They have grease fittings. One had an oversize hub bore that allowed the ball bearing cup to rotate in the hub. I fixed that by removing the wheel, dropping the bearing out and rapping the hub tube with a hammer and punch to make the bearing cup fit snugly.

The tires are still in good shape, not worn much.

I'm replacing the pull cord for the fourth or fifth time. It's not too hard - 4 screws hold the recoil housing to the shroud and one #3 Pozidriv screw holds the recoil sheave assembly into the housing.

It needs a fuel tank top mounting sems screw ($7.55 from LB) again. Despite checking tightness of the screws I've lost the second of these 3/8" head, star drive screws. I had to replace a bushing in one of the fuel tank mounting ears when a screw came loose and the bushing popped out. Fortunately it was a stock bushing from the hardware store for a few cents as LB no longer supplies it. It is necessary as the screw must be tightened against it, not squashing the plastic fuel tank ear.

It managed to eject the upper muffler shield/shroud screw, a $6.37 item from LB.

Recently the blade shot something that knocked the rear access door off and bent it all out of shape. I think it may have come loose and fallen into the blade (?) $29.02 from LB if I can't beat it back into shape well enough to reinstall. Maybe its screw (91c) came loose and dropped it into the blade?

Like any mower, the LB cuts best with a really sharp blade. I sharpen it by draw filing the blade held in a bench vise. I draw file the bottom of the edges flat so the bottom of the edge is horizontal. New blades have a severe rake to the bottom of the edge, which leaves a weak edge that is easily damaged and tends to grab objects like sticks. I do file the top of the edge to the original angle. This method of sharpening has done me well over the last 30+ years of mowing. Blades I have seen that were sharpened by (supposedly) professionals had goofy angles, mounted on the mower upside down, missing blade centering bushing, etc.

I think I'll install a plate on the underside of the deck to reinforce the deck before the left side breaks off. Aluminum alloy if I can find it, otherwise steel. And a liner for the rim of the deck, too, welded to the plate. I hope this will get me many more mowings out of this great mower.

I ran out of LB 2 stroke oil and used Briggs & Stratton 2 stroke oil. It smokes and stinks at 50:1 (original LB spec is 64:1, probably for emissions rating?). My chainsaw and auto repair friend recommended not going with 64:1 if I wanted my engine to live long. I am going to try to get more LB oil. Or if I can't find it, one of the premium synthetics. LB 2 stroke oil is really expensive by internet ordering - the shipping runs the cost way up.

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roadbike's time for a new mower if rocks and sticks are cracking the deck. Ignoring all of the other problems and expensive hard to find parts, you have a serious safety problem.

    Bookmark   September 8, 2010 at 4:28PM
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Alg: Give the Ole Girl a Break and Put her on Prominent Display in Your Shop . Spend a few Bucks and Upgrade before Her or You Dye a Untimely Death lol !

    Bookmark   September 10, 2010 at 5:39PM
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Keep her going...try finding a new deck used on ebay. You can get LB oil at HD and Lowes much cheaper than on line with shipping. The stores by me still sell it. Other choices work too. It is the whole LB 2 stroke experience, you will be bored with a new mower.

    Bookmark   September 11, 2010 at 8:17AM
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Heh heh, I repaired an aluminum deck using pieces cut from an aluminum stock pot, some pop rivets and JB weld. Not concourse, but a very strong repair.

    Bookmark   September 12, 2010 at 7:30PM
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I've patched my C21ZPRA magnesium deck with straps of aluminum from the hardware store. Most places I used flat head screws with nuts but in a few spots I couldn't drill through the housing, so I used self-drilling screws simply as self-tappers. So far it's working well.
Finally managed to slightly bend the crankshaft extension. I'm able to set the blade so it doesn't vibrate.
I replaced the spark plug when I was having starting problems last year, but the old plug is fine.
Parts prices are insane. If they actually have any decks left, no one is going to pay over $500 for one. Let it go for $50, maybe someone would buy it. $275 for a crankshaft? Out of sight. Guess they're attached to this stuff; don't want to sell any?
No one around here can weld magnesium. The stuff burns intensely if it is not welded with the right equipment and skill. Easy with the right stuff, mainly the correct filler rod and TIG, like aluminum. A shop that repairs old VW crankcases (magnesium, with some aluminum and zinc for strength) should be able to weld a Lawn-Boy magnesium deck. CO2 or water makes Mg burn more intensely as both have oxygen in them. Maybe if I ever get back out to Oregon with the mower I can get the VW specialist next door to my father in law's house to fix the deck.
For some reason I typed "1981" when it should have been "1991."

    Bookmark   April 14, 2011 at 4:27PM
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I can't believe that you actually found new replacement decks and cranks for the M series Lawnboy. Those parts in new condition are nearly impossible to find. Hope you can keep the old boy running.

    Bookmark   April 16, 2011 at 10:29PM
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