Friday, May 26, 2017

An MTD Lawnmower Find

My son picked up this MTD PRO 21" mower[1] for free at a yard sale.

It was free because it's inoperative because of a damaged control bail cable.

There was some electrical tape wrapped onto that cable jacket that I removed for the photograph. That taping was a futile attempt at repair that someone had made. How that tough cable jacket ever got into such a condition is a mystery.

Another repair attempt had been made to the cable's upper fulcrum, whose anchor stud had broken off.

That hose clamp is actually acting to good effect, but the ruined cable jacket negates it..

Anyway, I downloaded the operator's manual from MTD's website, and got the part number for the cable. As it turns out, MTD puts cable part numbers right on the cable jacket, which is decent of them.

"746-1130" is the part number in the operator's manual, and there it is right on the cable jacket. Neat.

That part number is for a 40.0" long cable. It appears that cable length is jacket length, not overall length. Overall cable length is, of course, longer than jacket length.

The local small engines repair shop got me a replacement cable for $18.14 CDN + HST.

For some reason, the '746' in the part number becomes '946' for the packaged replacement part.

Note the change that's been made to the cable's upper fulcrum.

The new style fulcrum is just a hook, instead of the old style stud-and-clip fulcrum. It appears that the old style was failure prone.

And here's the new cable's hooked fulcrum tucked neatly into its hole in the handlebar.

It works perfectly, and the engine starts on the first pull.

And now I suppose it's time to do what I should have done in the first place -- check the oil.

Hmmm. It's way down, and black as can be. Routine maintenance must not have been a strong point with the machine's previous owner.

I have SAE 30 four-stroke motor oil on hand, so I can get right on with an oil change. I don't know what the sump capacity is for this engine, and I couldn't find a user's manual on the Briggs & Stratton website. I'll have to wing it by carefully adding oil until the dipstick reads correctly.

Oil Change

There's what looks like a drain plug in the underside of the sump.

The plug has a square recess in it that will accept a 3/8" square drive socket wrench. That's all well and good, but elevating a lawn mower so you can drain its oil is an awkward bit of business that I prefer to avoid. (And tipping an entire mower up and over so you can empty the oil out the filler tube strikes me as not only awkward, but silly as well.) I find it more convenient to suck the oil out of the filler tube with a vacuum apparatus. That's complicated a bit on this engine by a bend in the filler tube that won't admit the rigid brass suction tube of my apparatus. So, I set about taking the filler tube off the engine so my suction tube could reach directly into the sump. Here's how that goes:

[NOTE: 'A/F' = 'Across Flats']
  • Two screws to release the upper engine cowl. (No. 2 Phillips recess.)
  • Three 5/16" A/F hex head shoulder screws to release the fuel tank.
That gets you to here.

The filler tube is fastened in place by another 5/16" A/F hex head shoulder screw. Remove that, pull straight up on the filler tube and you're here.[2]

Now it's easy to suck out the old oil. Needless to say, I took that filler tube to my parts washer tank for a cleaning before I put it back on the engine.

With the old oil out and everything buttoned back up, I poured in new oil a little at a time. 500 ml turned out to be about the right amount of oil,[3] so that's taken care of. 'Probably the first oil change the engine has had in a very long time.

The Blade

The blade is held on by a single 5/8" A/F hex head screw.

I didn't think to take a 'before' picture of the blade when I had it off; it was pretty badly rock-battered. I did a reasonable job of grinding it, and put it back on. I'm not a perfectionist about grinding rotary mower blades. At 3,000 or so rpm,[4] a reasonable facsimile of sharpness will cut grass satisfactorily.

The Spark Plug

It takes a 13/16" wrench. Here it is just out of the engine.

It's a Champion RJ19LM. There's a bit of carbon buildup -- nothing serious. The gap measures 0.030", which is standard for Briggs & Stratton engines in my experience.

Here's the plug after cleaning, filing and re-gapping.

Much better. I'll reinstall that item, and take a look at the air cleaner.

The Air Cleaner

A single screw with a 5/16" A/F hex head secures the air cleaner cover.

Loosen off that one screw and you have access to the paper element air filter.

That filter could stand to be replaced. The air filter element's part number is written on it. It's 491588S. Another trip to the small engines repair shop is in order.

Carburetor Teardown

See this post.

Finishing Details -- MONDAY, MAY 29, 2017

It never ceases to amaze me, the little needless insults that people manage to dish out to machinery.

One of the two threaded knobs that clamp the handlebar halves together has a broken lobe.

There's only one of two handle-fastening carriage bolts in place.

And there's only one of two handle-securing hairpin clips.

I bought a new knob. The other missing items I had spares of on hand.

So now the machine is complete and saleable. We'll see what we get for it.

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[1] Here's the complete mower and engine I.D. data:



[2] Yes, I know, the pictured filler tube is clean where it's still on the engine, but it's dirty after it's been removed from the engine. I made a boo-boo in my sequence of photographs, and could only correct it after I'd cleaned the filler tube. 'Sorry about that.

[3] I noticed later that the oil fill capacity is stamped right on the dipstick. It's 20 U.S. fluid ounces (591 ml). 500 ml is about right.

[4] I later checked the speed with a digital photo tachometer. Measured governed engine speed is about 2,600 rpm.

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