Monday, August 4, 2014

Noma Gran Prix Snow Blower Maintenance

My son recently acquired an old Noma Gran Prix snow blower for very little money.

The thing starts and runs, albeit a bit roughly, and doesn't appear to have been abused or badly neglected. The plan is for the snow blower to be a big time-saver this winter for my son at his house. For that to come true, I'll have to get the machine into absolutely flawless good order.

With that in mind, I'll embark on a little TLC journey here, and document what I do and what I learn. Here goes.

The Engine

The engine is an 8hp Tecumseh HM80.[1] The compression feels adequate, so the machine can be taken to be basically sound. I'll first attend to the spark plug and the fuel system, the fuel system being the most critical item of all. In my experience, fuel systems are the source of most small engine trouble. If an engine's fuel system is sound and immaculately clean, the engine will start and run reliably. If not, the engine will be balky and troublesome.

The Spark Plug

One can't complain about the spark plug's accessibility.

The plug was in barely finger-tight; that may explain at least part of why the engine didn't seem to run all that enthusiastically.

The plug  is a Champion RJ19LM, which is the correct type for this engine, according to Tecumseh's parts listing. Here's a view of the plug.

It's a gasketed type, with a 13/16" hex. The plug appears to have been replaced recently.[2] I'll clean and file it a bit, even though it really doesn't need it. The gap is a little excessive; I'll set that to the correct figure of 0.030".

The Fuel Tank

I'll dismount the tank, empty it, back-flush and rinse it with solvent and leave it to dry thoroughly in sunlight. That should ensure that there are no particles or water in it whatsoever.

The tank is attached by two 3/8" hex head screws up top.

Underneath, there's a single spring clamp securing the fuel hose to the tank's output nipple.

The tank perches on a hook at the side of the engine. Just tip and lift away the tank to remove it.

The Heater Box

At the left side of the engine there's a rectangular cover that conceals the carburetor; that's the heater box. It's there to trap heat from the muffler so the carburetor and intake pipe will be warmed as the engine warms up.

Note the rod that runs closely alongside the heater box. That's the control rod for the snow blower's output chute position, and it will interfere with getting the heater box off. The rod's front end is fastened by a cotter pin, like so.

Remove the cotter pin and washer, and the rod can be disengaged and swung out of the way without disturbing the adjustment of the big 'screw'. Then, pull off the choke knob and remove four screws, and the heater box can come away. You'll be left with the heater box dangling by the kill switch wire.

The kill switch is easily popped out of its mount to free the heater box entirely.

Note that there is no air filter. It appears to be taken as a given that snowy driveways are not very dusty places.

The Carburetor

Here's a view of the carburetor in place at the left side of the engine.

And here's a better view of the governor linkages.

NOTE the position of the link end in the throttle lever-plate. You'll want to be certain of getting that back in place as it was.[3]

To remove the carburetor, you'll need a 7/16" wrench and a No. 3 Phillips screwdriver. (You may need an offset screwdriver for extra leverage.) Slip the primer tube and the fuel hose off their nipples. Undo the two 1/4"-28 fasteners at the intake pipe, unhook the governor link and the carburetor is free of the engine.

And here it is inside on the workbench.

And with that, this post has gotten long enough. I'll end it here before Blogger or I can blunder it out of existence. For some further information on the carburetor, see this post.

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[1] The 'HM' stands for "Horizontal Medium Frame". I believe the '80' stands for 8.0 horsepower.

[2] Probably every small engine that goes to the scrapyard goes there with a brand new spark plug in it. Replacing the spark plug is conventional wisdom's answer to all small engine troubles. In fact, the spark plug is one of the least likely items to fail in a small engine, and it can almost always be salvaged by cleaning, filing and gapping.

[3] Most small engines will present you with governor linkages to be unhooked when the carburetor is to be removed. Always photograph or sketch their installation before dismantling them. Unless you have a photographic visual memory for such details, and I certainly don't, linkage connections are liable to be mystifying when it comes time to reconnect them, if you haven't taken a picture or made a sketch.

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