Question about storing small engines with valves closed
June 10, 2021 6:18 AM   Subscribe

Trying to learn about storing my small engines. I have read that it is best to store engines with the valves closed, ie, at tdc. And this seems best, but... is it possible to determine tdc when pulling the starter rope? I mean, doesn’t the compression release open a valve while pulling the rope, so that feeling tdc is impossible? Thanks in advance.
posted by atm to Home & Garden (7 answers total) 1 user marked this as a favorite
Remove the pull-cord assembly. Then you can use a socket wrench on the crankshaft to put the piston into TDC.

This is probably not a bad practice--- if nothing else it will keep out water, rodents, insects, etc.
posted by drstrangelove at 8:38 AM on June 10, 2021

Best answer: Exact TDC might be tedious to find, but that's not the only instant when the valves are closed. As you pull the rope, you feel a pulse of rapidly building and releasing resistance. The resistance increases as the piston moves into the cylinder while the valves are closed, i.e. the compression stroke assuming a 4-cycle engine. So, stop while the resistance you feel is still building; don't keep pulling past the peak of resistance.

(I have no idea whether this actually matters for engine longevity).
posted by jon1270 at 8:38 AM on June 10, 2021 [2 favorites]

Best answer: Because there's so much more resistance to free rotation during the compression stroke, when both valves are closed, I suspect an engine turned off normally will tend to stop in that condition. (I didn't test that, though.)
posted by fritley at 10:34 AM on June 10, 2021 [2 favorites]

Response by poster: jon1270,
Thanks, this is just what I was looking for.

Very interesting. Could be true. Thanks.
posted by atm at 2:20 PM on June 10, 2021

(I have no idea whether this actually matters for engine longevity).

Corrosion occurring on the rim of an open valve and its valve seat may cause problematic starting and running when the engine is put back in action, but I've never encountered this myself. Also, with the valves closed the valve springs are maximally relaxed, reducing the possibility of them losing their springiness (again, never ran into that). What does help is taking out the spark plug and spraying a bit of preservation fluid into the cylinder (with the piston near TDC, as already described), then putting the spark plug back in. If the instructions for the fluid state that it needs to be cleaned out in some way before using the engine again, opt for instead putting a wooden dowel, a cork or similar into the spark plug hole as a reminder.
posted by Stoneshop at 3:27 PM on June 10, 2021 [1 favorite]

With the spark plug removed, you'll be able to see the piston through the spark plug hole or feel it with a screwdriver. I would recommend putting the plug back in, though, however loosely and disconnected. Leaving it out leaves the cylinder open to (possibly damp) air, which is what you were trying to avoid.

I also don't know whether this matters much; I run the last of the fuel out of my mower in the fall and park it. Period. If you're planning longer-term storage than that, or storing it outdoors in the northern winter, I'd do as Stoneshop suggests but replace the plug.
posted by TruncatedTiller at 5:35 AM on June 11, 2021

or feel it with a screwdriver.

Use a very soft screwdriver there, please. A plastic rod, the shaft of a small brush. But you won't be able to distinguish between the end of the compression stroke (valves closed) and the end of the exhaust stroke (exhaust valve open) that way. So, with the sparkplug still in place you need to turn the crank until you run up against compression to find the 'valves closed' position
posted by Stoneshop at 7:19 PM on June 12, 2021

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