5.5HP Tecumseh won't start...valve not fully seated? - Snowblower Forum : Snow Blower Forums
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post #1 of 12 Old 01-07-2017, 06:27 PM Thread Starter
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5.5HP Tecumseh won't start...valve not fully seated?

This Yard Machine snowblower with a Tecumseh 5.5HP won't start, but only gives an occasional sputter. It gets spark, and I put a new carb on it, but no dice. I feel like compression may be weak, or that it's not pulling fuel up into the combustion chamber. Even when shooting a little starting fluid into the spark plug hole, it doesn't want to fire up. I opened it up and it seems to me that the exhaust valve doesn't fully seat tightly. Intake valve seems to seat okay. But the exhaust valve spins easily when the intake valve opens up, and I'm wondering if that is the cause of weak compression. Don't have a compression tester.
I'm open to ideas. Thanks.
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post #2 of 12 Old 01-14-2017, 07:57 PM
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Can you provide the exact model number and spec number for that engine.Awfully hard to help diagnose a problem without knowing exactly what engine is being discussed.

I'm curious especially in that I didn't know Tecumseh made a 5.5 hp engine,but I'm not that familiar with Tecumseh's later engine models anyway.Regardless,the troubleshooting methods are basically the same for all.

You have to keep in mind that these engines use a compression release device that holds one of the valves slightly open for easy starting .As rpm's increase,the device de-activates and the engine achieves full compression for optimum power.
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post #3 of 12 Old 01-25-2017, 08:36 PM
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It is common for those exhaust valves to do that. Pull the valve and grind in down a little until you get the right gap. I just fixed one today.
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post #4 of 12 Old 01-26-2017, 09:32 AM
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^^ YEP clean it up and you will be good to go. Make sure it's not running to rich though - probably how it got that way in the first place..... lean it out a tad to prevent that.

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post #5 of 12 Old 01-26-2017, 12:35 PM
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Buy a compression tester, $15. Maybe the flywheel shear key moved? If it turns out the valve, you would lap it in place but you need to buy grinding paste, a lapper, and a valve compressor, all totalled about $40 not including the tester. However you have to check the valve stem is straight otherwise a new valve. Most likely the valve seat came out rather than a bad valve.
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post #6 of 12 Old 01-26-2017, 12:55 PM
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An engine won't start with little or no compression. It sounds like you have found you problem in that exhaust valve if its loose enough to spin when the intake is open Have you taken a clearance measurement?

My guess is that you have no clearance and the lifter is holding the valve from closing, which may be a simple adjustment by grinding the stem a bit. Could be more than that, like a bent valve stem keeping it from snapping shut too.

Since you are already in there, you probably want to check the seats, guides, and valve stems and lap the valves so that you top end maintenance is complete. Check for any bits of shrapnel in the spring chamber as well, in case something broke.

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post #7 of 12 Old 03-27-2018, 03:07 AM
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What do think of when after you remove the spark plug; pull the engine over and you get no spark. I don't see the piston moving either. I put a screw driver in the plug hole, resting atop the piston and pull it over and the screwdriver doesn't move. I do get an occasional amount of pressure if I put my thumb over the spark plug hole and pull the engine over... it's confusing but I was told this Tecumseh 5hp Model HSSK50 motor ran when they put it away last fall. It's on a Yard machine MTD 31A-611D129 model, 22" snowblower.
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post #8 of 12 Old 03-27-2018, 07:52 PM
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If the piston isn't moving, that, to me, means one of two things:

- The connecting rod from the crankshaft to the piston is broken, so the connecting rod can't move the piston up/down.
- The pull starter is not actually turning the flywheel and crankshaft.

Is the pull starter definitely turning the crankshaft? One way to confirm that would be to tie down the auger or transmission handle (with the transmission in maybe a high gear). Remove the spark plug wire, and pull the cord repeatedly. You should see the impeller turn, or the machine should start to roll, depending on which handle you have squeezed. Or remove the belt cover, and watch the pulley on the engine when pulling the cord.

If the pull starter is turning the crankshaft, but the piston isn't moving, then that sounds to me like a broken connecting rod. Assuming that the spark plug hole is directly over the piston, which it typically is for a flathead engine.

A pull starter issue is probably a fairly straightforward fix. A broken connecting rod, on the other hand, would be quite a bit more involved.

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post #9 of 12 Old 03-27-2018, 08:25 PM
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Maybe the piston isn't going up or down........maybe a problem......
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post #10 of 12 Old 03-27-2018, 08:45 PM
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Take off the flywheel and check the woodruff key. You have all the symptoms of a sheared key.
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