Folks,

Is there any good reason to _not_ locktite (red) the key
into the pump shaft groove?

Dale R.

Ed Anderson wrote:

Very good point, Tom.

Don’t know how I could have forgotten the problem I had with the key for the oil pump shaft. In fact, I flew for 10 hours with the key missing – only the clamping force of the nut on the shaft holding the gear to the shoulder of the shaft. While at Shady Bend (Tracy Crook), I unintentionally left my throttle at full open after we had comparing throttle bodies and intakes.

The next morning was a bit cool and I was using 50 weight oil. I hopped into go do some flying with Tracy and Finn Lassen, when I fired up the engine (Having forgotten to close the throttle from the previous days inspection), the engine caught and immediately zoomed to 5000 rpm before I could hastily pull the throttle back. I noticed lower than normal (around 20-25 psi) oil pressure while taxing to take off and just told myself it was the cold weather, cranky sensor or gauge, but by the time I got to take off position, I notice the oil pressure had never gotten above 25 psi when normally at taxi rpm I would have around 40-50 psi.

Fortunately, I could not bring myself to take off with that condition (even though I kept telling myself there was nothing wrong). After much trouble shooting, I decided I had to pull the engine off (thankfully, Tracy Crook had a great facility to do that in) . I removed the oil pan and as I took it over to wash it out, I hear a metallic clanking in the pan – yes, you know what it was – a much battered key for the oil pump shaft. When I had pushed the sprocket on the shaft, I had pushed out the key but unfortunately, it did not drop down. It got trapped between the sprocket wheel and the soft aluminum oil pump housing (the indention was in the soft aluminum) from the force torquing the nut down. This had push the sprocket against the trapped key which in turn had pushed the key against the housing and trapped it there – probably until the first engine run. Fortunately, I had torqued the nut down as specified – which some folks think is a bit high for that small a nut, but glad I had. I’m also glad in hind sight I left the throttle open and it was a cool morning – who knows when it might have let go.

So now when I rebuild an engine, I take a small paper clip and bend the end out so I can stick it in the keyway hole after putting the sprocket on. If it goes in all the way – the key is not in its slot!

Moral of the story, it can happen to any of us – so take time and check. As Tom mentioned, it can be a bit of a hassle to get the keyway in the slot and sprocket on – if it falls out (as it will most of the time) and you hear it/see it you are OK. But, if it gets trapped as my key did – you won’t get that clue. So use a paper clip, inspection or something to insure the key is where you think it is.

Also pay attention to your gauges and your gut they are both always telling you something – if you will only listen {:>)

Ed

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