Help with P-mag installation

[Bavafa]

I received my P-Mag today and was planning on installing it this week. I pulled the right slick mag and pulled the gear off but when I try install it on the P-Mag, it seems it goes in too easy and the when the nut is tight to the spec (125-150 in/lb.) the shaft stick out beyond the gear by about at least 1/8? and I was wondering if this is OK. If my understanding is correct, there is not much clearance between the gear and the case of the engine inside. Also when I undo the castle nut, the gear comes out easily with hardly any pressure as the one on the slick Mag was very tight and required a pulley puller to get it off.

Which washers did you guys use, as there are two provided in the kit and the original Slick has one thick washer.

[rhill]

Is the Key way in place,they have a habit of moving during the install?

[johnfurey]

I was concerned about the same issue and called Brad. He said that is normal and nothing to worry about. Use 1 or both, whatever it takes to make the cotter key go in. I used both washers that came with the Pmag and the slot in the castle nut lined up great.

[SHIPCHIEF]

You seem to be on the right path.
The nut must not bottom out on the threads, which could strip the threads on the nut & shaft. The gear must be tight on the shaft.
The selection of washers is there to help seat the gear on the shaft taper, and not bottom the nut. Also so the cotter pin will fit thru the castelations of the nut & the hole in the shaft.
After you find the combination which meets that requirement, then make sure it fits the engine without interference, and engages the drive gear fully. An extreme case of tolerance stacking could mean you need a new gear that sits higher.
Lycoming probably has a spec on this. Maybe someone with more experience will jump in here.
I wish hold down clamps (to hold the P-Mag on the engine) were provided, or something reccomended. I made up a pair of clamps from a piece of angle iron. Some pictures of installations look like installers may have used automotive distibutor clamps. Some additional information would be nice, because this is different than the mounting ears on the mags being removed.

[Ironflight]

Originally Posted by SHIPCHIEF

I wish hold down clamps (to hold the P-Mag on the engine) were provided, or something reccomended. I made up a pair of clamps from a piece of angle iron. Some pictures of installations look like installers may have used automotive distibutor clamps. Some additional information would be nice, because this is different than the mounting ears on the mags being removed.

Huh? I have installed two sets of P-Mags, and unless my memory is really beginning to fail, I think I just used the same clamps that were holding the Mags in place. I certainly didn't fabricate anything.

[Andy Hill]

Hi Mehrdad

Are sure both your original Mags / Gears were the same type?

The P-Mag Gear required is the one from a non-impulse Mag. The Impulse Mag Gear is a different type and not to be used. It is likely from your original install that you had one impulse and one non-impulse Mag - although some engines (e.g. our Superior XP-360) came with 2 impulse Mags.

[Bavafa]

Use 1 or both, whatever it takes to make the cotter key go in.

Thanks John, it is good to hear that I am not the only one experiencing this. What caused my concern was the part in the installation manual that says the cotter pin should not be extruding pass the gear. Also, I can also use either the original washer or the ones that has been provided by Brad. The original washer is a tighter fit and thicker.

The nut must not bottom out on the threads, which could strip the threads on the nut & shaft. The gear must be tight on the shaft.

Scott,
I really doubt it that the nut is bottoming out as I can go pass the required torque setting but it is not an easy way to verify how close to bottoming I am. But I will take the nut off one more time without removing the gear to see if there is still any clearance for the gear to go any farther down the shaft or not. I am surprised however how easy the gear comes out if I remove the nut after torqueing it down.

Are sure both your original Mags / Gears were the same type?

Andy,
The one that I replacing is a non-Impulse Mag and the gear came from Lycoming (brand new engine)

[SHIPCHIEF]

Paul;
My T-18 has Bendix mags (well, now it has one) which have slotted ears that fit over the studs from the accessory gear case. Just a nut and washer retains these mags to the case and the movement to rotate the mag is limited by the slotted holes.
A quick look at a picture of a Slick mag, and I see the same mount flange as the P-mag. Now I understand. I would have bought a set of Slick Mag hold down clamps had I known.
So your memory is fine. Thanks for commenting, it jogged me enough to figure it out. (I've never had a plane with Slick mags before)
Maybe I'm being a bit picky, but the whole P-mag thing is so well done I was suprised this part had no note or accessory part etc.
Or maybe I'm a candidate for the 'Brown Bag'

The P-mag is great, as expected. I got an additional bonus: my comm radio quit acting up! The old assembly must have been periodically arcing inside or something, and the radio was auto squelching as hard as it could to suppress the noise, leaving me with a strangely weak radio and blasts of static, except when testing on the ground (of course)!!