Hartzell prop (or govenor?) squealing on startup

[Rich]

I replaced mine when the prop was overhauled with the part number listed in the IPC: 37A19773-376. The old one had the same part number, had been in there for 7 years and never needed adjustment. The new one went in and needed no adjustment, either.

I still have the original Prestolite alternator. A change in alternators might dictate a different belt part number. As most of you know, changing one of these belts if the prop hasn't already been removed for other purposes is no small task.

[mhoran]

Confirmed that is the belt I have as well. I suspect something else might be going on, but for now the squealing is addressed. We'll see if it comes back.

[Rich]

Check pulley alignment. The flywheel groove and alternator pulley need to be in the same plane and axes in parallel.

[Steve]

That is the P/N on mine as well. I changed to a PlanePower alternator and the same belt fits.

[mhoran]

Looks like everything is lined up:

You can see here that the alternator is pressing on the air box, hence the inability to tighten the belt any further:

The alternator is wearing a hole in the air box, which isn't great. I'll have to get that checked out when I get back from my XC trip. For now the squealing is gone. Hopefully the alternator doesn't eat through the air box in the meantime.

[mhoran]

When I dropped the plane off at SouthTec I took a look at another DA40-180 that was in the hangar. I noticed that the flange around the front of the alternator was much smaller than the one on my alternator. I had my alternator replaced a few years ago when the stud broke off my old one mysteriously after the brushes were replaced. It turns out that this replacement alternator was for the NG, not for the 180. I didn't think much of it at the time until the squealing started. Turns out the lack of adjustment was due to this flange hitting (and damaging) the air box.

I took this opportunity to have the Plane-Power AL24-70 installed. What a great unit. It's tiny compared to the alternator it replaced (and the one before it.) The NG alternator did not have the low volts problem I encountered with the original alternator (probably because it was rated for 100A) but the AL24-70 generates way more power at low RPM than any alternator I've had on the plane. The brushes are good for 1000 hours (probably more), and it's lighter.

Note for anyone considering the upgrade. Apparently the unit did not come with the correct bushings for install on my plane. So you / your mechanic may need to purchase some additional parts to complete the install. This was no big deal and SouthTec had everything fixed up in a matter of days.

[Steve]

Don't forget to recalculate your W&B. The PlanePower saves you a couple of pounds on the nose...

[mhoran]

Indeed. I plan to have the whole plane reweighed sometime soon as we've made a lot of modifications of "negligible" impact over the years. But a quick calculation shows the CG moved 0.10 rearward. We have the aluminum prop so the rear-heavy XL is somewhat balanced by that (still).