The Cessna 120-140 Association Forum

Good Morning Friends,

I am seeking assistance in identifying whether AD 46-44-05 / SLN-18 applies to the engine mount on our 1946 140. Per the aircraft serial number (9397) it does not apply however, the engine mount has the internally wrenching NAS146a-43 bolts. Because our mount has internally wenching bolts we assumed that it was the older (pre SN8517) mount, which had been installed at some point in the aircrafts history, and the AD applied. We purchased a set of the offset washers specified in the AD but they do not fit. The tube on the engine mount is larger than the recessed portion of the washer. So the question is, was there a version of the engine mount used on the later SN 1946 140s which had the internally wrenching bolts but was not subject to AD 46-44-05 / SLN-18? If so, how can we identify that we do in fact have that mount on our aircraft?

Thanks,
Patrick

The AD is because the washers welded to the front of the tubes are not strong enough. The AD, and the later mount, both change the stress from tension on the washers and welds to compression on the tubes.

So, if the washers welded to the front of the tubes are bearing the stress, the AD would apply, IMHO.

Are you saying the special washers fit completely inside the tube? What is the ID of the tube? My guess is your mount was repaired at some point, or the washers aren't correct. Do they match the drawing in the SB?

I took my calipers over to the hangar to get some measurements. The washers we purchased match the specifications in the SL in all dimensions. The portion that fits inside the tube on the engine mount is .600" and the ID of that tube is about .640" so while the washer fits the fit is loose. Is this how it is supposed to be? I just assumed that the fit should me snug. I would love to hear from someone who has complied with this AD in the past regarding how snugly these washers fit.

I also measured the thickness of the 1.5in plate on the front of the engine mount and it is .096". The SL/AD specifically mentions that plate being .049" which leads me to think that the AD does no apply?

OK, I thought you were saying the whole washer would be pulled down inside the tube. The portion that fits into the tube is intended to prevent the bolt and washer from shifting off center to the point where it wasn't bearing on the entire circumference of the tube. There's no need for it to fit tightly.

Interesting the washer is thicker than the original. Unless there is specific wording that states that mounts with thicker washers can be used with original socket head bolts, I would still use the stepped washers and AN6 bolts. (In fact, I think I would use them anyhow.) Better safe than very sorry. Again, the point of the AD is to shift the load from pulling on the washer to pushing on the tube.

Thank you, that was exactly the information I was looking for. (Though I didn't initially realize it and just assumed the washers were supposed to be a snug fit). We'll definitely utilize them and the AN6 bolts just to be on the safe side and because it will make sourcing hardware in the future much easier. NAS146A-43 bolts are impossible to find anymore.
I appreciate your help getting to the bottom of this, John!

Patrick