The International Cessna^® 170 Association

Hi Guys,

I need to replace the alternator belt on my Avcon Lycoming 180 hp 170 with a Prestolite alternator. For the life of me I can't seem to find the p/n though. I tried the STC paperwork, engine IPC, and a good old fashioned google search. In a last desperate attempt I even looked at the old belt, but this thing is from 1977 and it's either crusted over or wore off. Can anyone point me in the right direction?

Thanks,
DEM

Take the old belt ib to NAPA and have them match it.

Take a rope and wrap the pulleys and then measure.

John

Stretch a tape measure tightly around the outer (flat) surface of the old V-belt and measure the total length. Subtract any "stretch" of the old belt.

I noticed that Harbor Freight has a universal belt that I wonder if it wouldn't work for a guy out in the boonies with a broken alternator belt.

http://www.harborfreight.com/vibration- ... 43771.html

Actually BL isn't far off.

First, if you could find a part number and then purchase the belt from an aircraft part supplier and it fits, it would likely be the cleanest method from a legal stand point. Few would question it.

Fact of the matter is the Gates alternator belt bought at an aircraft parts supplier is the same Gates alternator belt bought at NAPA assuming it is the same size belt in all dimensions and construction designed for the intended purpose of driving an alternator.

A problem you have however is this. Your engine with the belt was installed per an STC. And the STC does not specify the belt as far as you can find. It could be argued even if you have a part number for a belt and you bought it from an aircraft parts supplier, installed it and it fits, you have no way of showing it is actually the correct and legal part. Of course as I said in the first paragraph is most wouldn't question it.

This case and others is exactly why AC 23-27- PARTS AND MATERIALS SUBSTITUTION FOR VINTAGE AIRCRAFT was written. You should read it. You can find it here: http://www.cessna170.org/forums/viewtop ... =43&t=6737. You have a vintage aircraft as described by this AC.

While the AC is not regulatory, and it is guidance for many things above and beyond parts substitution, parts substitution is addressed in it. And it just so happens drive belts for an alternator or generator is specifically addressed in Appendix 1

• AC 23-27- PARTS AND MATERIALS SUBSTITUTION FOR VINTAGE AIRCRAFT
  APPENDIX 1
  PART SUBSTITUTIONS
  1. DRIVE BELTS
  a. Alternator or Generator Belts.
  (1) For aircraft where the manufacturer no longer sells the original alternator or
  generator belt, you may use a belt made by the same belt manufacturer if the original part
  number is known. If the original part number is not known or the belt is no longer available, you
  may use a belt manufactured to a known specification such as SAE J636 and the belt properly
  fits the application. Pay special attention to fit of the belt to the pulley and proper tension of the
  belt. We highly recommend the use of technical information from similar aircraft.
  (2) The SAE J636 specification covers standard dimensions, tolerances, and methods of
  measurement of V-belts and pulleys for automotive V-belt drives. The V-belts that Piper
  supplies for the PA28-140 conform to this specification.
  Approval: This is a minor alteration and you may document it by a logbook entry. The logbook
  entry must reference the original (if available) and replacement belts' specification and
  manufacturer's identification.

Looking at 1.a.(1) you don't know what belt the STC called for and this says in this case you can use a belt made to a specification such as SAE. SAE just might be the spec that belt bought at NAPA conforms to. 1.a.(2) explains why this could make so much sense. And then last it says this is a minor alteration documented by a log entry.

I'd find a belt that fits and install it citing this AC regardless if you find a part number, but then I'm not your A&P so they would have to concur.

George, those link belts of high quality, which I don't know if the Harbour Freight model qualifies, are very desirable in the lathe machine world where total disassembly of the head stock is required for belt replacement. They also seem to dampen vibration. These tend to stretch a bit as the links settle in I've found in my limited use of them.

If I was in the boonies and a belt was keeping me there and a link belt was offered, I'd install it, top off with MOGAS and be on my way. (MOGAS optional of course)

That's the BEST reply.

The problem is that most owners find the prop must be removed and most owners wisely are reluctant to perform that feat without the A&P participation.
The A&P wants to know the exact replacement part because that's what he's most comfortable with. Advisory Circular 23-27 is the guidance you should provide to him to reassure him your NAPA V-belt is appropriate.

gahorn wrote:Stretch a tape measure tightly around the outer (flat) surface of the old V-belt and measure the total length. Subtract any "stretch" of the old belt.

I noticed that Harbor Freight has a universal belt that I wonder if it wouldn't work for a guy out in the boonies with a broken alternator belt.

http://www.harborfreight.com/vibration- ... 43771.html

image_17102.jpg

I know a guy that used one of those on his experimental VW motor.
It stretched just enough to slip off in flight. Wouldn't have been a terrible thing except he was running a single electronic ignition. No belt, no motor. Landed out and walked away, thankfully.

If I was concerned enough about an alternator belt to carry one of these, I'd just carry a second original belt.

bagarre wrote:[

I know a guy that used one of those on his experimental VW motor.
It stretched just enough to slip off in flight. Wouldn't have been a terrible thing except he was running a single electronic ignition. No belt, no motor. Landed out and walked away, thankfully.

If I was concerned enough about an alternator belt to carry one of these, I'd just carry a second original belt.

Yeah, I figure it's stretch more than the usual with all those links. The problem with carrying a spare tho' is the need to remove the propeller. Lots of owners install a "hot spare" behind the pulley... but the problem with that is it weathers poorly and there's no legal provision for storing the spare in that location. I watched one of the most heated arguments ever seen develop on a ramp with an inspector observing the owner cut the spare out of it's carrying-space under protest. (Late '70s before Appdx A fully developed, the argument being the legality of the owner making the repair, and the propriety of carrying a spare in such close proximity to the moving parts. Of course, most of that argument is now passe'.)

... but on the outside chance you want to use the correct part, try Lyc p/n 37A19773-376, formerly p/n 76026, Spruce p/n 08-00249 LYC ALT BELT. See O-360-A parts catalog figure ref 26-3. http://www.aceflyingclub.com/manuals/ly ... -306-1.pdf

[quote="Aryana"]Only $69.75!

That's only $0.69 in AMUs!

I found that the prop R&R helped take the sting out of the price of the belt.

Last tkme I checked the federal fuzz was too busy lobbying for more money to bother sending the troops out to check part numbers on alternator belts.

One other lame suggestion from me is to first install a spare belt on the nose of the engine, pulled back and secured out of the way with zip ties. The next ime you have a belt failure, the spare is right there and you wont have to pull the prop off.

According to the guys over on the Van's forum, a Gates 7375 also works.

Thanks guys. I'll go with the official Lycoming part for now. I know it's just a Gates belt that I can get at Napa, and if it were Dad's RV-8 that's where I'd be heading. But we are doing a full blown overhaul on the 170 so probably best to stick with the certified parts this time.

Not sure how I missed it in the IPC!

Thanks,
DEM