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Setting alternator belt tension

Here's a post I made in 2006 that should help:

"Belt deflection is an unreliable method of tightening the belt.

Instead, use a torque wrench on the pulley belt and adjust the tension so that you get about 12 ft-lbs before the belt slips.

A loose belt can lead to under-voltage or over-voltage from the alternator. Overvoltage is caused by the regulator trying to force more output from the alternator while the belt is slipping. When the belt grabs, it puts a surge of voltage on the bus.

Please don't ask me how I found out!

ref Lycoming s. i. 1129A

Lycoming SI 1129A Accessory Drive Belt Tension

New 3/8? 11-13 ft/lbs 132-156 in/lbs used 3/8? 7-9 ft/lbs 84-108 in/lbs

New ?? 13-15 ft/lbs 156-180 in/lbs used ?? 9-11 ft/lbs 108-132in/lbs

Vern Little 9A"
 
Bob Collins said:
What is the correct way to set the tension of an alternator belt?
Click to expand...

Lycoming: Apply torque wrench to the alternator pulley nut and turn it in a clockwise direction. Observe the torque shown on the wrench the instant the pulley slips.

Belt width 3/8"....... NEW 11 to 13 ft-lbs. USED 7 to 9 ft-lbs.
 
Sorry, belt deflection should only be used for Pilot pre-flight. Got my functions crossed.
 
gasman said:
Lycoming: Apply torque wrench to the alternator pulley nut and turn it in a clockwise direction. Observe the torque shown on the wrench the instant the pulley slips.

Belt width 3/8"....... NEW 11 to 13 ft-lbs. USED 7 to 9 ft-lbs.
Click to expand...

Anyone able to indicate where this is written by Lycoming?
 
Just installed the prop for the last time (I hope, until time for servicing at 72 months), and now need to tighten the alternator belt. Bumping this to see if anyone has a pointer to the Lycoming SI-1129A on this (can't find it on the Lycoming site).

TIA!
 
AK4x4 said:
If someone wants it I can e-mail it to them. Russ
Click to expand...

I'll take it just to add to my list of SBs, SIs, etc., that I'm compiling to show compliance prior to inspection. PM sent.

Thanks for the link to the PP document, too, guys...an excuse to buy a new tool :).

Steve
 
Arrggg!

az_gila said:
Yes... Lycoming SI 1129 - now up to "B" revision.

But not posted on their web site...:mad:
Click to expand...

....which brings up a problem I am having (please move post if this will hijack the thread). Ive recently started the FWF part of the build and I'm learning how to navigate the Lycoming site. That said, I've seen reference to 5 or more documents...none of which I've found on the Lycoming site. What am I missing?!?! Btw, it's clear that Lycoming send engines to Vans that they expect an A&P will be receiving, not a rookie builder!

David
 
Lycoming provides many documents only to hose A&Ps that pay for a subscription. Post which docs you need and sometimes elves get busy in the web-o-sphere.
 
Lycoming

Many of the Lyc service bulletins and service instructions are not available online. I was told by a Lyc rep a few months ago that they would mail out obselete info if needed.
 
Life of an alternator belt

I am in the middle of my second condition inspection. Alternator belt still looks like new, no cracks and tension is by the book. What average life span is expected from an alternator belt? It's over 760 hours on it now.
 
Vlad said:
I am in the middle of my second condition inspection. Alternator belt still looks like new, no cracks and tension is by the book. What average life span is expected from an alternator belt? It's over 760 hours on it now.
Click to expand...

On my -4, I replaced my belt when the alternator failed at 250 hours and put the old belt in the baggage compartment for a spare.
 
vlittle said:
A loose belt can lead to under-voltage or over-voltage from the alternator. Overvoltage is caused by the regulator trying to force more output from the alternator while the belt is slipping. When the belt grabs, it puts a surge of voltage on the bus.

Please don't ask me how I found out!

New 3/8? 11-13 ft/lbs 132-156 in/lbs used 3/8? 7-9 ft/lbs 84-108 in/lbs
Click to expand...

ARGHHHH! I am an idiot!

I've been flying since March 2012. For pretty much the whole time I have been chasing instability in the alternator system. Replaced regulator, replaced master, rerouted wires, checked ripple, etc.

I was doing spark plug maintenance recently and while walking past the alternator I stuck the wrench on it and tried to give a tug. Couldn't. It was WAY loose. ***(*&#)($&@!***!!!!! Proceeded to tighten it up. Finally flew today. Charging system stability improved dramatically.

It was my own fault. As a younger driver, I had to deal with a failed alternator bearing while deep in the backwoods of West Virginia in the dead of winter. Painful. I have tended to set belts loose since then.

Live and learn. :rolleyes: I knew about the torque test but had never applied it to my chariot. Sheesh.
 
gasman said:
Lycoming: Apply torque wrench to the alternator pulley nut and turn it in a clockwise direction. Observe the torque shown on the wrench the instant the pulley slips.

Belt width 3/8"....... NEW 11 to 13 ft-lbs. USED 7 to 9 ft-lbs.
Click to expand...

From my Piper service manual is where this information came from. PA28/151.
 
This torque rule seems to ignore several things. The condition of of the surfaces of the pulleys being the biggest. At least it addresses the belt age but not the condition of the the belt edge surface.
I used the torque rules to set mine when the belt was new and it 'seemed' horribly tight and potentially damaging to bearings. Backed it off to be more reasonable and all has worked excellent for hundreds of hours....?
 
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