Quest, nay thirst for knowledge
vlittle said:
ref Lycoming s. i. 1129A
Lycoming SI 1129A Accessory Drive Belt Tension
Vern Little 9A
I tried to get the Service instructions and found an Index on Lycoming's site,
but they only post a select few. I found index Ref. to SI-1129B, SB-536 and
SI-1254, but could not find a copy. I did find a Piper SL-636 which is the
same as Lycomings SB-355. It gives both methods of belt tension. This gives
A little more detail to Mr. Little's excellent post. Thanks for posting, nice
nugget of info. Another down side of the tension method is you need a Belt
Tension Meter to do it, where the torque method just needs the good old torque wrench.
(Notice below it gives info on new/used and 1 hour of use before checking. It the
torques match what Vern Little posted, so that is good. There is a SI-1129B.
I don't know how that differs from SI-1129A Vern referenced. )
1.
SLIP TORQUE METHOD: This method consists of installing a
torque wrench on the pulley retaining nut and measuring the amount of
torque required to make the pulley slip. Turn the torque wrench in a
clockwise direction, as viewed from the pulley end, and adjust belt
tension accordingly.
SLIP TORQUE SLIP TORQUE
BELT WIDTH.......NEW BELT........USED BELT
.....3/8 Inch .....11 to 13 Ft.....Lbs. 7 to 9 Ft. Lbs.
.....1/2 Inch .....13 to 15 Ft.....Lbs. 9 to 11 Ft. Lbs.
If a new belt is being installed the slip torque should be checked to the
used belt specification after 1 hour operation, at 25 hours, and each
100 hours thereafter. See Aircraft Manual or call Aircraft
Manufacturer.
NOTE: The higher torque value for the new belts is to compensate for
the initial stretch of the belt that occurs as soon as it is operated. Do
not use the higher torque value for a belt that has been previously used.
2. BELT TENSION METHOD: This method consists of installing a
belt tension meter on the fan belt at mid point of the longest
unsupported section of the belt and adjusting the alternator to obtain
the specifications listed below.
The following specifications are for a 3 to 1 pulley ratio with a belt
wrap of 140? on the alternator pulley.
TYPE................OUTPUT..BELT LOAD
ALE,.................40 Amp....50 Lbs.
ALH, ALT, ALZ....50 Amp....75 Lbs.
ALY, ANG...........60 Amp....75 Lbs.
ALU, ALX...........70 Amp....75 Lbs.
The meter used for these specifications was a Borroughs Belt Tension
Meter Model #BT-33-73F.
The above specifications are for a used belt, or a new belt after 1 hour
operation.
I found this Nugget that references SI-1129A and explains how to use a spring (fish) scale:
Check Alternator Belt Tension
Service Instruction 1129A gives the methods:
1. Torque method for 3/8 " belt; 11 to 13 ft. lbs. torque at the nut that holds the pulley on the alternator for a new belt and 7-9 ft. lbs for a used belt.
2. Deflection method; attach a
small spring scale to the belt 1/2 way between the ring gear and alternator pulley and
pull 14 lbs for a new belt and 10 lbs for a used belt. The
deflection should be 5/16". If it?s less than that, your belt it?s too tight.
Cheers George