flickroll

flickroll

Well Known Member
I have an RV-8 that had been previously flying with a B&C 40 AMP alternator. I upgraded to a 60 amp B&C, used the new belt that came with the alternator, and now the alternator pulley is chaffing on the inside of the cowl. The alternator is WAY down on the arm, so I believe a shorter belt could be used. Any idea of the correct belt so to fix this issue? I'm not too happy about pulling the prop to replace the belt but that sure beats a hole in the cowl. You'd think B&C would know which belt to supply. :mad:
 
I may not know the best way but I would pull the prop, take off the old belt and go to an auto parts store and get one a bit shorter. Maybe one inch as a start but take it and estimate how much it will move it away from the cowl.

Be there...done that.
 
For as long as I can remember, B&C has always supplied belts that are too long for RV's.
Get a gates 7360,7355,and 7350. Find the one that you can just barely get on and then take the other two back.
Note: the best clearance is provided by using a belt that has to be installed by putting it on the alt. pulley and the ring gear support pulley...then stretch it tight and put the ring gear support onto the crankshaft.
Doing this will allow you to install the shortest belt possible.
 
Last edited:
Watch the top

Jim,
Watch the top of the Alternator too.
The governor line is above it!
I'm pretty sure the slot in the mounting arm will allow the alternator
to go up high enough to rub it, so check that too.
Now that you have fiberglass skills learned from the rear fairing, you can
make a blister in the front of the cowling for the pulley to clear....;)
BTW......my Plane power unit is a 60amp...I think! and it is very small!
It is only money!!!
Good Luck
 
What Scott Said

I have had the same ecperience. B & C has been shiping the too long belt for awhile.
 
Well Houston, we have a problem..............

The 60 amp alternator is larger in diameter than the 40 amp. The belt that was installed with the original 40 amp alternator is a 7350 (35.0"). The belt that came with the 60 amp alternator is a 7365 (36.5"). Because the alternator case of the 60 is larger in diameter, it won't move very far up the arm before the alternator case hits the engine. I cut the 7365 belt so I could take it off and try to figure the minimum length belt that will work with this alternator. I then cut off 1/2" off the length to effectively make it a 7360 (36.0") and wrapped it around the alternator pulley and the flywheel. That is the shortest belt that will work. If I cut a total of an inch off (now a 7355), the belt will not go on because the alternator will not move far enough up the arm. Outside of putting a blister on the cowl which at this point I ain't doin', it looks like it's back to the 40 amper. Nothing is ever easy............
 
I have a 60 Amp B&C in the RV-6A

What you describe is a common problem for sure even with smaller alternators some of which have larger pulleys installed to slow the alternator rotation. Clearance is not good enough to prevent cowl damage. A friend of mine bought an RV-6A and replaced the engine. He asked me if there was anything he should lookout for. I looked at it and told him that the alternator pulley was too close to the cowl. He said he would keep an eye on it. That is very easy now since he has an inspection hole in the cowl directly in line with the alternator pulley. Mine had around 1/4" clearance but I saw the marking on the inside of the cowl from contact with the pulley. I dressed the forward edge of the pulley to smooth out the surface and I took one of our thick bladed stainless steel butter knives and cut off the major part of the blade and glued it the the cowl as a strike plate with structural adhesive from Aircraft Spruce. It still makes occasional contact but the cowl is fine - 500+ operating hours. The next time I have to replace the belt I will go to a smaller size as well.

Bob Axsom
 
7360 worked for me

My B&C came with the Car Quest XL 7365. I tried the 7355 and it could not even be installed. The XL 7360 was tight to get on but eliminated the cowl interference and still has some adjustment range.

Two different people told me to go ahead and put two belts (both 7360s) on while I had the prop off. Apparently a lot of people put a belt behind the working belt and hide it up against the case. Keeps you from removing the prop in the case of belt failure. Wouldn't fit on mine because the Lightspeed crank sensor is in the way.

Andy
 
Awhile back there was discussion on this issue and mention was made of a "snubber" to alleviate the alternator pulley/cowling interference. This is basically a padded standoff attached to the alternator bracket that prevents the pulley from coming into contact with the cowl. Since I was slowly wearing a hole in my cowl and didnt want to sacrifice my new paint job or remove my Whirlwind prop, I gave it a try. Seems to have done the trick so far - appx. 10 hrs since adding the mod. No pics, but could get some if anyone is interested - it aint rocket science though.

erich
 
I originally had a Gates 7365 belt on my B&C 60 amp alternator, and the pulley hit the cowl. I replaced it with a 7355 belt. That belt is a very tight fit, and you must do one of two things to get it installed:
  • Remove the flywheel, put the belt over both pulleys and then reinstall the flywheel, or
  • Remove the alternator pivot bolt, which will allow you to tip the aft end of the alternator down, so you can get the belt on the alternator pulley. Once the belt is on both pulleys you can put the pivot bolt back in.
 
Kevin Horton said:
I originally had a Gates 7365 belt on my B&C 60 amp alternator, and the pulley hit the cowl. I replaced it with a 7355 belt. That belt is a very tight fit.....
Click to expand...

Today when I cut 1/2" off the 7365, essentially rendering it a 7360, it looked like the pulley moved up about 1/4". But since with the 7365 it was cutting into the cowl, I actually gain less than 1/4"clearance with the 7360. I will try the 7355 and see if I can get it installed. I'll also put on a 7350 which was used with the 40 amp, and tie it off. If the 7355/60 amp alternator works without interference great; if not I'll go to the 40 amp alternator. Thanks everyone for all of the suggestions.

I am also going to see if I can take off the 60 amp pulley, take it to a machine shop, and have the protruding flange machined off. It sticks out a lot farther forward than it needs to. I may be able to do this at home with the pulley chucked in a drill press at high speed with a coarse file
 
A quick update...

Pulled the prop and tried various belts, including belts of different length from both NAPA and Dayco, the Dayco Top Cog. Actually the Dayco appears to be of superior quality over the NAPA. It has cord throughout the belt whereas the NAPA, made by Gates, has cord on only the outer (top) part of the belt. Also, belts by Dayco are slightly shorter in effective length than NAPA. For example, I could BARELY get a NAPA 7355 belt on and it had way too much tension, but the equivalent Dayco, 15355, would not go on at all. Next I tried a Dayco 15360. A NAPA 7360 was way too loose and would have resulted in very little clearance if I used it. But the Dayco 15360 was perfect. It went on, and when tensioned, I had 1/8" clearance between the alternator case and the engine case, and about 1/2" clearance between the alt pulley and the cowl. I'll fly the airplane and see how it goes with the Dayco. But I will want to see what happens when I pull a few G's, and hope that does not cause the interference that I had before with 1 G.
 
alternator belt length

One more data point for the history files.

Setup
  • RV-6A with epoxy cowl
  • Lycoming O360-A1A (new from Van's)
  • B&C 40 amp alternator

A Gates 7365 belt was supplied with the B&C alternator. This put the alternator adjustment in the middle of the adjustment bracket slot. Clearance between the alternator pulley and the cowl was maybe 1/4 inch. It was tight enough I could not get a finger tip between the pulley and cowl.

After a search of the VAF archive, some measurements on the airplane, and a trip to the aviation section of the local auto parts store, I returned with a Gates 7355 belt. The difference in belt length (circumference), per the manufacturers specs, is 0.9 inches.

The result is the alternator is all the way toward the "close to the engine" end of the adjustment bracket slot, and the pulley to cowl clearance is now about 3/4 inch as near as I can eyeball it and measure with "precision" fingers.

I am going to try running with this combination. If more clearance is required I can either lengthen the adjustment slot and use the next size smaller belt, or put fiberglass blister on the cowl.
 
You must log in or register to reply here.