Cowl/Alternator interference

flickroll · #1 04-19-2009, 07:33 PM

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.

Ron Lee · #2 04-19-2009, 07:42 PM

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.

rvbuilder2002 · #3 04-19-2009, 08:08 PM

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.

flickroll · #4 04-19-2009, 09:12 PM

Quote:

Originally Posted by rvbuilder2002

Get a gates 7360,7355,and 7350. Find the one that you can just barely get on and then take the other two back.

Great advice Scott. Thanks

Bob Martin · #5 04-20-2009, 05:49 AM

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

Jaypratt · #6 04-20-2009, 06:11 AM

I have had the same ecperience. B & C has been shiping the too long belt for awhile.

flickroll · #7 04-20-2009, 08:11 AM

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............

Bob Axsom · #8 04-20-2009, 09:24 AM

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

andyrv · #9 04-20-2009, 10:03 AM

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

erich weaver · #10 04-20-2009, 12:02 PM

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