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  #1  
Old 02-17-2019, 07:22 PM
Westerhuis Westerhuis is offline
 
Join Date: Sep 2016
Location: Boston (MA)
Posts: 88
Default Alternator pulley suddenly rubbing against bottom cowl

Hi

This morning during the preflight I discovered a little crack in the bottom cowl of my RV8. Furher inspection revealed that the alternator pulley touched the inside of the cowl and rubbed through it.

I have been flying for app. 70 hours since a prop overhaul and haven't noticed this issue before.

But last week I had the cowls off, did a oil change and put them back on, so I assume that putting the cowl back on was the moment from wich the pulley started to touch. I didn't touch or change anything else.

I'll repair the little crack with a bit of glass and a drip of touch-up paint on the outside.

But does anyone know what I might have done wrong when replacing to cowl or what else might I have to look at? If it happened immediately after replacing the alternator or work on the prop or then that might be the cause. But I didn't touch those.

Thanks

Roger



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Last edited by Westerhuis : 02-17-2019 at 07:33 PM.
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  #2  
Old 02-17-2019, 07:31 PM
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Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 11,226
Default Common.

Have you been doing any light acro? If your clearance is small, it doesn't take much positive "Gs" to cause this. 2 solutions. A shorter alternator belt or a "blister" molded onto the cowling.
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  #3  
Old 02-17-2019, 08:29 PM
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Jpm757 Jpm757 is offline
 
Join Date: May 2013
Location: Sherman, CT
Posts: 991
Default

Perhaps your engine mounts are a little tired?
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RV6 #20477 completed 1991 sold.
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  #4  
Old 02-17-2019, 10:39 PM
Tracer 10 Tracer 10 is offline
 
Join Date: Mar 2011
Location: Oregon
Posts: 152
Default Alternator pulley rubbing inside lower cowl.

We had the same problem on our RV6.
Solved by installing a B & C 40 Amp Alternator & regulator and a new belt.
This solved 2 problems.
2 Alternator failures in 2 years (automotive) & 100 flight hours.
Rubbing the lower cowl with the pulley.
The B&C alternator is smaller in diameter than the one we had installed; and now with 300 hours and no failures.
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  #5  
Old 02-18-2019, 12:09 AM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
Posts: 6,724
Default

Don't you have to loosen the alternator belt when pulling a CS prop? I am guessing the flywheel would pop off if you don't. I have a fixed prop extension so don't have to worry about it. Over time belts stretch a bit and when re-tightened after the prop was put back on, that might move the alternator down as much as a 1/4" or more, depending upon the rubber quality.

Belt looks new in pic. Any chance your mechanic put on a new one while the prop was off? A very common step. It's possible he put one on that was 1/2" bigger than the previous one. It is hard to tell a 1/2" difference without a special tool.

If you have enough slot left on the upper arm, try going to a belt size 1/2" smaller than the current belt. In some size ranges they are sized by inch and not half inch.


Larry
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Last edited by lr172 : 02-18-2019 at 12:20 AM.
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  #6  
Old 02-18-2019, 07:47 PM
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chrispratt chrispratt is offline
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Default

Check the belt designation. In case it is a 7365, then here's my post from June 2018. If it's a 7360 then -- "never mind" as Gilda Radnor would say.

"mm, interesting Carl. The belt B&C sent me was a 7365 and that was too long - by about a half inch. It rubbed the cowl and dug a nice furrow into it. I went back to a 7360 like I had on my old Van's Nippon Densu alternator and it worked fine. I checked with Walt Aranow at my home field and he said he has a drawer full of B&C 7365. They're too long - he uses the the 7360 also.

Debegeman: Perhaps the "XL" in the Gates is the issue. Try a NAPA 7360 without the XL."

Chris
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  #7  
Old 02-19-2019, 07:38 PM
Westerhuis Westerhuis is offline
 
Join Date: Sep 2016
Location: Boston (MA)
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Default

Quote:
Originally Posted by chrispratt View Post
Check the belt designation. In case it is a 7365, then here's my post from June 2018. If it's a 7360 then -- "never mind" as Gilda Radnor would say.

"mm, interesting Carl. The belt B&C sent me was a 7365 and that was too long - by about a half inch. It rubbed the cowl and dug a nice furrow into it. I went back to a 7360 like I had on my old Van's Nippon Densu alternator and it worked fine. I checked with Walt Aranow at my home field and he said he has a drawer full of B&C 7365. They're too long - he uses the the 7360 also.

Debegeman: Perhaps the "XL" in the Gates is the issue. Try a NAPA 7360 without the XL."

Chris
Hi Chris

That is interesting, as mine is a 7360. See picture. I have 1.5" between the alternator pulley and the pulley on the prop. Would a belt that is 1/2" shorter be an option? I have noticed that the alternator pulley will end up between the starter ring.



My A/P, who is still to have a look, commented that he thought it was strange this all over sudden became an issue, if it wasn't an issue for the last 400 hours. He didn't think the rubbers of the engine mount would start to sack through after 8 years?

Roger
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Last edited by Westerhuis : 02-19-2019 at 07:41 PM.
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  #8  
Old 02-20-2019, 08:53 AM
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chrispratt chrispratt is offline
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Default

Quote:
Originally Posted by Westerhuis View Post
Hi Chris

That is interesting, as mine is a 7360. See picture. I have 1.5" between the alternator pulley and the pulley on the prop. Would a belt that is 1/2" shorter be an option? I have noticed that the alternator pulley will end up between the starter ring.



My A/P, who is still to have a look, commented that he thought it was strange this all over sudden became an issue, if it wasn't an issue for the last 400 hours. He didn't think the rubbers of the engine mount would start to sack through after 8 years?

Roger
Curious-er and curios-er as the saying goes. I'd like to hear what your A&P says. Hopefully it's something as simple as a shorter belt.

Chris
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  #9  
Old 01-20-2020, 09:43 AM
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Nived17 Nived17 is offline
 
Join Date: Aug 2016
Location: Milwaukee, WI
Posts: 52
Default B&C Rubbing inside my RV-4

I am currently fighting this exact battle. I just went from the old 1978 Honda alternator to a B&C 40 amp. I installed the B&C with all included components. No clearance issues at all static. However, in flight I did get rubbing on the pulley wheel inside the cowl and a small visual spot on the outside of the cowl too. I cannot go back to the shorter alternator belt from my auto alternator without slightly modifying the tension arm. The slot will need to be lengthened. Just a heads up to RV-4 guys.


Quote:
Originally Posted by chrispratt View Post
Check the belt designation. In case it is a 7365, then here's my post from June 2018. If it's a 7360 then -- "never mind" as Gilda Radnor would say.

"mm, interesting Carl. The belt B&C sent me was a 7365 and that was too long - by about a half inch. It rubbed the cowl and dug a nice furrow into it. I went back to a 7360 like I had on my old Van's Nippon Densu alternator and it worked fine. I checked with Walt Aranow at my home field and he said he has a drawer full of B&C 7365. They're too long - he uses the the 7360 also.

Debegeman: Perhaps the "XL" in the Gates is the issue. Try a NAPA 7360 without the XL."

Chris
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  #10  
Old 01-20-2020, 10:04 AM
fixnflyguy fixnflyguy is offline
 
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Location: Winston-Salem, N.C.
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Default What mine does

On my -4, the end of the tensioning arm is close to the cowling, and after I started flying a little more aggressively, I had contact as well. I made a small relief well, and bonded a piece of rubber into it, so when deflection of engine pushes into it, there is no harm done. The pulley, however,would be another story and will require additional measures. Early RV-4's had a T-shaped support attached to the engine that would push against the cowling (old glass resin cowls) during deflection, so you may entertain doing that if you cant get better clearance.
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