Alternator Belt - Top Cog vs Bottom Cog

[Chachi7565]

My propeller is off for an overhaul, so I'm replacing my alternator belt. The installed belt was a Dayco 15355 Top Cog.

From online research (this forum, race forums, Claude) it sounds like I could use either a Top Cog or Bottom Cog replacement belt.

I'm curious if there is any advantage to either choice in this application (Plane-Power AL12-EI60 Alternator on an IO-360-B1B on an RV-8A).

I have both available (super easy to find online, neither are particularly expensive, <$20 each), so it's not a sourcing problem, I'd just like to know if given a choice, which would you choose and why? In the absence of any compelling reason to change, I'll reinstall the same (Top Cog) as was originally installed.

Picture shows both types, bottom cog on left, top cog on right.

 

[sansoneservices]

From the pic it appears the left has more meat. Dayco should rate one more robust, check their website

 

[sansoneservices]

Dayco claims the bottom cog is heavy duty but make sure the contact angle matches the pulley

 

[ArlingtonRV]

My propeller is off for an overhaul, so I'm replacing my alternator belt. The installed belt was a Dayco 15355 Top Cog.

From online research (this forum, race forums, Claude) it sounds like I could use either a Top Cog or Bottom Cog replacement belt.

I'm curious if there is any advantage to either choice in this application (Plane-Power AL12-EI60 Alternator on an IO-360-B1B on an RV-8A).

I have both available (super easy to find online, neither are particularly expensive, <$20 each), so it's not a sourcing problem, I'd just like to know if given a choice, which would you choose and why? In the absence of any compelling reason to change, I'll reinstall the same (Top Cog) as was originally installed.

Picture shows both types, bottom cog on left, top cog on right.

I just went through this on my -8. There was a top cog on there before and I was going to replace it with a top cog, but evry time I ordered one I received a bottom cog. As I was taking it off, I noticed chunks missing from the cogs on the top. It happened in several places. The old belt had only been on there for 10 years. I replaced it with a Gates 7355 bottom cog and expect it to work well.

 

[FORANE]

My planes also had top cog. Didn't know benefits or drawbacks of one vs the other. AI appears to favor the top cog:

Top-cog (or raw edge cogged) V-belts offer superior flexibility, better heat dissipation, and higher efficiency compared to wrapped/bottom-cog belts, making them ideal for high-speed, small-pulley, and high-load industrial applications. They are generally more durable, though standard wrapped belts are cheaper and better suited for drives with high shock loads. [1, 2, 3, 4, 5]

Edited to add I too have experienced some missing cogs as described in the prior post. Not sure if that is an issue isolated to top cog belts.

 

[skirting_virga]

I tried like hell to find a Top Cog belt. The Dayco Top Cog brand seems to arrive either as a standard bottom cog V-belt, or in some cases old stock >5+ years. I tried amazon and several auto parts stores. Eventually gave up and used a gates 15355. I subsequently had problems with belt slip and shredded a belt, even at the specified torque, before pulling the prop and putting a new belt on. I'm still not 100% confident that the belt can't slip at the highest amp loads.

I would have loved to put a Top Cog on for more contact area, but I couldn't find one.

 

[Chachi7565]

Thanks all! I think I will go with the top cog belt, if that's what actually arrives.

I'm pretty impressed with the one I pulled off - no cogs missing, actually looks like it's in pretty good shape, and per the logbook it seems to be the original one from 2008.

 

[skirting_virga]

Thanks all! I think I will go with the top cog belt, if that's what actually arrives.

Please update us when it does. I ordered "Top Cog" from several different sources. They were all branded "Top Cog" but were standard bottom/inside tooth V-belts. I'm beginning to think they are not made anymore. If you find a source, let me know!

 

[gasman]

Thanks all! I think I will go with the top cog belt, if that's what actually arrives.

I'm pretty impressed with the one I pulled off - no cogs missing, actually looks like it's in pretty good shape, and per the logbook it seems to be the original one from 2008.

Then take it to your local Napa auto parts store and purchase the same one.... I would not trust Amazon for this item.

 

[bjdecker]

My propeller is off for an overhaul, so I'm replacing my alternator belt. The installed belt was a Dayco 15355 Top Cog.

From online research (this forum, race forums, Claude) it sounds like I could use either a Top Cog or Bottom Cog replacement belt.

I'm curious if there is any advantage to either choice in this application (Plane-Power AL12-EI60 Alternator on an IO-360-B1B on an RV-8A).

I have both available (super easy to find online, neither are particularly expensive, <$20 each), so it's not a sourcing problem, I'd just like to know if given a choice, which would you choose and why? In the absence of any compelling reason to change, I'll reinstall the same (Top Cog) as was originally installed.

Picture shows both types, bottom cog on left, top cog on right.

I wouldn't pay much attention to AI-hallucinations.

From the installation manual --



This is a "top" cogged belt. You want as much contact area ("meat") in the pulley/sheave grooves.

As to the rest -- if your belt is missing pieces from the top, it's likely too loose and it's rubbing against adjacent structures (i.e. baffle). If you set the tension correctly, you should be able to get to over 60A at @2700...(use the shade tree method -- 1/8" max deflection at midpoint (1/4" total) of a belt).

 

[skirting_virga]

From the installation manual --

This is a "top" cogged belt. You want as much contact area ("meat") in the pulley/sheave grooves.

I have tried like hell to get a "Top cog" style belt and the best I could find was old stock. Ordering "Dayco Top Cog" from several auto parts stores resulted in standard toothed belts most of the time. The others were old stock.

 

[bjdecker]

I have tried like hell to get a "Top cog" style belt and the best I could find was old stock. Ordering "Dayco Top Cog" from several auto parts stores resulted in standard toothed belts most of the time. The others were old stock.

I have a couple - PM me and we’ll figure something out.

 

[Chachi7565]

Please update us when it does. I ordered "Top Cog" from several different sources. They were all branded "Top Cog" but were standard bottom/inside tooth V-belts. I'm beginning to think they are not made anymore. If you find a source, let me know!

As you suspected, the belt that they delivered was the standard bottom cog V-belt.

I called Dayco and spoke with their technical assistance team. The "Top Cog" line of belts has been obsoleted, and is no longer manufactured. The new belt (which is what I included on the left in my original picture) has the same part number and per their guidance is a direct replacement for the old top cog. They said that the new belts have a different, stronger, rubber formulation, and that while to cogs are required to accommodate pulley diameter down to 2", the top cogs, which were for cooling, are no longer required.

I looked on the Gates website, and they still list a 7355 Auto V-Belt XL, but the image shows a bottom cog belt.

I'm interested to hear all of your thoughts on this - legit new part, or do I need to find somewhere to buy true top-cog version, if that's even available.