Mercruiser MAG 350 Serpentine Belt Shedding-gctid404003

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Hi,

I thought that there may be some previous reference to my problem but a "search" on this website failed to bring up anything useful.

My boat is 2003 305 with twin MAG 350's and Bravo 2 drives. Usually the engine room has been clean, however the serpentine belts have both started shedding recently - so much that I have to vacuum out the engine bay from time to time to remove all of the small pieces of rubber. I have checked the tension of the belts and both are a few millimeters - certainly not loose. There are signs of wear on both the outer edges of the belts and the inner grooves - but the wear is not showing the white reinforcement material (in the gooves) yet - which I was told to look for as the time to replace belts.

My mechanic said that this is not unusual but happens on some motors not others (but why mine and why now ??) and suggested that the most likely problem is rust formation on the pulley grooves which bites into the belts. His suggestion is to remove the belts then clean the (metal) pulleys grooves with a wire brush then paint the grooves with a rust covertor paint - then replace belts.

Looking at the pulleys there is little or no signs of any rust so I was just wondering if anyone else had a similar issue and how they solved it ??

Re Dean

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If it's small pieces of rubber rather than black dust I'd say the belts are desintegrating and probably should be replaced. A disaligned pulley (such as a circulation pump pulley with heavily worn bearings) would also speed up the wear.

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DeanB wrote:
Hi,

I thought that there may be some previous reference to my problem but a "search" on this website failed to bring up anything useful.

My boat is 2003 305 with twin MAG 350's and Bravo 2 drives. Usually the engine room has been clean, however the serpentine belts have both started shedding recently - so much that I have to vacuum out the engine bay from time to time to remove all of the small pieces of rubber. I have checked the tension of the belts and both are a few millimeters - certainly not loose. There are signs of wear on both the outer edges of the belts and the inner grooves - but the wear is not showing the white reinforcement material (in the gooves) yet - which I was told to look for as the time to replace belts.

My mechanic said that this is not unusual but happens on some motors not others (but why mine and why now ??) and suggested that the most likely problem is rust formation on the pulley grooves which bites into the belts. His suggestion is to remove the belts then clean the (metal) pulleys grooves with a wire brush then paint the grooves with a rust covertor paint - then replace belts.

Looking at the pulleys there is little or no signs of any rust so I was just wondering if anyone else had a similar issue and how they solved it ??

Re Dean

Dean: Since BOTH are shedding and the pulleys look good, I'd guess that the serpentine belts are just shot by their age and exposure. (rubber does that) There should be a faint amount of belt dust, but nothing as you have mentioned. The new breed of serpentine belts are very popular and have a long service life. I'd say just replace them both. Good luck. Griff

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If these are original you should be saying " Wow got 9 years on my belts "

I change mine every couple three years just because. Not going to let a belt ruin the few boating days I get.

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DeanB wrote:
Hi,

I thought that there may be some previous reference to my problem but a "search" on this website failed to bring up anything useful.

My boat is 2003 305 with twin MAG 350's and Bravo 2 drives. Usually the engine room has been clean, however the serpentine belts have both started shedding recently - so much that I have to vacuum out the engine bay from time to time to remove all of the small pieces of rubber. I have checked the tension of the belts and both are a few millimeters - certainly not loose. There are signs of wear on both the outer edges of the belts and the inner grooves - but the wear is not showing the white reinforcement material (in the gooves) yet - which I was told to look for as the time to replace belts.

My mechanic said that this is not unusual but happens on some motors not others (but why mine and why now ??) and suggested that the most likely problem is rust formation on the pulley grooves which bites into the belts. His suggestion is to remove the belts then clean the (metal) pulleys grooves with a wire brush then paint the grooves with a rust covertor paint - then replace belts.

Looking at the pulleys there is little or no signs of any rust so I was just wondering if anyone else had a similar issue and how they solved it ??

Re Dean

My 350 mag just threw the belt off and it had seperated about 8-10 inches long. I had cleaned up the the pulley's as well as the circulation pulley. For good measure It looked like the circulation pump needed changing so we did that and the thermostat.So far all looks good. I would be willing to bet , cleaning the pulley's and new belts solve your problem.

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The belts are

Yesterday I removed both belts and the "shedding" appears to be between the grooves. There are no cracks or fractures in the belts just some rubber coming off from the grooves. The main rubber deposits are around the alternators (which were both replaced some $650 ea).

None of the pulleys or idlers are loose/worn/wobbly. Using a steel ruler I checked the alignment of the pulleys and all in alignment.

Now the alternators have the correct grooves in the pulley but the grooves are deeper than the other pulleys and they are not painted and quite rusty. The timing of noticing this problem was (if I remember correctly) some time after the alternators were replaced.

So (in line with my mechanics suggestion) I have used wire brush to remove all of the rust on the alternator pulleys and used a file to ensure no sharp edges. Then painted with rust conversion paint, then today went and sanded again and applied a second coat (per the paint instructions). The paint takes min 24 hrs to dry and as it is winter here I am going to leave the paint for a few days before reinstalling the belts - will follow up ....

Re Dean