It is a Dayco "W" profile belt.

I found this on the web.

http://www.daycow.com/

I did not know about it until I went to the local parts store for a replacement. I have no experience of how it actually works yet.

Dan

I have the automatic tensioner on my motors and some spotty rust on a few pulleys where the paint has flaked off. I do NOT have any belt debris.

2006 build HO's

I have aluminum pulleys and plenty of belt debris. Mine collects mostly in the air filter. BAD!!! The filter is right above the belt and the bottom of the filter gets coated with belt debris.

my hammer with the 7.4 was horrible, i only noticed it after i replaced the belt with one from a automotive shop, i don't know if they are any different, however my HO has absolutely no dust anywhere, ever, it has the tensioner idle pulley not the tensioner under the alternator

So - can anyone help me determine what parts I need to upgrade my '04 mags to have the different idler pulley. For the couple hundred bucks I'm def. in to solve this issue!

I believe it's going to be more than a $100.00 each, But here's a starting point for you.

Here is link to "your" engine parts to look over.
http://www.mercruiserparts.com/selec..._nbr=881784001

Take a look at the Starter and "Alternator" bracket section and the "sea water pump" bracket section. Your water pump bracket/idler pulley is non adjustable like the new one's are.
http://www.mercruiserparts.com/Show_...and+Alternator

http://www.mercruiserparts.com/Show_...=Seawater+Pump

Here would be the new brackets you would need to get,
http://www.mercruiserparts.com/Show_...=Seawater+Pump

http://www.mercruiserparts.com/Show_...and+Alternator

Here's all the newer parts to look over,
http://www.mercruiserparts.com/selec..._nbr=881784004

No disrespect but it will not satisfy you. It will mostly vary only by the boat that it's in and not the parts or pulleys.

You have several variables that affect how much and where you see most of the debris:

Boat shape, space in front of engine and proximity to bulkhead and engine hatch cover, amount or volume of air being forced into the bilge while under way or the lack of forced air.

I've tried everything from spotless, perfect pulleys to taking parts off of other boats for testing and even painting all surfaces of a back-up set of pulleys.

That serpentine system will always be dirty. But like the guy above, he says he does not see much or any. It's because of the boat - not his engine(s).

My engine had this problem when it was totally stock. I also saw it in my last boat. You can't tell me that every single 496 out there is covered in rust or has fouled-pulleys. But almost every single one of them has belt debris to some degree. Even the fishing boats that have that engine see it.

study the front of the engine and ask yourself...

What other big block out there has that many accessories running on one belt and particularly that sized belt??

WDIK Maybe I'm wrong but I've spent some time on it and have probably had some test opportunities that many 496 owners have not had as far as having a chance to rob parts and put them back when stuff did not work as expected..

In all fairness, I have NOT tried the auto-tension parts either.

Hmm - I can tell you my motors are really clean - pulleys have slight surface contamination. I have a TON of space in the bilge. I can pretty much sit in front of both motors. The bilge configuration is really pretty good IMO. The debris is all over the front of both motors, and it does a good job of covering the air intake. I would think the only extra accessory would be the Raw water pump, compared to a car setup...anyone running crossovers in lieu of the circ pump have this issue? Maybe dropping off circ pump will help...

I think to upgrade to the auto tensioner is a bit too involved and too much cash for an inconvenience like this...But I may look into the dayco belt.

I think the other main difference is that the engines in trucks will rarely see 3000 rpm and spend 99% of thier life operating at less than 2000 rpm. I seem to remember seeing a belt that was a different type material, I think it was green colored ? Not sure if it is available in the correct size but might be worth looking into ?

Bill Koustenis
Advanced Automotive machine
Waldorf Md