Best alloy for marine cam pulley..

[AllenH59]

I find myself tasked with making crankshaft, camshaft, and fuel pump pulleys for an automotive diesel being used in a boat. We found with a volvo gas engine that timing belt life was very short, and almost certain to fail in the dark, due to corrosion on the pulleys. Probably I will be turning down the existing pulleys and silver brazing something over it. Any specific alloy advice would be appreciated. I have little access to these materials up here, so it will have to be something I can order. Something with good machineability would be nice. Thanks
Allen

[rkcarguy]

I happen to own a boat with one of those Volvo gas 4-cylinder OHC motors in it, can attest to rust being a big problem on the timing belt pulleys.
The only thing that comes to mind is stainless steel unless you want to go more exotic and difficult to machine. Brass or bronze could be an option it will turn green and corrode to a certain extent but it doesn't get crusty enough to damage a timing belt.
I was thinking about having a couple sets chromed and then swap them out as the finish succumbs to the acid (salt water).

[AllenH59]

We considered Hard Chrome also, and it may be the way we go.. I do not think a few thousandths of an inch will have any effect. We are looking to make a marine engine out of a Volkswagon Turbo Diesel. It will be about 100 hp, and should run the fishing boat to fish just fine, and not burn an inordinate amount of fuel.

[TimTheGrim]

What about a 7075 aluminum with a Hard Coat Anodize geared towards corrosion resistance.

[RGS]

I made mine with aluminum, not sure what grade. Here are a couple of pictures.

[liveaboard]

Very nice, but a timing belt pulley as the op needs will be cogged; I don't know how you'd machine that.
marine grade aluminum would probably do, but bronze would work for sure.
Plating might work; it's cheap and easy enough to try first.

I just finished a new 45mm stainless prop shaft for my boat. the keyway was a challenge for me.

[NP317]

If a cogged pully is required, consider having Shapeways 3D print one in bronze-infused stainless steel. It is tough material!
A CAD drawing file would be required for the printing.
It might be the best of all worlds for a marine application.
RussN

[whateg0]

I got a shapeways quote to have the pulley cover on my 10ee 3d printed. $1500-2000 depending on the plastic used. Apparently too big for them to print in metal, but I can't imagine what it would have cost.

[Bill Shields]

i would not do a printed pulley for that application.

if you are going to braze something onto a existing hub, you need to consider not only the materials, but exact alignment of the new 'teeth' to the rotary zero of the existing cam center.

i am not a diesel tech, but a couple of degrees difference in alignment of the cam to the piston position can make a whale of a difference

[RGS]

Sorry I missed that it is the cogged pulleys. Can you make those out of aluminum and set up a divider that uses the existing ones as the master and make it on a mill similar to making a gear?

[Glenn Brooks]

Actually, Maybe you just need a better style timing belt - something designed for heavy marine use. Certainly if your existing pulleys are corroding badly, they should be replaced. Likely the low grade automotive application in the marine environment has a great deal to do with low hour failure rates

However, thinking back to running boats for 40 years in Alaska, I remember almost all pulleys were steel, or cast iron, with some mass produced painted or powder coated aluminum castings, such as in mercruiser outdrives in bow pickers. Never saw a chromed or bronze pulley. The chrome plating is fairly thin, and either wears off or in time, eventually lifts in flakes due to corrosion working underneath the chrome surface. If you do opt for aluminium, go with a known marine grade aluminium - won’t corrode and will offer high strength and anti wear characteristics. Or better, use steel with some % chrome molly content.

Glenn

[liveaboard]

My experience is that corrosion of machinery is worst during periods of non-use.
If that's the case, OP could consider using some sort of preservative on the parts during those periods. I'm testing some belt spray from Permatex; it's supposed to be for preventing slip but it's gooey stuff I'm hoping will stay on the pulleys while the boat is unused.
Or silicone, or anything that won't degrade the belt.
Spray it in there before shutdown.
If it works, it sure is cheap.