Aluminum cam sprockets - longevity?

[Jonny042]

Without getting into the gory details (just yet) I'm on a quest to build the lightest possible 911 engine that I can, to put in the lightest possible 911 I can build.

Starting with a mag case, mag chain cases and covers, mag valve covers, ti hardware etc. helps a lot and the pounds add up (subtract down?) a surprising amount.

Cam sprockets are available in aluminum and the weight savings would be significant - however I cannot find any information on their longevity. The closest I can come is this quote from Grady:

"In the early ‘80s, we rebuilt a ‘hot-rod’ that had the alu sprockets (all six).
The owner had driven almost 40k mi. not knowing they were installed by the PO.
While the sprockets showed wear (too much to re-use at a rebuild), they were clearly not ‘worn out’ using stock chains."

Of course there are commonly available adjustable cam (with AL teeth) sprockets on the market, so there has to be at least a few more data points out there.

I do notice that there are very rarely, if ever, aluminum sprockets used for oe applications.

From what I know, aluminum chain sprockets shouldn't initially wear as any sliding friction that occurs is between the moving parts of the chain, but as these parts wear over time, the chain "stretches" and the point contact pressure on the sprocket teeth would go up and cause deformation of the teeth. So you'd replace them along with the chains with the same frequency as you would steel sprockets?

Thanks in advance! Jon

[mepstein]

We pulled some out of a race engine. How often are you going to refresh the engine? It’s a different ball game if you are tearing it down every 80 hours vs 80k miles.

[Jonny042]

Thanks for the reply!

That's the thing - A Hot Rod, not a race car. At MOST 10K miles a year, so Grady's example of 40K miles could maybe stretch to 50k miles or beyond with care and monitoring? And I could get 5 or 6 or 10 years out of them. I like tinkering and winters are long up here!

How did they look coming out of the race engine? And when you say you pulled them out, was it to replace them because you weren't happy with them, etc.?

[JoeMag]

Where do you get them? ...I googled it and nothing came up.

[mepstein]

Originally Posted by Jonny042

Thanks for the reply!

That's the thing - A Hot Rod, not a race car. At MOST 10K miles a year, so Grady's example of 40K miles could maybe stretch to 50k miles or beyond with care and monitoring? And I could get 5 or 6 or 10 years out of them. I like tinkering and winters are long up here!

How did they look coming out of the race engine? And when you say you pulled them out, was it to replace them because you weren't happy with them, etc.?

They were worn out. Ended up building a completely new engine for the customer. Steel sprockets.

[Jonny042]

Originally Posted by JoeMag

Where do you get them? ...I googled it and nothing came up.

They seem to be a well hidden secret. Rose Passion in France:




If you were running something like a 2.0L Cup car these would be a no brainer.

A pile of 6 steel sprockets is pretty hefty so the weight savings is not insignificant, but they aren't cheap and would only be worthwhile if you've done everything else possible to save weight IMO.

[stownsen914]

Not a ton more expensive than regular steel ones.

I have no experience with them, but I’d ask what alloy and heat treat they are. Those specs can heavily influence durability.

[PeteKz]

Okay, I'll be the naysayer. I think it's a really dumb idea to use aluminum in a wearing application. You aren't competing in F1, where ounces matter. Aluminum sprockets on motorcycles don't last nearly as long as steel ones. Granted, motorcycle chains are out in the open exposed to dirt and water, but the fact remains that steel way outlasts aluminum.

How much weight do you really expect to shave by using aluminum sprockets in place of steel ones? Maybe a pound total? Find that pound somewhere else, like fabricating an aluminum rear cross mount.

[Magyar Kiwi]

Comment
Would be more than happy to use an aluminum sprocket at the two tensioner locations, where: there is very little power transmission, wear can be monitored and replacement is easy.
Cheers

[Jonny042]

Originally Posted by PeteKz

Okay, I'll be the naysayer. I think it's a really dumb idea to use aluminum in a wearing application. You aren't competing in F1, where ounces matter. Aluminum sprockets on motorcycles don't last nearly as long as steel ones. Granted, motorcycle chains are out in the open exposed to dirt and water, but the fact remains that steel way outlasts aluminum.

How much weight do you really expect to shave by using aluminum sprockets in place of steel ones? Maybe a pound total? Find that pound somewhere else, like fabricating an aluminum rear cross mount.

That's why I'm asking a bunch of guys who just might be dumb enough to try it and share their experience.

The total weight of the 6 steel sprockets is 3.375 pounds, so the aluminum ones would be exactly 2 pounds lighter. It's not nothing.

To meet my weight goal I am going to have to consider every opportunity, every ounce. I've already got the aluminum for a billet crossbar mount. And a titanium crossbar. And titanium bolts. Just making sure I leave no stone unturned in this quest.

Thanks for not suggesting I get my lard ass on the bathroom scale a little more often!!!

[PeteKz]

That would be like the pot calling the kettle black...

[dannobee]

If I was considering using them (which I'm not), I would most certainly check the hardness, and if needed, have them hard anodized to at least give them a fighting chance. A decent hard anodizing will put them at a hardness around 60 Rockwell C

[Rosco_NZ]

Aluminium cylinders weigh a heap less than cast iron. Forged pistons are lighter than cast. Use lightweight rods. Maybe shave a bit off the crank & flywheel.

[MoreGAS]

Those are serious wear items and not the place to try and save a couple lbs max. Guess where all that shed aluminum will go, in to the oil , and transported in oil to all the other parts of the engine. I don't have 100% faith in the filters catching everything either.

Once we upgraded all the race engines to a steel intermediate shaft gear assembly (from Aluminum) the amount of aluminum in our race oil samples (sent to Lab at regular intervals) was very reduced.

To offer an avenue not as "dodgey" you could try using a single row chain and sprockets, this will save considerable weight on all these parts. An associate did this years back on a 2.0 race engine, w good results.

IMHO, for a streeter this is a fools errand. Put all that dough in to making a bad ass 3.8-4.0 that will almost certainly do burnouts around your scheemed engines ass and stay together for years. If oyu don't have budget for a crazy NA engine, they do get expensive fast, make a mildly modified Turbo engine and get the 400-500 HP , w WAY more Tqe than NA , for half the dough. That said, reason has little to do w our passion for these cars lol, PM me if you need single row chain and sprocket info.

Kevin
GAS Motorsport

[Jonny042]

Originally Posted by MoreGAS

Those are serious wear items and not the place to try and save a couple lbs max. Guess where all that shed aluminum will go, in to the oil , and transported in oil to all the other parts of the engine. I don't have 100% faith in the filters catching everything either.

Once we upgraded all the race engines to a steel intermediate shaft gear assembly (from Aluminum) the amount of aluminum in our race oil samples (sent to Lab at regular intervals) was very reduced.

To offer an avenue not as "dodgey" you could try using a single row chain and sprockets, this will save considerable weight on all these parts. An associate did this years back on a 2.0 race engine, w good results.

IMHO, for a streeter this is a fools errand. Put all that dough in to making a bad ass 3.8-4.0 that will almost certainly do burnouts around your scheemed engines ass and stay together for years. If oyu don't have budget for a crazy NA engine, they do get expensive fast, make a mildly modified Turbo engine and get the 400-500 HP , w WAY more Tqe than NA , for half the dough. That said, reason has little to do w our passion for these cars lol, PM me if you need single row chain and sprocket info.

Kevin
GAS Motorsport

Thanks for the advice - I'm curious about the single row chain, but still hope to find someone who's used the alloy sprockets. They were "stock" on 935's from what I can tell.

As for the 2.7, it's a choice I made as the springboard into the project, and I purposely found a mid-year to take advantage of the lightness of the magnesium case and other components compared to the 3.2SS MFI motor in the previous project.

Project heavy metal was a fairly slim 2200lbs (1000kg) but the goal for this one is 20% lower and wouldn't be possible with a 3.6. I know the motor (with many lightweight parts as already suggested!) and exhaust will be at least 100lbs lighter than the 3.2 and will go a long way towards the eventual goal of 800kg.

Outright power isn't really the goal, I'd like to have 250hp which I think is more than reasonable, the point of the project is to make a quick revving NA motor with an amazing response and great soundtrack, running through a full set of very close ratio gears. Magnesium 915, too, BTW...something like 9 pounds lighter than an aluminum one! Every pound counts....

[Brookieslayer]

Good Evening Jonny,

You already have the information correct for the sprocket vs chain contact. The chain has rollers. There is a minimum sliding contact of the chain to the sprocket, Only during approach and departure is there any sliding friction. There is a certain amount of load on the sprocket of course, and premature deformation wear on the sprocket can occur with a chain that is too tight. Motorcycle drive trains used aluminum sprockets forever with little to no wear for many miles with almost no lube, and lots of ambient dust. The loading on the chain is not constant there either.

The hard anodizing idea is actually a pretty good idea as well, never thought of that. Be interesting to see what the BHN is now. Looks like you could easily achieve steel hardness for a surface hardness with the anodizing.

Just another .02

[Geneulm]

Wasn't the intent of alum sprockets to cut rotating weight (much more valuable) than overall weight? That said l, have several sets laying around but sticking with steel on the street for new hotrod motor.

[Jonny042]

Originally Posted by Geneulm

Wasn't the intent of alum sprockets to cut rotating weight (much more valuable) than overall weight? That said l, have several sets laying around but sticking with steel on the street for new hotrod motor.

Weight is weight, but yes, rotating is even better, albeit at 1/2 crank speed and a fairly low moment of inertia. Every bit helps! But again, in the context of what I'm trying to achieve, 2 full pounds is significant and worth chasing down.

You say you have several sets of aluminum sprockets laying around... do tell? I'm going to guess used race stuff headed for the bin?

I'm still curious about the aluminum ones, it's possible to choose an aluminum alloy that would be suitable for mid to long term use, given the loading, so I have a feeler out to the supplier as to what they are making them from.

[Geneulm]

My new engine (yet unrun) had a set in, along with alum idler cogs. They are being swapped off for steel. They look cool, but I think the steel versions are best for my application.

I have another set in my stockpile. The other set is clearly anodized. I'd be willing to find a good home for them.

[Jonny042]

Originally Posted by Geneulm

My new engine (yet unrun) had a set in, along with alum idler cogs. They are being swapped off for steel. They look cool, but I think the steel versions are best for my application.

I have another set in my stockpile. The other set is clearly anodized. I'd be willing to find a good home for them.

I'll send you a PM with my email address and we can discuss. Thanks!