Alxx Nova

I was reading something on a custom chopper/motorcycle web site and had an idea. Those guys were making a lot of custom parts. There was one guy called Fabricator Kevin that was making extended gears for old Harley Sportsters so they could run wider rear tires. He removed the teeth from a stock gear then bolted and welded another gear to the end of it to move the chain drive out and give more tire clearance.

So this got me wondering if anyone ever tried to make a timing chain set up to use in place of the timing belt. Yeah it would make more noise but I imagine it would last a lot longer. My bikes engine is aluminum, so is the tranny and the primary case that connects them. Yet there is a double row chain connecting them. The bike doesn’t have an automatic tensioner so I have to check and adjust it every so often, but there is an automatic adjuster available that I’ll be getting eventually.

Anyway, I’m not an engineer so I have no idea if it’s possible. Just that I was up way to early this morning and now it seems like it could be good idea. Or maybe I should just go take a nap.

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Alex Portanova
1989 944 N/A
1999 Chrysler 300M
1992 Harley FXSTC

theedge

The general consenus is that its pretty pointless. Unlike belts, chains need lubrication. Sure, you could fab up some toothed sprockets for the crank, cam, and water pump.... Then you need to tension it, and you need to seal the entire front housing around all those parts somehow, and make sure the chain gets enough oil on it to lube it.

Chains are also heavier, noisier, and the cost of the work would equal at least a few belt jobs in a shop.

tifosiman

Seems to me that trying to make a timing chain for our cars would be more problematic than just changing the timing belt at the prescribed intervals and ensuring that it is tensioned properly.

Legoland951

If you can somehow make the waterpump work with a chain and lubricate it constantly it would work. Its probably not cost effective though (can't imagine parts/labor costing less than thousands)unless you drop one of those v8s already with a chain in the car.

knfeparty

They stretch. My mechanic was telling me that he tunes up people's newer cars and adjusts the timing chains and it really brings the car back to its original performance. So apparently they stretch over time and slowly pilfer your horsepower.

tifosiman

Chains don't technically stretch. The rollers wear due to grit/dirt/oiling issues. Due to the increased tolerance in the roller/pin interface, the chain appears to be longer when taught for the same given number of links. As this happens over time, the gears that the chain works with also become worn. Given enough time, the gears wear bad enough that you can't put a new chain on the old gears because they no longer work together properly.

MPD47

Do a search, I think we've been over this about 10 times.

Mongo

More harm to your head thinking about the design than actually incorporating it on a 944 engine already designed for a timing belt

ibkevin

One main concern is the thermal growth between the pullys.

harrisonrick

Go back to bed.

inactiveuser92616

Cost to convert: $$$$
Cost to pay someone else to do your belts ~$300

I don't really think I will be doing three or more beltjobs any time soon...

User 41221

Sorry to open a can of worms by even mentioning this, but...

Does anyone remember the name of the guy that was racing a 944 (I think it was an old Firehawk car that had been converted for SCCA, but don't recall the details and he for sure wasn't in a stock class) that put an electric water pump on his car and a timing chain system (with no balance shafts)?
It was cool as all get out and fairly simple (I think I talked with him in Texas, and it was a bunch of years ago), but I couldn't see doing it for a street car. I also don't recall him winning all that much.

Regards,

pjburges

Another thing to think about with a chain is the issue of parasitic drag - chains are heavier which increases the the mass the crankshaft has to spin up and if it isnt lubed properly it becomes quite resistant to turning when you try to turn it say ... 6000 rpm?

JDeitz951

Timing chains do break now and then, probably sooner if home-built and poorly lubricated. I wonder what kind of damage a flailing chain would do?

Anyway, timing belts are a proven technology widely used today. When the 944 first came out, the quality of the belts was not as good as now.

FRporscheman

Stop worrying about the belt. Go buy a spare cylinder head like I did, and keep it in the garage as insurance.

Not so easy if you have a 968 or something, but 2.5 heads are cheap and abundant.