Timing belts vs chains

bryson · Post by **bryson** » Sun Apr 30, 2006 12:51 am

I'm trying to list the advantages and disadvantages of each, and I'm sure I've missed some things. I am just brainstorming for the Fiero -- I'm thinking about going with a smaller turbo (or twin-charging) and running much less power than the engine is built to handle. I figure since the engine has forged crank, rods, and pistons, along with .0015 bearing clearances and lots o' money in machine work, running around at 350whp at 15psi should yield a very drivable, reliable car. I really like the idea of seeing how much power I can make out of a given turbo and manifold pressure.

Anyway, I got a little off track. Advantages of a chain system: For one, it's already on the engine :bootyshake: Also, it should be more durable than a belt and last longer between required changes. That's about all I can think of. Oh, also, it's tough to tune cam timing, since the front cover would have to come off (wouldn't be hard to make a removable "window") and you would also need adjustable sprockets, which would probably have to be made (again, probably not terribly difficult to modify stock ones).

Advantages of a belt: The most obvious, the belt weighs less. A belt is also easier to tune cam timing with, because it wouldn't be terribly hard to make adjustable gears for a different car fit the cams, not to mention that it would all be open and easily accessible. Also a belt is easier to inspect, and to change if needed.

Anything I'm missing? A belt is more succeptible to weakening due to chemicals or oils being spilled on it. Hmm...any others?

Series8217 · Post by **Series8217** » Sun Apr 30, 2006 12:56 am

In regards to converting to a belt on the Quad 4 or just in general?
In general, timing belt replacement intervals are shorter than chains. Belts generally "last" only 60,000-80,000 miles.
For the Quad 4, isn't the chain oiled? The chain housing likely makes up part of the oil drainback from the heads. Converting to a belt may be harder than just adding the appropriate tensioners/idlers and sprockets..

bryson · Post by **bryson** » Sun Apr 30, 2006 1:15 am

The chain is oiled, but I think that the only drainbacks are small slots above each cam, and the oiling for the tensioner. I wonder how much it would affect drainback if those were blocked off -- I forgot that was there until you mentioned it. I'm sure that external lines could be run if significant gains were to be had by changing to a belt system though. There is also some drainback through the block. Making a section of the cam cover removable and modifying the cam gears to be adjustable seems like the best option so far. Any benefits of either system I haven't thought about yet?

Aaron · Post by **Aaron** » Sun Apr 30, 2006 1:40 am

Space, the chain is simply smaller in width than a belt.

All in all, I don't see a reason to switch. I'd stick with the chain and spend the money elseware.

bryson · Post by **bryson** » Sun Apr 30, 2006 1:46 am

Yeah, right now I'm thinking the best option might be to cut the centers out of the stock gears, leaving a few slotted tabs sticking inward. Then, have an aluminum "hub" cut out to go on the cam to bolt the factory teeth to. My only concern is loosening and tightening bolts into the aluminum -- maybe I'll helicoil and stud the aluminum, and just tighten a nut onto the outside of the gear ring.

The Dark Side of Will · Sun Apr 30, 2006 9:40 am

Just go with steel. The hub should be small diameter and the cams turn at half crank speed, so there really isn't much in the way of moment of interia reduction by going with aluminum.

There at least used to be a belt conversion for the Quad 4. It may not be available anymore and when it was available it wasn't cheap.

Stick with the chain. It's durable, it'll give you the RPM you want and it's already there. Any gains you get from going to a belt would only be meaningful in a racing context.

Do you have the early double row or later single row chain?

Shaun41178(2) · Post by **Shaun41178(2)** » Sun Apr 30, 2006 10:56 am

I dont' have much to add except I agree stick with the chain. Its pretty durable and going to a belt prob wouldnt' give too much benefit. I personally would want a chain on it. I think the dohc 3.4 would have been better with a chain drive instead of the belt as well.

bryson · Post by **bryson** » Sun Apr 30, 2006 2:25 pm

The Dark Side of Will wrote:Just go with steel. The hub should be small diameter and the cams turn at half crank speed, so there really isn't much in the way of moment of interia reduction by going with aluminum.

There at least used to be a belt conversion for the Quad 4. It may not be available anymore and when it was available it wasn't cheap.

Stick with the chain. It's durable, it'll give you the RPM you want and it's already there. Any gains you get from going to a belt would only be meaningful in a racing context.

Do you have the early double row or later single row chain?

I've got the early double row. When I built the second engine (this one) it had the single row chain, so I had to switch everything over from the first engine because I wanted to keep the double row chain. I also think it's a roller chain (I don't remember if that's what it's called).

Mantapart makes the belt drive conversion. Even if it was avaliable at a decent price, I wouldn't want to buy it -- I don't like the way they do business, and I don't really want to support them. They're the only people who sell Quad parts, and they refuse to give you any information about where they got the stuff you're buying...I know it makes sense but they seemed pretty jackass-ish when I talked to them about their lifters and valve springs. They supplied no information at all other than the specifications and price -- they wouldn't tell me why the lifters were any different than stock or anything, they just wanted me to take their word for it :scratch:

The Dark Side of Will · Sun Apr 30, 2006 4:26 pm

Yeah, I don't like that kind of jackassery either.