timing chains vs timing belts

Timing belts are statistically less trouble than chains. Chains contain hundreds of moving parts that wear, causing the chain to "stretch", causing valve timing to change. Belts suffer virtually NO timing change and no stretch in their lifetime.

Anyone who has owned a 2600cc Mitsubishi engine (used by Chrysler in their older minivans and K cars) knows how much trouble timing chains can cause.

The biggest problem with the 8r/18r/20r/22r toyota engines as well as the early M series engines was their timing chains and tensioners.

The later A seies engines, as well as the M G twin cam series with belt drives were virtually trouble free. Chains are very sensitive to lubrication. Belts require no lubrication.

Belts are also more efficient at transferring power than regular link chain - not any better or worse than "silent" chain - which is a lot more expensive, heavier, and more complex AND EXPENSIVE. For overhead cam engines, it is pretty hard to beat a properly designed and implemented belt drive.

The complexity of a chain drive on an opposed overhead cam engine like a Soob can introduce a LOT of new failure modes - I would not be surprised to see the chain drive "experiment" end up being short lived

- with a return to belts within a couple years.

Reply to
clare
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Very interesting.

I've always questioned the economics.

If chain tensioners are on average good for

160-180k miles (that is what people with the H6 have been reporting), and labor cost of replacing a chain tensioner is not much different than replacing a timing belt, then the savings of having a chain are not great.

Timing belt is good for 105k, on average, chain tensioner 160-180k. Saving is of 55-75k miles.

Basia

Reply to
abjjkst

I wonder if the new direct drive engines need their gears replaced on a set interval as well?

Reply to
Todd

Replacing the chain while doing the tensioners at some 150+k also adds to the cost, as the chain is a little bit more expensive than a belt.

Basia

Reply to
abjjkst

The chains supposedly never need replacement if this is the engine you're talking about:

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Reply to
Dean Hoffman

If you want to be logical, ask what does "never" mean? Or what product/engine life expectancy does Subaru have in mind when they say "never."

If your chain tensioners give up at 170k, you will probably want to replace the chain as well. It will be streched by then, it is a very long chain.

Basia

Reply to
abjjkst

"The double overhead camshafts are driven by chains rather than toothed belts. The chains are maintenance free and do not require replacement, helping to lower the cost of ownership.

The use of chain drive allows smaller sprocket diameters at the crankshaft and camshafts. That helps to keep engine width within convenient dimensions."

Reply to
Todd

Reply to
clare

Check the URL above. The Sube uses two chains, one to each cylinder head. The length of the chains is nowhere near 6 feet.

Reply to
John Varela

Check the length of both chains The engine is about 27 inches wide, You will have very close to 6 feet of chain - and I was talking about the Mittsu having 6 feet of chain - also 2 separate chains.

2 chains is more complexity than 1. Timing chains worked relatively well on cam-in-block OHV engines. Gears worked better, but were noisier. Belts are quieter than chains, and the tensioning is less complex. Another advantage is virtually no stretch, and resulting timing change. Belts are lighter too, making stresses less. Belts have improved a lot more over the last 10 years than chains have over the last 50.

I'll still bet Soob goes back to belts within 10 years - most likely within 5.

Reply to
clare

I had a car with that 2.6L engine way back. I believe that second change was for the counter-rotating shaft to keep the engine running smoothly. I got a lot of miles from that engine but it was bit noisy and it was the chain making the noise.

Reply to
PAS

That chain drove the countershafts and the oil pump. When the silent shaft seized (quite common) and sheared the teeth off the lower sprocket, the distributor kept turning, allowing the engine to run without balance shafts AND without an oil pump.

Ask how I know - - - - - -

Reply to
clare

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