Interference engines

valves

#1

are any of the manufactures still making interference engines with the cam driven by a belt? BMW quit this around 1986. Currently their engines are interference but they are driven by a excellent chain.


#2

I don’t know what you mean by an “excellent chain”? A timing chain is a timing chain. And instead of the timing chain failing, it’s usually the plastic timing chain guides that fail causing the timing chain to jump off the gears in these engines. And then you end up with the bent valves.

Tester


#3

Yes, many manufacturers still make interference engines with timing belts. Changing these belts on time is a must-do activity.


#4

A timing chain may not BREAK…but they do slip. And when they slip…same problem as when the belt breaks…MAJOR ENGINE DAMAGE.

Personally I prefer a belt for a interference engine…especially if you’re like me and keep your vehicles for 300k+ miles. If you only keep your vehicles 150k miles then a chain may be better.

. A belt now becomes a maintenance item. As long as you replace it regularly…no problem.
. Chains usually don’t last 300k miles. It will need to be replaced for the time period I own my vehicles. Replacing a chain is a LOT more involved then a timing belt. Usually involves dropping the oil pan.
. Since a chain is a LOT more complicated to replace…it’s NOT a job for the weekend warrier. A belt is NOT that complicated. Most shade tree mechanics can handle this. If you need to have a mechanic replace the chain…it will cost 2-3 times what a belt replacement costs…so there really isn’t any cost savings. If you can do the belt yourself…but not the chain…then cost difference rises to about 10 times more for a chain.

The only advantage for a chain is that you MAY start to hear it when it’s loose before it slips and ruins your engine.


#5

Have you guys seen the valve drive chain set-up on a v-8 BMW. I am talking aircraft quality materials and engineering. In the 15 years I have worked with this engine and its variants I have never seen a chain slip a guide break or any bent valves. Have seen plenty with the belt driven 6cyls of the eighties. Some companies get these critical areas right. I mean a work of art.


#6

I’ve seen 3 cars with slipped chains that have eaten valves. One even put a hole in the piston…So yes it DOES happen.

Have seen plenty with the belt driven 6cyls of the eighties.

And how many of those belts have you seen slip that were within the change interval??? Every belt I’ve seen that broke was because the owner went well past it’s life expectancy.


#7

Timing chains can fail, I have a couple of benz engines with similar timing chains (they have never used belts) and I still like to replace them somewhere in the 2-300K mile range. Even if the chains are unlikely to break, the guides do wear and the chains tend to “stretch” which affects the cam timing. As an alternative to installing off-set keys, I prefer to just replace the chain when the measured stretch exceeds a couple of degrees. I do agree that chains are more reliable than belts, and I personally wouldn’t own an engine with a belt.


#8

True! But with a timing belt, the vehicle manufacturer recommends a service interval. And if followed, you should never see a problem with valve damage because of a failed timing belt. With a timing chain, the vehicle manufacturer doesn’t recommend a service interval. Even though there are wearable components in the timing chain system, this causes those to think that a timing chain lasts the life of the engine. Which is a false belief. Timing chains and their associated parts are wearable components. And when these parts fail, they’ll take out valves as quickly as a failed timing belt.

Tester


#9

With a timing chain, the vehicle manufacturer doesn’t recommend a service interval. Even though there are wearable components in the timing chain system, this causes those to think that a timing chain lasts the life of the engine. Which is a false belief.

As with any car, there is plenty of required maintenance that is not listed in the manual if you intend to keep it beyond the warrantee period. You need a good shop that understands the “real” maintenance schedule for you car (usually based on seeing what has actually failed).