Interference engines

I now have the information from MB to answer my own question.....

ALL MB petrol engines since about 1980 have been Interference engines.

So now you all know.

David

What do you mean by interference engine?

Ed

It'a an engine where an open intake or exhaust valve can hit the piston if they both tried to occupy the same space at the same time, ie when the timing belt or chain brakes.

That's right - and to anticipate the next question... Are not all engines like that?

The answer is No, and the reason is 'performance' related.

Most common engines in typical cars before the 1980/90 era were low-compression. They were designed such that the valves and pistons could not clash when the timing was bad, ie, as trader4 said, when a timing belt or chain broke.

So with any modern MB, if your timing chain should break, you wreck your engine as well.....

On the Fiat X1/9, the 1300 was an interference engine, the 1500 w/5 speed was not. This made it nice when you lost the timing belt after you did not replace it every 60K miles as recommended. But with the lower compression ratio of the 1500, the 1300 had more power.

Same as the Fiat/Lancia twin cam engines. The 1600 and 1800's bent valves but the 2.0 did not. But the 2.0 ran the best.

But how long did any of those Fiats/Lancias run? :) In many cases a broken timing belt destroying the engine may have just put the owner out of a lot of misery.

on Tuesday 18 December 2007 01:58 pm, someone posing as David J took a rock and etched into the cave:

So these engines are interference but they have timing chains?

I was under the impression that only engines with timing belts were interference, such as my old Kia, my wife's Vue (with a Honda V6) and my new '99 Sebring with a Mistubishi 2.5L V6.

I used to own a bunch of them. Last one I sold was a 79 Lancia coupe. Honestly, they were great cars. What hurt them were the idiots that 'worked' on or at them. I would buy 131's that needed work. 9 times out of 10, all that was wrong was something real simple but I would have to spend 6 hours undoing all the butcher repairs inorder to spend 15 minutes fixing the original problem! I have never seen any other line of cars that were 'repaired' using cross-threaded nuts and bolts and SAE nuts and bolts on metric threads. For some reason, parts replacers [can't call them mechanics!] love to use those horrible 3M blue Scotchloc wire splicers. What crap they are..... built-in resistance and open circuits. "Let's bypass the wrong relay in this fuse box with a wire using the 3M ends" and hmmm, why does it still not work?? Instead of, "I wonder why this relay is in this hole and that relay is in that hole?" Fiat uses different styles of relays for different circuits. They look and fit the same but the part numbers are different. Unlike MB where they use

compression

There are lots of cars with interference engines that have timing chains.

My experience was very different. I owned a Fiat 124 Spyder and also had a friend who had the same car. Both were the worst cars with more problems than any I've ever owned. On mine, just about every winter, the brake calipers would seize. Probably because they couldn't withstand the salt. It was so bad, if I ever managed to wear the pads before the calipers seized, I'd just replace them at the same time. Friend had the exact same problem on his.

Then with maybe 25K miles, the clutch cable starting binding, and getting harder to operate. It broke in a great spot, the Hippodrome parking garage in NYC during a trip there. Car had to be towed to NYC Fiat dealer.

On a cross country trip to CA when the car was still relatively new, the voltage regulator failed and the battery boiled over. With the battery in the trunk where all my belonging were for a move to LA for a summer job, that could have been a real disaster, but luckily the acid only hit part of the outside of my $500 stereo receiver.

At 60,000 the head gasket blew. While doing that job the dealer told me the valve guides were badly worn and needed to be replaced. He asked if I hadn't been changing the oil. Which I had been doing regularly at 5K miles.

The clutch cable again broke, and the car had to be towed.

Oh, and I especially loved the valve adjustment method. You had to use a special tool to depress the spring, then change a metal disc from what was there to what was needed. Of course that's less than convenient considering DIY guys don't have an inventory of all the various sizes you might or might not need, so it's a trip to the dealer and hope one is around and they have the right thickness one.

And the dealer was a total moron too. They delivered the car with the pointed end of a screw sticking out from the radio and with the window crank handles missing.

I sold it at about 75K and was very happy to see it go. It was a lot of fun to drive though.

Rust and corrosion is/was a BIG problem with them on the east coast. I grew up with that problem in New Jersey, but when I moved to Fresno, Calif all I saw was mechanical problems. Now that I have moved to Coos Bay Oregon, I am seeing coast cancer all over the cars here.... Luckily my '58 Vette is fiberglas bodied, but the frame will still rust. I will need to spray it with Rust Bullet.

Thank you, I just call em dead when that happens. ;)