Timing Chains vs Timing Belts?

[Sharkbit]

I own a 1987 911 Carerra as well as my 928 (and my wifes 944). Never had any issues with the timing chain on the 911 or the timing belt on the 928. It is all keeping up with maintenance on these great cars, and investing the time in research to learn how to do it right. The extra time spent to maintain them properly is well worth it. If you cheap out now you'll pay later.

[riber.bentsen]

True that. It's all about confidently doing those thrilling high-rpm blasts.

[tisilrad]

well the porsche cheyenne engine has timing chains and i personally feel they are more dependable and robust. I think however that they would increase the rotational inertia of the reciprocating assembly and lower overall RPM capability...something that i feel is one of the strong points of my 5.0 engine..it hits redline rapidly. If you were completly rebuilding an engine for performance you could lighten the internal assembly to compensate for some of the increased rotational mass..maybe...but overall you could get better results with a belt in terms of shear horsepower(all frictional losses take away from RWHP of course...). I have heard of someone converting to a chain drive from an Audi engine but could find no information concerning this...would be interested ...

[JK McDonald]

The Porsche 911 engine has long had a bullet proof timing chain design for each bank of cylinders using engine oil pressured tensioners. These upgraded tensioners virtually eliminated all of their previous problems. It looks like the 911 engine photo that riber bentsen added displays the 1970’s non-oil-pressurized cam chain tensioners.

By the way - Mercedes used a single (extra long) timing chain design on their early 4.5 liter V8 engines. This design was basically similar in operation to the 928 timing belt. The extended length of these chains could cause LOTS of component failures, guide wear, centrifugal weight/stretch and valve train issues - especially if over rev-ed. It was not uncommon to replace both heads for bent valves if an aggressive driver missed a shift or spun the drive wheels in the mud.

The one piece, twin overhead cam timing chain design in some ways is better than the light weight timing belt but also has it’s drawbacks.

Michael

[harborman]

I don't see any problem with the timing belt as long as it's changed and properly installed. I see Gates has a heavy duty one out now for about $167. I put the Gates belt on my car last year, but the cheaper one as the newer version was not on the market yet. There had to be a good reason the Porsche engineers did not use a chain. All this had to be figured out before the engine was made. I am sure they did a lot of testing and looked into other options. As we know, the belts are widely used today. As pointed out here, the chain was not a good option.

[Landseer]

The regular Gates belt, stock tensioner, new pivot bushings, new gears/rollers and new Laso water pump is all you need, regardless of year, interference or not.

Valve crash happens to cars that were neglected. And also, to ones where redneck "feel my way through the job" mechanics installed the belt without following exact procedures (getting washers out of place, not retensioning, not measuring tension, neglecting the plastic pivot bushings, running without covers, etc). And ones where the old water pump of unknown origin is left on the car (especially a pump that sat on a stored car).

So, buy a car. And unless it was serviced by Greg Brown or Mr. Merlin, the first thing to do is disassemble and inspect. Doesn't matter if it was serviced 5000 miles earlier, in fact, that's an indicator that you'd better tear it down to inspect.

[harborman]

I did everything you mentioned last February. I down loaded a "how to" list from that Rennlist forum. My car had 38K original miles on it. When I took the covers off, I saw the belt had been changed once, probably back in 1992. I changed the water pump but my old one looked quite new. I put a new Laso one on. I refilled the tensioner with new oil. Checked belt tension with the gauge and then again after 2K miles. I drove it about 7K miles since, until the snow hit here. Also Mrmerlin was a great help as others.

Originally Posted by Landseer

The regular Gates belt, stock tensioner, new pivot bushings, new gears/rollers and new Laso water pump is all you need, regardless of year, interference or not.

Valve crash happens to cars that were neglected. And also, to ones where redneck "feel my way through the job" mechanics installed the belt without following exact procedures (getting washers out of place, not retensioning, not measuring tension, neglecting the plastic pivot bushings, running without covers, etc). And ones where the old water pump of unknown origin is left on the car (especially a pump that sat on a stored car).

So, buy a car. And unless it was serviced by Greg Brown or Mr. Merlin, the first thing to do is disassemble and inspect. Doesn't matter if it was serviced 5000 miles earlier, in fact, that's an indicator that you'd better tear it down to inspect.