Why is the timing belt such a concern
 

Yes, I know the answer, it will wreck valves.

More importantly, it seems that every day there is a post about a broken belt, lucky catches with missing teeth etc.

Does the 944 chew up belts? Are they at so high a tension that they are susceptible to breakage?

I have had 2 e30 BMW's with interference engines and you just don't see the same level of Timing belt paranoia

:confused:

944s themselves don't chew up belts... not putting on new rollers when they are needed chews up belts :) Stuff (almost) only breaks when it's not taken care of

Dave, When was the last time you checked your timing chain? The one that connects the two cams. The one under the valve cover. If/when that breaks you might as well throw the car away as it's over $3,000 to fix. Oh yes breaking your timing belt will cost almost as much.

It's not under much tension at all. If you felt the belt, it almost flops around. One thing is that it is an aluminum engine.
Aluminum engines expand when hot then retract afterwards. This changes the tension or even stretches the belt. Any rubber belt subject to this, as well as it is right up against the engine, so it suffers constant heat cylces (hot then cold) everytime you drive and turn it off.

This all contributes to why they fail, but the biggest is that it is an interference engines. Honda's are supposed to have their belts changed after 60k or so (double(ish) of 944's recommendation), but even then noone worrys because generally all it takes is a new belt and your good to go since most are not interference engines, at least civics and such.

About BMW's not having as much of a problem, I don't know much about them.. but, is the belt teh same size, thickness? Run the waterpump? Are the blocks aluminum? If they aren't i would bet that there is less stretching going on.

Another thing to recognize is BMW parts are probably a little cheaper as they are more readily available?

SoCal; I purchased the car from someone who wouldnt know a timing belt from a cam chain tensioner from a steel belted radial so I am left sifting through maintenance records trying to decipher bills. The good news is that he would drop the car off and tell the mechanic to "look after it" One bill I have is for $5800, and includes, Clutch master / slave, brakes all around, AC compressor and dryer and a cylinder head overhaul. 36 hours of labour in total.

The plan is to AutoX the car next spring so the plan is to have everything checked by my mechanic who races 944's and does repairs to 944's on a daily basis. The belt, rollers and waterpump are probably okay but will be replaced anyways. The cam chain tensioner will be replaced. All of this will take place this spring. A new set of Khumo V710 will serve as race rubber on the phonedials and I plan on picking up some D90's for daily use. I may buy a set of sport seats but that one is further down on the list of priorities.

Good that you are on this. Some who buy an 'S' soon loose their 'SS to a broken timing chain. Wouldn't hurt to pull the valve cover and check on the plastic pad for the chain tensioner.

I replaced my timing belt about two years ago (at about 50K miles), and then had it PROFESSIONALLY re-tensioned a couple thousand miles later... and it still broke. Sometimes crap happens.

Getting mine fixed (one bent valve) cost somewhere in the neighborhood of $1000. Guess I was (comparatively) lucky.

Belts have to be check and tensioned at every maintenance service...whichis at 15k miles. It's in the maintenance schedule.

I do believe most Bimmers use chains, and all the (recent) ones have aluminum blocks. The newest 3 has a magnesium/aluminum composite block.

Folks will disagree, but the Porsche engineering staff was on vacation when that timing system was designed. Even the 928 had hydraulic tensioners/ electronic indicators on their mile long belt!!

Can't find the figures I came up with, (old post, long time ago here) but the expansion between shaft centers is quite high relative to the fact that the expansion of a composite belt is virtually nil.

The 928 used a mechanical tensioner with bi-metal discs as the dampening part. The oil is just to add to the dampening effect.

Brit

Thanks. I knew about the tensioners, but didn't know the right words to describe it.

I believe there was only one single 4-cylinder Honda engine that was non-interferance. The only recent non-interferance engine from Honda are a couple versions of the V6. Every 4-cylinder in the Civic and in the Accord and in the Prelude since the 1980's has been interferance.

Aaron

I don't know then I guess, My friend had a civic hatchback, 92ish i think, and his timing belt blew on the highway and his dad came and put one in and it was fine till he wrecked it months later....


Maybe he just got lucky or was wrong about it being the timing belt, but I think he knew enough mechanically to not be mistaking a fan belt for a timing belt.

My mistake though if what you say is true, most of my knowledge is based on experience, rather then reading.. so sometime's (yes I admit) I'm wrong. :)

Think our selfs lucky, timing belt changes for Ferrari is every 2 years
regardless of milage. From what I have seen of most Ferrari engine bays
this would cost more than an old 944.
Russell

SOmetimes I long for my old 1977 924......

Didn't porsche recommend 45k or 2-3 years (whichevers first) on the 944's timing belt? or was it longer than that.

I don't worry about my timing belt. I check it bi-yearly, retension it if required, and change it every 60k km's. I don't lose any sleep over it.

My subaru on the other hand.... that was one interesting beast. It's a non-interference engine, aluminum block, so I was just waiting for the belt to break before I changed it.... 330,000km's on the ORIGINAL timing belt, before I traded it for getting a fence painted. I don't quite understand why 944's have so much trouble with tmiing belts. I would imagine those with the mechanical/hydraulic tensioners are better off than us with the manual tensioners, since they don't allow the belt to over-tension when the engine heats up.

Dumb luck on your friend's part.

Actuall my mom's 96 civic calls for the 1st timing belt change at 100,000 miles- crazy talk