triscadek

Mine is almost to 218,000 miles, I replaced the pad 3 or 4 years ago.

triscadek

Schtuff can "just happen" though, recently someone had a 4 Runner that threw oily parts through the side of the block with no warning.

There is always that fluke catastrophic failure set off by an inexpensive part.

nine-44

I'd say the chain would last for a bit longer but not indefinately. It will wear and strech, possibly to the point that the tensioner will not be able to compensate. The pad is mos likely to be the problem. Really, it's a case of, while I'm in here. I'd do both at 60K intervals and shouldn't have to worry at all. There are the flule instances tho, you can't forsee or prevent them.

eohrnberger

I just replaced the upper pad this year, and it was certainly worn out. Glad that I caught with, or rather was advised to check it in the strongest terms, and replaced it.

Bought only the top pad, as it was most worn, but I'd also like to replace the bottom pad. Yes, it's worn a little bit, but I'd just feel better if it was replaced.

The procedure at: http://boerger.golden-tech.com/image...eplacement.htm was very helpful in swapping the pad out at minimal cost and hassle.

Oddjob

Im not sure what the comparison with a 4-runner is? Sure, **** happens. But I think there are enough examples of this failure problem with the 16v heads at various age and mileage levels, and my point is that with the risk of catastrophic failures ($$), why chance running the pads, tensioner, and chain into the ground?

Are you recommending not changing these parts at a certain interval, because its a fluke that they fail, and there will always be some part or another that will cause an engine to blow up regardless?

tifosiman

Something to consider here in reference to the chain and service life (nine-44 touched on this a little bit but I want to expand on it):

The chain will stretch over time. In the bicycle world, it is common practice (on higher end bikes) to replace the chain at certain mileage intervals to save the gears/chainrings. The reason for this, is that the chain stretches with use, and a stretched chain starts to cause rapid and un-even wear on the gears. To simplify the explanation, basically the gears wear and get ground down to match the link spacing of the stretched/stretching chain. Now, if a chain is left on there too long and it wreaks havoc with the gears, the bike will still work fine (more or less), until the chain breaks and needs to be replaced. Then, the new chain will not match the tooth profile of the worn out gears (performance will not be smooth, and the chain will want to skip and possibly jump off) and the gears need to be replaced as well.

My concern would be that if the chain in the 16V head is not replaced at a specific interval (like George B suggests), the gears will begin to wear. And if the wear is bad enough, just a new chain won't fix it. New gears would be in order, and IIRC that means new cams as the gears are fixed (someone correct me if I am wrong). The other thing to consider is that as the teeth on the gears wear and lose material, they become more prone to breakage. There was a thread awhile back on the 928 BBS regarding the ex-Holbert (record holding) 928 and the teeth breaking off the cam gears. The car has seen some serious race/track time and use, and those being the original gears, one wonders if that problem had something to do with the wear from a stretched chain.

Tom R.

Interesting view from the other side Tifo. makes a lot of sense when put that way.

craig001

Here's a simple question. Do you have the cash to have the heade repaired or replaced? I would have the chain replaced while you have the toe end opened up so you just do it once. Another while you are in there part. I just had to respond to this as I saw it while trying to see of anybody has received their Rennlist Coin yet. There is a thread from a group of us in the 964 forum still waiting for ours.

ANd yes, I miss my S2 Cab. The 964 is fun, but nothing was better than riding topless.

eohrnberger

Is there a way to inspect, measure, quantify if the chain has stretched and perhaps by how much?

As with all threads of this nature specific to the 16V head, I start to get worried. Perhaps needlessly, but still, better safe than sorry.

500

As a long-time cyclist, I too agree with what Tifo is saying re. chain stretch, which is actually wear in the link rollers which ultimately allows the chain to pull out a little longer. A new vs. old (couple of thousand miles or so) comparison on bicycle chains will show maybe a difference of half a link over the length of the chain.

Having said this, I had wondered about the same thing when I remove the 147K mile chain from my car when I got it. I was not able to measure any stretch compared to the new chain. I guess the main difference is that a bicycle chain is exposed to grit, no matter how well maintained.

But it is a cheap part ($25 or so) so why not just replace it anyway...

eohrnberger

It's not the part that makes the procedure so expensive. It's that you are dissassembling 1/2 of the head, and you've got to re-time the valve timing belt. Consider also the great damage you'll cause if you get the timing wrong.

Some, I'm sure, are not that confident in their mechanical skills to get the timing right on the first try. So then you are left with paying a pro to do the job, and it runs around $800, from what I understand.