RyanPerrella

UH,

CHAINS NEED TO ONLY BE REPLACED WHEN THERE IS A TBF

To replace chains you have to pull cams. The OE Porsche chain has no link (THANK GOD, i wouldnt trust one with a link)

They are lifetime parts, when they stretch the tensioner is there to compensate, so no worries on chains.

Good point about painting the valve covers, if your going to repaint them buy the gaskets and the pads and replace. Otherwise if your covers are nice then you dont need to change pads even. Seriously, they wear but its not going to kill the car, and at 120K which is what my engine had when i rebuilt it the pads had grooves in them but nothing to serious. I replaced them and the chains because the engine had a TBF.

David L. Lutz

Roger,
How much are a pair of chains?

Dean_Fuller

Thanks guys....I feel better. Actually the covers are not leaking on my car. The pan is, so I will focus on that.

fraggle

What is the trick to keep track of the crush washers for the j-tubes for the tensioners so they don't disappear down into the block?

I was paranoid as heck and still managed to lose one when we were doing this on Mikeathome's car.

RyanPerrella

you may want to use some assembly lube

or try and plug the drain holes before hand.

I dropped one down the pan when the engine was on the stand. That taught me to button up the oil pan LAST!

Vilhuer

I would change chains every 100k kilometers or miles despite how they look. Reasoning behind this is that they wear and distance between sprockets gets longer. When this happens less and less number of sprockets does actual pulling on cam gear. Less sprockets there are more pressure for each cam teeth and more likely teeth break. This logic might be wrong but if its not it might save from premature cam gear death.

AO

Erkka- I usually hold your advice in high regard, but this one seems a bit...

I would imagine this wear is less than 0.00x mm. Maybe less, maybe zero. But if I follow your logic, wouldn't the cam lobes wear like the chain? If so, you might as well replace the cams... Not worth it IMHO.

hacker-pschorr

I remember when the dealership back in 1998 told the the entire system (including the pads) were not a wear item....want to see the repair bill I ended up with a year later?

When this system fails it's far worse then a timing belt failure since it usually destroys the cams and the head (along with the valves).
This is far more common on the 944S than the 928. Not sure why since they use the exact same parts.

10 years ago the pads were not available (at least through the dealer). The only way to do the job was to buy a complete tensioner.

Fact - chains stretch, there is nothing special about the 928/944S cam chain to prevent this.
Then why don't you replace the cam gears everytime you do a timing belt? If the belt wears, they must to, correct?

Just like on a motorcycle, replacing the chain is regular maintenance. Replacing the sprockets the chain runs on is not.

The metal the cams are made from is a hell of a lot harder than the chain.

AO

Hacker-

You are making an assumption that the cam chain is subject to the same stresses as a motorcycle chain. They are not. The chain on a motorcycle is a drive-line component used to transmit the HP and TQ of the engine to the rear tire. Our cam chains are merely subject to the resistance of the valve springs - which should be relatively constant and not vary along the power band (I think... don't quote me on that last point).

I agree the tensioner pads are a wear item. The cain is not IMHO.

Vilhuer

If chains wear more than cam gear then I think my logic is valid and its good practise to change the chains at some interval. If chains wear less then cams should be changed first and chains in every second cam chance for example.

There is more load to chain than just valve springs. Intake cam itself and all valves too resist and do not want to move as fast as exhaust cam is pulling them.

dr bob

Erkka is correct. If the chains actually stretch, the wearing surfaces of the cam sprockets will wear to match. Put on a new chain, without new cam gears (in this case that means new cams...) and the wear will be localized on the last teeth of the drive sprocket and the first teeth of the driven sprocket. With that in mind, the wisdom would be to either replace the chains very often, avoiding the eneven wear on the sprockets, or never replace them.

I disagree with Eric's suggestion that the 'metal the cams are made from is a hell of a lot harder than the chain'. The cams are heat treated and Parkerized at the lobes, but are generally not hardened to that extent anywhere else. If they were, they'd be way too brittle. It may be that the sprocket areas are also heat treated for hardness, but again the localized treatment would make the teeth brittle, so it's they are likely not as hard as the lobe faces. In the meanwhile, the rollers on the chain are very hard. There are bushings inside the rollers, and the pins are also hard. It's the bushings that wear against the pins that eventually causes most apparent stretch. From my limited experience designing drive systems.

RyanPerrella

interesting discussion. So do you suggest replacing chains because they stretch and therefore cause more wear on the cams right?

Well I recall looking at my 110K mile TBF chain and the brand new Porsche one side by side and thought the old one would be longer then the new one. Well it wasn't IIRC. I dont even think it was noticeable, but maybe could have been 1-2mm longer. THATS IT, it wasn't a link longer or anything, it was very very slight. The tensioner is plenty capable of handling that stretch though, thats what its there for no?

I have my 112K mile chain still. Let me know if someone wants to compare it to the out of the box OE Porsche chain and we can settle this. I don't recall it being any longer, of course i never took a pic though.

I agree with Andrew, chains are not a consumable, its not a WYAIT job, it just isnt!

Hacker, interesting point about 944 heads, apparently they do suffer from some top end problems we never see. Someone on a 944 board suggested it had something to do with the redline but i dont agree with that, but there is something different because the cars do have their issues but RARELY share the same ones.

Lizard928

While motorcycle chains have alot more force on them andrew, they are a HELL of alot bigger. And as to the gears (or sprockets) not needing to be replaced. Not the case. They get replaced all the time on the type of bikes I ride. In fact I just did it on a bike this past week.

That being said I have the factory chains and pads in all my cars, the 86 engine has well over 300k km on it now and the chain has not stretched to the point where the chain isnt lining up with the sprocket teeth anymore.

Vilhuer

If both cam gear and chain wear equally I'm wrong and they should not be changed like Bob says unless there is some outside cause like bent valves to suspect they are bad. I'm not sure this is the case. If chain wears clearly more than gear then chainging it often enough should buy more time and miles out from cam.

944 S2 and 968 have different valve springs. This could be one explanation why those have more cam teeth problems than 32V 928 but this doesn't explain 944 S which had same springs from the factory as 928 IIRR. Maybe difference in rougher running of 4 cylinder engine. Balance shafts can stop engine from shaking itself but will they also prevent drivetrain parts from shaking?

ROG100

Just to clear up a statement I made earlier - the racing chains do not have a master link.
OE Bilstein chains are $12.95 each and the stronger IWIS chains are $29.95 each.