Let's think about this a bit. Components expand with heat, and chains, even the whole engine share this characteristic. That chain's gonna stretch and the engine is actually gonna "grow" a bit wider. Not much, but it is measurable. The function of the chain tensioner is to keep tension on the chain, which gains slack as the engine warms up and as the chain wheels wear. That's why we have the chain support wheels on a pivoted arm. I figure the closest the chain guard is ever going to be to the body of the tensioner is going to be when it's freshly installed in a cold engine. Note, I "could" be wrong on this, but I think it's a pretty safe conclusion. I agree there may even be some slight extension of the shaft after turning the crankshaft a dozen times or so, but it might not be easily observed. In this case, I think I might be inclined to install the guard as close to the tip of the shaft as is practical and go with it.

The Cap'n

I would say that you are one of the fortunate ones with chains and sprockets in as-new condition. Presumably the rest of your engine is as fresh? I replaced both chains and all sprockets on recent rebuild I did, and had the similar result of tensioners being much more compressed than we normally see. Its a good thing.

Just eye-balling it, I think your collars are thicker than the ones I remember. On the old ones (usually anodized blue or gold), the aluminum collar was actually slightly less in thickness than the diameter of the the heads of the cap screws.

Personally, I would leave them out. Tensioners give lots of little light warning rattles as they are getting soft. If your ear is paying attention, you will know something is up before it becomes a catastrophic problem. The collars could lull you into a false sense of security (whats that noise-oh, probably nothing--and anyway I've got tensioner guards). Could catastrophic chain failures have been caused by the collars banging up and down on a soft tensioner, loosening or breaking, and falling down into the works?

DG

Oh, and just for kicks, have you rotated the engine a time or two after reinstalling the tensioners. Not impossible they would pop up a little more if you do so. Plus a good chance to eyeball the crank/cam alignment and make sure nothing moved, in spite of what appears to have been your good precautions.

The engine is 90,000 miles old and I have all the receipts and no record of it being rebuilt or having chain/sprocket replacements. Could be fresh and not documented but that would be at odds with the rest of the records which account for all other work done (mostly external stuff like gaskets and oil tubes)

I do know what noise you are talking about as this is what caused me to inspect the tensioners in the first place. So it's not fresh, but at the same time it is pretty clean inside and it's been a warm climate car averaging 3,000 miles per year. Only the original owner really used it as a DD.

Yes I have spun it around to TDC twice, and worked the idler arms with a screwdriver to make sure they are making the chain as tight as possible. There is no binding and the engine rotates freely (plugs are out)

I am leaning toward leaving them out - the engine has lasted this long without them, and it will never be a hard driven engine while in my ownership - redline changes are not my thing. I respect the cap'ns advice here and if there was a bit more room I would put them on. I'm worried about not having enough shaft to clamp onto, thus having a substandard clamping and ending up with loose (or worse, loose in case) collars.

Which is annoying as I could have had the car back together a week ago had I not been waiting for the collars. But I will put them away and if I'm back in the engine in 10,000 or 20,000 miles time then I can see if there is more tensioner shaft to work with.

Inherited. Can't speak to when or how well they were installed. One of the collar halves failed, may have been to the bolt failing or coming loose, maybe the aluminum just broke. There's a picture at the end of this post:

http://forums.pelicanparts.com/porsche-911-technical-forum/789817-start-maintenance-end-disaster-opportunity-5.html#post7907612

<img src="http://forums.pelicanparts.com/uploads22/split41392240984.jpg" border="0" alt="">

One side is buttoned up, moving onto the other today. I elected to leave out the collars. My first rule is that the factory knew what they were doing. Ok, so the factory knew that the 'reservoir' hydraulic tensioners wouldn't last the lifetime of the engine (so they swapped to pressure fed when they decided not to end of life the 911). Actual stories of tensioner collapse are rare so I'm OK with keeping an ear to the engine (which I'm obsessed with anyway).

No doubt I'll be back under those chain covers at some point and I'll re-assess then.

Glad you got over that hurdle. However, in many cases, the factory did get it right, but as for failed tensioners, it's not as rare as you think. Early stories of tensioner and/or chain ramp failure were more frequently reported at early 911 sites; fortunately not as much in later cars as Porsche gradually introduced the required fixes, but it took awhile.

The latest versions are called "Turbo tensioners" and the pressurized lube system introduced in '84 along with idler arm modifications have made this area fairly trouble free. Still, if you should experience any audible signs of low speed rattling, stop the engine. You know the routine. :)

Sherwood

Sure, I wonder how many tensioner failure stories are with the earlier 'cup fill' tensioners as opposed to the later sealed unit tensioners as in the SC?

I guess it's a bit like single vs double row IMS bearings - so much conflicting information out there it's hard to know what is real and what is just mangled data passed from one thread to another.

Probably enough feedback from Porsche dealer warranty reports to motivate PAG to develop fixes to limit potential engine repairs on their dime.

And NEVER listen to anyone who tells you "If you keep the revs up, you can drive it to a shop .................". I've heard that one, and, sooner or later, you have to shut it down.

As a final comment, I've never reused a tensioner guard. Maybe that's why I've never had one come apart.

The Cap'n

[Submerge the entire tensioner in a container of clean engine oil, then work the plunger until all air bubbles are expelled. When difficult to move, it's ready to install.

Sherwood]

I have my tensioners out for a top end rebuild and they seem fine. However, should I follow Sherwood's instructions above nevertheless just to make sure all air is out of them before re-installation? Can't see how this can hurt.

Thanks

I'd be willing to bet the guards that came apart were installed like your photo, with no space between the guard and the tensioner. Watch a video of the tensioners in action and they bounce around quite a bit. With no space for plunger movement they will simply hammer themselves off. From the witness marks on RDMs failed guards, that is what it looks like to me.

Failed o-rings, that is what my tensioners suffered from, same as yours. Probably all of them.

When an O-ring fails, the plunger will gradually collapse as oil escapes. The collar merely acts as a manual stop to avoid excessive chain slack which could cause it to skip a sprocket tooth. Continuous engine operation can cause the flopping chain to beat up the collar until it fails. Performing forensics on a failed collar might be difficult to determine whether one of the fasteners broke or loosened, whether the aluminum material itself failed (for whatever reason) or was hammered to the extent the collar failed.

Tensioner collars are a short-term stop gap product to help prevent immediate catastrophic damage. The collars' effectiveness diminish with extended engine operation.

Sherwood

Rebuild them with the Porsche kit, why risk old o-rings and potential failure.

Ok, so I have the car all back together and it sounds just right. I now realise that the failing tensioner was contributing to all sorts of noises. Or maybe it's just the fresh oil.

Anyway, after 24 hours I got one drip from the RH chain cover.

Can anyone tell me the correct order or have an exploded view of this fastener and the oil tube bracket? I suspect I have not put it on the right order and so it is not torqued correctly.

http://i1283.photobucket.com/albums/...psfrkrdyd9.jpg

This one...

great read, I am about to rebuild my tensioners.

regarding the leak, I suppose its possible that one of the covers is slightly warped. Just like valve covers. I just put mine down on a nice flat granite remnant and could feel it rock slightly. I attached sandpaper with spray adhesive to the granite and planed them flat