Need Help: Timing Chain - pics attchd

[Dauner]

Hello:

Trying to diagnose a an infrequent rattle/noise. Car is 1989 Carrera 3.2 with 205K miles and no top or bottom end work done. roughly once per month on the daily driver, there is a rattle from left timing chain cover. If shut down engine and restart 2 or 3 times, sound goes away. Removed timing chain cover and took pics. I can take and post more pics if it would help.

• Does the timing chain look stretched to limit of tensioner?
• If stretched beyond limits, what is the rattling sound coming from (what two pieces of metal are hitting), and why does it only happen once every 25 starts of the engine?
• What is the black debris inside the case? Other pics from the forum show things much cleaner inside.
• Is there supposed to be axial motion of the tensioner arm on the shaft? I can move it back and forth ~ 0.100"

Thanks for your help and wisdom in advance...

Mark

[Walt Fricke]

1) The idler arm centers itself as it rides the chain. If that is the axial motion you have, not to worry. You don't want any side loading on the idler gear.

2) The top of the idler arm looks rather close to the chain housing. But hard to tell from the picture. You could measure the gap. I don't have a figure for that stored in my head, but someone may know what one might expect. So what you hear might be contact there. If so, perhaps you could see evidence of that on the housing?

3) I once noticed I had a gap there that looked way too small (and the tensioner end seemed to be sticking out farther than I was used to as well). On inspection I found that the idler arm had cracked , which allowed its lever end to bend upward. Easy fix.

I've circled the suspicious gap, and where my idler arm cracked, on your picture.



But what happens if you don't go through your stop/start routine, and just drive the car? Does this noise continue the whole time?

Maybe the tensioner is getting a little leaky, and needs some time to get enough pressure inside to dampen the normal oscillations of the chain? Which is its function, as there is a stiff spring inside the tensioner which actually does the tensioning. The oil just acts as a shock absorber. An important one, to be sure.

[Targalid]

"What is the black debris inside the case?" Are you talking about the black spatter on the walls of the case or the black chunk in the pool of oil at the bottom?

[Dauner]

OK, that's embarrasing...

Thanks Targalid! I believe you found the culprit. I don't know how I didn't see that... Attached is a pic of the foreign object, and a pic into the middle portion of the timing chain housing. I assume the metal pin with the groove is part of what holds the broken ramp in place.

So, I need to do more research on my next step in Bentley, but how bad is this?

Is what lies ahead substantially more difficult than what I have done so far?

As a note, I actually was talking about the black spray debris on the back of the case. What is this?

To address some of Walts questions:

• I have roughly 0.080" of gap between the tensioner and the case. Is this still a concern?

It now makes sense that restarting would make the noise go away. I was just moving the chunk around until it settled on the bottom. It isn't particularly chewed up, so I don't think it got into any of the gear teeth.

I assume I may still have an unidentified root cause to why the ramp broke. Any thoughts? Is this a typical result of a different failure?

Thank you again for your help! This is my first 911, and so I am in complete uncharted territory.

Mark

[mike635]

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[sc_rufctr]

Originally Posted by Dauner

Hello:...

Thanks for your help and wisdom in advance...

Mark

Years ago I read about a company that had "improved" the geometry of the left tensioner arm.
The basically bent the arm so there would be more clearance to the top of the chain box area than OEM.

I wish I could remember who they were. I think it was an ad in Excellence magazine.

[john walker's workshop]

when the arm gets that close to the housing, the chain's pins and links have worn, making the chain longer. the sprockets wear as well. the tensioner is pretty much at the end of it's travel. at that mileage, without any wok done on it, you really should consider a rebuild,

[Walt Fricke]

I don't know for sure of 0.080" is adequate clearance, but that seems like it is too small. But you don't need my opinion, because John Walker, who sees worn stuff all the time, says it is too small, and chain wear is to blame.

So now you have decisions to make.

Do you just replace the broken ramp? That is inexpensive, and not really all that difficult. And not much harder with the engine mostly together than it is with the chain housing off, as it would be during a rebuild?

With a chain that worn, do you replace it in situ? Easy enough to do, as there are chains with a master link made for just that purpose. You grind off two pin ends and remove a link of your chain. You use the master link to attach your new chain to the old one. Then you carefully rotate the motor so the chains don't skip a tooth on either of the two gears (the idler doesn't count)?

Or do you pull the motor completely apart and install all new chain gears, both on the intermediate shaft and the cam (plus the idlers)? And, while you are in there - - - replace all the bearings and seals. Maybe rering the motor? Have a valve job done? Might find some valve guides have gotten too big - have a shop attend to those also?

Whoa, now you are into some serious money, even if just for parts and machine shop services and you do all the rest yourself. Though at the end you do end up with a motor good for another 200K miles or so.

Tough decisions ahead.

But in a way you are lucky. The first 9f11s had a sort of rubber compound chain ramp system. These hardened and broke off. And often the broken piece got wedged between the chain and one of the gears at either end. Which caused the cam to jump timing. Which led to bent valves, and blown up motors if you ignored things.

Walt

[Dauner]

Thanks for the continued feedback and thoughts from everyone...

Honestly with it being summertime, I would prefer to not get into "nice to haves" at this point, saving those for wintertime (northwest WI). The problem is delineating the "nice to haves" from the "truly neccesary due to high likelihood of catastrophe".

I spend a lot of time at work making Risk Assessments via stating knowns, and then assumptions. Unfortunately, my list of knowns is pretty short, except that I have a broken ramp and stretched chain(s), and a motor with 205k miles. I also know that the car starts, drives, and idles perfectly, doesn't smoke ever except for startup, and seems at least as quick as healthy SC's I have driven. So therein lies the rub.

My gut says buy and install new ramps and chains, and drive the car. Please comment, as my experience is obviously limited.

Does anyone have a video of the technique that Walt mentions? I can visualize fairly well, but either having help from someone that has done it before, or a video of the process would be invaluable..

With respect to the chains: I posted an earlier thread, and also asked in this thread what people's opinions are on what two materials are incorrectly making contact.

Video: YouTube - ‪1989 Porsche 911 3.2 Timing Chain‬‏

Again, extremely infrequent occurance, and I can't see any evidence inside the chain case of displaced or scratched metal. Why does it go away if I shut down and restart several times? I may try to thoroughly clean the inside and inspect again for witness marks.

Thanks again for all of the input...

mark

[Peter Zimmermann]

As others have said, the distance between the idler and housing is much to small, which means your chains are stretched. When that occurs the tensioner is forced to operate at the extreme of its effective range. That means that your noise is most likely chain rattle, because the tensioner is failing and intermittently allows the chain to become loose. You will not find signs of that inside the housing.

Replacing chains is straight forward for an experienced 911 mechanic, but a bit complicated for a beginner. You must remove rocker arms so the cams can turn in their bores (this will avoid piston to valve contact), which means you must know how to install those rockers so they won't leak, and correctly adjust your valve clearance. You need the tools required to remove the chain sprockets from the camshafts.

Once you have the new, left side, master link chain installed, you can replace your chain guides, and replace the rear cam o-ring (if it's not leaking yet it will soon). Then hook up the camshaft/chain so its on cyl #1 (and the engine is on cyl #1!), and proceed with installation of the cyl #1 intake rocker, adjust the valve clearance, hook up your dial indicator and holding block, and time the cam.

Every time you turn the engine you must know exactly where you are regarding crankshaft/piston position, it's easy to get confused and end up with a piston hitting a valve. Establish the marks on your crankshaft pulley and be sure that you know what each means, the ignition distributor rotor will help you with this.

While you're working with the rocker arms be sure to check your cam lobes for pitting. I don't know what make oil that you use (I've seen dirtier housings than yours), but there's enough build up there to suspect that pitted cam lobes are possible. Do not try to do both sides of the engine at the same time, do one side start to finish and then do the other side.

[gregwils]

As a point of reference, here is a photo of a tensioner with 92k prior to some top end work. The angle of the photo isn't great for evaluating the arm/case gap, but if you compare the amount of piston exposed you can see a difference. I did not replace my chains or sprockets since neither showed much wear.

PS - if you pull the tensioner out, I would guess the bushing for the idler arm is shot, probably tensioner too.