SC Chain Tensioners - How to test?
 

I heard some noises I didn't like so on a weekend full of torrential rain I popped off the cam chain covers to take a look.

http://i1283.photobucket.com/albums/...ps2df191cb.jpg

LHS

http://i1283.photobucket.com/albums/...ps668cf1ea.jpg

RHS

The Bentley says something like 'use screwdriver to lever the idler arm, should be no movement'.

My question is : what is the right amount of resistance in the tensioner? The bentley shows testing by levering down the LHS tensioner against the case. I don't need to lever - pushing directly on the idler arm downwards I can move the idler and can see the chain start to lose tension - I assume this one is in need of rebuild. I plan to purchase a rebuild kit and fit collars instead of going the pressure-fed route.

On the RHS there is no place to lever. Pushing down on the idler arm with the same amount of force as the LHS doesn't budge the tensioner at all. How much pressure should I be putting down?

Side Note : where does the diesel-at-idle rattling come from? I can see no evidence of chain contact with any part of the case. There is no debris in the case (in fact it is very clean as per pics). I can't really see the chain guides under the chain but I see no signs of degradation anywhere.

Any tips on checking for wear/tear in the chain/ramps/tensioners welcome.

My car had a bad rattle @ idle/shutdown. I swore it was the tensioners. Turned out it was the muffler rattling against the rear valance. I would check for that/or any loose engine sheet metal in the shakedown, especially if you have an aftermarket exhaust. I'm subscribed for tensioner tips!

Yes, I should note that I don't necessarily blame the tensioners for the diesel rattle. The diesel noise was only intermittent and throughout the rev range when it was happening (though I never revved it above about 2000 rpm when it was rattling. I have listened to several youtube videos talking about worn tensioners and the sound was similar, and I have no record of the tensoiners being replaced/refurbished in the books. In the end I decided to go in and see for myself, otherwise the paranoia would never let me enjoy the car.

IMHO, if you can push it with finger pressure, replace it.

The tensioners should not move (quickly) at all under finger pressure, so your LHS is definitely bad. This will be the source of your "diesel rattle". Probably the noise itself is generated by the tensioner piston/ idler arm bouncing up and down and against each other. If you could run your car with the chain box cover off, you'd see the tensioner piston on the bad side hopping up and down like one of those old monroe-matic shock absorber commercials, while the good side would be stationary. The tensioner itself is just a shock absorber. The spring pressure is not even that much, but the valving is extremely slow. It doesn't take all that much force to compress one, it just moves very slowly. Constant pressure applied by hand will compress one, but if you relax even for an instant the spring pushes it up and you have to start all over. Thats the key to understanding how they work. As long as there is sufficient oil in them, they work. If enough oil leaks out, they don't. No big mystery in "rebuilding" them. Just a matter of refilling the lost oil and getting all the air out. It is a bit of an awkward thing to do, but not difficult. The two o-rings can be sourced at your FLAP.

"Constant pressure applied by hand will compress one."? Really? Constant pressure with a vise, maybe but not by hand. If you can move it by hand it's in need of a rebuild. There's quite a bit of resistance with the tensioner open, much less fully assembled and bled.

The Cap'n

Ok, thanks. So the required pressure to move it would be like putting in a vice and tightening. Any movement at all I can exert by screwdriver means it is bad.

Should I do both while I have it open? I'm assuming the answer is yes.

When I remove the tensioner is there any risk of the cam timing moving? The Bentley doesn't mention this. I have seen photos of other people tieing the chain up with zip ties. Is this necessary with tensioner removal? Or can I just compress and lock it, then remove?

Here's what you need (part number and kit contents in bag) along with a disassembled view
http://i160.photobucket.com/albums/t...ps5ce22401.jpg

and how to hold the chains (~2" bolt and nut) and you can use a big C-lamp to compress the rebuilt units and then slip them in
http://i160.photobucket.com/albums/t...ps07db8de3.jpg

no sense in not doing both

Thanks- I saw tha Porsche make a special tool for that, I'll just get a bolt and nut like you show.

Is there any risk of the camshaft moving ? Do I have to be super careful? Or as long as everything is kept in the same place while the tensioner is out it should be ok?

Look at the picture above. Got it? Now, listen up. DO NOT EVER remove the chain tensioners unless the camshafts are set at TDC #1! Why, you ask? Because when they're at TDC #1, they're unlikely (not to say they can't) turn by themselves and potentially bend a valve or jump timing. Unlike the camshaft in the illustration, the wrench flats on the cam will be parallel with the seam in the case, or vertical if the engine in in the installed position. A simple precaution that might just save you from a massive mechanical headache. It's a good habit to acquire, and cost you nothing but a few seconds.

You should also note that the bolt trick won't work on the right side, but there are other ways to hold the toothed roller tight against the cam. For installation, buy yourself the little steel holder sold by our host. It's not as good as the factory one, but it works fine. You'll never get in there with any kind of pliers holding the tensioner compressed. When you compress the tensioner, close the vise slowly and evenly until you can get the tool on it. And buy a pair of chain guards, which have to be installed AFTER the tensioner is installed.

The Cap'n

I set the engine to tdc/Z1 before removing anything based on my reading. The engine is installed and the cam nut ends are vertical (see top pic). So I am reading as long as I am at TDC and keep the idler arm tight, I should be OK. My main concern was that pressure from the valve springs might turn the camshaft if the chain tension is removed, and I understand that camshaft timing is a matter of single degrees.

What is the method for the RHS? Is using zip ties to hold the chains together and on the idler a good method?

Nut and bolt works on the right side tensioner just fine, and BTW this pic is from an engine in the car tensioner replacement ;)
http://i160.photobucket.com/albums/t...ps3a7496ea.jpg

Do you start the nut and bolt loose and then unwind the nut until it starts to take the tension off the tensioner? Or just put it in snug and compress the tensioner to get it out?

Takes a little finessing, but make the nut/bolt a little longer than it needs to be and then slip it in, you want the lever/chain tight.

Well, I've learned something new today. Thanks!

The Cap'n

Ok so I have progressed on this front after many days of doing other things.

I have used zip ties and a bolt between case and idler arm to hold the tension on the chains.

http://i1283.photobucket.com/albums/...ps0030d16d.jpg

LHS

http://i1283.photobucket.com/albums/...ps919e5773.jpg

RHS

I had a bit of trouble getting the tensioners out until I realised that it is a case of gently does it and make sure you pull out on all sides parallel, then it just pops out.

I bought 2inch/50mm nuts and bolts but I had to cut the ends off with a hacksaw and then wind the nut out a bit and just work it in to get it snug. I think I cut about 10mm off one and 5mm off the other. The RHS was a little dicey to pull the tensioner out and keep the nut in place but it all worked out. Thanks to eastbay for the tip!

Still waiting on the rebuild kits to arrive...while I am waiting - how do I remove the old gaskets? One has stuck to the chain cover, and one has stuck to the case. It's OK along the 'straights' but around where the studs go through the cover, the old gasket is very firmly attached.

Any tips on removing the old gasket, and what should I do (if anything) to surface up to get a good seal on the new gaskets?

Ack oops I've just realised I have put the LHS one in the wrong spot. Shows what working on the car upside down will do to you.

OK quickly went out and fixed that. Surprisingly even though it was in the wrong place it was kind of holding tension because of the friction and because of the ties, I guess. When I popped it out of the position it was in the idler arm moved a tiny bit, which shows it was holding some tension. I put it back in the new position and wound it out to take up the tensions again, it's nice and firm.

http://i1283.photobucket.com/albums/...psc1855f96.jpg

I'm glad I took the time to get to TDC and have the ties as a backup plan. The cam hasn't moved at all as you can see the lock nut is still vertical as before.

SO back to my question - anyone have a good method for cleaning off gasket, and should the surface be prepared at all to accept the new gasket? I know these motors are prone to leaking on this gasket so I am paranoid about getting it right.

My former partner used to use a commercially available gasket remover spray. Takes time and patience, and a little hard work with a razor blade. I did the job without the spray, but there's more tedious hand work involved. CAREFUL is your operative word. VERY careful. We also used small wire brushes (welding supply store) and offset holders for the single edge blades. You don't want to gouge, scratch, or otherwise compromise the surfaces. Finish the job with some carb spray or a little lacquer thinner.

The Cap'n

Assume you're doing this with the engine still residing in the car, yes?

As a back-up to insure the engine doesn't rotate during this procedure, shift into 1st gear, then set the hand brake. While you're in there, inspect the plastic chain rails, sprocket teeth, chain, etc.

BTW, an upgrade to later idler pulley arms (wider bearing) is suggested as a solution for shortened tensioner life.

Sherwood

Yes engine in car. Car is 81 SC so I believe has the later idler arms.

http://i1283.photobucket.com/albums/...psg5omg4ws.jpg

This is the top plate on the faulty tensioner. The lower o ring is square and hard, the upper o-ring is missing completely. I found a couple of rubber scraps but the rest is gone.

http://i1283.photobucket.com/albums/...psjrz6xe08.jpg

Exploded view. New parts from the kit on the right.

On gasket removal, I used a commercial foam that did a good job taking most of it off or loosening it. Permatex Low-VOC Gasket Remover (4 oz) 80645: Purchase the best Gasket Makers, Removers & Sealers at Advance Auto Parts Let it sit for more than the 15 called for.


Then, I carefully used a straight razor blade to scrape. To finish up, I bought the white 3 M Roloc bristle pad recommended by Lapritis on last page of this thread.

http://forums.pelicanparts.com/porsche-911-technical-forum/820624-78-sc-engine-teardown-head-stud-repair-9.html

Good luck. Doing my ramps and cam timing soon and this has helpful tips.

Two tensioners rebuilt and ready to go back in.

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

The hardest part was getting the lower circlip back in. In the end I used a bicycle tyre lever which was the perfect shape to hold in one side of the circlip, keep the plunger down while I worked the other side of the clip with a small screwdriver. The first one took me at least an hour of trying. The second one took 30 seconds as I knew my approach.

The other trick was using line trimmer cord to push down the ball valve to bleed the air, and using a coin to press the end of the plunger to save the thumb.

As others have posted, it's pretty straightforward but having the exploded view in the Haynes manual really helps when you are reassembling to make sure everything goes back in order.

The tensioners are rock hard now and cannot be moved by hand. Now comes the part where they are compressed ready for fitting. I will use the vice or a clamp for that, and I have the special tool on the way.

Edit : I got some gasket cleaner today. That stuff is toxic but works. I put a small nick in the metal on the outside edge while scraping, but I think I'll be ok.

Used to travel a lot; I save old hotel room keys to use as scrapers for this kind of purpose. Stiff enough, flexible enough, and a square & sharp edge that won't score softer surfaces. And you can cut them to fit hard-to-reach locations. Also work well as putty knives and disposable mixing boards for epoxies, etc.

HTH

Coastr,
I hate to be the bearer of bad tidings, but looking at your photo I think I see a slight problem. After a fresh rebuild, the upper aluminum sealing plug should be protruding above the steel cap. The upper chamber thus created between the piston and the sealing plug becomes an oil reservoir. As the tensioner slowly loses oil, it can then be replenished from that reservoir up until the point the sealing plug bottoms out against the housing. From then on, the loss of oil starts to soften the tensioner. Even with renewed seals, there will still be some slight loss of oil past the seals. So your fresh rebuild will not last as long since there is no reservoir of oil above the piston.

Creating this reservoir makes it trickier to install the sealing plug. You get the piston all filled with oil and bled, then top up the housing with oil to the point that you can just install the sealing plug, spring, cap, and circlip. Too much oil and the circlip won't fit. Too little and you don't have as much reserve oil capacity. When full, the spring above the sealing plug gets about 100% compressed, so you have to press pretty firmly to get the circlip in. If it is too full, the bleed screw on the side can be opened, but just the tiniest amount. You are working with a very small volume of oil in that reservoir to start with, under a fair amount of pressure from the spring, and it will come out that bleed port pretty darned quick. You may have to fill and bleed it a couple times to "get the feel" for doing it.

DG

Ok... I don't think the piston (the double O-Ringed aluminium piece) can protrude above the cap. However, I did push down the piston until the point that the bleeder was no longer pushing out air.

I was working on a combination of the Haynes manual and instructions posted from this thread :

Rebuilding Tensioners

Neither instruction really says how much oil to leave in the top reservoir between the piston and the plunger top - both just talk about bleeding. The Haynes manual says to just push the piston down firmly and then bleed.

I can pop the top back off them, lift the piston up and put more oil in, but I'm just following the instruction to tilt the tensioner in the vice at 20 degrees off vertical and bleed until no more air. Each time I try and top up the oil, I assume air will remain at the top and bleed until the piston is more or less past the bleeder hole, and that will be the correct reservoir level...There is no way to introduce oil underneath the piston and have the oil level higher than the bleed screw without also having air in the system.

Someone can correct me where I am wrong...the tensioners are not in the car yet as I am waiting on delivery of safety collars. I might pull out the top snap ring and re-check, but I don't see how you can get a fill level to the point that the piston top would be visible at the top of the steel disc. The top spring would be under a lot of tension at that point, and that means you haven't bled air because you haven't pushed the piston down to the point where an air gap would allow air to escape the bleeder at a 20 deg angle.

OK I just looked at that other thread I referenced and I see this picture with one with the factory retainer in place:

http://forums.pelicanparts.com/uploa...1310902756.jpg

I see now what you mean. I am going to undo the top ring and re-fill and re-bleed.

THanks for the catch, I think you saved my bacon which is why I post these things...

Ok I pulled out the top pistons and re-filled the reservoirs and re-installed everything. I also re-bled the lower plunger ball valve for S&G and got a few more tiny air bubbles out - I guess leaving it overnight helps any little air bubbles make their way to the top of the oil.

http://i1283.photobucket.com/albums/...ps6pm8j7kf.jpg

You can now clearly see the top of the piston just below the steel cover, though it is not quite as high as the image I stole from the other thread. There is about 2mm of drop available in the steel plate on the spring before it hits the top of the piston (or the spring binds, whatever it is). It is impossible to bleed the reservoir without creating some drop in level.

I re-read my Haynes manual and it says

This is the complete opposite to what I have since found out I should have done. To me this is pretty clear - you fill it up, open the bleed and push it down. This is why I did it the way I did. Seems like Haynes is completely wrong.

After doing it again, the instructions should read "Fill the upper part with engine oil until it is overfull. Place on the piston and fit the circlip. Place the Tensioner in a vice at a 20 degree angle and bleed by exerting pressure on the piston. It should then say 'the piston should be visible at the top of the tensioner just under the spring retainer'.

Anyway...hope my trial and error helps other people going down this path for the first time.

Hmm. I just had a thought. Maybe the secret to bleeding them is to leave them upside down and sideways with bleed screw up so all the air rises to the top of the reservoir? However, I don't really see the problem with air in the reservoir as it doesn't provide the damping force, that is achieved by the ball valve in the plunger shaft.

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

Coastr,
I think you have the idea. The Haynes manual doesn't get it right. Once you've got the piston/cylinder purged, filling the upper reservoir can be done with the bleed screw in and the unit sitting upright. When you push the aluminum sealing plug down onto the oil in the reservoir, it should pretty well eliminate any air under the plug. The bleed screw is really only necessary if you can't get the circlip in place above the steel retaining cap, and then you can leak a drop or two of oil from the reservoir to get it all to fit. I thought I recalled the sealing plug protruding a little through the steel cap when done, but your photo of the one with the retaining clip looks right, and you can see how the aluminum plug is up snug against the underside of the steel cap. That is why there is the deep relief groove machined in the sealing plug for the spring to reside.

Well, in any case you've got the concept now, which is to have the piston/cylinder purged of any air, and a spring loaded oil reservoir above the piston to prevent (for a while anyway) air from being drawn in when the piston extends after having been compressed. It is really just a shock absorber, and exerts surprisingly little spring pressure against the tensioner arm. As you noticed, you can actually compress one with just finger pressure (your coin is a good idea to prevent a sore thumb). It just moves extremely slowly under that pressure as the oils moves through the check valve, and if you relax for even an instant it pops back up. Now that you know it secrets, you will never have to buy another 911 chain tensioner.

Yeah I'm surprised at the Haynes manual. The advice is bad. I wonder if the entire manual is full of misunderstandings like that.

Really, I think the side screw is misleading calling it a bleed valve because it connototes getting air out of the chamber. Seems it's more for lowering the level of oil in the reservoir to the correct level for the piston.

OK well I have progressed onto the next step of re-installation.

I used a zip tie to hold the special tool in place after a couple of slips. Slotted the tensioner straight back in, cut the tie and the tool popped off and the bolt holding the tension fell out. All good.

http://i1283.photobucket.com/albums/...ps46426f6c.jpg

I got a set of safety collars for the tensioners

After a bit of fiddling, I get them started and.....oh

http://i1283.photobucket.com/albums/...psff300c27.jpg

http://i1283.photobucket.com/albums/...ps349080fa.jpg

There isn't enough tensioner shaft showing to attach the collar + the spacer tool that comes with the collar, and still have any shaft showing at the top.

I checked the photos I posted before I took the tensioners off - it's the same amount of tensioner showing...which means that that's just how it is with the chain on.

I did try turning the motor a few revolutions and prying the idler arm upwards to take out any slack in the chain...only a minute change.

I guess I just have short chains?


Putting this question out to those with learned opinions:
(a) ditch the collars and go without them
(b) do them up at a lower distance off the top of the tensioner (i.e., use a thinner spacer than the supplied one
(c) use the spacer even if it means the top of the collar is flush with the very top of the tensioner (which is slightly bevelled, meaning they might not have 'grip' all the way along)

All the other pictures I see there is much more tensioner shaft sticking out. I wonder why.

Having fished a collar (along with various attaching hardware) out of my engine sump this winter, I'm not a fan of retaining collars. And yes, there was a collar on each of the tensioners as well (different color), so this was a known issue.

RDM - did you fit the collars yourself, or did you inherit them?

I guess that is one vote for do not use collars.

Interesting. I've used the collars since they were in pre-production and have yet to have one fail or come loose. Before that, we used 912 valve spring retainers turned upside down.

I find it fascinating to read of various component failures here that I never, or only rarely, saw as a 45 year wrench and 35 year shop owner ........................

The Cap'n

Cap'n, any comment as to why I don't have enough shaft to attach the collars to?

I've occasionally seen this. New chains and all the wheels can result in very little tensioner shaft showing. I've installed collars with less than ideal clearance, and I've left the collars out in a few cases.

The Cap'n

If this was in the shop...what would be your call? If I used less than ideal gap, it restricts the ability of the tensioner to function correctly?