SC Chain Tensioners - How to test?

[911pcars]

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

[Coastr]

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



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.



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

[lespaul]

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.

'78 SC Engine Teardown for Head Stud Repair

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

[Coastr]

Two tensioners rebuilt and ready to go back in.



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.

[Flat Six]

Originally Posted by The cap'n

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

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

[Daves911L]

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

[Coastr]

Originally Posted by Daves911L

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

clamp the unit in a vise at the lower mounting point. pop out the top snap ring by slipping a pointed tool under it by way of the notch and remove the steel disc and weak spring below it. loosen the side bleeder bolt and grab the center of the aluminum disc with your real small pliers and pull it out. the o-ring around it is a common o-ring and usually that's the only thing wrong with it. it blows out and lets in air. air is compressable, ya know. usually, when you remove the top clip and steel disc, you see a section of that o-ring blown out. the plunger is removed the same way, by removing it's snap ring with a pointed tool. CAUTION, to retain vision in your eye, do not look directly down on the plunger. if it pops up and pokes your eye, i'm not responsible. turn the body upside down and remove the plunger with it's internal parts. observe the positions of the big spring, aluminum cup, tiny spring and check ball and check ball seat. if you have a repair kit, these come in it. otherwise clean and be sure the plunger is not scarred and moves freely in it's bore. reassemble the items into the plunger, turn the plunger upside down and lower the tensioner body onto it. keep your thumb on it. clamp the base of the body in a vise again, push the plunger down and get the snap ring started on one side and hold it there with a small screwdriver. use another small screwdriver to push the other side in. AGAIN, don't look directly down on the plunger. a few cuss words and a few tries and the snap ring finally pops in. snug the side bleeder screw. fill the body 1/2 way up with oil, slowly so as not to introduce air bubbles. you noticed the two holes in the top of the plunger when it was out. insert a tiny piece of wire into one hole to depress the check ball, and slowly work the plunger in and out. add more oil if needed. the idea is to get any air out of the lower chamber. pull out the wire and test for firmness. no play is what we want. with about 1/2" of oil in the body, open the bleeder, tilt the tensioner so the bleeder is angled up and insert the aluminum disc with the little pliers and push in until all the air goes out the bleeder. tighten the bleeder. install the top snap ring, metal disc and spring. compress slowly in a vise and then release and check for slop. don't want any. compress again and slip the installation tool over it and mount in the chain housing. channel-locks work in a pinch, but they're clunky.

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.

[Coastr]

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



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...

[Coastr]

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.



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

11. Secure the tensioner in the vice at an angle as shown in Fig. 1.31 and fill the upper part of the tensioner housing with engine oil. (note : 1.31 shows tensioner at angle of 20 degrees off vertical)
12. Install the new 'O' rings, and then press the oil retainer piston onto the plunger shaft. Open the bleed screw and depress the piston until it is well down the housing then close the bleed screw.
13. Install the spring, the spring retainer and the cir clip.

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.

[911pcars]

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

[Daves911L]

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.

[Coastr]

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.

[Coastr]

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.



I got a set of safety collars for the tensioners

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





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)

[Coastr]

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

[RDM]

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.

[Coastr]

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

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

[The cap'n]

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

[Coastr]

Originally Posted by The cap'n

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?

[The cap'n]

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

[Coastr]

Originally Posted by The cap'n

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?