SC Chain Tensioners - How to test?

Coastr · 08-24-2014, 02:31 AM

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.

LHS

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.

LEAKYSEALS951 · 03:06 AM

Quote:

Originally Posted by Coastr

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.

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!

Coastr · 08-24-2014, 03:08 AM

Quote:

Originally Posted by LEAKYSEALS951

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. Rule out the simple first. 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.

bourgeois911 · 08-24-2014, 04:51 AM

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

Daves911L · Daves911L's Garage

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.

The cap'n · 08-24-2014, 07:30 AM

Quote:

Originally Posted by Daves911L

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

Coastr · 08-24-2014, 02:03 PM

Quote:

Originally Posted by The cap'n

"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?

eastbay · 08-24-2014, 02:47 PM

Here's what you need (part number and kit contents in bag) along with a disassembled view

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

no sense in not doing both

Coastr · 08-24-2014, 04:47 PM

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?

The cap'n · 08-24-2014, 04:58 PM

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

Coastr · 08-24-2014, 05:59 PM

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?

eastbay · 08-24-2014, 06:40 PM

Nut and bolt works on the right side tensioner just fine, and BTW this pic is from an engine in the car tensioner replacement

Coastr · 08-24-2014, 07:04 PM

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?

eastbay · 08-24-2014, 07:13 PM

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.

The cap'n · 08-24-2014, 07:34 PM

Quote:

Originally Posted by eastbay

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

Coastr · 09-01-2014, 02:36 AM

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.

LHS

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?

Coastr · 09-01-2014, 02:43 AM

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.

Coastr · 09-01-2014, 02:53 AM

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.

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.

Coastr · 09-01-2014, 02:56 AM

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.

The cap'n · 09-01-2014, 10:08 AM

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