Interesting topic. There seems to be a couple of theory's that seem to overlap.

The early tensioner did not have the block passage or the fill hole.

I have never had a late tensioner apart. The boot is larger in diameter.

Q) Are the discs also larger?

I guess I could check part numbers but it's sunday, I'm not on the computer that stores my CD and I'm too lazy to walk up two flights of stairs to me office.

Also, it's been stated that the tensioner stack acts like a spring to dampen the pulse of the cam rotation. That was my assumption when I took mine apart.

Q) Do we agree this is on function of this part?

The other part of this discussed here is the lubercation theory. I guess this fuction would be a given and most likely required based on the design and likely hood that these will eventually stick due to mosture intrusion. Also the harmonics would cause wear to the contact surfaces.

Q) Agreed?

The cooling would also be a given as we all know the oil is a good way to transfer heat. I'm not a chemist or an engish major. Which prompts the next question.

Q) Will the type and weight ...viscosity... of lubercation effect the heat transfer?

And a second part of the weight question..

Q) Will the weight effect the dampening?

Great info

 

Factory changed oil specs few times IIRR. Sometimes it was gearbox oil, others SAE 30 engine oil. Changes were gone through in here few years ago and some references to factory documentation posted too. I don't think it makes much difference what it is, important thing is that tensioner is not dry. When it has been empty for a while result isn't pretty. Bimetal washers are same in all MY. Its just number how many there are which was changed when oil heating drillings were added.

 

I think if we combine a few of the answers, we will have an all inclusive/conclusive answer I DO like 69gaugeman's comment about the discs also working as stiffer than a spring. I hadn't thought of that, but I bet based on the cuping of the discs and copper being a relatively soft metal, one would think there has to be some flex in the discs under load...maybe not much, but I can see it.

I think we have the answer surrounded...ay?

 

The copper coating on the discs is there to help make friction predictable, and to minimize corrosion. The concept of that tiny amount of plating affecting the amount of pressure available is, um, a myth. We have steel belleville washers.

The oil is in the housing for friction consistency, but much more important it is there to dampen motion of the piston. Looking at the piston at the bottom of the washer stack, there's a one-way check valve that manages oil flow when the piston moves. Like an oil-filled shock absorber that dampens at different rates depending on direction of travel. In my later tensioner, the check valve allows the piston to extend with less damping, but it closes when the piston tries to compress again. When the check valve is closed, oil below the piston must travel back through all the passages in the housing to get to the top of the piston during compression. So the oil viscosity does make a difference. Keeping the housing filled correctly also makes a big difference.

The heat transfer from the block to the tensioner housing is incidental. The rate of expansion of the aluminum block and the housing itself are pretty consistent so it makes sense to have them expand and contract at the same rate so the gasket doesn't suffer. The expansion of the steel piston rod is small in comparison. Consider that the springs only 'push' on the aluminum housing in one direction, so expansion of the hosuing never really makes a bit of difference to the belt.

The belleville washers, in a stack, have a very non-linear compression curve. Consider a wound coil spring, where compression is often expressed as pounds-per-inch of displacement. The numbers are fairly predictable until you get to a point where the coils bind. The washers are already in 'coil bind' before you apply any significant pressure to them, so the rate changes significantly with displacement. Loading is a curve. In our application with stackes of washers, the number of washers determine the displacement pressure at a particular point, and the number of stacks determine where we are on the loading curve. Target would be a fairly flat/linear portion of the loading curve of course. In a perfect world, the stack of washers would have a loading curve that exactly compliments the stretch on the belt through the expansion range of the block. Reality is that they are probably not even close.

The tensioner needs to manage the tension on the belt as the block expands, and also as the belt itself stretches during the various load (tension) changes it sees during engine rotation. The oil pretty much manages dampening the effects changes during rotation, while the spring washers manage the changes during thermal expansion cycles of the block.


It would be a very interesting experiment to put a small CCD video camera and light source in the housing for a loo at tensioner "movement" during normal engine operation. I would be very surprized if there was more than maybe 0.100-0.200" total movement from cold to hot, idle to redline.


I think the Porken tensioner is a great idea. I'm ready!

 

I'm waiting for the laser cutting quote for (10) of the brackets, so I can price the system for 'early adopters'.



I see ~1.5mm (.060) movement in the piston of my tensioner, cold to hot. About the same for a new belt to 2K miles old. I'm not sure how that would translate to the movement of the factory tensioner. (Math makes PK's head hurt. )

 

I ran into the same thing on my 79. 928gt supplied me with an adapter to make teh new boot fit. It looked like a vaccume cleaner drive belt.

 

Thanks. Your answers did help me