DonT

Very nice ! ! !

6.0-928S

I don't know, I don't have a Volvo engineer to ask but it is a tensioner, I assume it has necessary tensioner properties. It is oil filled but not under pressure. And it does contract. I'll be finding out on my own car.
Hammer

borland

Since it's not thermally compensating, do you plan to adjust the belt tension with the engine hot?

Bill Ball

It would be worth checking the static tension with the motor real hot as well as cold - a bit of a trick to do.

I admire the ingenuity, but I need to get comfortable with the dampened spring idea. Even discounting the Bellville washers, I'm not sure how the dynamic spring compares to the essentially pure mechancial stock tensioner in a running car.

Jim bailey - 928 International

Since tension is maintained /set by the spring if it has a fairly linear spring rate tension would be about the same over a small range. The test will be after it is running tension cold , tension hot ? Besides MOST 928s are running around with the belt tension far from spec....trust me on this .

Larry928GTS

This setup will increase belt tension as the engine warms. How much it does that depends on the spring rate.

928ntslow

Nice idea! I have the same concerns though that others had mentioned. The heat/cold, expansion/contraction was a key element to Porsche design as far as I know. A "spring" submersed in oil may not give the same effect as the washers, but I would expect the oil will of course serve for the purposes of heat dissipation. What is the rating of the spring? How was it used on a Volvo with what type of engine? V8, overhead cams? What kind of belt did it have? What did the tensioner look like?

My first thought to this was really "belt wrap". At fluctuating rpms, the harmonic frequencies through the belt change, this is when you see the flutter of the belt. The Porsche tensioner was rigid enough to deal with this in the heat and cold. If the spring is not rated for this kind of work load, there could be some "slappin'" goin' on ...then there would be worry about cam tooth jumping.

Nice going no matter what! Definitely let us know what happens with this.

6.0-928S

Hi Keith,
The spring is not "submersed" in oil. The oil is inside the center tube of the tensioner under the spring. When mounted on my engine the belt tension barely compresses the spring when bought to proper tension. Trust me, if I compressed this spring one half inch it would stretch the belt beyond it's load limits I'm sure.

I have considered every angle that everyone brings up. Hopefully no one thinks I just popped this on my stroker motor that I've invested 20 big ones in, without checking into everything first. I intend to test the tension under several conditions before putting it under heavy load situations. This is an idea I've had for months. I had to get it to fit into the space limitations on the front of the engine. I had to mount it, adjust things, see if the belt would come to correct tension specs, etc. I'm going to do it. I just thought I'd show it to the List.
Hammer

AO

Might want to install it in a 4.5L OB first since they are non-interference engines. Just a thought.

PorKen

I don't know if the Volvo damper is the same, but the one I'm using resets itself hydraulically to a new set point, slowly, if the tension increases past a certain level for longer than a few seconds, so it's always at the same basic tension, hot or cold. The reaction is immediate if there is a decrease in belt tension (increased belt length), like when starting a cold engine.

There is also a separate, high frequency damping effect around the nominal tension level. I'm guessing the Volvo damper has only this function.

6.0-928S

Hi Ken,
Thanks for your input. I'm aware of the reset function. Volvo used the hydraulic reset function style until late '98 when they phased them out in favor of their newer what they call 'mechanical' tensioner which they have used since. Actually I could take a picture of their older tensioner & you wouldn't be able to tell it apart from the Audi tensioner you use. After watching the Volvo tech training videos (can you tell I work for Volvo now?) I opted for the later style. I'm not looking to cramp your style. I'm also not looking to sell anything. I just thought some listers might find it interesting.

Regards, Hammer

marton

What Jim wrote
Interesting, I have had a gut feeling about this from the fotos that I have seen from people doing TB jobs.
I have always found it hard to believe that the 1 or 2 mm that the tensioner moves from cold to hot is significant. I mean what percentage of 928 owners adjusts their belt to tolerances that are less than one mm?

I have some difficulty to understand some of the questions here, I can not believe that Volvo would build a tensioner that had different design requirements (in concept) from the Porsche one. I mean that it would be designed to maintain the correct belt tension as the motor cycled from cold to hot, etc.

Marton

JKelly

Very cool. I hope it works!

Garth S

The adjustment bolt on the factory tensioner has a thread pitch of 1.25 or 1.5mm ( forget which) .... meaning that one full turn moves the piston ahead 1.25 (1.5)mm ... minus whatever the compression loss is within the Belville washer stack.
For arguments sake, one turn nets 1mm: anyone who has set TB tension with a gauge has likely experienced a significant shift with as little as 1/4 turn when near the optimum ..... which is ~0.25mm.

928ntslow

Hammer, I think the reason some of us are making comments just beyond observing, is because it certianly would be nice to have a tried and true tensioner that does NOT need to be adjusted manually. As Jim said, most belts aren't even close to spec...and I know this first hand from checking several myself. It's a wonder there aren't more failures! This is an important subject because it is the difference between peace of mind having an automatic, reliable, constant belt tension and ...well, catastrophic failure. Stuff like dis get attensheeown!