PorKen

New and improved!

While researching for a future variable advance mechanism, I came across a BMW (M20) timing belt tension adjuster that was less than $20! (The SAAB pulley I was using previously cost $60.)

I had to design a new mounting bracket to use it, but in doing so, realized that I could have two adjusters, one for advance, and one to syncronize the cams. On my engine the right cam was ~3 degrees (cam) retarded when the left cam was on it's mark! (The left was ~1/2 degree advanced to the crank mark.)

With it installed and all marks aligned, the engine is much smoother, especially at idle. At idle I had a lope that I could not tune away, which is now gone.

I haven't gotten squirly with it yet, so I can't tell if power is up, but in regular driving, it shifts differently now. I'm guessing because the manifold vacuum is increased.

I bought the same part number from different suppliers, and received pulleys from different manufacturers, both made in Germany. The 'Ruville' on the right, is much sturdier built than the 'SKF' on the left.


This version is much easier to install, setup, and remove if necessary.

I reckon there's an additional benefit; the extra pulley before the water pump should take some of the bearing load off the pump!

*Cam Advance V1*
*Update*
~thread~start~

pvoth

are you installing one on each side ????
did you have to.....well how was the mounting done....was there drilling- tapping
involved
i like this one better than the last
maybe interested
keep me informed

Garth S

Very slick! - especially the addition of cam syncronization.
Now, if the tabs on the idler mounts would take a threaded adjuster anchored to a tab on the plate........ hummmm...

PorKen

pvoth,

No modification required.

Only one plate, (two pulleys), on the left (US driver's) side. The plate's base mounts over the rear Power-Steering brace, and replaces the PS bracket's allen head bolts with longer hex head bolts.

There is a second mounting tab on the front of the plate, which goes to the PS front bracket, under the PS adjuster screw.


...

Garth S,

Thanks!

On the BMW engine, there is a post which goes through the idler mount tab, and a coil spring which pushes against the idler mount to keep the belt under tension while adjusting. After the bolts are tightened, the spring is unused:

Tony

Cool stuff!

GoRideSno

Porken youda man!

Andy K

Normy

-How could your cams be off that much?

N?

PorKen

Norm,

It doesn't look like much on the cam pulley, just a few millimeters, but consider that one tooth is 7.5 degrees. BTW: Changing the timing belt didn't change the offset.

The manual says that if the belt teeth don't line up when installing a new timing belt, to rotate the cam counter-clockwise (retard) until the belt slides on.

Newer V6/8 engines with timing belts have adjustable idlers all over the place. I wonder why Porsche didn't at least make the cams adjustable.

...

People that have changed their own belts: how close were your marks to the pointers?

PorKen

Now that I think about it, there's no way (that I can see) to measure the cam lobe position (like you can on the 32V cars), because of the single cam tower design.

Perhaps this is why Porsche did not make the cam gears adjustable.

SharkSkin

PorKen,

Now I see how you were planning to use that part! I seem to recall that you had a ~7HP gain and a reduction in peak HP RPM with the 3º advance and a touch of ignition advance, correct?

D

sparks

porken,

when I changed t/belt, the drivers side cam lined-up while the passinger side cam was 1/2 tooh off either advanced or retarded. I set it up advanced. I was told by Devek that as t/belt stretched, the cam "retards" to become aligned. I have done many t/belts, but my engine is the first I've seen with the cams off alignment that much. When I first changed the t/belt, passinger cam was 1/2 tooth retarded. Has anyone else experienced this?

2V4V

PorKen,

Nice piece, well integrated to boot. I am kinda surprised that the SKF piece is so cheesy looking compared to the Ruville. SKF makes nice bearings, guess this was a strictly functional piece for them.

Greg

PorKen

Another thing I've noticed: She starts quicker when cold. It just barely turns over and fires.
...

SharkSkin,

3 degrees cam (+ six degrees ignition) advance made +5TQ, -5HP. Also, each degree advance moves the torque peak (similarly, the start of useable torque) down 200 RPM, so 3 degrees moved the torque peak down 600RPM.

I am curious now to know what having both cams at 3 degrees would do, instead of 0 and 3 as tested.

I need to go dyno again to really see what this change does. (I'm starting to hate the dyno though, @ $80 bucks a pop!)
...

sparks,

My pulley is about 1/3 tooth retarded. Any idea if you're cylinder heads have been machined?
...

gbyron,

I did a quick search, Ruville is a brand of the INA group, which also owns *** bearing. The pulley is stamped INA.

The shaft of the INA pulley is half again as wide as the SKF, and the bearing fills the pulley.

PorKen

I cranked the fuel pressure back up to 43PSI (3bar).

It works just fine! 0-100 (mph) definately comes faster now, and she runs fine at cruise, with the mixture meter going back and forth nicely.

When I was on the dyno, that's what made the best numbers, but on the street, the O2 sensor loop wouldn't work, so I had to go down to 41PSI.

Another thing, the needle on my fuel pressure gauge is steady now. Previously the needle would bounce 2 or 3 PSI downwards at a high frequency, less after the cam sync, but dead straight with 43PSI.

Now I have an unwavering 34PSI at idle.

heinrich

Ken why is this a 16V-only mod? To the untrained eye (me) it looks like it should be fine for the 32V cars too?