Neil Forn

It is important to set the cam timing. People should not skip the procedure in the WSM. In order to properly install a cam in any engine the cam timing should be degreed. Even a Detroit push rod lump of cast iron. With multiple cams the situation is even worse. It will run if you don't bother but not exactly as designed. Valves can be opening at different times within a single revolution. (actually two revolutions) When you blueprint an engine, degreeing the cams is one of the things that you do. Porsche provided adjustable cams for the S4 they must have had a reason. To degree the two cam motor you need to use offset keys. They must have felt the need to insure that the cams were properly synchronized. 911s have to have their cams timed.

blown 87

They (how far off the marks are) seem to be different for various cars, and it is critical to ensure that the balancer is really reading TDC, with a large degree wheel IMHO.
I do not understand if the cams, the gears, or the balancer (my guess is on the balancers as I have found some out of perfect spec)

Just looking at the pointer from a slightly different position can impact not only the reading on the 9201, but on the cam timing as well.

Good luck with your investigation.

Greg Nettles

blown 87

Also understand that unless the gears, all of them, are perfect, you are going to not get repeatable readings.
Some also suggest that belts from different manufactures, or even within the same manufacture can be different in the amount of stretch.

aaddpp

I saw a few threads mention some of the cheaper belt issues. I think that given the poor, but I believe well intentioned, work on the car between 35k and 70k miles there is a good chance there was a belt in there capable of some 'give'. New TB is a Gates belt. Gears thankfully were in near mint condition (all around) with perfect coating and shape.

Dave

Neil Forn

I don't understand how the Porken tool can reliably set the cam timing. It doesn't seem to me that it will correct for any inaccuracies in the system. Just lining the gear up to the mark, however accurately, doesn't set the cam timing like the WSM specifies. But maybe I'm missing something.

Landseer

Its keying-off the threaded holes behind the gears.
Those holes are fixed with respect to the camshaft profiles.
I think its a completely acceptable alternative.
Can't see why to pull covers to use dial indicators at all.

Another error is introduced if the outer portion of the harmonic balancer (the degree marks we use for setting crank) has twisted relative to the keyed center of the balancer. That might be worth verifying with some little toolbox jig, especially as these cars age.

blown 87

I only use the factory method, so you will have to ask some one else that question.
My understanding is that is works pretty well.
I have one but have never used it.

Hilton

When you use one, it'll be obvious how it works.

It attaches to the cam spider behind the gear. The 3 legs of the spider are locked in position relative to the camshaft, and can only be in one position, so you're actually measuring the cam position.

You then set the position of the gear relative to the Porken tool (i.e. relative to the cam), before bolting it down tight and removing the tool.

blown 87

The pointer is relative to the position of the back cover, which can change a little bit from engine to engine or even on the same engine if the back cover has been off.

Am I wrong about that?
I am not sure I have ever seen that question addressed.

aaddpp

I'm away from my car now, so I can't look at my ballancer, but how can this twisting happen? Is the ballancer two pieces? I never examined tit hat closely, but always thought it was a single piece, locked to the drive shaft position by the woodruff key.

Dave

Landseer

Inner and outer are separated by rubber.
Typical harmonic balancer.
Sometimes they get screwed up by somebody manipulating them wrong, but its rare I suspect.
Unless you are having a completely unsolvable problem, I wouldn't anticipate it is a problem.

aaddpp

Good to know. Its worth a look to make sure I'm not heading down the wrong path.

Dave

Neil Forn

There are errors (tolerance) with the indexing of the cam lobe to the key way, the key itself, the hub keyway to the hub spider, the drilling of the bolt holes on the hub and then the position of the back cover. Even if everything is within tolerance the total of all the tolerances could stack up to a noticeable discrepancy. One of the 944 sites claims that they have found up to 3 degrees mismatch of the cam to the hub. I don't have anything against Ken or his tool. Anybody or anything that makes 928 ownership easier is a good thing. I just don't understand how the Porken tool can do it's job unless it allows for these sources of error.

Mrmerlin

FYI to measure the damper quickly, put the keyway pointing at 3 O clock, this should have the damper pointing at the 45 BTDC

TDC has the keyway pointing at 4 O clock

borland

Also, the tool doesn't account for in service wear of the cam chain sprockets and cam chain. I have yet to see a post of someone independently calibrate the tool against the WSM cam timing procedure.

Since cam timing doesn't need to be that precise, the tool is probably accurate enough for most mechanical perfectionists.