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Pretty sure there's a note about that in the WSM or one of the writeups I was using when I did my motor last year, or maybe it was just offered up in my thread by the gurus here.
Yes—^ in WSM.
Also in many many treads. It’s just that there are so many threads....
OK guys - how do you get that woodruff key out? Picture:
It's just slipped in there, but probably now stuck. Pull it out with vice grips or channel locks and get a new one from Roger. Heating up the end of the shaft where it's installed and then icing the key to contract it might also work. Clamping on vice grips and then tapping the vice grips gently with a hammer might also work.
Heat the shaft and key. Then take a small punch and with gentle tapping with a hammer, tap the back of key into the shaft. The key and slot are ‘half-round’ so the front part of the key will ‘rotate’ away from the shaft. Once you have enough of the front of the key proud of the shaft, you can tap it the rest of the way.
If you make a divot in the key, you’re tapping too hard. In that case you’ll need to resort to heat and ice. And tapping.
Thanks guys. I also found the reference to leaving off that 1mm washer when replacing the oil pump gear with the new steel one. Boy was that an obscure reference. I would never have found it if I wasn't looking hard for it - buried in a table with a parts blow up diagram.
The key is half moon shaped. I tapped the "high" side down, then tapped it the other way until it loosened up. I might have even used some penetrating oil (I forget).
Back to the camshaft drive gears. As previously stated the gears are "good to go" for many more miles. The driving faces are within the groves and they all look in good condition. I did a lot of research on cam gears years ago and the hardness of the coating in these drive gears is around 6H. The only damage is on the flats at the top of the gear teeth and the belt driving faces are within the groves are good. To cut down the wear/damage on the flat tops of the gears and the driving groves faces I have put filter material in the spigot that fits into the inlet pipes. You will note that the two inlet pipes for the engine have the spigot holes which are situated before the Venturi section of the said inlet pipes, therefore they have increased pressure in this area and any dirt etc will be forced into the camshaft drive sprocket/gear area, hence the filter material inserts..
I have a theory that clean rubber against the coating will not cause much wear. But grit in the air or adhering to the rubber might. If "Desert Rat" FredR thinks the coating is good for him, it will be even better for Pittsburgh. Just a theory.
I have a theory that clean rubber against the coating will not cause much wear. But grit in the air or adhering to the rubber might. If "Desert Rat" FredR thinks the coating is good for him, it will be even better for Pittsburgh. Just a theory.
Curt,
I replaced my cam gears a year or so ago after they had covered approx 90k miles. The fact that they wear out on the flats concerns me in that they do not take the drive load- that should be distributed across the tooth although maxloading happens on the right edge of the tooth or so I would think.
If the system is working as it logically should, one would think the part of the belt that rides over the flat should not be in contact or at best lightly so. That we see the coating on the flat go first and the trough of the tooth is virtually untouched that is the bit that has concerned me for some time. I fully expected accelerated wear over here but from what I have been able to glean 90k miles is about the going rate for a correctly adjusted belt.
The fact that they wear out on the flats concerns me in that they do not take the drive load
The fact they wear on the flats tells us that they do take a considerable load and or friction from belt movement. The evidence is there on every single gear I have seen.
IMO when that wear appears it is time to re-coat the gears or save up for new gears on the next belt change.
You will note that the two inlet pipes for the engine have the spigot holes which are situated before the Venturi section of the said inlet pipes, therefore they have increased pressure in this area and any dirt etc will be forced into the camshaft drive sprocket/gear area, hence the filter material inserts..
Are you sure of your fluid dynamics?
When I got my 90S4 20 years ago I was fascinated as to why they stuck a venturi where they did. Porsche must have figured it was a complete waste of time given they dropped it for the GTS with no other compensatory modifications. I did wonder if the venturi was a trick to get over the various clutter on the passenger side but to be fair I felt I never really understood the process logic and that takes some doing!.
Be that as it may, your logic appears somewhat flawed to my way of thinking but maybe my grey matter is getting mushed as the years pass by. For air flowing through a conduit it starts off at atmospheric pressure, there may be a small ram effect to increase pressure a tad at speed and then air enters into the trumpets. It flows a foot or so over the cam vents and then enters the venturi. The air flow through the system is constant and what goes through the entry section then passes through the throat of the venturi at higher velocity. To achieve the higher velocity requires a requisite pressure drop [Bernoulli theory]. As the air then passes through the trumpet section, the cross sectional area increases and the velocity drops so there is some recovery of the pressure lost across the throat but not all of it. The notion that the pressure increases as the air flows over the spigot does not seem to fit with what I was taught in fluid mechanics and process engineering design but kindly feel free to help me understand how you arrived at the pressure increase above the spigot theory. Beyond that I would suggest the very reason that spigot exists and protrudes into the airsteam at 90 degrees to the axis of flow is to act as an eductor. The intake stream hammering over the spigot should suck air out of the cam chamber and thus induce air to enter elsewhere and cooling things off some given the power transmission of the drive is not 100% efficient and things are thus going to heat up. If my thinking is correct inserting some media to filter the air is simply going to block the normally educted air flow. I would be delighted if you can convince me otherwise- always keen to learn.
04-28-2020, 11:08 AM
