Valvetrain Inspection
#46
Rennlist Member
Raj
#47
Rennlist Member
Yes, it will put $$$ in certain people's pocket by getting this sort of info out there so I do understand their intentions.
Raj
#48
Rennlist Member
Raj,
I need to do the clutch first (starting to slip - original) - but probably in the next 6 months - its been on the todo list since I hit 100,000 miles - now at 104,000.
Is common wisdom still pads and chain at 100,000 and full unit at 150,000? Porsche recommends the full unit, but I thought most people feel that is overkill
I need to do the clutch first (starting to slip - original) - but probably in the next 6 months - its been on the todo list since I hit 100,000 miles - now at 104,000.
Is common wisdom still pads and chain at 100,000 and full unit at 150,000? Porsche recommends the full unit, but I thought most people feel that is overkill
Raj
#49
RL Community Team
Rennlist Member
Rennlist Member
I've got 223k on an original variocam tensioner unit and it works fine. They love you long time. But pads and chain at 104k should be changed some time soon. They will last longer, probably.
Would chain stretch cause a perceptible difference in performance? My car lacks power... maybe it's not only the timing, but my 170k-old chain.
Would chain stretch cause a perceptible difference in performance? My car lacks power... maybe it's not only the timing, but my 170k-old chain.
#50
Three Wheelin'
Join Date: Jul 2001
Location: San Francisco, CA Porsche: '92 968 Blk/Cashmere
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#51
Race Car
#52
RL Community Team
Rennlist Member
Rennlist Member
Will do! I need to order some dial indicators. I don't understand why the timing is even adjustable. Why didn't they just make the cam gear with a narrow keyway, like so it only goes on one way, the right way?
Maybe because chain stretch would necessitate adjustments to get the intake cam corrected...?
Maybe because chain stretch would necessitate adjustments to get the intake cam corrected...?
#53
I doubt the factory didn't have the cam timing right because they notch the cam pulley after they get the timing down. That is how the pulley was notched. Just because someone can't backtrack their records or have no way of knowing if this sort of work was ever done to the car does not imply the factory got the timing wrong.
Yes, it will put $$$ in certain people's pocket by getting this sort of info out there so I do understand their intentions.
Raj
Yes, it will put $$$ in certain people's pocket by getting this sort of info out there so I do understand their intentions.
Raj
Arash, in order to make up for manufacturing differences and other things, the sprocket is slotted so that the timing can be dialed in for that specific car. It also doesn't help that these cars were built by Germans either.
#54
Rennlist Member
How would you be able to buy a new cam sprocket and time it if you had to put the notch in it yourself? I have worked on two cars that have been off from the factory. One had 25,000mi and the other one had 19,000mi. So I doubt that it would have been anyone elses fault but the factories. Which makes sense if you consider the mass quantities of engines that Porsche built.
I understand you are Mercedes factory trained but 968 factory manual has a section just for this under Volume I (engine) on page 15-7. Go have a look.
Were the owners the original owner? I know one of them is definitely not and its well documented how there were vibration problems for months that could not be sorted out. Since the blame was layed on the mechanics inability to time the bs belt, who is to say, he didn't mess with timing to troubleshoot.
Sorry, I don't buy it.
Raj
Last edited by RajDatta; 01-28-2008 at 11:29 AM.
#55
Well the one owner was, and the other one wasn't. So at least one of them hadn't been opened up yet. Im not trying to argue about it, im just saying that some cars were done more accurately than others, thats all. As for the mark on the sproket, I stand corrected. It doesn't make sense though why they would not just put the mark on the gear when they make it. Seems like a wasted step to me. You learn something new everyday.
#58
Rennlist Member
The advantage is with variocam and slightly bigger valves. If you change your harness and it works on a S2, you might. You should also look at it as a system, maf, dme etc.
I think S2 compression is also .1 lower than 968's so its bunch of things, not just cams.
Raj
I think S2 compression is also .1 lower than 968's so its bunch of things, not just cams.
Raj
#59
The S2 head doesn't have the proper mounting points for the variocam assembly. If you look at the specs for the S2 cam and the 968 cam, the S2 falls right in the middle of the base and torque timing of the 968 cams. Meaning that there wouldn't be any real gains from just switching the cams. As Raj stated, there are many factors that make a difference, even the intake manifold has a part in the power differences.