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As mentioned in post #4, we are talking about an 84 928S US Auto.
The driver side mark is an equal amount off as on the passenger side. About 1/2 tooth. I am going to be locking the flywheel in the next day or so to finish the tear down and will report back here on the tensioner and various pulleys/water pump.
I'll keep the green wire in mind if the TB repair does not solve the rough running.
If both sides are only off half a tooth, the rough running is not cam timing related.
Ok, but it doesn't make any sense.
I only use the manual for important things like torquing the heads and such, the rest is done by common sense. I've done things that the manual said are not possible (pulling the heads twice with the engine in the car on a early 32V that has studs).
How many times can a jumping cam jam a valve into the top of a piston before the valve bends a little? I don't know the answer to that question, but with the crank at 45 BTDC I don't need to know.
And if you've never had a cam jump by a quarter turn you've never worked on an '87+.
Originally Posted by Imo000
I only use the manual for important things...
I really don't know how to respond to this. I get to waste part of every week fixing something because I have engineers on my teams that think they can pick and choose which directions to follow or to ignore the directions because they think they know more than the writer of the directions.
While doing my timing belt, on my 84, one timing mark was right on and one was about half a tooth off. Yours look acceptable, though the one picture is quite poor and I'm assuming it is close.
After getting the belt and related parts squared away...I'd look at your relays, fuel system and green wire for running condition issues.
How many times can a jumping cam jam a valve into the top of a piston before the valve bends a little? I don't know the answer to that question, but with the crank at 45 BTDC I don't need to know.
And if you've never had a cam jump by a quarter turn you've never worked on an '87+.
I really don't know how to respond to this. I get to waste part of every week fixing something because I have engineers on my teams that think they can pick and choose which directions to follow or to
ignore the directions because they think they know more than the writer of the directions.
The jumping cam doesn't cause bend the valve to cause problems. I've done enough 32v timing belts to be confident of this.
You work in cars long enough and will develop the ability to feel when a bolt is tight and I don't mean turn it until it gets solf. Hard to explain how but you just do. I stopped using air tools a long time ago because they take away this feeling/feedback. Am I over tightenning things a bit, probably? To appoint that is a problem, no.
How many times can a jumping cam jam a valve into the top of a piston before the valve bends a little? I don't know the answer to that question, but with the crank at 45 BTDC I don't need to know.
And if you've never had a cam jump by a quarter turn you've never worked on an '87+.
A. Do we know without question that when a cam jumps after belt removal, it jams a valve into the piston? Here's my experience; On both the GT engine and an S4 engine, I was able to move all four cams(chained together of course) at least 3 teeth in either direction from it's 'jumped' position without any interference. At TDC, piston 1 and I think 6 are the only two at the top of the cyl.
B. For those who've done a few, it's a simple thing to get a wrench on the flat of the cam, and release it down off the cam lobe before it springs on its own.
C. Since the valve train is hydraulically isolated from the cam by the lifter, having a valve face touch a piston top under the snap pressure will be softened slightly by hydraulic bleed-off. The lifter operates at far higher pressures when operating, than when the engine is stopped, and the action is not under much torque. Guess what, I've turned a cam gear all the way around with lifters bled down and not touched a valve anywhere(not a recommendation of course).
snapped off cam snout,
this usually happens when the belt tensioner is too tight ,
and or one of the pulleys gets loose and then cracks radially from the keyway ,
this jambs the belt and then the snout snaps off
04-11-2016, 07:49 PM
