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Checking cam timing

 
Old 05-10-2019, 07:57 PM
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Boeing 717
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Default Checking cam timing

I made a magnetic base to hold my dial indicator this morning. I'm pretty proud of that contraption because I was considering going to a machine shop to have it made.

I still need to make the Variocam pressure hose tomorrow.

So before I go all psycho and try and time my cams, I would like to check it first. Am I correct in that when cylinder 4 is at firing top dead center that the dial gauge on cylinder number 1 should read between 36 and 42 mm?
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Old 05-10-2019, 10:03 PM
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0.39mm is the target with 3 bar in the oil feed. will the cam lobe clear the framing square when you run though a couple revolutions?

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Old 05-10-2019, 10:09 PM
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Yes it clears. But am I correct on the way to check it?
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Old 05-11-2019, 09:29 AM
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yep, raise the car a little so you shimmy underneath. with the crank rolling toward tdc on number 1, set your dial gauge on the base circle of the cam and preload the gauge. rotate the crank until the gauge reads 0.36mm. hold the cam in place and verify that; a: the cat eye shows in the flywheel cover hole or, b: the other/second dial indicator on the piston shows the piston at its peak. hold the cam at 0.39mm and move the loosened cam pulley with the crank until the crank is at tdc. tighten the three rotor bolts on the spider. rotate the engine over a few revolutions to check your adjustment.

the dial gauge on the piston will be less definitive than the hole in the flywheel cover but do both. if the motor is out, one must use the gauge but that method might deviate with rod wear. plus 0.03mm is advancing the cam for torque and minus 0.03mm will let it breath on the top end a slight amount.

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Old 05-14-2019, 03:42 PM
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This is very interesting, and potentially helpful. Is there a published document on how to do the cam timing procedure from beginning to end, including the very nice description you've given for the part of it you've described for Boeing 717? The description in the manual leaves a lot of steps out. Something that walks through the procedure from beginning to end, with several pictures, including the dial gauges mounted to Boeing 717's fabricated base, and exactly how to pressurize the Variocam, would be incredibly useful to us novices who don't do this kind of thing for a living. Thanks.
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Old 05-14-2019, 05:00 PM
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I have the procedure to set it.
I just wanted to make sure I was checking it correctly. Turns out my valve is at around 1.5 mm at non firing top dead center instead of the .36-.42 mm it's supposed to be.
Of course as I was trying to loosen the bolt for the cam gear to adjust the timing and I stripped the bolt. I even used the correct triple square bit.
Whoever designed that bolt is a complete idiot, the driver doesn't even go in far enough to get a good bite on it.
So now I have to drill it out. This car has been fighting me for three years and I'm starting to hate it. But I'm going to win.

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Old 05-14-2019, 06:46 PM
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Originally Posted by Cloud9...68
This is very interesting, and potentially helpful. Is there a published document on how to do the cam timing procedure from beginning to end, including the very nice description you've given for the part of it you've described for Boeing 717? The description in the manual leaves a lot of steps out. Something that walks through the procedure from beginning to end, with several pictures, including the dial gauges mounted to Boeing 717's fabricated base, and exactly how to pressurize the Variocam, would be incredibly useful to us novices who don't do this kind of thing for a living. Thanks.
The part that's s F'd up is that the Variocam unit moves up and down while your rotating the crank. Which is altering the timing. So is the Variocam supposed to be up or down when you measure the valve movement?
Plugging it up to an air source doesn't do anything as far as I can tell. The Variocam unit behaves the same.
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Old 05-15-2019, 04:08 AM
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H.F.B.
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Originally Posted by Cloud9...68 View Post
This is very interesting, and potentially helpful. Is there a published document on how to do the cam timing procedure from beginning to end, including the very nice description you've given for the part of it you've described for Boeing 717? The description in the manual leaves a lot of steps out. Something that walks through the procedure from beginning to end, with several pictures, including the dial gauges mounted to Boeing 717's fabricated base, and exactly how to pressurize the Variocam, would be incredibly useful to us novices who don't do this kind of thing for a living. Thanks.
Some time ago I posted my DIY 968 camshaft timing document.
https://rennlist.com/forums/attachme...ft-setting.pdf

To pressurize the Variocam, you need a steady flow of 3 bar or 43.5 PSI.
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Old 05-15-2019, 12:14 PM
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Drilled out bolt, took like 10 minutes at slow speed. Now just waiting on new parts. Went ahead and bought a new hydraulic timing belt tensioner since I was in here.
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Old 05-15-2019, 12:33 PM
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If anyone wants to know how to build a magnetic base to sit a dial indicator on this is what I did.

7x2 in piece of metal. The used some old cam cover bolts. Drilled and Tapped the center, they make the perfect base.
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Old 05-15-2019, 04:32 PM
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Thanks for the tool info - I will make the same metal base and use those cam bolts.

Since there is variation in the valve #1 position during this timing procedure, what is the optimal valve position to generate the most power?
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Old 05-15-2019, 10:32 PM
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Very nice Boeing! Job well done. Thanks to H.F.B, thomasmryan and all contributors to thread. Great information and pictures. I am planning to do this soon. Thank you all.

Boeing, three questions;
1. I assume the pressurization of the variocam oil line moves it, and yours was faulty, which position/direction is it supposed to move in (up or down) under pressure?
2. What did you do with the rest of the framing square? (Still has 16-1/2" of good square left). I have a perfect candidate that my wife caught with a saw at about 13 to 15 inches.
3. Do you play the guitar? Looks like you were working on a e-minor chord in the last pic.
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Old 05-15-2019, 11:09 PM
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Haha that's funny. I have been playing guitar for almost 35 years now. Must be muscle memory. Got pretty darn good at it as it was one of my passions but haven't hardly touched in the last few years since my kids came along.

So you think my Variocam unit may be faulty? Why do you say that? I'm asking because I have no clue. When I turn the crank it moves up and down. I called that guy at RS barn and he said the same thing.....that they move up and down when your trying to set the timing. When I undid the oil line and hooked up the air line it behaved exactly the same way. It seems to me that it should have some electrical signal to it when your trying to do this. But the Porsche manual doesn't say anything about it so I'm guessing just let it do whatever the heck it does.
When I get my new camshaft gear bolt on I'll try and take a video of it before I set the timing.
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Old 05-16-2019, 09:16 PM
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I knew it! Just looked like you are playing guitar.

My understanding (have not done this yet on 968, but have experience on 986) once the pressure is introduced, without voltage, it is supposed to raise up, This is the timing advanced position. When in down position, variocam is in basic timing, or retarded, position.
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Old 05-17-2019, 07:21 PM
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The Variocam chain tensioner only works for the correct direction of engine rotation. When I applied enough air pressure the piston went up. There was no up and down when turning the crank. No voltage applied here enables to fill the interior of the chain tensioner that supports the force of the springs. With +12V applied the solenoid forces the piston down.
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