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nrwheele
Joined: 07 Apr 2019 Posts: 22 Location: New York
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Posted: Wed Apr 27, 2022 9:37 am Post subject: Flywheel Marks (and other timing concerns) |
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I am presently working on my first timing job after replacing my 1981 N/A's valve stem seals (first "major" engine work I've ever done, so I apologize if these are basic questions for those more experienced than I). Unfortunately, the flywheel was moved while in the process of working on my car, so my current task is getting the crankshaft, camshaft, and ignition back in sync.
I've heard several different opinions on whether to go by the markings on the crankshaft pully or by the marking on the flywheel. Originally, I wanted to go by the markings on the flywheel, but I've been a bit confused by the descriptions in the Haynes Manual/Porsche Shop Manuals. This is what I'm looking at on my '81:
This picture I took is of the 0 degree mark on my flywheel. As it stands, I can see three ways for this to line up:
1) The dash under the 0 lines up directly with the horizontal protrusion, meaning that the 0 degree mark would be partially obscured (near the orange dot)
2) The 0 is supposed to be fully visible in the window, with the 0 degree "resting" against the protrusion (again, near the orange dot)
3) Having the 0 degree mark fall between these two dashes towards the top of the viewing window (near the red dot) - not sure if this is factory of something that was added by a PO? Haven't seen any reference to this before
I tried lining it up once already, and while I can get the car to run, it barely runs, so something is definitely off.
I'd also like to confirm the ignition timing for the '81 model year. The Haynes manual implies that it's supposed to be set to 0 degrees (+/- 1), which seems odd to me, but I'm guessing this is a result of the electronic ignition stability system, which modifies it? Just wanted to make sure this makes sense - when I originally tried timing it, I lined up the TDC marking on the distributor correctly, so with it being set to 0 by default, it makes me think that no additional timing adjustment with a light is needed (in theory)? I'd of course still check it with a light to confirm, but I just wanted to make sure I was understanding the process correctly.
Any help/advice here would be very greatly appreciated!! _________________ 1981 Porsche 924 N/A, Black - "Brunhilda" |
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924RACR
Joined: 29 Jul 2001 Posts: 8794 Location: Royal Oak, MI, USA
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Posted: Wed Apr 27, 2022 9:52 pm Post subject: |
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Option 1, as you have it shown with the orange dot, is correct.
If you're having trouble with the motor barely running after this - it's possible the issue is the cam being off a tooth, entirely possible if you're not careful how you take up the slack in the belt. _________________ Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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ChrisMadge
Joined: 16 Dec 2020 Posts: 28 Location: Bristol, UK
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Posted: Wed Apr 27, 2022 10:30 pm Post subject: |
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There should be a notch on the crankshaft pulley which will align with the pointer on the engine casting to help confirm the flywheel '0' marker. _________________ 1984 MY 924 2.0 NA
1975 MG Midget |
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nrwheele
Joined: 07 Apr 2019 Posts: 22 Location: New York
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Posted: Thu Apr 28, 2022 12:44 am Post subject: |
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Thanks for the clarification! I'll double check and make sure the flywheel mark and crankshaft pulley are in agreement.
As for taking up slack in the belt, I've seen it described like so, and just want to confirm this is correct:
1) With the crankshaft in its proper position, the camshaft should be lined with the the pointer on the valve cover.
2) Turn the camshaft clockwise (when viewed from the front of the vehicle) so that the dot marking goes past the pointer on the valve cover (note: not sure how far past the marking is recommended, I assume just a tooth or two on the gear itself)
3) Mount the timing belt and set the tensioner pulley to the proper amount on tension
4) Turn the camshaft counter-clockwise, so that by the time the crankshaft starts turning, the camshaft markings are aligned and all the slack is out of the timing belt.
Is this the correct procedure? _________________ 1981 Porsche 924 N/A, Black - "Brunhilda" |
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924RACR
Joined: 29 Jul 2001 Posts: 8794 Location: Royal Oak, MI, USA
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Posted: Thu Apr 28, 2022 3:25 am Post subject: |
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nrwheele wrote: |
2) Turn the camshaft clockwise (when viewed from the front of the vehicle) so that the dot marking goes past the pointer on the valve cover (note: not sure how far past the marking is recommended, I assume just a tooth or two on the gear itself) |
That would be maybe half a tooth width off when properly installed... sounds like maybe you went further? _________________ Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype |
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nrwheele
Joined: 07 Apr 2019 Posts: 22 Location: New York
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Posted: Thu Apr 28, 2022 3:51 am Post subject: |
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I definitely could have (and probably did lol)
I guess it's just trial and error then, because I assume the ideal here would be to back off the camshaft just enough that when you remove the slack by rotating the cam counterclockwise, it lines up perfectly with the cam dot/valve cover pointer
I'll give it another go tonight and see if I can get my poor car back on the road again _________________ 1981 Porsche 924 N/A, Black - "Brunhilda" |
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nrwheele
Joined: 07 Apr 2019 Posts: 22 Location: New York
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Posted: Fri May 06, 2022 1:01 pm Post subject: |
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Well, it took longer to get back in the garage than expected, but it turns out that my timing was indeed spot on - I even went to the length of getting a piston stop tool just to confirm that my crankshaft markings/flywheel markings were good, and they were.
On a gut instinct, and based on the job I just did, I decided to do a compression test:
1 - 135
2 - 135
3 - 130
4 - 0
I guess I wasn't as careful as I thought while replacing the valve stem seals, and now Cylinder #4 has no compression
Since this car was running fine before I replaced the valve stem seals, I'm going to guess that one of the valves is stuck open somehow and preventing a good seal? I guess I'll have to take it apart the cam and tappets again to try to fix it; I'd really like to avoid having to pull the head if possible, because I know that if I do, my poor car will probably never run again.
If anyone has any advice on what to do in this situation to get this cylinder up and running again, I'd be extremely appreciative!
_________________ 1981 Porsche 924 N/A, Black - "Brunhilda" |
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ChrisMadge
Joined: 16 Dec 2020 Posts: 28 Location: Bristol, UK
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Posted: Fri May 06, 2022 5:00 pm Post subject: |
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Take the cam cover off and turn the engine by hand whilst watching the cam followers on the cylinder with no compression. You should be able to do a visual check to confirm your thoughts.
Once you know thats the problem then its a case of taking the cam shaft out and see why the valve is stuck.
You should also check your valve clearances. _________________ 1984 MY 924 2.0 NA
1975 MG Midget |
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