Never ending problem for the 13th engine rebuild (very long post)......

[Harry998R]

H Tony,

Congratulations and well done!

Whilst you will be probably be frustrated at the amount of time it has taken to rectify, think of all the good you have done by documenting everything here for the rest of us backyard Porsche mechanics.

Thanks for your contribution to this wonderful knowledge base.


Cheers,

Harry.

[Tippy]

Oh, I thought you redid the timing which requires torquing of the cam bolts?

Great you figured it out!

[mreid]

Originally Posted by boyt911sc

Tippy,

I intentionally delayed the announcement because I am embarrassed and at the same time elated that the culprits were identified. Here are the culprits.....





The two (2) camshaft bolts were the culprits. There were installed but not tight or torqued causing a slippage between timing chain, the sprocket teeth, and camshaft after the rocker arms pass the high lobs of the cams.

I have just applied sufficient torque to keep the bolts tight and everything is back to normal!!!! The crankshaft is rotating smoothly and quiet with no discernible sign of problem. The fix took only several seconds of work but the discovery took me forever! Thanks to all.

Tony

Tony, I'm confused about what was "slipping"? The pin locks the sprocket to the cam. The bolt and washer simply keep everything in place.

[john walker's workshop]

The cam gear can be walked back and forth with the pin in the hole. The pin doesn't solidly lock the cam in place all by itself. Redo the cam timing procedure now.

[boyt911sc]

Originally Posted by mreid

Tony, I'm confused about what was "slipping"? The pin locks the sprocket to the cam. The bolt and washer simply keep everything in place.

MReid,

The pin does not lock the sprocket to the camshaft per se. The adjusting pin sets or aligns the sprocket to the camshaft flange. The camshaft flange and woodruff align with the camshaft. Without the sprocket mounting bolt and washer installed tightly (sufficient torque) there is a small play or movement between the sprocket, flange, and camshaft. It was this very small sudden movement or travel of camshaft from/to the rockers that was something peculiar with my camshafts caught my attention.

Without any rockers installed, you could turn the crankshaft without experiencing or hearing the weird noise (whatever name to call it). But once you install a rocker/s, the noise starts to appear after going over the high lob/s.

After I applied some torque to the camshaft sprocket mounting bolt with washer the mysterious sound disappeared. And you don't observe any slipping or jerking of the camshaft during crankshaft rotation. If you have some doubt, loosen your camshaft bolts and do the test.

Tony

[Flat6pac]

Tony, I'm glad you got it. That's the .15 movement between front and back of the locator hole.
Everybody learned something and your extended descriptions are thought out.
Bruce

[boyt911sc]

Originally Posted by john walker's workshop

The cam gear can be walked back and forth with the pin in the hole. The pin doesn't solidly lock the cam in place all by itself. Redo the cam timing procedure now.

John,

I will torque the cam bolts to spec and repeat or redo my cam timing several times like I always did in the past. Like you said, the pin alone does not lock the cam in place. Thanks for sharing the information because some people might be thinking I was imagining this mysterious and sudden rotational movement of the camshaft.

Tony

[boyt911sc]

Originally Posted by Flat6pac

Tony, I'm glad you got it. That's the .15 movement between front and back of the locator hole.
Everybody learned something and your extended descriptions are thought out.
Bruce

Bruce,

I would not be in this position rebuilding engines without your unselfish assistance and help. Someday, I will come and visit you. I still owe you some $$$$ for the parts you gave me. Thanks.

Tony

[VFR750]

This is great news.

[Alan L]

Good news - disaster averted.
90 ft/lb?
Alan

[mreid]

Thanks, Tony, that makes sense. Great lesson! I never would have thought that little bit would make that much of a difference.

[kenikh]

Congrats. I was entertained.

[timmy2]

Good job finding the cause and solution. Time to bolt it all up and get it installed.

[Alan L]

The chain under cam tension would have been riding the slightly mis aligned tensioner/cam teeth, then dropping into place under load. Had the same thing a couple of days ago as I was timing the cams. Noticed the chain slightly riding the teeth. But the cam sprocket at that point was slightly out of line as it hadn't been torqued up.
Alan

[boyt911sc]

Thanks Al lkosmal for the oil pressure check. I should have posted it here than having it in the other thread. Anyway, for those of you who have followed this never ending saga, there is another added chapter.

While I was able to get the engine to run after replacing the defective fuel distributor (FD), there is another problem I am having now. The oil pressure seems to be a problem. The engine test stand I am using was basically built for CIS troubleshooting. It does not have an oil pressure gauge connected and it was only a few days I ago that a tachometer was hooked up.

The engine starts and run every time you turn the ignition switch. Everything seems good when the engine is cold. But once the engine gets warmed up and sits for about 30 mins., an engine restart would reveal another problem. A very loud and tapping/knocking noise is coming from the engine during the initial warm re-start. Less noise after another re-start and a third re-start seems to get lesser annoying noise. The abnormal noise is very reproducible when the engine is hot and warm but nothing when the engine is stone cold.

Without a suitable pressure gauge connected I have no idea what oil pressure I was having. So the next action is to install an oil pressure gauge and monitor the oil pressure during start (cold and warm) and during idle. Any suggestion or recommendation are highly appreciated. Thanks to everyone.

Tony

[boyt911sc]

It was suggested to measure to the valve to piston clearance @ overlap (360° from TDC).

Here are the information I gathered this week after measuring the number of turns of the valve adjusters before coming in contact with the top of the piston/s:

@ Overlap:
Cylinder #1 intake valve--------------3.25 mm (3 turns + 1/4).
Cylinder #1 exhaust valve------------3.75 mm (3.5 turns + 1/4).

Cylinder #2 intake valve--------------3.25 mm (3.5 turns + 1/4).
Cylinder #2 exhaust valve------------3.25 mm (3 turns + 1/4).

Cylinder #3 intake valve--------------3.25 mm (3 turns + 1/4).
Cylinder #3 exhaust valve------------3.65 mm (3.5 turns + 1/8).

Cylinder #4 intake valve--------------3.50 mm (3.5 turns).
Cylinder #4 exhaust valve------------3.50 mm (3.5 turns).

Cylinder #5 intake valve--------------3.25 mm (3 turns + 1/4).
Cylinder #5 exhaust valve------------3.75 mm (3.5 turns + 1/4).

Cylinder #6 intake valve--------------3.75 mm (3.5 turns + 1/4).
Cylinder #6 exhaust valve------------3.75 mm (3.5 turns + 1/4).

Another set of measurements done @ TDC and numbers were very similar to the above data.

I was expecting to see some obvious problem from the data but can not imagine what is causing the tapping noise coming from the engine. Could anyone tell anything from the numbers I collected? By the numbers above, there is ample clearances between valves and pistons. So what could be the culprit causing the knocking or tapping noise coming from the engine?

BTW, a mechanical pressure gauge was installed to determine oil pressure during cranking and run. Picture to be posted later. Thanks.

Tony

[VFR750]

Did I mention my loose cam drive gear? Gear was clicking back and forth against the woodruff key on the crank. Very noticeable when hot. But quiet when cold. Unfortunately it required welding and a replacement gear. Noise went away after repair.

[boyt911sc]

In order to monitor the oil pressure during cranking and actual operation, a mechanical oil pressure gauge was temporarily installed.



During a brief run, oil pressure gauge showed about 30 psi. (2+ bar). I have been calling and contacting people from this forum seeking advices, ideas, suggestions, recommendations, etc. to get to the bottom the problem. The response and support I get from some members of this forum is overwhelming.

Tearing the engine apart now without knowing or understanding the root cause of this problem will probably bring me back to the same situation. I welcome any idea you could bring to the table or PM me. Thanks.

Tony

[boyt911sc]

Originally Posted by VFR750

Did I mention my loose cam drive gear? Gear was clicking back and forth against the woodruff key on the crank. Very noticeable when hot. But quiet when cold. Unfortunately it required welding and a replacement gear. Noise went away after repair.

VFR,

When I get to the point of tearing the engine apart, I will place this suggestion on top my list to check. Were you referring to the gear sprocket/s? I could inspect them right away. The noise seems to be coming from the chain box but I could be wrong. I was thinking it was a failed tensioner but they have not collapsed.

Would installing a mechanical tensioner for test run a good idea? I was discouraged not to try one. Any opinion? Thanks.

Tony

[Sub8]

Oil pressure hot or cold? Was 30psi measured whilst your problem tapping was occurring?