Mechanical Overrev - The Plot Thickens

Very interesting, but could someone explain how the timing became unadjusted? Did they put the distributor back wrong, take off the timing chain or what? And if so, how did you get it timed correctly?

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Kurt B
'84 Carrera Cab.
carrera_cabriolet@yahoo.com

Hello

I just would like to say what Maestro says beware off the t.....

It is possible to remove the heads and P&C with engine in the car. But normally it is faster and safer to remove the engine.

Inbordoperation is done on race events in crowded pits or at rallye resorts. Those mechanics there are experts and wrench while sleeping. ( and get an huge paycheck if the team wins )


Well two trained race mechanics do change said parts under two hours. A single good mechnic can manage it under 5 Hours. ( Well this is my time but on a race engine all nuts turn loose and some icky things are missing anyhow ) Donīt forget the time to rebuild the headīs prove the parts.

But you canīt work that way on a normal car and not every day.

The best way to find out how much time is needed is to ask the Porsche dealers. Porsche has given out "Richtwerte" on specific works.

This is based on proffesional workers who have all the needes tools and are good organized. Most mechanics are a bit faster. On old cars you have some problems you where runing in like rustet bolts or some idiot ahead had rounded a nut..........

So you start to add the additional time as separate "bad circumstance" billing.

Well i think 20 hours would be a good time if everything "runs". 27 would be oīk if the MFI and Ignition would be perfect and nothing else had happend. Never rush on work as you might fall on your nose.


Also if i had been that mechanic i would have messured the deck hight to make sure the rod isnīt bend and in any doubt had splittet the case.

Normaly it is an good sign if the rockerarms splittet avoiding to hard hitīs. But euro spec RS have the early "S" rockers and those things break at last.

Just read Bruce Anderson and compare your rockerarm and what parts the mechanic used.

An other observation is that the left bank drives the MFI Pump so that thing was out off timing. An good check is to syncronize the strobe to FE at idle. then use an mirror and flas the pumpmark. Every expierienced MFI mechanic does exactly that to prove the work after finishing. The cam out of spec would not have been visible but the pump would be correct alignet to TDC and maybe the thing would run without any problem.

Well those things are making your neck break and loose hair ( especially with worn gas springs ) but it is an good work out too.

As Iīm a lazy guy a hang on an used mail the shows an easy way to find out if both cams are synchronized:

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Hello again, just hadnīt time for all.

Thanks for the input on the 2.2T compression test. I am running the Zeniths. You've helped me out before on checking cam timing on this engine as well. As it turns out, the cam timing is off on the drivers side. The tolerance is 2.3 - 2.7mm and I measured 3.5mm! I am going to adjust it this weekend and possibly change the tensioners. You said to use the turbo tensioners. Just stock 79 turbo tensioners?

Well with the 930 came new tensioners. They have an embosed 930 ordernumber. The old ones have 911. Also use the old tensioner to adjust your timimg as turning backwards to lossen the big 46 mm Nut ( 130 NM ) will over tension the new parts and will let them fail much earlier.

Just an other trick:

If you have one side correct then mark the maximum lift from the valve on the rear beltwheel/pulley. Now turn the engine 360 ° forward until the mark is back again. Now for the oppesit cylinder. Loose the nut and then pull the adjustpin with an M 4 bolt. Or use the threaded end from an old Sparkplug. Now with an 17 mm spanner you turn the cam until you have maximum lift there too. reinsert pin and turn nut loose on. Now turn the engine 720° and check the position again.

Both sides for maximum lift musst be on the same marked spot.

Allways welcome for further quest but iīm off saturday to monday

Grüsse

The saga continues...

You may recall that after straightening out and synchronizing my cam timing MUCH of the power in my motor had returned. It seemed to be almost as strong as before, but that annoying roughness that appeared after the missed shift and all of this thread's history is still present. You remember the buffeting exhaust, window rattling roughness that I described earlier. It is wierd because now, most of the power is back, but there is still that gremlin somewhere that is causing this roughness and I'm sure robbing at least a little power.

On another note, and another thread for that matter, I embarked upon the rebuilding of my Bosch Distributor. The ignition advance seemed to be sticking, causing the hanging of the idle in the 1,300 rpm range. So I pulled the distributor out, completely dissassembled and cleaned and re-lubed it. THANKS WARREN!!! I found that the centrifugal weight mechanism was gummed up, and the breaker plates had seized together, probably from some hardened grease and heat. I ordered a new rotor (7,300S instead of the 7,100E that is on there, a new cap, points, etc..) but they have not arrived yet. I put the distributor back in and re-gapped the points, and re-timed the engine. I wanted to mention a few of my findings and talk about next steps:

1) Idle dropped about 300 rpms and is much smoother. I figure the vacuum retard was not able to pull the timing back at low rpms because of the seized breaker plate, so it was hanging in the 1,300rpm range at idle before. Now it is right at 1,000.

2) Oddly and unexpectedly, the mixture seemed to lean substantially, making things run much cleaner. I noticed this winter that I could not get my operating temps above 120 degrees, no matter how long I drove it. I know that is not good, but I could not figure out what was causing it. I just figured the thermostat for my secondary oil cooler was stuck open. I now believe that I was running so rich that the excess fuel was keeping it cold. I am judging this leaning out on a couple of things... one, I have one of those L.E.D. exhaust gas analyzers on board (probably not worth much, but does give some indication), and secondly, the sound of the engine. Basically, the mixture seems to be perfect right now.

3) When timing the engine, it just happened to be at about 10 o'clock at night. Before I could get my shop light outside, I noticed that I had a corona light(no lime included!) show going on in my engine compartment!! I had sparks arcing from at least two plug wires.

So I have suspended any further diagnosis, either mentally or mechanically, until I get my tune-up parts installed. I am doing the following: Cap, rotor, points, air filter, new vacuum hoses, and plug wires (7mm HD metallic core, silicone insulated bulk wire - reusing my Beru connectors hopefully). THANKS JOHN WALKER'S WORKSHOP!!!

I am sincerely hoping that the arcing plug wires is causing my roughness. I don't know if you can kill a plug wire instantly, and if it would cause these symptoms....roughness and lost power, but no real noticeable mis-firing. I am hopeful, but not optimistic that this is my problem. I still feel there is something internally out-of-whack (technical term)!!

One question I have for you. The shop I bought my car from 3 years ago in Colorado said that my motor was a 2.8L. This guy was a pretty solid mechanic who ran the Pike's Peak hill climb every year in highly modified 911's. His name is Bill Vader and he ran a Porsche shop called "On the Edge Performance". He said that the car was intended be an RSR Replica and used a 2.4S 7R case with MFI to go to a 2.8 like the RSR's. My understanding is that the 2.8's were basically the 2.7RS engine with 92mm pistons instead of 90mm like the 2.7's. Other than that, some of the high HP 2.8's had twin plug and different cam grinds etc... but case-wise they were the same as the 2.7RS's just with a slightly bigger bore.

My question is this. If I do have a 2.8, is it possible that the mechanic who started all of this mess put the wrong valve in when he replaced the supposedly bent one? Do the 2.8's and 2.7RS's use the same valves? I am just trying to figure out what could be causing this roughness. Hopefully it is a tune-up issue, but like I said before, I'm not sure if these tune-up items could have died at the same time the bent valve occurred. Could it be coincidence or a direct cause of the missed shift that a tune-up part failed?


Sorry for the long note and gory details.... I love this stuff!!!


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John
70/73 RS Spec Coupe

First try at a photo...

Here is a picture of the victim.



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John
70/73 RS Spec Coupe

john, your wires are on the way.

[This message has been edited by john walker's workshop (edited 04-02-2001).]