Cam timing on 73 911 E 2.4

[David D]

I have a 911E 2.4 which was purchased with the engine dismantled due to the previouse owner having a look and its been a year of hard slog putting this baby back together. The parts of the engine were in a so called Porsche specialist workshop here in New Zealand. we suspected that bits had been robbed and just junk given in the box of bits we recieved.
We have managed to get the engine running but the engine back fires and splutters occasionaly through the inlet stack on the right hand side of the engine looking towards the front of the car from the back. after replacing the electronic ignition and having the mechanical injection unit apart and re set it still backfires on the right side front and back cylinders.
We had the cams re built and checked the cam timing as we thought a valve was bent on the inlet. I poured a small amount of petrol down the valve but the petrol stayed there for about 15 mins before we removed it so it looked as if the valve was seating correctly and a compression test came out ok.
After checking the cam timing we found that the valve was opening at about 35 degrees before TDC and the valve was in its closed position about 60 degrees after BDC which caused pressure back up the inlet valve. We re measured the left hand side timing and that was ok so presumed the Cam on the right hand side had been ground wrong. I sent the Cam back to the guys who re built the Cam for a re check and they said all was ok and they had borrowed a set of cams to confirm the profile to be ok.
We have the cam back we are about to re fit it again could you offer any advice on the cam timing and also the valve lift dimention.
could we have a cam gallery of another car?

I look forward to your help
Regards
David D

[Tim Walsh]

That right side cam sounds like an S cam to me but that is really odd.. The intake on an S cam opens at 38 degrees before TDC and closes 50 degrees after BDC. (According to Bruce Anderson)

An S cam as .459 inches of lift and an E cam has .408 inches of lift

[David D]

If the cam is a S cam will it still run in the E engine with the MFI.
It would be good if I could get the proper specs for the engine I have 2 books and one says 20 degrees BTDC and the other says 29 degrees. confusion
and I would realy like to get this beast going.

thanks Tim for the comment any help is good.
Regards
David D

[Tim Walsh]

David,
If BOTH cams are S cams it'll run but I wonder if you've got one side as an E and the other an S. According to the haynes manual the E's timing is:
intake.
opens 18 BTDC
closes 36 ATDC
exhaust
opens 38 BTDC
closes 8 ATDC

Waynes engine book
intake.
opens 18 BTDC
closes 36 ATDC
exhaust
opens 48 BTDC
closes 8 ATDC

[Tim Walsh]

Bruce Anderson
intake.
opens 18 BTDC
closes 36 ATDC
exhaust
opens 38 BTDC
closes 8 ATDC

[David D]

Thanks Tim
I suppose you couldent tell me the lift measurement of the valve when setting with a drop clock ie is it 2.7 to 3.1mm. at TDC
Once we set the timing its back to the distributor it works with a vaccum retard untill the butterflies open when the throttle starts opening, thats where we found the fault there was no vaccum on the right side due to the valve timing.

What a learning curve eh?

I hope to hear from you soon.
Regards
David D

[dtw]

Let's hear more about the backfiring and sputtering...under what conditions (rpm, load) is it occurring? How does the engine run otherwise? Other issues that will come into play with your symptoms:
-What are the results of compression and leakdown?
-Did you properly time the injection pump?
-Have you gone through check/measure/adjust?
-Are you getting good fuel pressure out of the injection pump to all injectors? What is the condition of the pump? How long was it out of commission? Was it stored properly?
-Is the ignition timing good?
-Are the plug wires on in the right order?
-Are the throttle bodies on the right side in good repair? Worn out throttles will cause problems at idle like you are experiencing.
-Are you backfiring through the exhaust as well or just the intake? Have you checked your plugs, and are you getting combustion on all right bank cylinders? A dead hole could result in unburnt fuel lighting off in the exhaust.

Just had the problems you indicated after building a 'boxed' engine just like you had! So I can relate, and can assure you that I had to address all the above questions between myself and my mechanic before getting the engine running right. Turns out that:
-the injection pump was no good, and resulted in one completely dead hole
-most of my plugs were fouled
-my injection pump timing was way the hell off, resulting in very rough running on the remaining holes
-mixture was way off
-plug wires on 2 cylinders were crossed up

[David D]

DTW
The backfiring and spluttering was through the inlet stacks when the throttle was opened from tickover when we took the inlet throttle bodies off there wes plenty of black soot in the front and back cylinder inlet ports.
Yes the injection pump has been timed according to the book and new injectors were fitted and tested several times. The pump had been stored for about 2 years with oil in and looked good. we did find there had been some attempt to adjust this pump by someone who compleatly adjusted it wrong and dissconected one of the links.
we bench tested the pump before re fitting it but this still may need a careful tweek after we get the car running
The engine has been compleatly re built new eveything including big end shells, pistons rings etc etc.
Ignition has been replaced and new leads and yes we have them on the correct plugs.
The Distributor could be causing problems due to the vaccuum in the one side of the engine not working causing the retard on the distributor to not work which we think is caused by the inlet port having pressure blown back through it from the inlet valves hence the cam timing being wrong.
Throttle bodies were also checked and re bushed where they needed it.
Yes the plugs are as black as after only a few mins running.

Hopefully we will get the Cam in this week and start it up again.

anyone got those measurements for the valves at TDC is it 2.7mm to 3.1mm

Keep the good info coming please
regards
David D

[Bobboloo]

There were 2 versions of the E cam. The first one in 69' (only) was actually a Solex cam.
29 BTDC
39 ATDC
39 BBDC
19 ATDC

Your car should have the 2nd version which came out in 70'
20 BTDC
34 ABDC
40 BBDC
6 ATDC

In 72' Porsche retarded the same E cam by 2 degress to

18 BTDC
36 ABDC
38 BBDC
8 ATDC

Lift at TDC overlap was set at 3.0 to 3.3mm in 70' and that was changed to 2.7 to 3.1mm in 72' when the cams were retarded. So 2.9mm lift at TDC overlap would be what you want.

Keep in mind that the right side of the motor, cyl. 4 thru 6, are a 180 degrees opposite the left side, cyl. 1 thru 3.
So when the left side cyl. 1 is at TDC with both valves closed on #1 then the right side is at TDC overlap on #4 and vice versa.

The numbers you gave above are way off. Are they 180 degrees off?

[David D]

Thanks Bobby just what I wanted. I will check all when we put the Cam in later this week.
David D

[911pcars]

With sufficient valve-to-piston clearance, the engine shouldn't run this way with S cams. If only a couple of the right bank cylinders are acting this way, I wouldn't suspect cam timing; no. 4-5-6 cylinders would all act similarly, yes?

Have you checked the firing order? Any secondary wire crossfire? How about excess wear in the throttle bores?

Sherwood

[Wayne 962]

I doubt this is a cam problem. Check:

- Exhaust leaks
- Fuel Volumetric flow
- Do a compression/leakdown test
- Recheck valve adjustments.
- Check CO on left/right banks...

-Wayne

[camgrinder]

((There were 2 versions of the E cam. The first one in 69' (only) was actually a Solex cam.
29 BTDC
39 ATDC
39 BBDC
19 ATDC))

I dont know for sure but I suspect the 901/09 and 901/11 cam specifcations are incorrect in the little Porsche handbook.
I have never seen a Solex spec cam with a 901 105 181 casting number.
The book lists the correct lobe height, correct setting (3.0-3.3 mm) but wilder duration specs for the "E" camshaft
Bruce Andersons book lists what I believe the correct specs are for the '69 2.0 E
which are the same as the 1970 version.

John

[David D]

John
the numbers on the cams are (901 105 181 OR )and (901 105 110 OR) I think there is a S132 mark on the 181 cam.
We will put the cams back in the car over the weekend and re measure to see what we have got.
Regards
David D

[camgrinder]

David,
Most "S" cams had a small s stamped into the snout of the camshaft.
Right below the little timing dot
John.

[NevenM]

David

Where are you in Auckland?, I'm in Sandringham and building my 73 2.4E (just in the process of checking V to P). I have a 73 tech spec book and factory manuals so if you want to chat call me on
620 1356 (hm) or 621 0001 (Work). I can also highly recommend and engine machinist with lots of porsche exp.

Also I don't know if it is a misprint but the Valve timing specs are given at 1 mm clearance which may account for your measurements. Are you sure your throttle bodies are synched left to right? There may be other reasons for lack of vacuum, Are all
three cylinders popping and farting? and does it idle OK?

Neven

[David D]

Nevan
I will give you a call I live up at Red Beach, my wk ph 442 0840 ext 861 or 021 128 3609.
The actual gap setting was .1mm as per the book we have could you confirm the 1mm gap for the tappet clearance. this would explain a lot of the problems.
Regards
David D