1989 Carrera 3.2 HELP Sucking air into exhaust

[BackyardCarrera]

Hey guys!!
First post and definitely not the last. I bought my dream car, 1989 911 3.2 coupe. It was a complete basket case. parts in boxes, everything in shambles. I have been refreshing everything the past few weeks, inspecting bores, valves and everything else i can get my scope camera down in and all the internals look great.

I set valve clearances this weekend and was going to check compression when I noticed it doing something odd.

Engine is SUCKING A TON of AIR from the exhaust and pushing air out of the intake when i crank the car to check compression. (Seems to be completely backwards obviously from what a typical motor should do)

Has anyone else ran into this or have any ideas what could cause this?

I plan on pulling timing chain/cam covers next weekend to inspect and see if there is something obvious or blatantly wrong with cam timing. Could Cam timing be off so much that it gives symptoms described above?

[BackyardCarrera]

Just for reference, Car does not run at the moment. has sat for years in owners garage. Said it was in the process of getting a full rebuild done on it.

Has strong spark. I tried spraying a couple squirts of starting fluid but no fire. Seems like timing is completely off as to why compression is so wacky and it is sucking air into exhaust and blowing it out of the intake.

[brighton911]

Weird problem and I think you are on to the possible cause and that is the valve timing is wonky and not just a little. Do you have a good manual (Bentley) that you can reference ?

[BackyardCarrera]

Originally Posted by brighton911

Weird problem and I think you are on to the possible cause and that is the valve timing is wonky and not just a little. Do you have a good manual (Bentley) that you can reference ?

Yes sir, Ive got a Bentley that has been fantastic so far.

After racking my brain I'm wondering if the previous owner incorrectly stabbed the distributor 180 degrees out and i set the valves essentially on the wrong stroke (180 out)

When i get more time to check it out I am going to pull dizzy out and recheck cylinder 1 is on true TDC intake and not TDC of exhaust stroke.

[yelcab1]

check to see if you even have the right cam in the right bank.

[PeteKz]

Clarification: Was the whole car a basket case, or just the engine?

Do you have all the spark plugs out, or just the one for the cylinder you are checking?

If your cam timing is way off, you can get pistons hitting valves, so be sure you can crank the engine through by hand before using the starter.

[BackyardCarrera]

Entire car was basket case. However, previous owner is sure the rebuild was going properly as he had a shop go back together with motor.

When I got it home I had all the plugs out and lubed up all the cylinders with stabil upper cylinder lubricant and marvel mystery oil. Let sit for a few days, then turned motor over by hand slowly. Everything was clean and free moving.

Set the valves this past weekend and still made sure motor turned smoothly by hand. No resistance was ever felt.

I’m starting to think previous owner had stabbed the distributor in 180 degrees off so in turn when I matched up TDC on crank to dizzy rotor aimed at cylinder 1 it was actually on cylinder 4’s tdc.

I plan on pulling off cam covers and verifying true TDC along with correctly placing dizzy rotor back to cylinder one if it is indeed 180 out.

[BackyardCarrera]

Originally Posted by yelcab1

check to see if you even have the right cam in the right bank.

Is there a marking I can check to confirm this on the outer edge of the cam? Not sure if I can verify with cams still installed.

[boyt911sc]

Two things to check:

• Check if your camshafts are correctly installed.
• Check that ignition distributor is not 180° off.

Twelve (12) straight engine rebuilds without any problem. Engines started and ran well until the 13th motor. I was not superstitious but that motor humiliated me and committed several blunders that I never made before namely the 2 items above and inadvertently forgotten to install the rear crankshaft oil seal causing heavy oil leak during start up and the motor failed to start. Took several weeks to discover the problems.

Just like to share some embarrassing moments and memorable experience. Getting ready for my 19th motor this winter/spring seasons.

Tony

[PeteKz]

I asked about the spark plugs because if you have them out, the pistons are sucking air in and out of the spark plug holes, thus the normal movement of air from the intake to the exhaust will not occur.

The distributor has nothing to do with the cam/valve timing and could not cause what you describe. Check its orientation, as that could be responsible for not firing on starting fluid.

I'm certain that if your cams were installed incorrectly, or way off on the timing, you would have bashed the pistons into the valves. From what you described, that did not happen. Nevertheless, since someone else built the engine, check the cam timing. Start by removing the intake valve covers and set up a dial indicator as described in the books. If your timing is within specs, then don't pull off the timing chain covers. You only need to remove those if you need to reset the cam timing.

[yelcab1]

Originally Posted by PeteKz

I'm certain that if your cams were installed incorrectly, or way off on the timing, you would have bashed the pistons into the valves. ....

Have you ever noticed that on air-cool boxer engines, the opposing pistons always move up and down at the same time? When 1 is at TDC compression, 4 is at TDC overlap.

So, if you flip the cam shafts left to right, the pistons will never be in a place to smash into the valves because the pistons will travel in exactly the same manner as before.

It will not run but it won't bend valves.

[BackyardCarrera]

Originally Posted by PeteKz

I asked about the spark plugs because if you have them out, the pistons are sucking air in and out of the spark plug holes, thus the normal movement of air from the intake to the exhaust will not occur.

The distributor has nothing to do with the cam/valve timing and could not cause what you describe. Check its orientation, as that could be responsible for not firing on starting fluid.

I'm certain that if your cams were installed incorrectly, or way off on the timing, you would have bashed the pistons into the valves. From what you described, that did not happen. Nevertheless, since someone else built the engine, check the cam timing. Start by removing the intake valve covers and set up a dial indicator as described in the books. If your timing is within specs, then don't pull off the timing chain covers. You only need to remove those if you need to reset the cam timing.

Spark plugs were installed during the tests. My concern with dizzy being out 180 degrees is that i set all of the valves in accordance to the crank being on Z1 and the dizzy pointing to cyl 1. Meaning I set the valves technically on cyl 4 TDC.

This would mean that i have all of the valves set on the Exhaust stroke instead of the intake stroke of the engine's cycle.

When Cyl 1 is on TDC the piston for cyl 4 is also at the top of its stroke, however, it is on the exhaust stroke instead of intake. for a brief moment both valves close during this time as the valves are switching from exhaust to intake.

In theory this makes sense as to why i am getting suction from exhaust pipe and blown pressure from intake manifold.

It's a tad tricky to describe but does this sort of make sense and is correct?

[BackyardCarrera]

Originally Posted by yelcab1

Have you ever noticed that on air-cool boxer engines, the opposing pistons always move up and down at the same time? When 1 is at TDC compression, 4 is at TDC overlap.

So, if you flip the cam shafts left to right, the pistons will never be in a place to smash into the valves because the pistons will travel in exactly the same manner as before.

It will not run but it won't bend valves.

Yes Sir!! My thoughts exactly and what I have come to realize is my only saving grace at this moment.

[BackyardCarrera]

Originally Posted by boyt911sc

Two things to check:

• Check if your camshafts are correctly installed.
• Check that ignition distributor is not 180° off.

Twelve (12) straight engine rebuilds without any problem. Engines started and ran well until the 13th motor. I was not superstitious but that motor humiliated me and committed several blunders that I never made before namely the 2 items above and inadvertently forgotten to install the rear crankshaft oil seal causing heavy oil leak during start up and the motor failed to start. Took several weeks to discover the problems.

Just like to share some embarrassing moments and memorable experience. Getting ready for my 19th motor this winter/spring seasons.

Tony

Hoping I can get some time to dig into it this weekend but will be checking both for sure. Trying to be diligent and thorough.

[boyt911sc]

Originally Posted by PeteKz

I asked about the spark plugs because if you have them out, the pistons are sucking air in and out of the spark plug holes, thus the normal movement of air from the intake to the exhaust will not occur.

The distributor has nothing to do with the cam/valve timing and could not cause what you describe. Check its orientation, as that could be responsible for not firing on starting fluid.

I’m certain that if your cams were installed incorrectly, or way off on the timing, you would have bashed the pistons into the valves. From what you described, that did not happen. Nevertheless, since someone else built the engine, check the cam timing. Start by removing the intake valve covers and set up a dial indicator as described in the books. If your timing is within specs, then don't pull off the timing chain covers. You only need to remove those if you need to reset the cam timing.

Pete,

Are sure you know this for a fact? I was manually turning the motor by hand and using the starter for weeks without any sign of ignition until I realized something about the camshafts. Pulled out both camshafts and confirmed they were installed incorrectly. If there was any sign of piston to valve contact, you were WRONG! As long as you set the cam timing as per spec, there will be no piston to valve contact. And won’t start if incorrectly installed.

Tony

[PeteKz]

I will defer to those of you who have installed your cams on the WRONG side of the engine. I haven't made that DUMB mistake! (yet)

Yelcab1: Yes, the pistons are on opposite sides of the cycle, so they should not interfere, however the cam lobes are in different places too. I'll have to think about that some more.

As for the cam timing being way off, I have experienced valve to piston contact, fortunately only cranking the engine through by hand. That happened when I pulled the pin out of the sprockets to adjust the timing, and the cam moved under the pressure of the valve springs, and I didn't notice it. Drove me nuts resetting the timing until I realized what happened.

BackyardCarrera: To go back to your question about which cam goes on which bank: The mnemonic is that the "r"ight cam lobes will be close in angle and look like "r"abbit ears when viewed from the end of the cam. The "l"eft cam lobes will be spread more, like a wide "L".

[BackyardCarrera]

Originally Posted by PeteKz

I will defer to those of you who have installed your cams on the WRONG side of the engine. I haven't made that DUMB mistake! (yet)

Yelcab1: Yes, the pistons are on opposite sides of the cycle, so they should not interfere, however the cam lobes are in different places too. I'll have to think about that some more.

As for the cam timing being way off, I have experienced valve to piston contact, fortunately only cranking the engine through by hand. That happened when I pulled the pin out of the sprockets to adjust the timing, and the cam moved under the pressure of the valve springs, and I didn't notice it. Drove me nuts resetting the timing until I realized what happened.

BackyardCarrera: To go back to your question about which cam goes on which bank: The mnemonic is that the "r"ight cam lobes will be close in angle and look like "r"abbit ears when viewed from the end of the cam. The "l"eft cam lobes will be spread more, like a wide "L".

Thank you for the tip identifying the difference between them. I will take note of this when I pull the covers and inspect.

[BackyardCarrera]

Originally Posted by boyt911sc

Pete,

Are sure you know this for a fact? I was manually turning the motor by hand and using the starter for weeks without any sign of ignition until I realized something about the camshafts. Pulled out both camshafts and confirmed they were installed incorrectly. If there was any sign of piston to valve contact, you were WRONG! As long as you set the cam timing as per spec, there will be no piston to valve contact. And won’t start if incorrectly installed.

Tony

When you swapped the cams and reset timing did everything fire right up? I’m thinking that’s what is going on in my situation.
Do you by chance remember is you had suction/vacuum from your exhaust?

[yelcab1]

A leak down test will tell you if this is the case. Just do the test.

[BackyardCarrera]

Originally Posted by yelcab1

A leak down test will tell you if this is the case. Just do the test.

Yes sir, that is in the cards to do as well. I apologize for a dumb question but just want to confirm..
In theory if the cams are swapped in this engine and in the wrong banks when I run a leak down on TDC cyl 1, it would in turn be during the valve overlap meaning the cylinder wouldn't pressurize at all?
And if thats the case that is another way to confirm that they are indeed installed in the wrong bank?


P.S. Thank y'all so very much for all the info and help chiming in on this. It is all GREATLY appreciated.