I recently bought this 2.7L motor as a possible candidate to put into the 914 for the 914-6 conversion. Since then I found an original 2.0L 914-6 motor and have to decided to go that route instead.
Since I will be selling this motor I want to document it as well as possible and do a leak-down test so that the new owner knows as much as possible what they are getting for their money.
About the motor
- Year: 1975
- Type: 911/44 (911S California)
- Number: 6551456
This 2.7 was running when it was taking out of a car with front end damage. It has been sitting ever since, stored indoors for at least ten years possibly more.
It turns over freely, and is still full of clean looking oil.
One of the first items on the list was to check the condition of the head studs. These 2.7L magnesium-case engines are notorious for breaking or pulling head studs, and don’t last very long if the problem isn’t addressed.
One of the more obvious ways to tell if there is a broken or pulled stud is that when the stud lets go, there isn’t enough friction to keep the barrel nut on the stud, and the nut will fall off and rattle around under the valve covers.
I removed both valve covers on each side, and I was quite happy to see that all of the nuts were exactly where they’re supposed to be:
I also got a good look at the cams which seem to be nice and smooth, I’ve turned over the motor while watching each cam and didn’t see any signs of pitting or anything like that. You can also see some excess gasket material, which is evidence that this motor has definitely been taken apart before:
Next I wanted to see where the head studs thread into the case to check for case savers. I was pretty sure this motor had been rebuilt before, and was curious whether the builder had dealt with the weak stud problem. If the head studs were still threaded directly into the case this would mean the motor is basically a ticking time bomb, eventually studs would start pulling out of the case and the motor would need to be completely torn down to fix the problem.
Luckily for me, and for the next owner of this motor, this work has already been done:
As you can see in the photo, the stud goes into an oversize, one-piece, threaded insert (ie it’s a case saver, not heli-coil).
I originally took the photo through my bore scope, but the way my camera and the scope work together ends up making everything all blue and grainy. Here’s how it looks for comparison, you can still get the idea:
Bore scope cylinders
After confirming that the head studs had been sorted out, I checked each cylinder through the spark plug holes with my bore scope. From what I could see, all of the pistons and cylinders looked normal enough.
No obvious signs of damage, although cylinder number 3 was full of oil. Probably because the motor spent some time tilted on an angle while I was carting it into the shop. Anyway, I got the oil out easily enough with a syringe, which also made it easy to inspect. Looks nice and fresh, no sediment:
Here are the spark plugs, layed out as they were on the engine, with cylinder 1 at bottom left. Notice the plug from cylinder 3 (the one that filled up with oil) is totally clean:
OK everything’s looking good, time for a leak-down test. The motor is supposed to be warmed up for a leak-down test, but I don’t have a test stand or a car to put it into to try to fire it up, so a cold test will have to do. Keep in mind this engine hasn’t been run in many years and has only been turned over a handful of times.
- Rotate crank to TDC on compression stroke for cylinder 1 using pulley markings
- Look through the bore scope to find the exact point where the piston pauses at the top of its stroke.
- Thread in the spark plug hole adapter and plug it into the leak-down tester.
- Make sure air compressor pressure higher than the test pressure of 80psi.
- Turn the dial on the leak-down tester until the pressure rises to the target pressure. Take a reading at 70psi and 80psi.
- Remove the plug hole adapter.
- Rotate crank 120 degrees and move to next cylinder in the firing order (1-6-2-4-3-5).
- Repeat steps 2 through 7 for each cylinder.
And here are the results:
- Cylinder 1: 13.75%
- Cylinder 2: 87.5%
- Cylinder 3: 7.5%
- Cylinder 4: 72.5%
- Cylinder 5: 25%
- Cylinder 6: 3.75%
As you can see, there’s definitely something up with cylinders 2 and 4. Most likely the rings have not come loose and aren’t making a very good seal against the cylinder. I’ll check these cylinders more thoroughly with the bore scope and take some photos this time. Those cylinders looked OK before and the motor turns smoothly so I don’t think there’s anything seriously wrong in there.
Cylinder 6 is quite amazing for a motor that has been sitting for so long, and Cylinder 3 is quite good as well. This makes me think that the mileage since rebuild is quite low, and the other cylinders may post similar numbers once they are warmed up and the rings are freed up and making a proper seal.
Cylinder 1 is the sort of number you’d expect from a warm motor, so for a cold one that’s been sitting it’s a pretty impressive number.
So there we go, not quite the straight A’s I was hoping for but there’s still a good chance this motor will run well without a rebuild.
It’s hard to assess its condition more accurately without getting it running and warmed up, or by tearing it down further. I may do one or the other, or just sell it as is and let the next owner decide how to proceed.
Thanks for reading