Assessing engine health

[Swallowtail]

Hey guys,

I’m in the slow process of restoring my ’73 911t. I stripped the car a couple of years ago and the engine has been sitting in my garage since then. I’m now at a point where I can see light at the end of the tunnel with the rest of the car so I’m going to spend some time on the running gear.

Unfortunately I did not do any tests when the engine was still in the car, because I expected to do a full teardown anyways. The engine ran but there was a lot of smoke from the exhaust.

Now that I took a closer look it seems there was some money spent on the engine before. There are case savers installed on all studs. Also the newer style pump cover (without drain bolt) is installed.

This led me to some cautious hope, that maybe the engine is better condition than I expected. I’m hoping to get some input on how to get a better understanding of the engines health.

My ideas are:
Compression test (have to mate the engine with the gearbox)
Leak down test
Oil analysis
Checking the cylinders with a bore scope

Anything else I can reasonably do?
I’d appreciate any tips since this is the first time I’m doing any of the above.

thanks,
Andreas

[Discseven]

Hi Andreas... I'd say you're on right track with your plan. I, and perhaps others here, believe knowing more of your T's history alone would provide a window into your engine's life/health. To this end, a few questions:

How long did you own "T" for when it was running?
During your ownership and while "T" was driven, did it always smoke?
A "couple of years ago" since the tear down is exactly how long?
Do you and "T" live in tropics or dry zone?
.

[Swallowtail]

Hi Karl,

thanks for your input. Unfortunately I know very little about the cars history. The car had the typical rust problems but nothing out of the ordinary. The engine has very little corrosion but that may be due to the oil leakiness.

The car last ran in Illinois and is now with me in Germany . I bought it as a restoration object so I only drove it on and off the trailer.

[E Sully]

Just for reference, what engine is in the car? There should be an engine type number to the right of the fan housing. The 911/91 was second half of 1973 for the CIS 7R case. This was a better reinforced case than the earlier 1973 911/51.

[Swallowtail]

Originally Posted by E Sully

Just for reference, what engine is in the car? There should be an engine type number to the right of the fan housing. The 911/91 was second half of 1973 for the CIS 7R case. This was a better reinforced case than the earlier 1973 911/51.

Another thing learned today

My case says 911/57. It is the ROW Version with Zenith carbs.




By the way - is it possible to check if piston oil squirters have been retrofittet, and if so how?

[tperazzo]

Hi Andreas,
I agree with tests you have planned to determine the health of your engine. If you already have your engine on a stand, I can supply you with a starter adapter for cranking or running the engine outside the car or not attached to the transaxle.
If your engine is on the ground then it might be just as easy to just attach the transaxle for the purpose of checking compression, etc.

[Swallowtail]

Originally Posted by tperazzo

Hi Andreas,
I agree with tests you have planned to determine the health of your engine. If you already have your engine on a stand, I can supply you with a starter adapter for cranking or running the engine outside the car or not attached to the transaxle.
If your engine is on the ground then it might be just as easy to just attach the transaxle for the purpose of checking compression, etc.

That is an amazing offer - thank you! The engine is indeed on the stand and an adapter would make things easier. However I'm located in Germany and I believe shipping may be difficult.

Could you post a picture of your adapter so I can get an idea what it looks like? Maybe I can rig up something similar...

[tperazzo]

Starter adapter


A guy in Austria stocks these, but I'm not sure if he has the 911 version. He's mostly a 356 guy.

https://www.classiccarconsulting.com/

[Swallowtail]

Okay, that looks a lot more professional than what I had in mind

I guess remating the gearbox will be the least trouble.

What are your thoughts on doing a compression check with only the residual oil left in the engine? I didn’t drain it but the oil cooler, etc. is disconnected of course. I could squirt some oil into the cylinders but that will influence the results.

Will the compression test tell me anything the leak-down test does not?

[BK911]

Personally I would do a leak down and go from there.
Pump some oil in spark plug holes, rotate a few revolutions, then do the leak down.

[Travis Neff]

I would just do a leak down test and that's it.

They are best performed when the engine is hot, but obviously you cannot do that. Your leak down readings will be higher on a cold engine as the pistons and rings have not had a chance to expand.

Leave all the plugs in the engine except for the cylinder that you are testings (this will help prevent turning the engine when you charge the target cylinder). Once you get 100PSI, listen to your intake on that cylinder, exhaust and oil breather. Where you hear sound that is where the leak is coming from.

Intake sound - intake valve issue
Exhaust sound - exhaust valve issue
Oil Breather - rings.
Spark plug - you don't have your test hose seated tight (I put a little oil on the o-ring to help seal)

Even with a small leakage (lets say 1%) you will hear the sound. Use your ears, sense of smell and feeling with your hand.

[tperazzo]

Originally Posted by Swallowtail

Okay, that looks a lot more professional than what I had in mind

I guess remating the gearbox will be the least trouble.

What are your thoughts on doing a compression check with only the residual oil left in the engine? I didn’t drain it but the oil cooler, etc. is disconnected of course. I could squirt some oil into the cylinders but that will influence the results.

Will the compression test tell me anything the leak-down test does not?

A leak down test will tell you all you need to know. The only issue is you can only get a cold engine reading.

Clearances and seating surfaces change with engine operating temperature.

I wouldn't put oil in the cylinders because that will cheat your leak down numbers.

Let us know what you find.

[Swallowtail]

Thank you all! I will do the test first without and then with some oil.

It will take me a couple of days to get the equipment but I will post the results, asap.

[Travis Neff]

I like the leak down gauges that shows PSI for charge and PSI for residual, rather than the 2nd gauge showing a leak down percentage.

[BK911]

I hear what you guys are saying about oil helping the rings to seal.
However, engine has been sitting for years in a garage.
No way I would spin a dry engine.

[Swallowtail]

So, I have some news on my progress. I decided to spray some oil into each cylinder before turning the engine over.

Unfortunately I was not able to get any kind of repeatable readings with my cheapo ebay leak down tester. At least I was able to determine that there is considerable blow by on all valves (it blows out of both the inlet and exhaust ports). Cylinder 1 seems to be the worst with almost no compression at all.

To me it looks like at least a top end rebuild will be necessary. Likely more than that.

Here are some things I noticed:
1. Are Nyloc nuts allowed here or should there be metal locking nuts? One nut was loose.


2. There is some corrosion here at the bottom. Looks like the Case Stud was repaired with a through bolt. Is this an acceptable case solution?


3. Found this screw next to a spark plug. Anybody know where it is from?


4. Spark plugs were wet (remember, engine has been sitting for years). All look similar to me. Some gunk on cylinder 2 plug.


5. Any way to tell which oil pump this is? Does the colour mean it's the 4 Rib version?


For reference (curtesy to Tom Butler)

[Travis Neff]

From your photo, it looks the same as an SC pump I have right in front of me. It is an aluminum front section. Yours should have come stock with an Mag pump, so it has been replaced with something else.

However, the reference photos don't show that same view. It may be odd that the pickup is epoxied on?

[ClickClickBoom]

A leak down test on a cold dry motor is pretty much useless as a diagnostic tool. The motor has to freshly run, and at operating temperature. Even if the valves are leaking, it could be debris on the seat. The simple act of removing the spark plug could drop carbon on the valve seat. And the rings could be aligned on the gaps. The simple act of minutely rotating the crank under pressure less than 1 degree can cause the ring to seal, and bump the pressure 5-10 lbs. I have been doing differential compression testing on piston aircraft engines and cars for 35 years and have done thousands. In reality, differential compression testing is a trend monitoring tool, as an absolute one time diagnostic it is iffy.
https://www.aircraftspruce.com/catalog/pdf/servicebulletin.pdf

https://www.lycoming.com/sites/default/files/Cylinder%20Compression.pdf

[BK911]

That bolt is a rocker arm shaft through bolt.
Pull the valve covers and look for a loose rocker arm.
Not sure how it would have gotten on top of the cam box though.

[Swallowtail]

Originally Posted by Travis Neff

From your photo, it looks the same as an SC pump I have right in front of me. It is an aluminum front section. Yours should have come stock with an Mag pump, so it has been replaced with something else.

However, the reference photos don't show that same view. It may be odd that the pickup is epoxied on?

That at least would be good news and save me some money. How sure are you? I searched for images from the same angle but didn't find anything conclusive. I agree that the epoxy does look odd.

Originally Posted by ClickClickBoom

A leak down test on a cold dry motor is pretty much useless as a diagnostic tool. (...)

Sounds like you know what you're talking about. What would you check before deciding weather to tear the engine apart?

Originally Posted by BK911

That bolt is a rocker arm shaft through bolt.
Pull the valve covers and look for a loose rocker arm.
Not sure how it would have gotten on top of the cam box though.

Thanks - very keen eye I double checked it is indeed Screw #45 (999.067.008.00). Not very confidence inspiring finding this in the plug hole. I will remove the covers tomorrow and check.