Low compression on cylinders 1 and 2

[StephenT]

Hello, I am trying to resurrect an S2 that has been sitting since 1976. I have gone through the breaks and am now working on getting the engine running. I have rebuilt the fuel pump and the webers. (When I first got the car I put a little oil in the cylinders and rotated the crank by hand. I then filled the carb bowls with fuel and got the engine to fire. This is all I did at that time.) Now with the carbs done it is time to get the engine running properly. My first attempt was a success, sort of. The engine started easily but was a little ruff, actually running only on cylinders 3 and 4. Initially I thought that the carburetor for the first two cylinders was not working. I pulled the plugs and they were wet with fuel, I then checked the compression. Cylinders 1 and 2 are at 70 pounds and cylinders 3 are 4 are at 165 pounds. I have been told by a couple of people that it is not unusual for an engine that has been sitting for a long time to have low compression and after running a while MAY recover. I would like to get some feedback from the group on how best to try an accomplish this miracle. At this point in time the car is not drivable. The oil pressure and water temperature gauges are working so I can monitor these functions.

Thanks for reading this and all suggestions are appreciated.

Steve

[mbell]

Just to confirm, you did have the throttle full open when doing the compression test?

If not compression values could be effected by unbalanced carbs, limiting air flow to cylinders 1 & 2.

[StephenT]

I did not. I will repeat the test and report back.

Thanks for the advice.

Steve

[Ianashdown]

Where in SoCal are you?

Have you looked in the cylinders with a scope? It should run, albeit roughly, with these compression values.

Are the valves moving freely. If it sat with some of the valves open there will likely be corrosion on the seat and that will not give good values.

Ian

[StephenT]

I have not looked into the cylinders don’t have a scope but will see what I can come up with. I haven’t pulled the valve cover off yet, hopefully I will have an opportunity tomorrow to look into this further. What should I be able to learn by removing the valve cover and rotating the engine by hand?

I am located in Temecula.

Thanks,
Steve

[StressCraxx]

On compression checks:
Preferably done with engine warm.
Throttle wide open, make sure both butterflies on the #1 carb are fully open.
Good battery.

If results still the same, check with a piece rubber hose up to your ear and the other end in #2 spark plug hole while you check compression on #1. If you hear a brief SSS noise in the hose when cranking, it may be a head gasket leak between #1 & 2.
It's possible the rings are stuck to the piston grooves. Put some Marvel Mystery Oil down the spark plug holes, rotate the engine, leave it overnight and try again the following day.

[StephenT]

Thanks for the suggestions. I will try them.

I have a question about low compression. How much compression is needed for the cylinder to fire? It seems to me that even with the low compression, with fuel and spark there would be some ignition. But with engine running, when I pull the spark plug wire on cylinders 1 or 2 there is no change in rpm.


Steve

[alan.barker]

Imho Stephen,
testing to see if all the cylinders are the same it doesn't matter if throttle open or closed.
The problem here is 1 and 2 are much lower than 3 and 4.
70 psi is no good at all.
I suggest you remove the Head because leak could be between 1 and 2 Gasket leaking.
I would also if no dameged Gasket remove the Valves and check Seats.
If lots of carbon on top all all Pistons, Rings could be suspect, so deglaze cylinders and fit set of new Rings.
Good luck and have fun
Alan

[rgh0]

Once you confirm the compression test results as discussed and if you still have low compression on I would then do a leakdown test to try to confirm the source of the compression loss and what could be done about it before stripping the engine.

cheers
Rohan

[Roland]

One thing to take care of with compression tests is the gauge you are using.

On my last compression test I decided to replace my ancient Gunson gauge. So got my nice new compression tester out of the box and all my cylinders were 40 psi down compared to the old Gunson. I didn't have a simple means of testing or checking the gauge calibration so I bought another brand of new gauge, this agreed with my old Gunson.

R

[alan.barker]

It depends on how well equiped your workshop is.
Alan

[2cams70]

Squirt some engine oil in 1 and 2 and try again. Compression still low it's likely the valves or head gasket are at fault. Compression improves significantly it's likely piston and rings at fault.

[StephenT]

Ok had some time to spend with the Elan today. First let me say thanks to everyone that responded with suggestions, I tried most of them. The first thing I did was put about 30cc’s of motor oil into cylinders 1 and 2. I rechecked the compression and it jumped up from around 70psi to about 100psi. So I’m guessing it’s the rings and I’ll be pulling the engine apart soon. I also tried the hose to my ear trick to see if I can hear any leaking from one cylinder to the other, I did not. So I decided to try the Marvel Mystery Oil. I had several errands to run and so it was a few hours before I made it back home with the oil. Before adding the mystery oil I thought I would try the compression test one more time with the carb butterfly open. This time I got 175psi on cylinders 1 and 2. I have to imagine that the oil I dumped into the cylinders this morning loosened things up. I fired the engine up and it was defiantly firing on all four cylinders.

One thing I noticed is with the engine running I get a greater drop in rpm’s whim I would pull the number 1 or 4 plug wires, about a 500 rpm reduction. When I pulled number 2 or 3 plug wires I would only get about a 200 rpm reduction. This was with the engine idling at around 1000rpm.

Thanks,
Steve

[StressCraxx]

One thing I noticed is with the engine running I get a greater drop in rpm’s whim I would pull the number 1 or 4 plug wires, about a 500 rpm reduction. When I pulled number 2 or 3 plug wires I would only get about a 200 rpm reduction. This was with the engine idling at around 1000rpm.

Thanks,
Steve

Sounds like great progress!
Try adding Marvel Mystery Oil to #3&4 and try again, perhaps they are also slightly sticking.
Another thought -
RPM drop difference is possibly the carbs are slightly out of sync.

[StephenT]

I’ll try the oil in cylinders 2 and 3.

I recently went through the carbs and had just mounted them when I discovered the issues with the compression. I know the carbs need to be set up. Any advice here would be greatly appreciated.

I ended today on an up note. We’ll see what tomorrow brings.

Thanks,
Steve