Hi all.
Recently get a 65 Mk2 with some restoration looks like a partial frame off spray and leather redone.
when buying it, i did a fast dry-cold compressiontest, to found all cy at 115-120 psi although with Cylinder 1 slow pressure build up.
I tried some old way to pour some Marvel Mystery in each cylinder, and let it soak for a whole night, then did a second wet-cold test, found all cylinder at 155-165 psi. And the cylinder1 issue is gone.
Then i ran the engine for a couple min to burn the oil away, and did a third test, find all cylinder at 150-155 psi range.
So I would assume i have a 8:1 ratio XK engine with every good engine health right?
Or it is possible a rebuild engine at some time point, but the previous driver only drive it for every short distance(under 1 mi), which all the ring clogged up and sticky. And MMO free them up and now they are back to full health?
All test did with Throttle NOT open, cuz i only have one person.

 

the compression ratio is stamped at the front inner valley wall of the cylinder head. ("valley" is where the spark plugs are).

 

Those are excellent compression numbers, I'd say you have a healthy engine.

 

The engine number is stamped there which will guide you. See last digit. i.e. 9 to 1 in this case.

 

Found mine end with a -9. Guess my engine is still loosing some health.

 

9:1 compression, just like mine, a California Black Plate engine.

 

Auriga
Compression test results like this on a relatively cold 9:1 engine with the throttle closed are very good.
I think that with some more time running, a warm engine and throttle open you should see about 160.
Don't fret. You have a good engine

 

Bill/Auriga ~ It seems this engine might still be running in. With modern lubricants this can take forever. Suggest you run-in/break-in with a Monograde of Max SF quality. You might have to go to diesel oils to achieve that (MAX SF). SAE 30 or 40 is fine. SAE 40 in hot countries.

Ignore Jaguar's run in procedure. It is no longer valid. After the first 300Km's give the car bursts at full throttle. Always watch the temperature gauge. If it rises unduly back of the throttle as the engine is still a little tight. At all costs avoid constant throttle running. You need to back off frequently to draw oil into the ring belt. You can use higher revs than Jaguar suggest.

In plain English don't be too gentle with the engine in it's early mileage or you will have an oil burner for life. (Cylinder bore glazing or polishing ~ Two different Mechanisms). Lubricants have come a long way since the XK engine was designed.

 

I agree with Bill Mac. Before I rebuilt my engine I had compression results with 8:1 piston around the 115 mark with the highest at 120. I rebuilt my engine with 9:1 pistons and I now have compression results of 165 across the board but that is on a brand new rebored engine with new pistons and rings and all the valves renewed and recut.. For an older engine your compression ratios are spot on and I would not touch the engine other than giving a good run out to blow away the cobwebs.

 

Thanks.
The previous owner have it for 1 year, only park it in the parking lot for showing purpose. Before that, i have zero idea. But the whole car been spray in some blue paint, including jthe enginebay and trunk and almost everything. So I was assuming the engine is been rebuild at some time point. But the previous 1 year of only move in the parking lot clogged the rings which i only read number of 120 in a 9:1 engine. Now they are been freed up and looks good on the paper.
And yes Im using 15w-40 diesel oil in the car now. With some ZDDP additive. Im in TX.

 

Use that oil for a few thousand miles to run in/break in then you can move to top Synthetics ~ Don't use higher than SF at first. You don't need the ZDDP additive unless you are using a 15W-40 (where the restrictions lie). All other grades have been reformulated not to need ZDDP. There are other additives that can do a better job in top synthetics. Even the base oil plays a part.

Don't use diesel oils once the engine has properly bedded in. Their formulation is wrong for cam & tappet wear etc. Their HTHS (high temperature high shear) is not good because they are rev limited by the diesel combustion process. Other than the low revs of diesel engines their oils are not designed to handle low temperature sludge as in gasoline engines.

 

As Glyn says "run in" procedures are quite different from Jaguars 60 year old advice.
When we are running in an aircraft piston engine we give it a good workout .
The first couple of hours are done in a ground test rig and after installation in the aircraft the engine is worked as hard as possible within manufacturers max performance tolerances.
Failure to do this can result in glazed bores. I have seen this on a number of occasions where the owner has "babied" a new engine.
This results in rings not bedded in with loss of compression on a leak down check and excessive oil consumption.
I suggest you follow Glyn's advice

 

Thank you for the support Bill. I have so much trouble explaining this to club members. The guys that listen have more powerful engines that don't use oil. The sticklers for the past always drive in with a light blue haze of burning oil behind their cars.

The ZDDP restriction on 15W-40's is sacrificing your engine to extend Cat life on the modern car. Why people like Mercedes use synthetic 5W-40s in their approval programme. You hear the cry "it's too thin". They forget that it is an SAE 40 at operating temperature and very high VI.

You also hear the cry you must use 20W-50's. That treacle was produced for Alec Issigoni's combined engine/gearbox creations. The VI Improver was junk in those oils & very soon sheared to a SAE 30 with the gearbox chopping up all the polymer.

If you have a worn engine you can stick any old thick crap in it. You are just delaying the inevitable. ~ an engine rebuild.