I’m wondering if I should do a compression test or not. The engine is running on my 1970 E. Bought in 2012, it was sitting in the garage until roadworthy in 2017, with the occassional startup/warmup. Doing nothing to the engine, just fixing car stuff that needed attention using as much of the old parts as possible. After the roadtest I put on about a little over 2000 miles, runs ok and I like driving it as it is, as a scruffy driver. (I‘ve no comparison to compare the engine against). Needs at least 3 qts oil/ 1000km, plus the oil needed for staining the parking lot. So other than recently doing the valve clearance nothing has been done to the engine. What if I find the compression to be way out of spec? Will I have to pull the engine? Can I still further drive the car wit
hout damaging the engine? Although its not important to myself, it is the original engine and I would like to keep it with the car. Will I bend it beyond repair if I keep using it without knowing if compression is good? Should I test it or not?
If that’s the only issue then no! You could burn out a valve maybe but if it’s running on all six and performs reasonably well why bother? Does it chuck loads of smoke out the exhaust? Again if not don’t worry.
Is the oil pressure good?
Is a quart in the US less than in England
If so,oil consumption is not too dire!
Martin,
I highly recommend that you perform a compression check of your engine.
Look at it like doing a blood pressure check or taking your temperature as
a measure of health. If you have a compression test gauge and a remote
starter switch it should only take you about 15-30 minutes to complete and
you will have some helpful data about your 4.2 L in line six cylinder
engine.
Make sure that the engine is properly warmed up, the throttle is wide
open, the spark plugs are all removed, and the fuel pump disabled. Then
apply some antisieze to the gage fitting before you test each cylinder.
When doing a compression check you are applying much less stress than when
you are actually running the engine. Depending upon the temperature,
altitude, and calibration of the gauge that you use the absolute values can
vary. What you are looking for is good even reading plus or minus about 10
percent of each other. More than that could indicate a possible valve or
ring problem. But more on that after you do this compression check.
In my opinion this is nothing to lose and knowledge to be gained by
doing a compression check. I encourage you to do one to learn more about
the condition of your engine. In fact I can’t think of a single reason why
you shouldn’t do a compression check.
Well frankly I don‘t want to have to do an engine out this year. I‘m hoping to put on about 5k km on it this summer so finding out that things are amiss just might spoil the fun. Actually the engine is running fine. It’s just, being to meetings in Bicester and Goodwood, all the other engines I hear seem to be quieter or so I think. It quieted down after valve adjusting, hardly doesn‘t smoke, is dry on top and drips from the bottom. Oil pressure is good and heat gauge always in normal. The exhaust does spew little black oily particles so when up to a wall (or the neighbors silver car) when starting leaves two distinquished areas of spit.
Thank you for your replies. Since no harm done, when I run across a compression measuring device I just might do the test. I‘ll post here the results here but not too soon. Thank you for the detailed instructions Paul.
If it runs well enough to keep you happy and you can deal with the puddles, keep on driving. I was less than thrilled with mine. When I checked it, I understood why. One cylinder was like 25 psi less than the rest, and they were pretty low also. You actually can do a fair amount with most of the engine in, changing bearings, timing components, head, even new rings. The main thing that will lead to catastrophic failure would be losing the timing chain or tensioner.
What you can’t easily do is fix your leaking rear main seal, or clutch work. That’s why led to me dropping the engine. Ultimately, it’s useful information to know, even if all it is, is a baseline for continued ownership.
Agreeing with Paul, I do a compression test every year on my 120 and keep a record. Get a compression gauge with a long hose and a quick-disconnect and a compression release button.
Much easier than trying to hold a cheap rubber ended gauge over the plug holes.
In case you are still pondering what to do, here are my 2ct: same moderate (20%) compression loss on #4 dry and wet would indicate a top issue (not a ring - though the oil consumption is high at 3//1000km… to put in perspective with what you know of the engine). The #4 plug is whiter, indicating a leaner condition (I understand you’ve checked that this cylinder is actually operating, spark not wet and getting warm like the exhaust when starting up) : I would perform a leak down test, the equipment is not much more expensive than the compression tester (though you need an air compressor), which would help locating where the leak is (which valve, possibly head gasket…). You may want to remove the cam covers to check if you notice anything (e.g. broken spring making the valve softer to push and sealing poorly - make sure the piston is at top dead center before pushing to avoid valve clash, and use wood or something soft to make sure you don’t risk scoring an operating surface).
I note that you indicate a valve adjustment (recently with respect to the compression issue?) : I would first double check carefully the valve gaps, esp. that of cyl #4. If the engine has run with zero gap chances are that a valve problem could have developed.
I would not embark on a long distance trip without knowing for sure what the problem is (might do so with a known worn engine behaving in a consistent and slowly evolving manner, using oil from wear but not broken ring, but not with a poorly sealing valve which may burn and drop, potentially destructing the head and piston to begin with).
thanks for your comments. I bought a used leak-down tester (Bosch). Hooked up to the compressor it has a slow leak of its own so I want to resolve that before hooking it up to the engine. Clearances were not totally out of whack, though we did have all the tappets out for adjusting. Maybe I‘ll open the cam cover and check #4 springs, after a wednesday appointment for measuring and adjusting the front suspension. I‘ll post here once I know more. Today near freezing temps, (but no rain!) took the open E out. My youngest son recently got his driver license was his first time driving the E. Great fun.
pretty dull weather here (even snowing, which usually turns the traffic to total chaos) so I’m sitting in front of my screen rather than being in the workshop doing real stuff… I’m sure you know that a leak down tester normally has a built in “leak”, in that some air goes to the cylinder under test through a calibrated small hole, and the comparison between that known leak and the cylinder under test (which leaks mostly via its rings if valves close properly) is what leads to the diagnosis. Then if the engine leak is larger than normal, one needs to listen where this extra air is escaping to (radiator, bottom, intake …) rather straightforward to figure out when there is a problem.
Congratulations on your son’s license, mine don’t even want to pass it, to my great dismay…
