spegru
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| posted on 13/10/25 at 10:46 AM |
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Zetec Compression Problems
A little while ago our Dutton Phaeton fitted with a 2 litre zetec black top (running fine up to that point) was driving up the A12 dual carriage way
when alot of smoke was noticed.
Pulled over, bonnet up, and there's a huge oily smoky blow coming out of the cam cover breather. It also smelt terrible. After that it would not
start.
No obvious sign of over heating but it was def low on coolant. Not really sure what happened
Back to base and checked compression - which is bad: 100, 20, 20, 20 psi Cyls 1-4. Note: not using a screw in tester as I dont have the right thread,
so it's only a push in type and so there could have been a little leakage.
Inspected the bores with a camera probe thing and it didnt look awful, although there was what I'd describe as a dark stripe on the side of the
cylinders
This weekend we had it out of the car and dismantled No 4 cylinder/piston
Yes the dark stripe is visible to the eye but undetectable to the finger nail. No scoring or lip can be felt on the bore.
Removed piston rings to check gap when inserted to the cylinder: Top ring gap is 0.53mm. 2nd ring is 1.18mm. No apparent difference further down the
bore.
I'm going this by hand as I cant get the oil ring off the piston so as to push the rings down squarely but it looks straight
Also inspected main and big end bearings. No copper or scratches visible but feel oil there feels very slightly grainy (for want of a better word). I
suppose this is roasted oil.
Questions:
1. Is this ring gap enough of a problem to explain the poor compression?
2. Assuming overheating has almost caused a seize - what other damage should I look for?
Thanks Spegru
Check out Invader Garage on Youtube
https://www.youtube.com/channel/UC3C55qk-tbKc0WjmxGqFoXg
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JAG
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| posted on 13/10/25 at 02:32 PM |
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Based only on the results you shared - it looks like 2,3 & 4 (20psi??!!) are FUBAR.
Even No 1 cylinder is low at 100psi.
I'd expect over 120 and nearer 170 but that depends upon the spec' of your engine.
First thing I'd do; go and buy a proper, screw-in, compression test and read up how to use it. THEN repeat this test.
Justin
Who is this super hero? Sarge? ...No.
Rosemary, the telephone operator? ...No.
Penry, the mild-mannered janitor? ...Could be!
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obfripper
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| posted on 13/10/25 at 04:21 PM |
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That looks too much loss for just rings, from the size of your losses I would expect either for it to be valve train related or cracked pistons (which
i would have thought would be totally visible across the three low pistons and quite unlikely).
I would expect to lose 2-3bar for overheated rings that have lost their tension, i have seen a few engines with the rings stuck in the grooves that
still had sufficient compression to run okay but burn oil at a stratospheric rate.
I had cold compressions issues with mine in the spring, was due to inlet valve seating face recession which is a bit of a strange thing to get,
however I also had quite significant valve guide wear on the exhaust side when I stripped the head so ended up replacing all the guides with bronze
instead of the cast iron original type, as well as replacing all the inlet valves.
The head was ported and rebuilt in 2014 (approx 25k miles ago), the cast iron type don't seem to wear well at all as the original ford ones were
replaced then for the same reason, I didn't expect them to wear out so soon again.
At this point when the head was rebuilt, I did replace the short block for the bores being polished smooth causing excessive oil consumption, this
type of wear didn't affect the compression though (at the time I could get a new short block for less than a set of pistons, probably not an
option now).
I would definitely check the valve clearances first if you've pulled the head complete with cams (valve/seat wear will close up the tappet
clearances) , then pop off the cams, tappets and springs and check the valves/guides/seats for wear and sealing pattern with engineers blue, i suspect
you may have exhaust guide wear and oval wear on the valve seat combining to give a significant loss of compression.
Dave
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spegru
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| posted on 13/10/25 at 05:48 PM |
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Thanks both.
Yes that seems alot of loss just for worn rings.
The cams had to be removed in order to get at the head bolts. We did also experimentally fill the chambers with white spirit to test for leaks -
which they did although it was not pouring out. I suppose cams being out for that test is no issue since the springs were still there. So yes we shall
have to examine those further.
I did also think that Cyl1 was a bit low but it was also cold.
The compression tester problem is a bit of an issue the kit I have has the correct thread but it appears to be too short to screw in. What do you guys
use?
I am also worried about valve seats and indeed head/block flatness. What would expect for that?
That slightly grainy oil is a bit of a concern but not sure how serious that is
Any more comments please?
spegru
Check out Invader Garage on Youtube
https://www.youtube.com/channel/UC3C55qk-tbKc0WjmxGqFoXg
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obfripper
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| posted on 13/10/25 at 09:53 PM |
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I welded the lower portion of an old m12x1.25 spark plug (flat bottomed, with same thread length as zetec) to a threaded section that would screw to
the compression tester, removed the metal seal and replaced with a rubber o-ring. Just make sure you can get a socket onto the made up adaptor as they
usually end up staying in the head when you unscrew the tester.
It does drop the measured pressure slightly as the 1-way valve is slightly further from the head, but for comparison purposes is fine.
I think that you can buy an adaptor from sealey or laser that should do the same sort of job, for whatever reason the zetec threads start about 8mm
from the top of the plug bore, so any adaptor needs to be at least 4-5 threads longer than this depth.
I would expect the valves to have held white spirit if OK, I usually use brake cleaner (which is alot thinner) for this after lapping valves, and
usually is fine if I've done a good job.
It's definitely worth checking the valves for radial play with a dial gauge or just by feel with the valve at about 8mm lift - the inlet guides
are unlikely to be worn, the exhaust guides will feel the same if they are in good condition, but will wobble more than the inlets if the guides are
worn and may show more wobble in the left/right axis than the front/rear axis. Generally if you can feel obvious movement it will have fairly
significant wear.
The official clearance values are 0.017-0.064mm, but you need plug gauges and a micrometer to calculate the clearances, or some trigonometry to
convert radial movement at the valve head to a clearance value (it is quite difficult to be very accurate this way, but may show if things are in the
right area or not).
To check the seat without engineers blue, clean the seat faces and then apply some sharpie type marker pen to the seat face, then just bounce the
valve into the seat a couple times, this will knock off the ink where the contact is good and leave it where there is no/poor contact. Can also be
done by pressing the valve head towards the seat and twisting the head slightly each way, again will displace the ink where there is good contact.
The head should have a maximum distortion of 0.1mm in any direction, the block should be 0.05mm. A good quality straight edge will help here, as you
don't want to chase faults that don't really exist.
Without physically seeing the bearings I'm not too sure what you have going on there, does it feel like a residue/deposit that would clear off
with a cloth, or is it the actual surface of the bearing you can feel? There will be a degree of texture to a babbit coated shell bearing to give it
the ability to hold oil and be lubricated before the oil pressure has built up, this can also hold contaminants in the same way.
Any contamination should clean up with some brake cleaner and compressed air leaving the shell bearings ready to be lubed and refitted.
Dave
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spegru
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| posted on 14/10/25 at 07:52 AM |
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thanks for all that detail Dave.
I can see that I will need to obtain a valve spring compressor. I may have one but that was last used on a Mini A Series head so I doubt that's
any use.
I cant run a compression test at all at the moment of course as the engine is all in bits
The bearing shells themselves look fine on the one cylinder I've examined so far. The grainyness I was talking about was in the actual oil -
which stinks.
I may also have to get some plastiguage or similar to see what the clearances are - or maybe I should just get some new shells anyway. The journals
look absolutely fine.
Wow it's about 25yrs since I did any valve lapping!
thanks again
Steve (aka spegru)
[Edited on 14/10/25 by spegru]
Check out Invader Garage on Youtube
https://www.youtube.com/channel/UC3C55qk-tbKc0WjmxGqFoXg
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