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Very LOUD engine rattle/knocking

7590 Views 11 Replies 6 Participants Last post by  white220
Hope someone can help.
I have a 2.0 Zetec. Mileage 215,000.

Engine was hunting at idle, got my mate to put his diagnostic reader on it. It said there was a missfire on cylinder 3. Took plug out, plug was knackered. Carried out a compression test on all cyclinders and all looked good. Put new plug in and hunting stopped, all seems good.
Went for a drive next day and after approx. 120 miles loud knocking/rattling coming from engine. Made it home, car will start but knocking coming from top of engine. Suspected air inlet flaps had disintegrated so removed inlet manifold. All flaps still intact with bar although very badly worn so removed flaps and bar and refitted manifold. Started engine same noise. Removed rocker cover and turned engine. All cams/tappets seem to be working fine, chain tight and no links missing/broken. No noise with HT leads removed. Checked compressions and all high but cyclinder 3 slightly down.
Any help/idea's appreciated. :sad:
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what's the oil like?

i suspect it's going to be valve train associated, possibly a blocked up valve or the like that's getting hot and then pinking
Oil looked fine, clear, and level was up to the top mark. Only changed 3 days ago.

My mechanic mate suspects a dropped valve, but to see we'd have to take the head off.
If valve was dropped you would get very low.
is that tapping sound like you were hitting metal with hammer?
this could be spun rod bearings and piston is hitting head. :shocked:
Yes it does sound like that.

Do I need to drop the sump to check?
Compression test should have pointed that one out.

Take the plugs out & gets some long rods & a dial guage to measure the depth of the pistons, Turn the engine over by HAND and see if the pistons rise and fall at the same rate & same amount. If its serious you may notice the difference by eye.

If a bearing has failed you might get a slight pause at the top and bottom of each stroke due to the play in the bearing.
Broken ring on No 3. would be my guess. Broken near the end so slapping about possibly causing the piston to slap horribly.

Had a car years ago with a bad noise like that. Eventually wore through the piston and ended up in the cylinder (embedded itself in the piston and head). Possibly this has happened and stuffed the plug. The offending bit may have since gone out the exhaust or worse, could still be jumping around or embedded in the top of the piston and hitting the head with each rotation. One ring down (and probably damaged bore too) will drop your compression.

Ok thanks for the pointers.

I'll turn the engine by hand and check the travel of the pistons.

If I need to remove a piston to check the rings and cylinder bore, can this be done from under the car if I drop the sump?

Thanks in advance for your help
Checked piston travel - looks ok.
Dropped sump and found lots of metal fragments in bottom. Found big end caps on cylinders 2 and 3 loose ie. bolts tight but play on crankshaft. Found shells on no.3 completely disintegrated - fragments in sump bottom. Crankshaft looks ok, no sign of wear. Fitted new shells to all 4 bigends, cleaned thoroughly and new oil/filter.
Started up and engine running smooth.
Let engine warm up and after a short while knocking noise starts to return, although not as loud as before. Piston slap?
Back to the drawing board
Update 2
Dropped the sump again and found the cap on cylinder 3 piston again had play. Shell looks ok. Was wondering if the bolts had worked loose or the cap had a hairline crack (had used original bolts when renewing shells). Now looking for replacement cap and bolts (Fraud don't supply the caps - only engine block complete!).
you can buy engine components off independent engine builders, but the parts you're talking about will be expensive, i.e. more than the cost of a secondhand engine, as the cap you're talking about are mated to the con-rod they are attatched to.
the cap of every con-rod is different as the con-rod is made as one piece and they fracture them which leaves you with a "cap" seperate from the con-rod. maybe you put the wrong cap on the wrong con-rod, or put one of them the wrong way round. tbh for the cost of new con-rods you're better off getting a second-hand engine and replacing all of the cheap components (i.e. piston rings, bearings, valvestem oil seals, gaskets etc before fitting it tbh, or just take the chance that the second hand engine is good.
brand new pistons and rods just needs a new set of rings for £80 on ebay here
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