big_wasa
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| posted on 6/2/05 at 07:32 PM |
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Engine experts Please?
Was well pleased with my zetec ,and the strip and inspection was going well untill it came to Number 1 piston(see photo)
the bore is not to bad but what will have caused this pitting and what are my choices/options?
I have seen this on 2 strokes but not on a 4 stroke?Your advise one and all please.
 
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mookaloid
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| posted on 6/2/05 at 07:46 PM |
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are there any corresponding marks on the head?
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andylancaster3000
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| posted on 6/2/05 at 07:59 PM |
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From the picture it looks as though it breathed a solid in bashed it about a bit then chucked it out, if this is the case you'll never find out
exactly what it was for obvious reasons!!
I would doubt that it is damaged caused by detonation/preignition as i would imagine it would have happened to the other three too.
Andy
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gazza285
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| posted on 6/2/05 at 08:06 PM |
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Looks like pre-ignition to me. Could be causes by the ignition system running advanced until the knock senser retards the spark a bit, hence why
it's only on cylinder one. That sounded good didn't it? Or a dodgy injector/cable causing that cylinder to run weak.
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big_wasa
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| posted on 6/2/05 at 08:21 PM |
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The head has the smallist of nicks in it so would doubt the ingress of metalic items as I have found in the past it will mark head and piston as it
plays ping-pong.
So whats my options ? Do I rebuild (sounds expensive £350-£600 on burtons website for the pistons £150 ish worth of machining .So it could be easyer
to scrap it and buy another motor? Have given it a polish the skirts and rings are ok so if I put it back together whats the reliability going to be
like?
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big_wasa
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| posted on 6/2/05 at 08:30 PM |
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forgot to mention will be changing induction to bike carbs the ignition to megajolt and the exhaust aswell so if it is pinking that should stop.
But will the motor last?
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rusty nuts
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| posted on 6/2/05 at 08:49 PM |
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Could have been caused by a broken plug? looks like some sort of debris has been inside cylinder.
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britishtrident
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| posted on 6/2/05 at 09:16 PM |
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I have seen very similar damage on a Lotus Twincam cause by the screw on termminal bullet of old type spark plugs dropped down the plug hole.
[Edited on 6/2/05 by britishtrident]
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zetec
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| posted on 6/2/05 at 09:33 PM |
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Go and find another engine. For the cost of a gasket set and a few parts you should be able to pick up a good runner. I normally go to the bigger
salvage yards as they have crashed damaged cars which you can hear running. I wouldn't even bother striping down, fit it and try it, if
it's duff take it back (unlikely) it it's good thrash the living daylights out of it!
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NS Dev
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| posted on 6/2/05 at 09:38 PM |
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I would say detonation, but without looking myself it's difficult to say precisely. Are the holes really "angular" like grains of
salt or are they like "pits" in the surface.
If they are more pitted than anglar then almost certainly detonation. Also, if it were debris in the cylinder, it would usually be more uniform across
the piston face, not in two small areas. Also the head would have corresponding damage in the same areas, as the debris must have bounced off it to
hit the piston again!
If the head looks ok, and the bore is ok, you don't mind wasting a head gasket set then I would be tempted to tidy up the worst of the damage to
the piston and stick it back together and try it! it'll certainly get you going as long as the bore is ok and the piston ring area is intact.
A complete "new" engine would be the real answer, cheaper then messing about with that one if you weren't happy running it as it is.
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omega 24 v6
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| posted on 6/2/05 at 09:41 PM |
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Have seen similar to this on a diesel pug. It looks from your photos as though something solid has been in there however why is the marking confined
to the 2 areas shown. Both areas are next to the water jacket holes is this just co-incident. Check for a crack in the bores in this area. Also look
at the head gasket and head face. The prob one the pug i seen was a crack in the liner 1 inch long letting water into the bore. Sorry if this is a bit
long winded.
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jollygreengiant
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| posted on 6/2/05 at 09:59 PM |
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It is NOT foreign object ingress (too localised ). That leaves ignition/heat related. Proximity to water jacket could be a factor in conjuntion with
AN injector fault (or wiring to AN injector), would neeed to see head gasket AND sparkplug to make a definative answer.
Enjoy.
Beware of the Goldfish in the tulip mines. The ONLY defence against them is smoking peanut butter sandwiches.
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Mark Allanson
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| posted on 6/2/05 at 10:09 PM |
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I think the fact that No1 is steam cleaned and No2 is fully carbon blacked is a bit of a give away, and the damaged areas are at 180° and adjacent to
the water galleries.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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big_wasa
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| posted on 6/2/05 at 10:29 PM |
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Number 1 piston was the first I cleaned,it did look like the others. the piston is just sat in the block and not conected.And the damage should be
side to side not front to back.It is in the same place as the flat spots on the head with the worst damage being on the inlet side.
Head gasket and block looks fine(looks more scored in photo than in the flesh?
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big_wasa
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| posted on 6/2/05 at 10:31 PM |
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pic
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kaymar
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| posted on 6/2/05 at 10:45 PM |
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could this not be from a previous cam belt failure?
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big_wasa
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| posted on 6/2/05 at 10:56 PM |
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I had wondered about that .But not in my opinion .As the valves would hit the piston about 5-10 mm in from the damaged area.But its not far from the
lowest point of the open valves
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Mark Allanson
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| posted on 6/2/05 at 10:59 PM |
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Cam belt would possibly cause damage to No4 as well
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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big_wasa
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| posted on 6/2/05 at 11:03 PM |
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Would pre ignition not happen nearer the center of the piston in one place?not at the most opossite sides of the crown?
The carbon deposites where about the same as the other pistons and actually covered the damage sujesting that this had happened earlier in the engines
life?
If I take the valves out would a foreign body have damaged the head/seat.
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DEAN C.
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| posted on 6/2/05 at 11:36 PM |
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Having stripped quite a few engines I think Mark Allanson is closest.
The piston was obviously steamed or had been running hotter than the others.
I would ted to think this is more likely due to head gasket failure and the damage could be on either side because it is nearest to the valves as the
combustion process flows in and out.
Other options are water ingress due to cracks ,not always the easiest things to see.
If the pistons are ok down the sides and in the ring areas then a bit of pitting on the top is not too critical,but i'd definately get the head
pressure tested and skimmed.
Once I've finished a project why do I start another?
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DEAN C.
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| posted on 6/2/05 at 11:45 PM |
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After looking at the photos again I think the engine has definately been run hot and if you look at the head photo doesn't the head gasket look
to have been leaking from the waterway on left of the photo,it's hard to tell in pictures but there also seems to be far too much carbon and
staining all over the head and block,if I was asked for an opinion professionally I would say it has been run low on water or very hot for a while.
Once I've finished a project why do I start another?
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bob
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| posted on 7/2/05 at 12:13 AM |
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my 1600 zetec escort leaked water into number 1 ,i was told by the mechanic who fixed it that it was an inherant prob on the zetecs something to do
with a plug between the water way leaking.
If that sheds any light on it.
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locogeoff
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| posted on 7/2/05 at 01:32 AM |
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I have a piston in my BSA Bantam that looks a lot like that, I physically pinged a bit of a broken ring out of the crown. However the damage was far
more widespread around the edge of the crown not localised as in your photo.
Geoff
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britishtrident
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| posted on 7/2/05 at 08:15 AM |
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Detonation damage piston generally faill in the centre of the piston, while heat damage piston either suffer crown failure through burning or edge
burn damage from the piston rings seizing --- this is neither. Water damaged pistons (due to water not being compressable) generally crack
across the centre in line with the gudgeon pins.
Foreign object damage like this is very comon on engines with deeply recessed plugs.
Also look closely at the pictures the piston is not aligned in its normal working orientation -- the damage is exactly in line with 9 o'clock
and 3 o'clock positions when viewed from the front or rear of the block --- this is exactly in line with the very small squish area of the
combustion chamber -- exactly here foreign object damage occurs, the head damge is consistant with this.
[Edited on 7/2/05 by britishtrident]
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NS Dev
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| posted on 7/2/05 at 08:47 AM |
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Detonation can be anywhere on the piston, it depends on the quench characteristics of the engine!!!!!!!!!
On the Zetec, as was said, the damage is lined up with the flats (quench bits) at the sides of the chamber.
If it was foreign object, it would have done exactly the same to the head in the same area, which it hasn't!
I would say heat/detonation, both will do the same anyway, it's chicken and egg with these anyway, until the heat seizes the piston in the bore,
which again hasn't happened. (unless there are pick-up marks on the piston)
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