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Cylinder bore damage

 
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Thu Jun 03, 2010 10:33 pm    Post subject: Cylinder bore damage Reply with quote

Hi all,

Last month i've stripped down a 1.3 engine with 140 000 kms on it. The engine was running satisfactorily before the teardown. Upon careful inspection of all the parts, I found a deep straight scratch in cylinder #1 cylinder bore, 3mm wide. Just like if some grit got trapped between the piston rings and scratched the bore all the way. It's not very deep but honing the bore will not be sufficient to make it disappear.
There is no apparent damage to the piston, the rings, or the rest of the engine. Maintenance seems to have been regularly performed, oil and coolant were clean, no bearing or tappet wear.
Ever seen such a disaster? Any ideas what might have caused it?

Regards,
zp
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gritsop
Green Cloverleaf


Joined: 23 Apr 2003
Posts: 766
Location: Ekali, Athens - Greece

PostPosted: Thu Jun 03, 2010 11:43 pm    Post subject: Reply with quote

HI ZP,

Only thing I can think of is the motor being left unused for a long time. Oil had turned to solid and a piston ring was frozen hence the scratch on the bore.

Regards,
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Thanassis Gritsopoulos
1991 Alfa 33 1.4 IE
2001 Alfa 147 1.6 Distinctive

http://www.alfa-restoration.co.uk
Parts Shop: www.alfa-restoration.co.uk/shop
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tvatavuk
Gold Cloverleaf


Joined: 13 Mar 2003
Posts: 673
Location: Split, Croatia

PostPosted: Fri Jun 04, 2010 8:28 am    Post subject: Reply with quote

Hi,
If any of piston rings were stuck long enough to scratch cylinder bore so much that could be seen on rings as big flat spot.

Maybe some dirt or debris from spark plug failure/change entered cylinder.
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Tino Vatavuk
Little black dress which replaced Alfa Romeo 33 S 16v Permanent 4 GMo
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RFlower
Alfa 33


Joined: 17 Feb 2004
Posts: 432
Location: S of France

PostPosted: Fri Jun 04, 2010 10:43 am    Post subject: Reply with quote

Did you match up the scratch alignment with the piston you removed from that bore?
It would be unusual for the piston to be unmarked.
Is it posible it was caused by the gudgeon pin/piston pin?
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)
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ZeNiTh-PbArM
Alfa 33


Joined: 14 Mar 2003
Posts: 388
Location: Paris, France

PostPosted: Sat Jun 05, 2010 10:55 am    Post subject: Reply with quote

Hi,

Thanks for the replies, I carefully checked piston and rings and no apparent damage is visible. I tried to take photographs of the scratch but it's very difficult to take a proper picture due to all the light reflections inside the bore.
Since the scratch stops a few mm before the top of the cylinder, I would suspect the rings more than the pistons. Would it be possible that the sharp edge of the ring could cause the scratch?

regards,
zp
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RFlower
Alfa 33


Joined: 17 Feb 2004
Posts: 432
Location: S of France

PostPosted: Sat Jun 05, 2010 11:42 am    Post subject: Reply with quote

I have seen such damage from broken rings, but the cause was obvious, I assume you have removed the rings to make sure they have no damage and no buildup of deposits behind them.

Last year I had a 3mm brass nut and spring washer (from the filter assembly) inside my boat's diesel engine. There was damage to the piston crowns and valves but none to the bores, although that could be just lucky.
Both items stayed in (different) cylinders for several revolutions before they went out of the exhaust. They were gone before I got the engine stopped, but left clear prints on the pistons, so are there any marks on the piston crowns?

Do you have any record of previous work? It could be possible the cylinder was damaged previously, and someone just replaced the rings as a cheap fix. If you can't find anything at all wrong, this would be my best guess. A lot can happen in 140,000 km. My Imola's camshafts and several tappets were destroyed after 130,000, for no obvious reason.

It may be that some small foreign body found its way into the cylinder, lodged above the top ring, and is now long gone.
Possibilities:
Engine was run with the filter removed.
Something dropped into the filter housing when the filter was being changed.
Something got inside auxiliary piping connected to the inlet - are any of the pipes broken or damaged?
Are there any hard carbon deposits on the valves which could have detatched and gone in? - this would only happen if the engine was burning oil or running very rich.
Have you examined the plugs closely?
I once had a plug insulator disintegrate due to overheating, I had temporarily fitted a regular plug instead of a high performance one. I suggest you look closely at the plugs and their insulators.
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Dick Flower, Nr. Carcassonne. '94 Trofeo 1.4 ie (F), '93 Imola 1.3/1.4 ie (now for breaking) (F), '91 1.7 ie (GB)(spare car), '86 Sprint 1.5 QV (F). '87 VW Syncro camper (F), '73 NSU Ro80 (F), '99 Fiat Seicento (F)
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