Race Engine Forum UK

Hi !
Dear Guy , it's been a while since my last posting here , do hope you're well .

As always , please , need your help/assistance with this one :

I'm trying to help one of our forum members fixing and diagnosing engine issues .. well , diagnosing the most (hes already decided to skip fixing this engine , which is good choice , and fitting a used one instead ..)

The car/engine is : Peugeot 205 GTi with 1.9 8v engine (XU9JA D6B , compression ration 9.8 , Bosch LE Jetronic engine management with mechanical ignition i.e. distributor ..) .. the engine is standard , so no modifications .

Complains where that one day , during the motorway run , upon accelerating harder "something went inside the engine" , couped with loads of white smoke from exhaust and oil leaking everywhere around the engine (from the head to block base joint , head gasket area ..)
He reported that afterwards there was - no coolant loss , coolant and oil temp. was normal and oil pressure normal.
Engine running history - said that it was good , apart from using smaller amounts of oil , that the spark plugs where oily and particularly spark plug from 4-th cylinder (2 Bar compression) which had a thick oily carbon deposit .

So i suggested compression and leak test , compression test done with the results as follows :

Cylinder
No.1 - 11 Bar
No.2 - 12 Bar
No.3 - 10 Bar
No.4 - 2 Bar

They removed the head and found this :






(sorry , i do not have better pictures than this ones !)

Melted piston crown on cylinder No.4 .

My assumptions why did this piston melt are : uncontrolled combustion - excessive heat (because it's molten off the edge areas towards the center ..) , or lean mixture on this cylinder because partially blocked fuel injector , wrong/few grade hotter spark plug , leaky inlet manifold gasket (which caused this cylinder to go lean) , cracked head or liner (cylinder lubrication diluted by coolant ..) , some kind of valve/valve seat problem .

I do insist on chasing the cause of this problem because all the engine management fueling and ignition components from this blown engine will be reused on the "new" one , and if it's a bad injector or something fueling/ignition wise it can damage this the new second hand engine as well , so i recommended :
1 Injectors testing (marking this injector from the affected cylinder especially) on ultrasonic machine - resistance measuring first , then leak/pressure test , then spray pattern/volume test ... then cleaning .
2 Spark plug inspection - in case if they've had by any chance a few grade hotter spark plug on this cylinder .
3 Head inspection - combustion chamber for discoloration , valves/valve seats for improper sealing , cracks .
4 Inlet manifold - gasket inspection .

What might happened with this causing piston crown melting ?

Thanks !

Kind regards
Damir

Well, it's definitely chronic detonation.

G

Hi !

Ok. , so can it be lean air/fuel mixture (on this particular cylinder) causing this to happened ?

Also , what do we mean by "chronic detonation" ?! is this the same thing as usual detonation ? because he hasn't heard engine knocking/pinking .

Thanks !

Regards
Damir

OK - I have read your comments Damir, I think this was a detonation event occuring over some period of time. Extreme detonation will hole the piston or burst the gasket, here the excessive pressure and temperature has eroded the piston crown and sides.

If it was pre-ignition caused by something like a failed head gasket causing leakage between 3 and 4 cylinders and erratic firing, or a way-too-hot plug in cyl 4, yes he would definitely have heard the pinking/pinging.

Unless the problem has been caused by exhaust valves not seating it is possible that an injector fault on cyl 4 could have caused this, you need to get them flow tested. I would not care to guess what else has caused it at this time, do that first.

G

Hi

Understood Guy , thanks for info !

Will report back when/if they let me know what went wrong with this ... would investigate myself but it's not my engine , nor i have access to it .

All the best
Damir

It may not be the cause of your problem but I was talking to someone today who had the same end result - melted piston - caused by fuel surge in the tank when level was low. I suggested a fuel swirl pot might be the solution.

If you are not familiar with them do a quick 'Google' search.

GC