Is 200 Piston Replacement

blackbus · May 16, 2011

Hi all, some months ago my IS 200 engine stripped teeth on the timing belt and there was valve contact, my fault for not changing sooner. Ive just removed the cylinder head and found a snapped exhaust valve. An engineering shop say they can fix any damage to the head but unfortunately the sharp end of the broken valve stem has punched a 3mm deep dent in the crown of no4 piston. The engineering shop say this piston crown will have to be replaced. My question - is it possible to remove the sump on a 200 while the engine is in the car in order to remove the piston from below. I have done this on cars before to change rings etc. Any help would be appreciated.

egg · May 17, 2011

is there a hole in the piston or just a dent ? ive done hundreds of cars that have snapped belts and bent all 16 valves which have then all dented a nice valve edge mark in each piston but have never ever had to change a piston . its suprising how thick the piston material is . have you got a picture ?

blackbus · May 17, 2011

thanks for your reply, i will take pics tomorrow but unfortunately its not a valve edge dent on this one, its 5mm diameter and looks like a hole but its not right through and about 3mm deep caused by a broken exhaust valve stem. The engineering works say there will be sress fractures on the piston crown and if i dont replace it, it will probably burn through into a hole.

The aluminium is slightly raised around the dent so there must have been some force involved. I have just tonight removed all 12 exhaust valves and each one is slightly bent as i expected as slight contact marks are visible on all of the exhaust valves and piston crowns, only one valve broke. the inlets appear ok at the moment. I just need to know if i can get the piston out by removing the sump on this car.

Thanks again

blackbus · May 18, 2011

As promised a pic of the damage to the piston, top centre. I still dont know if i can get the piston out by removing the sump. Any help appreciated. Many thanks

egg · May 19, 2011

blimey that is a dent ! i would agree that a punch mark like that in the piston will mean new piston . i would put money on that if you rebuilt it and started it up it wouldnt be long before fuel/spark/bang would put a hole straight through it !

if it were my car i would get a secondhand engine as i would not bother with replaceing just one piston doesnt seem viable , getting a full top end rebuild (valves/skim/pressure test and guides if needed) and to then just replace one piston ? i would source a good secondhand lump and keep the old piston as a trophy ! not sure if you can change piston by removing sump in situ but will try and find out .

mpls24 · May 24, 2011

Had the sump pickup replaced on mine recently and im pretty sure they had to lift the engine off the mounts as the crossmember prevents getting the sump off.

blackbus · May 25, 2011

thanks mpls24, looking at the engine diagram I thought the sump might not come off due to the crossmember and the oil strainer pickup extending deep into the sump. Car is in my driveway so no means other than jacking to lift the engine. Im thinking might be better to scrap the car altogether. Thanks again for your reply.