blown head gasket- vapor lock - bent piston rod?

I'm pretty sure this is the sequence of events that happened to my '87 300E. the other day when I started her up immediately ran violently rough heard some metal contact and shut car down. pulled the valve cover and all valves looked fine; yanked the spark plugs and all but #6 was fine -- it had scrapes and scratches on it, and was bent a bit but strangely enough, the gap had not changed. check tail pipe and water was inside. pulled the fan clutch and turned crankshaft manually and motor seemed to turn just fine. next day I replaced #6 plug and car started up a bit easier this time but still ran rough with a light tapping sound heard. again, #6 plug was scratched and scraped, but gap was unchanged.

Does this sound like a bent piston rod? If piston is hitting plug, why is the gap the same? Could timing have been thrown off somehow?

Last couple of questions.... if it does turn out to be a bent rod, and I do the head r&r, how much is involved after pulling head and replacing the bent rod? What type of bill would I be expecting to pay?

thanks all, I really love this site

joe

[Behind the Star]

joesb,
it sounds to me like there is something in that cylinder.
If the rod is bent,then the piston will not come up as far,so it would'nt be hitting the plug.
I would not run it any more and would bring it to a shop to have them look in the cylinder with a borescope to see if anything is in there.If you keep running it,it may cause serious damage.
Brian.

I think your analysis is right on. Hydrolock could've caused a piece of valve or piston crown to shear off. Hopefully the former. This would explain the extreme engine roughness that is occuring if a hole was in either of those and the marks on the spark plug.

BTW. are these pistons hollow?

thanks again

joe

[Behind the Star]

Yes ,the pistons are hollow.
How do you know it hydraulic locked?
Water in the tailpipe is pretty common (not massive amounts)
just from condensation.

I assumed that water did something to that piston because I was getting exhaust fumes in my coolant. this was confirmed today when I pulled the head and saw carbon buildup on the head gasket water passage seals. so I assume that prior to being started (when this all occurred) water had breached that piston somehow.

the #6 intake valve appears to be bent -- it should be fully seated at 6 TDC correct? if so it is not. when I pulled the head there was no visible foreign matter whatsoever. whatever had broken loose in there had either completely disintegrated or is hiding behind the exhaust valve. (no metal bits, shavings, etc) the piston itself had scrapes and scratches (lots of them) but nothing that would warrant it being replaced. I did find some watery oil in 5 and 6 but not a whole lot. I will post pictures of both the piston and the valve squish area of #6 soon.

so right now I have a bent intake valve, a scarred up piston, and no idea how the hell it happened. btw, head was pulled not long ago so the gasket was new, valves, guides, seals were all done. the gasket I used was Elring OEM, and it looked just like the one it replaced. it must be a POS because I heard that MB has made 3 changes to the m103 head gasket since original production.

I will be using whatever gasket the dealer peddles ... anyone know what brand they use, if not their own?

thanks again

joe

Anyone know if these things are know to have the timing belt jump or slip? It seems like more than one valve would be bent. That is my first thought though.

Steve

Smalltime:

I set harmonic balancer to TDC prior to yanking head and pistons 1 and 6 were in perfect timing, both being right at their crest.

thanks though..

joe

[Behind the Star]

With engine set to TDC, #1 is at TDC compression stroke while #6 is at TDC exaust stroke.
That means that #6 exaust valve should be open.Turn the camshaft and see if it closes.
If it does,and seats good,it's not bent.
I use elring head gaskets all the time and have never had a problem

The valve scar you see at the bottom of the piston was from a different incident. All valve tappets have been accounted for. whatever was in the chamber must've been blown out the exhaust. intake valve is definitely bent, not sure about the exhaust valve.

Any ideas how to clean up that piston crown?

joe