Spark plug hit by piston, valve? M103 engine - PeachParts Mercedes-Benz Forum

Ron in SC · #1 12-01-2007, 01:25 PM

Photo below of spark plug out of M103 engine. Something has hit the end of the plug don't know what. Must have been a valve or piston, but how?

I just put head back on after doing heat gasket. Apparently I screwed something up. Before removing head engine was set at TDC for Cylinder one and cam grear sprocket was put back on exactly as taken off. Chain was put on at same place on cam gear as it was removed

What could have caused my problem and what can I do to fix it?

Edited: The spark plugs are all less than one year old but could it be that that one plug just goes to far in the hole that it threads into? I don't think I can shim it out since the plugs seat into hole, ie no washer.

t walgamuth · #2 12-01-2007, 02:53 PM

I don't see how the piston can hit the spark plug unless the plug is too lorng or you had an object in the cylinder that does not belong.

Tom W

Ron in SC · #3 12-01-2007, 03:30 PM

Quote:

or you had an object in the cylinder that does not belong.

I checked cylinder before I put head on and blew them out with air to make sure they were clean. That said it seems I did something wrong or knocked something in there when I fitted head to block. Is there anyway to check without taking head off.

I put cylinder 3 in TDC and could not see anything in there with pen lite and also put a magnet in to see if I could get anything out, but no luck. I don't have a borescope.

Is there any way a valve could have hit the plug?

ILUVMILS · #4 12-01-2007, 03:44 PM

OK, let's see if we can figure this out.

First, when did you know something was wrong? Does the engine turn over? Did you realize something was wrong when you first cranked the engine over? Did the engine run at all after re-installing the cylinder head? Did you leave the spark plugs in the head for the duration of the job? Give us some details and we will figure out what happened!

Ron in SC · #5 12-01-2007, 03:55 PM

First, when did you know something was wrong?
When I started the engine and I heard what thought was valve lifter noise.

Does the engine turn over?
Yes

Did you realize something was wrong when you first cranked the engine over?
Yes

Did the engine run at all after re-installing the cylinder head?
Yes, I was thinking maybe the valve lifters need to pressurize.

Did you leave the spark plugs in the head for the duration of the job?
Yes

t walgamuth · #6 12-01-2007, 07:29 PM

The other plugs look fine?

I would work on the premise that there is an object in the cylinder. My favorite machinist has a little periscope he can put in places like that to look around, maybe you can borrow one.

Oh and in case you are feeling like a knuckle head I once dropped a 3" stud into a cylinder and forgot it was there and so when i cranked the engine over it fell in there and then pushed a hole in my piston. Ouch! That cost me about 2k to fix. I had to buy a piston and all new bearings plus have the block stripped and cleaned IIRC.

Just don't run it this way and you wont spread debris into your bearings. (like I did).

Tom W

Ron in SC · #7 12-01-2007, 07:33 PM

Quote:

The other plugs look fine?

Yes

This vehicle has 153K miles. The head gasket I installed is the vehicles 3rd; don't know if that's of any significance.

Tony 12 · #8 12-01-2007, 08:21 PM

Maybe a bit of an 'out-there' suggestion, but is it possible that the spark plug was knocked while in the head but off the car, and the ticking noise really is just a lifter.

t walgamuth · #9 12-01-2007, 09:20 PM

Good thought. Did you try replacing the plug?

Tom W

Hatterasguy · #10 12-01-2007, 10:39 PM

Well you must have gotten the timing off, I'd start by timing it.

Not sure what the chain drives on an M103, but getting the crank and cam on the timing marks would be a good start. Is the distributer driven off the chain?

Chas H · #11 12-01-2007, 10:52 PM

Since pistons and valves are hooked together, even if incorrectly, and spark plugs can't move, I'd say that all the plugs would exhibit this damage if it was caused by a piston or valve. I think the damage was done while the head was off or there was something foreign in that cylinder.

Old World Auto · #12 12-01-2007, 11:27 PM

Ron,

Something is wrong, be it major or minor. Do not run car until you have performed your checks.

Like Tony said, maybe you just whacked the plug while the head was off the motor.

Note to all: remove all plugs, injectors or other things from the head that you may have to before removing it. It is much harder to after the fact. I have a nasty scar from when I was 16 from pulling injectors off a VW diesel head because I was too much in a rush to remove them before pulling the head.

Regardless, you can not assume this as you have noises and a damaged plug.

Pull valve cover, pull all spark plugs, set crank and cam to TDC. Do the marks line up? Let's hope they do, if not timing must be reset, but more importantly, how many degrees/teeth are they off? I think 2 teeth out, and the valves are hitting the crowns of the pistons. Not an m103 expert. Let's assume timing is correct and continue.

Next you should assess if you have FOD (foreign object debris) in the cylinder. This could be a nut, rag, bottle cap, who knows what. A borescope would be ideal right about now. You could insert a fine magnet through the spark plug hole. May get lucky. Back track your steps. How careful were you? What are the chances you let something fall in? We all make mistakes, trace your steps.

If by whatever means you have did not find any FOD, crank the motor over by hand. Listen as you do this. Any strange sounds? Feel for resistance, does something feel choppy or abnormal in the motor?

If all seems good, crank the motor over with the starter, plugs still out. A remote starter switch is ideal about now. That way you only activate the starter, no fuel or ignition, and can stand by the motor and listen. If all sounds good excellent. Also you can move about the engine bay listening to the motor from various vantage points.

All this time you will have the valve cover off. Now you can check to see if you are getting oil pressure to the camshaft, lifters, etc. Ensure nothing falls into the head while the valve cover is off.

Assuming all is well, I would do a compression test for grins. Good to know where things lie. If you can do a leak down test, even better.

If all checks out for the good, bottom it up and give it a fire. Listen carefully. Keep fingers crossed.

OK, now onto possible bigger issues. This is the 3rd head gasket in 153k miles? Something is not right! Warped head, poor installation, improperly milled head are all initial thoughts.

Here come the questions:

When starting the motor after this head R&R did you ever get oil pressure? If so how much?
Why was the head pulled the first time?
Did the car ever overheat?
How long did the last gasket last?
Was the head serviced by the machine shop when it was off the first time? (as it seems it was not this time?)
If so, was it checked for warpage and/or was it milled?

FWIW, if the head was milled too far down interference can happen. Seen it before on a 603. Also have seen a head that was not milled straight. Head gasket blew in less than 10 minutes on that one. That was an m103 also. A good machinist is worth his weight in gold!

Take a deep breath. Clear the mind, and approach this systematically. It may be something insignificant, but best to do your homework to be sure. Best case all is well, worst case the head comes off again.

Lastly, before cranking it over more, when you pull the valve cover, if there is no oil on the cam, followers, etc, you really should put some assembly lube on those bits. Standard procedure during assembly. STP works in a pinch, Motor oil if in an even greater pinch. Something is better than nothing. WD40 will not cut it.

Let's help Ron figure this one out ILUVMILS.

Hatteras, the distributor rotor is driven directly off the cam. It is not like the earlier motors.

t walgamuth · #13 12-01-2007, 11:44 PM

you have given a good thorough descriptoin of all steps necessary. My only further comment is to ask how a valve can hit a spark plug if the plug is the right length? Seems impossible to me.

Tom W

Matt L · #14 12-01-2007, 11:54 PM

A valve head could hit the proper-length plug, if it separated from the stem. But in that case, the engine is unlikely to turn over with the starter.

Old World Auto · #15 12-02-2007, 01:35 AM

Quote:

Originally Posted by t walgamuth

you have given a good thorough descriptoin of all steps necessary. My only further comment is to ask how a valve can hit a spark plug if the plug is the right length? Seems impossible to me.

Tom W

not the valve, FOD or the piston. head has been milled too much, piston comes up, hits plug. chances are slim of it, but may be possible depending on how the sp. plug is oriented. like i said, not an m103 expert.