Catastrophic Engine Failure

[Benz Dr.]

I've seen a couple of engines that let go in this fashion and none of the connecting rods were left attached to the crank. However, none of them came out through the side of the block like this engine did. In every case, the connecting rod came apart at the parting surface of the rod cap. I suspect that the rod bolts, while very strong, will break when pushed beyond their normal load limits when the sudden shock breaks them in two.

As hard as it might seem to be able to believe, extra compression from rebuilding a cylinder head can and will make a rod bearing fail. If everything is in good nick, then you won't have a problem. A bit too much bearing clearance and it can fail quickly.

 It happened to me in a 220SEb Coupe once after a head rebuild. I made one shift over 4K and it started to make a soft noise. Since I was in the middle of nowhere in a torrential rain storm, and this was long before cell phones, I limped along the side of the road until I got closer to help with an ever increasing knock . The crank was toast anyway and with the engine full of metal shards there wasn't much to save. This was in 1988 so it was a while ago.

Most of the time a fresh cylinder head will bring your engine back to life but every once in a while it can also kill it. This is, unfortunately, one of those uncommon times.      

[G$ 993]

I've seen a couple of engines that let go in this fashion and none of the connecting rods were left attached to the crank. However, none of them came out through the side of the block like this engine did. In every case, the connecting rod came apart at the parting surface of the rod cap. I suspect that the rod bolts, while very strong, will break when pushed beyond their normal load limits when the sudden shock breaks them in two.

As hard as it might seem to be able to believe, extra compression from rebuilding a cylinder head can and will make a rod bearing fail. If everything is in good nick, then you won't have a problem. A bit too much bearing clearance and it can fail quickly.

 It happened to me in a 220SEb Coupe once after a head rebuild. I made one shift over 4K and it started to make a soft noise. Since I was in the middle of nowhere in a torrential rain storm, and this was long before cell phones, I limped along the side of the road until I got closer to help with an ever increasing knock . The crank was toast anyway and with the engine full of metal shards there wasn't much to save. This was in 1988 so it was a while ago.

Most of the time a fresh cylinder head will bring your engine back to life but every once in a while it can also kill it. This is, unfortunately, one of those uncommon times.      

Great post. Thank you!

[G$ 993]

Does this engine number look like a factory stamp?  The shop is suggesting that it may not be a factory stamp and that the block may be unoriginal.  The number does match.  I have detailed records on the car back to 1980 with no indication of rebuild or accident.  Thoughts?

[Cees Klumper]

The number does look less 'clean' than the ones I am used to seeing on factory original blocks, more like what a garage might have stamped into a replacement block, so I can see where the shop is coming from.

[Benz Dr.]

The stamps that MB used tend to be somewhat larger than what is being used today. This is not an original stamping but none of this matters in my opinion. When people start paying 50K more for a numbers matching car at auction then it will.

[G$ 993]

Thanks for the comments.  This helps confirm that the engine is not original and may have had a poor build at some point.  Turns out the main bearing slipped which blocked oil to the #2 cylinder causing the failure. 

[Benz Dr.]

Interesting findings. Did it turn or move before this happened or after? My main question has to be, why did it turn? I've seen where a main bearing was installed upside down - maybe this is what happened? It's pretty hard for the bearing to turn under normal running conditions unless it's run dry.

[Shvegel]

For reference here is the stamp on my block.  I have heard of Mercedes dealers stamping factory replacement engines with the serial number of the old engine. I assume this is what was done with your car.  It bothers me that we are now seeing the term "Numbers Matching" becoming important in the world of European cars. What was once a way to verify that the particular high performance engine was correct and was the supplied type of engine on American muscle cars (where there were several engine options) has now filtered down to European cars where there is usually only one available engine doesn't make sense.  Of course you will have strong opinions on both sides of the aisle usually delineated along the lines of who has and who doesn't have a matching numbers engine.   

I guess the "Good" news is you didn't destroy the original "Numbers Matching" engine.

[GGR]

Weren't factory replacement engines' blocks pailted red? Or am i confusing with another make?

Rgarding matching numbers, it has always been a big deal on Jaguars, which are european cars. Not so much on Mercedes, go figure why.

[Shvegel]

No Jag experience so thanks for the info.  Porsche cars have only recently starting getting into the Numbers Matching game.  There is actually a hierarchy where numbers matching has a certain value.  Below that a correct date factory replacement unstamped block (can't just grind off the serial number as the block isn't machined where the serial number is.) and finally a miss-matched numbers block.

[Jonny B]

Use the overall search function and type in "engine block color" limit the search to "search in topic subjects" and you will get three hits. These give a pretty good explanation of the underlying red on the engine block. When installed the block should be black.

[G$ 993]

Interesting findings. Did it turn or move before this happened or after? My main question has to be, why did it turn? I've seen where a main bearing was installed upside down - maybe this is what happened? It's pretty hard for the bearing to turn under normal running conditions unless it's run dry.

From my shop: "The crankshaft bearings have been replaced and the main bearings are showing some uneven edge wear which is not typical. A more extensive tear down and complete measurement of the old engine assembly may reveal more findings pertaining to the previous workmanship done on the block and crankshaft."

[G$ 993]

Wanted to give a brief thread update.  The car is now at Motoring Investments (these guys are awesome) for a full rebuild with a new block!  The old engine is now out and the engine bay and underside of the car will be getting a full pressure clean.  I'll update the thread periodically as the build proceeds. 

[Cees Klumper]

Thanks for this and future updates, it's always nice to see how a story gets concluded. You're getting it done right, that's for sure!

[G$ 993]

Engine build update!

The build will also include full cosmetics

The “new” SE block has been disassembled. The taper is “zero” and wear is minimal.   87.0mm pistons have been ordered.  The crankshaft from the old engine looks excellent.  The aluminum parts (intake manifold, oil filter assembly, etc.) have been sent out for cleaning, aka tumbling.  The fuel injection pump has been sent out for mechanical overhaul and cosmetic restoration.  The oil pump is also in excellent condition.

Note the light surface rust in the engine bay.  Pics show the bay after power washing and after being prepped for paint. 

The undercarriage is in excellent original shape. The car does need a full new exhaust and suspension refresh.

Pics for your viewing pleasure.
 

[G$ 993]

More pics

[Garry]

Whilst you have the engine out you may want to consider having the engine bay repainted, its something that you won’t regret and will never be cheaper than now without engine etc.

[Benz Dr.]

Two things: 
1 ) any engine that spit/s out a rod bearing/s has a very good chance that the crank will be bent. I would make sure it's OK that way.
2 ) I would never re-use an oil pump that had any shards that went through it which would likely involve this engine.

[G$ 993]

Whilst you have the engine out you may want to consider having the engine bay repainted, its something that you won’t regret and will never be cheaper than now without engine etc.

Oh yes, this is being done!

Two things: 
1 ) any engine that spit/s out a rod bearing/s has a very good chance that the crank will be bent. I would make sure it's OK that way.
2 ) I would never re-use an oil pump that had any shards that went through it which would likely involve this engine.

Thanks for the advice. Great points.  Trusting the Motoring Investments team on this one.  Needless to say, they were surprised by the good condition of these pieces. 

[G$ 993]

A few more pics.  New paint in the engine bay complete.  Also a pic of the cylinder head after it was surfaced, the combustion chambers cleaned, and the valve seats resurfaced.

[ja17]

Failure is usually caused by some type of lack of lubrication. Bearing wear is most often the cause. Which can cause it to overheat and spin, closing off the oil passage. Next extreme heat builds up from no oil circulation at the specific area. The metal rod ends and  the bolts turn red hot and the connecting rod "stretch bolts" or the connecting rod itself fails. The fact that your camshaft had failed, could have been a sign that some type of lubrication problem was occurring. Dan is correct,  with a crankshaft problem like this, the cranks usually becomes warped or bent from the heat and pounding.

[Benz Dr.]

I had a 280SL spit out a timing chain while running on my hoist. I blipped the throttle a couple of times ( lightly ) and the engine stopped dead. I've never seen  anything top that fast! The chain broke and at less than 2,000 RPM  and it bent the crank about .012'' If the kinetic energy contained within a spinning crank was still enough to bend it when it stopped dead, what do think would happen to an engine that had a connecting rod fly apart?

[G$ 993]

I was mistaken.  The crank from the new short block will be used.  Not the old crank.