450SL Engine Knock

[TBS]

I recently drove my recently acquired 1976 450SL at 80MPH for approx 75 miles on the Interstate and ran fine. Upon exiting the Interstate I noticed a very noticable engine knock and am presently trying to diagnose it. Because it came on suddenly and has continued without increase or decrease I question that it is a Rod. Could be. Thinking more a collapsed lifter but cannot find such upon valve cover removal & inspection. Would anyone have some suggestion?

 

[television]

I recently drove my recently acquired 1976 450SL at 80MPH for approx 75 miles on the Interstate and ran fine. Upon exiting the Interstate I noticed a very noticable engine knock and am presently trying to diagnose it. Because it came on suddenly and has continued without increase or decrease I question that it is a Rod. Could be. Thinking more a collapsed lifter but cannot find such upon valve cover removal & inspection. Would anyone have some suggestion?

Con rods give a definate knock where as a lifter is more a tap, normally with a big end the oil presure will be low. Little ends a more of a tap noise and have no effect on the oil presure.

A skilled mechanic would know if it was a big end instanly, you cant mistake that sound.

Malcolm

 

[TBS]

please explain "big end"/"little end"

 

[television]

The con rod is the piece that connects the piston to the crankshaft, the large bearing at the bottom is oil preasure fed from holes in the crankshaft, this is the big end.
The little end is where the con rod is atteched via a gudgeon pin to the piston and is only lubricated by oil splash from the crankcase.

http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=203707&M=646.962&CT=M&cat=63R&SID=03&SGR=030&SGN=02


Malcolm

 

[TBS]

In your opinion can a rod bearing be removed/repaired/replaced whith engine in car?

 

[television]

In your opinion can a rod bearing be removed/repaired/replaced whith engine in car?

If you can get the sump off,then yes the big end bearing can be replaced in the car, if it is Big end gone replace all of them.

malcolm

 

[eric242340]

Its quite a difficult to do the big end (on this model) in situe. Plus you will need to measure the crankshft. If the crankshaft is out of round or badly worn you will have to have it re-ground and fit oversize shells. Should this be the case you will have to take the engine out.

 

[TBS]

reply

Thanks for the info. This being my 1st MB I am beginning to realize there is much more to this car than many others. I hope I won't have to pull the engine. Thanks again for the help.