Author Topic: 1969 CL350 Head Ache!  (Read 3041 times)

Offline K2-K6

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Re: 1969 CL350 Head Ache!
« Reply #45 on: September 15, 2017, 09:36:16 PM »
Given that the original problems with this engine are to be repaired it's always gutting if you get a repeat, especially as it's so difficult to readily get parts for some of the older examples.

With that in mind I thought I'd forward a discussion as to what went wrong in the first place as it appears to me to that there is a story within it waiting to be observed. It's trying to tell us something, I believe.

It's unusual that the previous owner seems to have stopped using it as the problems were building, which gives a fairly unique look at the problems before it blew itself to bits.
I'm maybe putting two and two together then coming up with five but think it's a plausible theory which may gather some further thoughts.
It looks like it's run with no valve clearance on the exhaust of the damaged cylinder. This has the effect of compromising the lubrication to that lobe (can't see the whole effect from the photos) . If it has,  the cam wear is one consequence. The second path of effects could go as follows;- running with the exhaust valve slightly off its seat allows the valve head to go over temp as seat contact is critical to control heat build up. Also it allows compression to leak away just as it comes up to ignition event,  this compromises the burn formation in that cylinder, which being incomplete, promotes carbon buildup in that chamber.
Here's where it comes together more,  carbon buildup insulates the combustion temp from reaching the aluminium and so partly cuts off its transfer out to the fins for dissipation.  This results in both a hot cylinder and a hot exhaust valve, probably above sensible operating temps that would normally be experienced.
Given these temps and some unburnt mixture are still present,  this is exactly the conditions that propagate detonation. Commonly known as pinking or knock. As above, it's not often you see this stage as it usually, when run further, will take out the top land of the piston which let's the rings go. It's this mess that is usually found when the motor fails and someone takes it apart. The rings get the blame when often they were the last things hanging in there.

I feel that ultimately it's a story of no valve clearance causing a whole trail of problems from such a simple start point.
« Last Edit: September 15, 2017, 09:40:32 PM by K2-K6 »

 

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