Quote:
Originally Posted by C5GTO
Thanks Ed!!
After seeing the Miura project, it's probably more obvious why I'm trying to tightly manage the spending on my Cobra (every dollar that goes into the Cobra doesn't go into the Miura). But alas, the Cobra is going to require some "investment" if I'm going to keep it "drivable". On the first road trip after fixing the gas tank venting, I think the engine spun a rod bearing 
I haven't published this adverse outcome yet as I haven't pulled the engine to verify, but the rpm variable clack and metal sheen in the oil are fairly telling symptoms. A friend and I checked the whole top end and no major issues found there, the compression is good on all 8, and so there's only one thing left that it really can be. So I'm now collecting up information about all the issues in my Cobra so I can create a "budget" for fixes to make it safely drivable again. I guess it's true that owning and enjoying a Cobra is a fairly constant drain on the wallet  |
I am not attempting to tell you how to build your engines but rather offering a thought that might be helpful.
Whenever an engine has run for some period of time without having spun a bearing and then suffers a spun bearing, it is always an
oil starvation issue. Sometimes it arises from a high volume
oil pump used with a stock or near-stock capacity oil pan. The oil level above the pickup can become marginal if the engine has a slow oil return path to the pan or just poor oil control in the pan.
In the scenario where the pickup is marginally covered with oil, any braking, turning, or acceleration can momentarily uncover the pickup allowing it to draw air instead of oil. The sporadic but repetitive presence of air bubbles in the oil feed to the engine will be a cumulative sort of failure scenario.
The first few times, probably no serious damage. Eventually, the bearing surface is sufficiently damaged that the oil film that usually supports the load on the crank pin is thinner than the physical scarring on the bearing. The first time this occurs, the crankpin grabs the rod bearing insert and rotates it between the other insert and the crank. At this point, the show is over, and the damage is done.
The mechanical failure process is always the same. The cause of the starvation is always an uncovered pickup. Drawing air into the oil system is always less oil in the pan than is necessary to cover the pickup. The fix is always one of the following;
• A larger capacity oil pan, if possible,
• Better baffling of the pickup to maintain oil coverage,
• Use of a dry sump system,
• Use of an oil accumulator.
Even when we attempt to run the largest capacity pan with the best baffling that is prudent, the oil starvation problem can still rear its head. Dry sump systems remove the opportunity to uncover the pickup because of their physical design — but they also cost an arm and a leg.
The last item, using an oil accumulator, is the poor man’s dry sump system for this type of failure. The accumulator retains oil under pressure and is “T’d” into the oil delivery line between the oil pump and the engine. When the pickup is uncovered and draws air, the accumulator sees the drop in oil pressure and begins to discharge oil into the oil engine oil galley to protect the engine bearings.
The accumulators are relatively inexpensive and great insurance for the engine. They also can be used to prelube a collectible car that we don’t start every day. Here is a pretty good YouTube video by Moroso to better explain the protection process; click here =>
Moroso Oil Accumulator.
In addition to Moroso, Canton offers the original oil accumulator called the Accusump. Both work equally well. You can not go too big, you can go too small. Get the 3 quart gizmo.
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