Quote:
Originally Posted by C5GTO
On the first road trip after fixing the gas tank venting on my Cobra, I think the engine spun a rod bearing 
I hadn'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  |
Quote:
Originally Posted by eschaider
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. |
Moving this topic to it's own thread as it has nothing to do with brake sizing...
Here are some specifics about the engine. It's a Ford Motorsports X302 crate engine (
https://performanceparts.ford.com/do...-6007-X302.pdf - details on page 20) purchased from Summit about 10 years ago. It is outfitted with a Canton 8qt. 15-630SM Ford 289-302 Front Sump Road Race Pan and pan specific oil pickup. All the rest of the engine internals (e.g. oil pump, crank, rods, cam, etc.) are whatever Ford Motorsports put into the engine. For example, I don't know if oil pump is standard or high volume. The engine has about 25,000 miles on it from new and until now, no problems with it at all. After purchase and installation, it was dyno tuned and EFI ECM augmented with add-on chip to hold the tuning data. The oil level read full at the start and through out the road trip. The oil pressure read as normal through out the trip even after the motor started clacking. I seem to recall the motor oil being a Castrol 10w40 in either a
synthetic or
synthetic blend. The oil was about 3 years old or so as I had changed to oil prior to garaging/parking the car for about 3 years. During this 3 years, the engine was started and warmed every 2 - 3 months. Prior to the engine starting to clack, the oil showed pretty much clear/clean on the dipstick.
The road trip was an early morning drive (so ambient temps in low 70s) around Northern AZ. The first leg from Chino Valley to Ash Fork, no issues. The second leg from Ash Fork to Flagstaff on I40 is where the problem started. Posted speed limit is 75 mph. We traveled at least that fast and sometimes up to 85 mph when passing. My Cobra does not have overdrive so for this 50 minute segment, the engine RPMs were held between 3,800 to 4,000 RPMs. So somewhat high RPMs for extended period but not excessive for an engine carrying 8 qts. of oil. The Interstate is fairly straight for that whole stretch so no hard cornering to slosh the oil from pickup. Coolant temps were 180 degrees and oil pressure showed 50 lbs. (electric gauge so maybe not precise but pressure didn't waver at all) for this segment.
I first heard the clacking sound when we exited the Interstate for the segment down to Sedona. You can't hear anything in a Cobra at 75 mph so it likely started prior to the exit. When I first heard the sound, it sounded like an exhaust leak and I thought it was at the flange joint between header and side pipe so we kept driving. This segment was 2 lane road through the magnificent Oak Creek Canyon so speeds and RPM were very low but you could hear the clacking sound bouncing off the rock canyon walls.
We stopped for a visual inspection after about 10 - 15 miles driving after exiting the Interstate. The side pipe flange bolts were tight so the exhaust leak theory was ruled out. The consensus was that the sound was coming from the top end and likely a rocker arm had loosened. Given the EFI intake hangs over to valve covers, we couldn't take a look without upper intake manifold removal. The sound had become a bit more pronounced but not all that loud yet. Oil level and pressure were normal still and engine seemed to be running fine except the clacking sound.
I elected to drive the car for the 60 miles or so to return home. Since I first heard the clacking sound till getting the car home, the sound became a bit more pronounced but not the low knock that I've heard prior with spun bearings. The clacking sound would lessen and almost go away at about 2,500 to 2,800 RPMs during the remaining drive home.
At first, we were convinced it had to be an issue in the valve train. After going through the top end with a fine tooth comb, the only issue we found was a few roller rocker arms showed some wear in the aluminum where the roller tips contact the arms. There was no looseness anywhere, no loose rocker arms or bent push rods. The compression is between 115 and 120 on all eight cylinders. The top end is absolutely clean and all oil drain backs are open so no oil trapped anywhere. So conclusion, the sound is not being generated in the top end.
After draining the engine oil, a slight sheen is visible when moving oil around in direct sunlight. Through process of elimination and given the symptoms, I'm now thinking it's a spun rod bearing. I haven't pulled the engine yet as I don't have enough garage space until I get a new detached garage constructed.
Any ideas? Does anyone with experience on the Ford Motorsports X302 crate motors have a similar issue? I would hope an extended 4,000 RPM run would be fine with this engine, but if so, what's going on here?