I am having a camshaft wear issue that is a bit mystifying. I bought my car about 3 years ago, and it has always had a miss at idle. The car drives fine, and has no issue as long as the idle is above 900RPM, or if I am driving.


After changing out all of the electrical items in the system - plugs, wires, coil, injectors, I was never able to get rid of the miss. If I were to let the car idle, it would throw a CEL for intermittent misfire, in cyls 3 &4.


I had some milkshake in the coolant overflow bottle, and in a moment of brain fade, I assumed that this was a blown head gasket. So, I went ahead to change the head gasket, but found no issue with it. It was obviously the oil cooler failure, but I was committed. I put a different head back on with a new gasket and some head studs.


The item critical to this issue is that when I pulled the rocker shafts, I found a badly worn cam, on mainly the exhaust lobes. There was some damage on the rollers of the rockers on some of these lobes.


So, in that repair, I replaced the head with another that I had rebuilt, I changed the cam to a good used one, and changed the rockers to another set, all in good shape. I changed the oil quickly after the work, to get rid of anything that might need to be cleaned out, and then did the next oil changes at around 5,000 mile intervals. I also have been adding a zinc additive, thinking that the change in oils might have caused the wear. I baby the car until the car's oil gets up to temp,

The issue is that I now have the same symptom again - the miss is back after about 12,000miles. The miss is only in cyl 3, and the wear is much less than it was last time.


I am stumped as to what is causing the issue. It is obviously oiling related at this stage. The oil pressure light does not come on, but I have not installed a gauge yet. I am wondering if there isn't enough flow, or if the oil pressure is only a little bit below spec, or even if there is something else going on, like worn rod bearings bleeding off the oil pressure.


The oil pump looked good internally when I had it apart, so I am a bit confused.


Any hints at all? (Sorry for the length) Thanks guys.

 

You need to check oil pressure to ensure it is within spec. I have no idea what it should be. My limited experience is say a factory will state the oil pressure should be about 6.5 bar at 5K RPMs with the oil at 90C.

I have not had a chance to study the inside the Mini engine and its valve hardare in any detail but generally speaking if oil pressure is ok you need to suspect that maybe oil supply to the valve hardware, at least some of it, is compromised.

You want to be sure the oil supply to the head/valve train is ok. If the oil flows from the block to the head you want to be sure the head gasket is the right one and installed correctly. I'm thinking maybe the gasket could be blocking at least partially the oil flow from the block to the head.

You may have to remove the head and strip its hardware -- be sure you keep track of which hardware goes to which cam lobe, it ain't nice to mix this up as it can lead to accelerated wear -- and blow air back through any oil supply holes or use something to make sure a piece of metal swarf or a piece of sealant or something is not lodged in the oil supply hole that supplies lube to the areas that are suffering from wear.

 

That does not look good. All point to excessively low oil pressure at working RPMs. That is oil starvation. You cannot rely on the oil pressure switch/light as it is set extremely low so not to give false alarm at idle. It is circa 3-5 PSI. Do a search on oil filter housing drain back valve failure.

If you have 2 damaged cam, cam journals, and rockers very likely the crank and conrod bearings are also damaged.

Get yourself a mechanical oil pressure gauge and jerry rig it to check what pressure you have at say 3500 rpm before doing anything else.