With the copious help of several here and at the track I diagnosed the failure of my engine at Putnam as a connecting rod bearing. A bottom end disassembly confirmed that the bearing in cylinder 6 was severely worn while everything else appeared to be okay. While discussing this with a muscle-car era buddy of mine he posed the simple question as to how cylinder 6 and only cylinder 6 could have failed. For reasons having to do with early onset dementia :huh: , this had not occurred to me before. He postulated a blockage in the cylinder 6 oil delivery passages. 6 happens to be the furthest point in the motor away from the pump and conventional wisdom is that the M20 oiling system is not really up to track use without baffles and scrapers. Is this the only explanation needed, or should I start searching for a galley problem?
Con rod bearing failure
My perception is that the rods in the back of the engine, all else being equal, are the ones to go first. That was the cause of failure for engine #1.
Wow, engine #1. Now that’s a blast from the past. The one that started it all. All that excitement when I first got my SpecE30. And the downer when the engine lasted only 3 months. And so the learning began.
I think that the rods in the rear of the engine tend to fail first because they more susceptible to oil starvation, but I’m not sure I understand why. Certainly #6 rod is at the very end of the galley -> crank -> Rod circuit.
Not that the thrashed bearing could be a symptom of a problem and not the proximate cause. Oil pressure requires resistance to flow. The oiling system is pushing oil down a number of paths and too much gap in any path can mean the loss of flow resistance for the whole system. Low flow resistance would mean low pressure. Low pressure would lead to bearing failure and #6 would likely go first.
Anything short of a full rebuild accepts some risk. Don’t get me wrong…it’s common enough to do something short of a full rebuild so accepting those risks is pretty routine, but one should still go in with their eyes wide open. That allows you to check a few other areas for possible problems, depending on the hassle and cost.
On the other hand it’s possible that the engine was just starved for oil at some point and the rod bearing wiped. That’d be the ideal situation because it means the rest of the oiling system is healthy.
Possible causes of low oil pressure:
Gap around oil pump gears too big.
Oil pump check valve weak.
Rod, crank or intermediate shaft bearing gap too large.
Cam or cam journal (soft aluminum) damaged so too big a gap. This is common.
Head sprayer bar damaged or unscrewed. Not common.
Oil check valve weak. Engine #7 failed for this. Or was it #8? Sigh.
I would suspect simple lack of oil pressure during cornering. Without adequate oil, bearings fail quickly. An accusump or PP pan will certainly help if not alleviate the problem, and they are much cheaper than an engine.
IMHO, no engine should be built without a new oil pressure regulator valve. These are problematic in that they bleed off OP at all times…when they get hot they bleed more. That is not the scenario we want. Modifications to the oiling system can be made, but the best solutions are listed above. Chuck
So should I plan on rebuilding the oil pump and replacing the check valve while everything is already apart?
So should I plan on rebuilding the oil pump and replacing the check valve while everything is already apart?[/quote]
There is no right answer. The list of things to spend money on is endless. That being said…
A replacement checkvalve is probably cheap insurance.
Altho I learned at Metric Mechanic some of the stuff needed to check out an oil pump, I don’t have the “depth micrometer” to do it, nor did I learn how to inspect or improve upon the oil pump’s check valve. I think Chuck Baader has the check valve figured out tho. Budget unlimited, buy one from MM. If you want to spend less, buy one from Chuck or buy a new one. Or don’t spend anything and just put in your old one.
Now that you’ve gotten pretty comfortable with your engine you could just put your old check valve and pump in, run the engine hard and see what happens. If your hot oil pressure isn’t what you hoped for, lift up the engine, pull the oil pan off, replace the oil pump and checkvalve and see if there’s an improvement.
There is no right answer.
You might want to check the clearance between the gears and the pump cover using a feeler gauge. Clearance should be .0025" or so.
Based on your previous comment to this effect I spent about 20 minutes lying under the motor and staring at the oil pump wondering how one would go about this. I was reluctant to disassemble the oil pump at the time for a number of reasons, not least of which is I’m guaranteed to drop any balls, springs, spacers, tiny fasteners, or whatever else an oil pump might contain besides large gears and they will go to the same place that socks in your dryer do. I’d like to have the e-bay store concession linked to that place wherever it is.
Oil pumps are simple. Remove the 4-5 10mm head bolts holding the top (bottom) on and you have two gears inside…that is all. Polish the removable top if it has scratches, and sand the top of the body if the gear clearance is over .0025". (Use a piece of glass with 400 grit sandpaper and WD40 to lubricate. Sand in circular motion and rotate body at same time.)
Replace the PRV with a new one or one from MM. There are other things you can do to insure longevity. Chuck
Stay within your comfort zone. Engines have a low tolerance for screw ups. As well intentioned and charismatic as I may be, being on engine #11 isn’t because of a membership in the "engine of the month club. If you’re determined to fool with your oil pump, either buy a new one or have Chuck blueprint a used one. If Chuck doesn’t have a used one handy, I’ve one I can send him.
As if it were that easy. I’m genetically programmed to push the edges of my comfort zone at every opportunity. About half the time it ends up costing me some to a lot of money for the education I could’ve gotten for free by listening to well intentioned, charismatic forum moderators 
As if it were that easy. I’m genetically programmed to push the edges of my comfort zone at every opportunity. About half the time it ends up costing me some to a lot of money[/quote]
Hail brother.
As someone who’s never replaced a rod or crank bearing I thought disassembly of the pump was pretty easy. After diagnosing the pump as totally junk I decided to leave the new pump in the box and let it ride until total failure. I saved the pump for the new motor build.
I think you need to be monitoring Op to make informed decisions about oil pressure and starvation problems. You’re an EE. Even I could get my arduino to log multiple sensors and record them for under 100$. It’s building a realtime display that I wouldn’t know where to begin.
On the topic of comfort zone. My rare launch model Ps3 died thursday night during some intense MW3 gaming. I’ve built gaming PCs before but a PC cpu isn’t soldered directly onto the board. After watching some how to youtube videos I tried to reflow the gpu and cpu solder with a heat gun. Probably permanent toast now. Later I found a place in MN that can fix it for 70$ with a cnc controlled reflow machine made just for the process, and that a nib launch model ps3 is 1700$ on amazon. I almost cried.
Yah, trying to reflow BGA’s with a heat gun is pretty much doomed to failure (except on X-boxes where you start with junk anyway). Especially big ones like GPUs. We have a 250K BGA rework station and trained techs that have a fairly marginal hit rate on big BGAs. I used to have to send boards to Texas or Mexico to my OEMs to get 'em fixed. Bummer dude! 
As to your suggestion that maybe I should monitor OP before launching a rework campaign, sounds like good advice. I’m sure there are 10,000 threads here dealing with OP sensors and sensor locations, but if I just wanted to use the stock location, what’s the sensor of choice? And what’s conventional wisdom on what pressure one should see here for proper lubrication?
What straight line oil pressure you’ll see is a direct function of the wear in the engine & pump and the condition of the OPR valve. My first (+200k) engine could only get ~40psi @ 6k on a 90deg day. My second engine did better with pressures approaching 60psi under the same conditions. My built engine exceeds 60psi from about 4.5k up.
[quote=“RRhodes” post=66282]Yah, trying to reflow BGA’s with a heat gun is pretty much doomed to failure (except on X-boxes where you start with junk anyway). Especially big ones like GPUs. We have a 250K BGA rework station and trained techs that have a fairly marginal hit rate on big BGAs. I used to have to send boards to Texas or Mexico to my OEMs to get 'em fixed. Bummer dude!
As to your suggestion that maybe I should monitor OP before launching a rework campaign, sounds like good advice. I’m sure there are 10,000 threads here dealing with OP sensors and sensor locations, but if I just wanted to use the stock location, what’s the sensor of choice? And what’s conventional wisdom on what pressure one should see here for proper lubrication?[/quote]
Those old threads are a fine historical resource of info. It’s not reasonable to ask us to write about it for the 10th time.
OP should be taken from the stock location…that is the main oil gallery to the bearings. Do not mount an electric sensor there…they break or fail. Run a -3 or -4 line to the fender well and mount an electrical sensor there. I personally want mechanical gauges and -4 line connecting them.
Cold OP on my motor is 95psi with 10W30 oil. Hot pressure (210-220 degree oil) is 15-20 at idle (1500rpm) and 60-65 psi over 3500rpm. I really like those numbers. I use an Oberg type oil filter (screen disk) and it is checked/cleaned after each race. I instantly know the condition of my motor after each filter inspection. Also highly recommended if you want your motor to last several seasons. Chuck
Thanks Chuck, again I wasn’t thinking. A simple, reliable, mechanical gauge. I like that.
The downside of a mechanical gauge is that there’s no way to connect it to a datalogger. At Chuck’s suggestion I went to a mechanical oil pressure gauge too 3yrs ago. I like it mostly because I trust it, but it did make it complicated to get OP data to the data logger.
This isn’t the right place to talk about logging sensor input, I just wanted you to be aware of the downside of a mechanical gauge.
Ack. The datalogging capability is still somewhere in my future. I just want a short term method to check OP during runs. A mechanical gauge and a video camera provide a good low cost interim solution.