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Clearances and oil pressure
#1
Still waiting on my engine's final autopsy and getting different stories/theories every week
In short I rapidly dropped oil pressure on a fresh 406C stroker resulting in engine noise and a $400 towing bill
Decided to send it to my machinist a couple of long weeks ago and his initial diagnosis after removing a couple of bearing caps was the thrust bearing was wiped out due to the crankshaft being pushed forwards
This led to "a" conclusion it must be my transmission having excessive charge pressure or a misalignment issue which is certainly a possibility but the fact there were no witness marks on the flexplate or convertor I was not convinced
Having excessive pressure in the trans would also cause excessively harsh shifts which was certainly not the case at all
Regardless I took the trans to a local shop and he can't see any evidence of this so far

Get another call from my machinist to say they have removed the crank/pistons etc and after measuring the wear on the thrust, end play and the fact that all the bearings have prematurely failed/worn he no longer blames the trans but thinks the clearances might have been too tight
I told him my oil pressure was consistently 80-85 psi cold, 75-80 hot revving with approx 50 psi hot idle which to me is not excessive for a new engine
I don't remember my exact clearances but checked them with plasti-gauge (I know not perfect!) and they were certainly within spec at about 0.0025-0.0030 mains and 0.0020-0.0025 rods
The crankshaft turned freely even with pistons installed and although plasti-gauge is not ideal even at the tighter side of the above clearances I am far from convinced it was the clearances causing this failure
The oil was always clean even when I stopped the vehicle and wasn't until I got home the dirty oil finally mixed in
Machinist is yet to check oil pump, galleries and cam bearings so could get another story next week

My "theory" is something caused a drop in oil pressure such as a blocked oil gallery or an internal leak such as a slipped cam bearing or oil pump issue which led to the bearing failure and major scuffing in no 4 cylinder with minor scuffing in the rest

Would be interesting to hear from members what oil pressures they have had on a fresh engine especially with new crank, rods etc
Oh and you're welcome to add to the theory list, I could use a laugh right now
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#2
The numbers you stated are in the general ballpark. What was the failure mode causing you to be towed? What do the bearings look like? What were the ring gaps set at? Picture are usually helpful. Chuck
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#3
What does the cam and lifters look like? Did you use zinc additive in your oil?
When I worked in race shop you opened up the clearances for couple reasons. The flow of oil cooled the bearings for car that run on track for 500 mile races. The other was pure friction reduction. What we saw with too much oil pressure was that the bearings eroded looked just like when water washes out a section of soil. Most people are not looking at engines that are ran at max for 500 miles and do not see this. A 1/4 mile engine will probably never make it 500 miles. We ran pumps with higher volume not necessarily high pressure. 
We never ground the cranks to the factory numbers. We would get the new bearings and install them and mike the inside diameter of the bearing. The boss would then tell the crank grinder what diameter to grind each journal. They would vary sometime .001" from the spec. number but usually a few tenths of a thousand of an inch. 
I would double check the clearance given for the pistons and check with the mfg. for the proper clearance. Some forged pistons need extra clearance due to expansion being more than a cast piston. 
Did you grind your ring end gaps or just put the rings on and slap the pistons in? Rings might have been butting ends and caused scuffing of the walls.
I think one of the members had an issue with the journals on his new crankshaft not being aligned with the bores of the cylinders. Do you have pics of the bottom of the engine when you assembled the first time? When he bolted the rods to the crank the small end of the rod was not centered with piston. 
Also check the clearance on the lifters. Being a wet lifter galley if there is excess clearance there all the oil leaks out around the lifters starving the bearings. 
The position of the front cam bearing is also important. 
Did your main bearings have oil grove all the way around or 1/2 way. My old boss preferred the 1/2 way around. 
For sure you do not want to go back together with the engine and do the same way as last time. Will probably get the same results. 
I am suspect of end gap on rings being cylinder issue then the resulting crap gets into the oil and causes other issues. Or piston clearance issue.


When a man is in the woods and talks and no women are there is he still wrong??
Tongue
David
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#4
(07-25-2019, 08:28 AM)c9zx Wrote: The numbers you stated are in the general ballpark. What was the failure mode causing you to be towed? What do the bearings look like? What were the ring gaps set at? Picture are usually helpful. Chuck
G'day Chuck

Sorry no pictures yet as block etc at the machine shop 50 miles away

Story in short I was driving along the highway 50-60 MPH all going well and constantly checking the gauges
Heard a noise like loose tappets then looked at the gauges, oil pressure 40 and slowly dropping
Had to drive a couple of miles, very slowly, to find a parking bay and shut down, checked for leaks, none, checked oil, clean as a whistle and full, so clean I had trouble seeing the oil on the dipstick. Checked it several times, same.
Got vehicle home and perhaps from getting on/off the tilt tray the oil had mixed so it was now a dark color on the dipstick

What I'm having trouble comprehending is that if the bearing clearances were too tight there should have been some wear from the beginning and there would have been some discoloration in the oil much earlier on especially after the dyno testing
Ring gaps were set at where they should be but don't quite remember exact measurement, I did file a little too much off a couple but that wouldn't cause any problems
In my opinion it is more likely an oil starvation issue considering all bearings including thrust surfaces are worn, number 4 cylinder badly scuffed perhaps as one of the last to receive oil

Machinist is yet to examine the oil pump, galleries and camshaft so will have to lose some more sleep waiting
Luckily the crank can be saved and the block will only need one sleeve at this stage
Hopefully I have more news in a week or so
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#5
Hi David

Cam/lifters looked fine but yet to remove cam, machinist will do this
Pistons were clearanced by the machine shop and he is certainly aware of the need for extra clearance for forged pistons
Ring gaps were filed to spec although I did file a little too much off a couple of compression rings but this wouldn't cause any issue
Machinist reckons piston/cylinder wear due to oil starvation
Pistons perfectly centred, crank end float spot on and rod side clearances spot on
Not sure on mains, ACL Race series I think 1/2 grooved?
Machinist reckons cam all good but hasn't reported on cam bearings yet, lifter bores look good but will double check this and front cam bearing

I have assembled half a dozen Ford V8s always checking bearing clearances with plasti-gauge and never had an issue
Plasti-gauge while not very accurate will still show a pattern and from memory there was nothing out of the ordinary
Unfortunately with age my memory not so good and don't remember exact clearances but would expect with all new components they would have been slightly on the tight side. Everything rotated freely 
I have my doubts that a slightly tighter clearance would have caused a sudden failure but I could be wrong
Perhaps it's the chicken or the egg question - did the oil pressure drop first causing the damage or the other way around?
Thanks for your input, will post more info if/when it comes to light and hopefully get a better night's sleep!




Carolina_Mountain_MustangsWhat does the cam and lifters look like? Did you use zinc additive in your oil?
When I worked in race shop you opened up the clearances for couple reasons. The flow of oil cooled the bearings for car that run on track for 500 mile races. The other was pure friction reduction. What we saw with too much oil pressure was that the bearings eroded looked just like when water washes out a section of soil. Most people are not looking at engines that are ran at max for 500 miles and do not see this. A 1/4 mile engine will probably never make it 500 miles. We ran pumps with higher volume not necessarily high pressure. 
We never ground the cranks to the factory numbers. We would get the new bearings and install them and mike the inside diameter of the bearing. The boss would then tell the crank grinder what diameter to grind each journal. They would vary sometime .001" from the spec. number but usually a few tenths of a thousand of an inch. 
I would double check the clearance given for the pistons and check with the mfg. for the proper clearance. Some forged pistons need extra clearance due to expansion being more than a cast piston. 
Did you grind your ring end gaps or just put the rings on and slap the pistons in? Rings might have been butting ends and caused scuffing of the walls.
I think one of the members had an issue with the journals on his new crankshaft not being aligned with the bores of the cylinders. Do you have pics of the bottom of the engine when you assembled the first time? When he bolted the rods to the crank the small end of the rod was not centered with piston. 
Also check the clearance on the lifters. Being a wet lifter galley if there is excess clearance there all the oil leaks out around the lifters starving the bearings. 
The position of the front cam bearing is also important. 
Did your main bearings have oil grove all the way around or 1/2 way. My old boss preferred the 1/2 way around. 
For sure you do not want to go back together with the engine and do the same way as last time. Will probably get the same results. 
I am suspect of end gap on rings being cylinder issue then the resulting crap gets into the oil and causes other issues. Or piston clearance issue.
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#6
Oz, This sort of failure is puzzling. I wish I had some helpful insight to offer. The only thing I can suggest is start checking every tolerance, especially the big end of the rods. I say that because I lost a new engine on the dyno a couple of years ago. It showed good oil pressure and coolant temp, it just wasn't making the power it should have been. We shut it down and disassembled. Bearings damaged and crank throws scarred. It turned out that all 8 (new) rods had gone out of round on the big end effectively removing clearances. I hope you get it sorted quickly. Keep us updated. Chuck
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#7
Were any oiling system modifications made? Were you using a high volume oil pump?

73 conv. 460, D0VE large valve heads, Performer RPM manifold, Voodoo 227/233 cam, Holley 950 HP carb, C6 trans, 3.25 trak-loc.
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#8
Did you check the clearance between the bottom of the oil pick up and oil pan ? I recall a thread on this in the past.
Just thinking.......
Thanks, Jay
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#9
Still nothing conclusive and machinist still holding to the clearances theory and maybe he's right?
Chuck - you're right it is a difficult one and even the machinist is not overly confident but will be checking everything

Both mains including thrusts and the rod bearings failed which to me is oil starvation and perhaps if the clearances were a little tight that would certainly have contributed to the bearings early demise

One thing that gives a hint of oil starvation is the oil filter when removed had very little oil in it

TommyK - No oil mods, not necessary for a mild build and standard volume Mellings pump 85 psi cold, 75 psi at revs and 45 psi hot idle

Jay - Oil pickup to pan clearance was spot on - can't remember but maybe 3/8 inch and machinist did also check this

Anyway I have 2 choices to fix this
One was to sleeve no 4 cylinder, new piston, grind crank, new bearings, rings etc
Second option was to put all new pistons boring it to .030 which would not need a sleeve but this option would cost about $500 more and I would rather keep my block at .020 o/s to leave room for future rebuilds so will go with the first option
Only issue is will have to wait a couple of weeks for a piston from the USA
I only wish my memory was good enough to remember the exact clearances I came up with, next time I will record everything!
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#10
Did you or the machinist measure the volume of oil that remained in the oil pan?



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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