Clearances and oil pressure

OzCoupe72

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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

 

c9zx

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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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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.

 

OzCoupe72

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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

 

OzCoupe72

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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.

 

c9zx

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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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Were any oiling system modifications made? Were you using a high volume oil pump?

 
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clevelandcoupe

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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

 

OzCoupe72

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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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Did you or the machinist measure the volume of oil that remained in the oil pan?

 

OzCoupe72

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Did you or the machinist measure the volume of oil that remained in the oil pan?
Don - I drained the oil before removing the engine, dipstick was on the full mark and about 6 litres came out with a little remaining in the pan and filter

Oil was contaminated no doubt mostly due to number 4 cylinder and there was a small amount of oil in this cylinder

I suppose if the clearances were too tight it would cause the bearings to overheat and since this was the first drive over 10 miles distance they finally gave up with the loss in oil pressure scouring the cylinders

Unfortunately there is no way to confirm what exact clearances were on the bearings as they are all shot

This is a mistake on my behalf and although I've had success in the past with plasti-gauge I won't be using it again except perhaps to check how accurate it is once I get my short block back

Hopefully will have it back on the road in a month or so and it will be a nerve wracking experience driving it for a while without a 100% conclusive diagnosis

 
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I believe you are getting the failure thoughts in reverse, think about this.

The cylinders start to seize which causes excessive pressure and force to be applied to the bearings which causes the crank to beat them out. Withe the bearings beating out oil pressure starts to fall. Rod bearing should show the most wear. As the pistons start to stick in the cylinders it pounds the bearings. Mains not as much just rotation but would also see much more force. You should have noticed the extra drag and would have to give it more gas to overcome the friction. 

If you had ran until a piston actually seized that is when you break a rod and boom there goes the side of the block usually. 

Some older engines had a hole drilled in the upper side of the big end of the rod to squirt oil up on the piston skirt and wrist pin to help oil the upper side but a Cleveland stock rod does not have that. Does the aftermarket rods have hole or not? If they do were they turned the right way?

You have to figure out what happened or same thing will happen if you go back together the same way.

If you could turn the engine by hand the bearings were not too tight and would not over heat without long period of high rpm. 

I want to build mine this winter if I can get the Yates heads but might use the 70 cc if I cannot. Would like to know what the failure was on your engine for sure.

 

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I agree with David. I dont think the root cause was your bearings. Although Plastigage is not that accurate i dont think it will be off by 5 thousands to create a tight bearing issue. Based on your Platigage measurements even if off it would have worked with slightly higher pressure but not to the point of destruction.

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OzCoupe72

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I also agree it may not be the bearing clearances that caused this but this is all the machinist can come up with so far

He reckons number 4 cylinder/piston (wasn't seized just badly scuffed all the way around) was due to the lack of oil pressure

Cam bearings not bad but will be replaced

I will get all the old parts back and post some pics in a few weeks

We've pretty much eliminated 95% of all possible causes so far but will be persistent in getting an answer

I can only hope he finds something conclusive and I don't have to pre-book the tow truck next time!

 

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Going back to the oil pick up, was the tube checked for cracks and I'm assuming it was still firmly attached to the oil pump?

Still trying to come up with a reason for oil starvation.

 

OzCoupe72

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I'm hoping the machinist has already checked this

I could not see any cracks and pick up was tight with correct alignment/clearance

I'm certainly no expert but would expect if clearances were the sole cause it would have been a more gradual progression with some contamination in the oil especially after the dyno session but this was a sudden drop in oil pressure

 

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Did I miss something here? Did the person who ASSEMBLED this engine check the thrust clearance?  I think the original posting says that the thrust was wiped out, and has anyone asked any questions about the thrust clearance? I do this ( engine assembly ), for a living, and on my worksheets, EVERY engine gets the thrust bearing clearance checked prior to the crank and rods being assembled into the block. Off the top of my head, I think the window is something like .004"-.008" thrust clearance, again just off the top of my head, but whatever it is, WAS THIS CHECKED? It is totally not an un-common occurance, especially when using an aftermarket crank, for this measurement to be too tight. the thrust bearing sides ( #3 bearing )is lightly flat plate sanded to bring the clearance into the window, and, it is done on the flange side facing away from the flywheel, leaving the most bearing material where all the thrust pressure will be, on the flywheel side. This is not as critical on an automatic car, as it is on a stick shift, which puts a heavy loading on the thrust bearing flange. Another thing to be aware of is, checking the crank's endplay by just laying it in the block's main saddle inserts isn't accurate, you MUST install the main thrust bearing cap just finger tight, set the lightly lubed bearings by rapping ( I use a dead blow mallet and aluminum bar ) the crank to the rear, then forward, and torqueing the thrust bearing cap, and dial indicate the crank snout for endplay.

You may have had some other issue as well, but to wipe out a new thrust...….bets are on improper thrust bearing clearances.

Shown is a 427 SOHC Ford at .005" thrust check, and a 250 Ferrarri at .004" thrust check.







 
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How is the finish on the crank journals? Friend of mine had 50 miles on a rebuilt engine when it started losing oil pressure. The machine shop put to rough of a finish on the crank when they ground it causing a similar failure to what you are describing.

 

OzCoupe72

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I wish I had all the answers, believe me I do!

Spike - the machinist probably removed the centre main cap first and assumed the worn thrust was the main issue however after further investigation both mains and rod bearings were prematurely worn so his diagnosis moved from a thrust failure to bearing failure due to tight tolerances which lead to a cylinder(no 4) failure with minor scuffing on the other cylinders, obviously due to lack of oil pressure

When I assembled the engine the thrust clearance was the first thing I checked and it was certainly within specifications as were the bearings

The question is what specifications did I use?

After many nights with little sleep trying to get my failing memory to work I realised I may have got my clearances from a book by George Reid called - 351 Clevelands How To Build For Max Performance so I had a look and there is a whole page with most clearances/torque specs

Upon looking at the recommended bearing clearances it had approx .0009 - .0015 which I now know is not for performance builds but OEM stock specs

I had a vague memory of how wide the plasti-gauge was and sure enough it was about .0015 or possibly less

The thrust clearance would have been within OEM specs but shouldn't be an issue however if I did have my rod/main bearing clearances at OEM specs then this could cause a problem with a performance build

IA Rider - it was a brand new Scat crank and was checked by the machinist, journals looked perfect to my untrained eye

Anyway I've gone with boring it to .030 over, new set of SRP pistons (ouch!!) and the crank is being ground to suit new bearings with clearances at .002 rods .0025 mains

Hopefully have the block back by the end of the week and on the road following week but it will be a nervous first few hundred miles

Oh and lucky I got my C4 trans checked out, nothing wrong with how I put it together but the front band and a few clutch plates show some feathering which is probably due to old(new) parts getting moisture in them. This could have caused some issues so getting them replaced

 
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