Engine Bearing Failure

[dynomatt]

Finally pulled the engine that developed a knock from 3 years ago.

Quick background:

Stock bottom end, with original cooling problem (ie, overheated in a blink), then ran a stage of a rally, temps off the scale the whole stage.

Bottom end knock.

This is the bottom end of cylinder number 5...I think this confirms Tom's comments that number 5 fails.

[Dessertrunner]

Has anybody got any ideas as to why this is happening?
Tony

[Cam]

I can't remember to main bearing oil clearance tolerances but I believe the rod bearings are .0002" on the low side. These clearances could have something to do with it maybe.

EDIT: Oil Clearance
Standard
Journals No. 1, 3 & 7 ....... .0002-.0014 (.005-.035)
Journals No. 2, 4 & 6 ....... .0005-.0015 (.013-.038)
Journal No. 5 ............... .0005-.0013 (.013-.034)

These oil clearances seem extremely restrictive (.0005 on the thrust bearing). When they get hot there is more thermal expansion and I believe those clearances just won't cut it.

[TomsSVX]

Failures are sudden and usually not accompanied by low oil pressure prior to failure. This indicates there is something that happens that allows the bearing to spin right out...

The bearing is getting too hot from an oil film that was too thin.

Too hot from an oil that was too heavy with clearances too small.

Or my best guess, the rod bolts are stretching at High RPMS which is enough to misshape the bearing.

Tom

[SilverSpear]

Originally Posted by TomsSVX

Failures are sudden and usually not accompanied by low oil pressure prior to failure. This indicates there is something that happens that allows the bearing to spin right out...

The bearing is getting too hot from an oil film that was too thin.

Too hot from an oil that was too heavy with clearances too small.

Or my best guess, the rod bolts are stretching at High RPMS which is enough to misshape the bearing.

Tom

Do you think that the Eagle rods and ARP bolts will fix this issue?

And why the problem is happening always with #5?

[TomsSVX]

Originally Posted by SilverSpear

Do you think that the Eagle rods and ARP bolts will fix this issue?

And why the problem is happening always with #5?

Should address it but might not be a "fix"

Not always #5... but it is late in line for oil and it is on the thrust bearing feed... Not entirely sure

Tom

[dynomatt]

Thrust bearing feed? Without the book in front of me, what could that mean?

And other than #5, what others have you seen go Tom?

M

[TomsSVX]

#2, #4, & #1

No real logic to it but the stretching theory holds a little Merritt. Reason being, the rest of the bearings don't look overheated or worn out totally like you would see if there was an oil system error or fault. Its simply is the first bolts to stretch and cause an issue while slinging the bob weight around at high RPMS

Tom

[dynomatt]

Is there a way to identify if stretch was the culprit? Are there obvious signs? Or is it just measuring bolts?

[Cam]

Originally Posted by TomsSVX

#2, #4, & #1

No real logic to it but the stretching theory holds a little Merritt. Reason being, the rest of the bearings don't look overheated or worn out totally like you would see if there was an oil system error or fault. Its simply is the first bolts to stretch and cause an issue while slinging the bob weight around at high RPMS

Tom

It would seem that if a bearing was starved for oil due to the oil being too thick to pass through the clearance it would be isolated to a single bearing as well. Are the bearings that are used on the EG33 from the factory tri-metal?

[TomsSVX]

Originally Posted by Cam

It would seem that if a bearing was starved for oil due to the oil being too thick to pass through the clearance it would be isolated to a single bearing as well. Are the bearings that are used on the EG33 from the factory tri-metal?

Problem with identifying the fault is that the bearings and rods with the bolts are usually toasted.

The factory bearings are AL. meant to withstand high mileage not high heat

Tom

[SilverSpear]

Other than a super expensive drysump system, any ideas how we can permanently fix this problem?

[TomsSVX]

Stock components are not gonna hold up to 7500RPM abuse for long. You have the lighten the rotating assembly using high quality parts and make sure the oiling system is perfect with the proper clearances

Tom

[Trevor]

Originally Posted by TomsSVX

Failures are sudden and usually not accompanied by low oil pressure prior to failure. This indicates there is something that happens that allows the bearing to spin right out...

The bearing is getting too hot from an oil film that was too thin.

Too hot from an oil that was too heavy with clearances too small.

Or my best guess, the rod bolts are stretching at High RPMS which is enough to misshape the bearing.

Tom

Surely everything indicates a lack of oil cooling. An efficient external oil cooler is required, as is normal practice when an engine is called on to produce above normal power output.

As a means of guarding against stretch and fatigue, it is accepted practice in these circumstances to tighten the big end bolts in excess of normally specified torque figures. The proper way to do this, is to first tighten a sample and measure the stretch while noting the torque applied, until the elastic limit is found and then be guided accordingly.

[TomsSVX]

Originally Posted by Trevor

Surely everything indicates a lack of oil cooling. An efficient external oil cooler is required, as is normal practice when an engine is called on to produce above normal power output.

As a means of guarding against stretch and fatigue, it is accepted practice in these circumstances to tighten the big end bolts in excess of normally specified torque figures. The proper way to do this, is to first tighten a sample and measure the stretch while noting the torque applied, until the elastic limit is found and then be guided accordingly.

Assuming the bolts that have seen thousands of heat cycles are equally different from their OEM specs... Not to mention the stock rods are heavier than they could be and their weights I am sure are not quite as equal as many would prefer. it would be who of whomever is building an engine to simply replace them with better ones.

I agree it could be overheating as well but since the stock engines I have taken apart without failures (not raced either) show relatively equal measurements for film clearance I would not put money on just one bearing overheating while the others show no signs of it. I am not saying its not possible, just saying I believe the answer is not so cut and dry

Tom