Tighter Bearing clearance Vs looser

[PackardV8]

The better the parts are, the tighter you can run them.

To that, add "the more accurate the machining, the closer the temperature control, the tighter you can run them."

Today's OEM economy car engines have more accurate machining, better metallurgy and better temperature control than the best blueprinted race engines from back in the day. Check out the radiators in today's cars. They have less water in the block and radiator than the heater and defroster cores of an older car. (Those of us old enough can remember when they were two separate systems.)
As I mentioned earlier in the thread, .0005"-.0025" was an acceptable range for main bearing clearances back in the day. With better, lighter oils, better parts, more accurate machining available to us, temperature control is the one area which is still not done to best science on most builds today.

thnx, jack vines

[Warp Speed]

Hmm.. lest see....

$13,000+ engine vs. MAYBE a few hp through better oil ctrl...

Without a NASCAR engine building budget....I'll take the larger clearance.

Doesn't take a Nascar budget, just spending what you have wisely.

[robert1]

I did a fair amount of research on this last winter for a project I was working on. I got a couple of names of Nationwide builders from someone close enough to these guys that they would give me reliable data. First off the only ones I know of running .0015" clearance are IRL sized journals, 1.850". I talked at length with the builders about the oil they used and their clearances. From what they told me 0wt oil made 7-8 hp over 20w 50 at temp. I opted to stay with standard clearances and thick oil. This is a circle track application. In a drag car I would think you could easily run standard clearances and thin wt oil.

[rmcomprandy]

The oil, the temperature, the oil pressure, the amount of engine torque at what RPM all play a major role in deciding upon the amount of clearance. To loose is always better than to tight; being "just right" is well - just right.

That could be almost anything and reading the bearings during much testing is the only way to get there.
Finding that dimension where it is as tight as you CAN run them is not an easy proposition and that is the point I was trying to make.

You'll need to go past the point of being "just right" to the point of being to tight in order to find it.

[Ron C.]

In a drag car I would think you could easily run standard clearances and thin wt oil.

You can and I do. Redline Racing Synthetic and coated bearings and....blown gas to boot. The bearings are always happy.

Blessings................Ron.

[Engguy]

Unless your engineering your own parts, rather than using a mix match of off the shelf performance parts. And not knowing the charateristics of the materials. Your are much better off, listening to someone that knows from years of experience. I would go with Joe on this one.

[3V Performance]

Unless your engineering your own parts, rather than using a mix match of off the shelf performance parts. And not knowing the charateristics of the materials. Your are much better off, listening to someone that knows from years of experience. I would go with Joe on this one.

Has anyone done any testing with the lower viscosity oils and tighter bearing clearances?
I was trying to decide whci way to go this winter if its worth it power wise to use the lighter oils vs the heavier wt.

To answer the origanal question. YES.

To say to run tighter in a street engine and NOT in a race engine just does not make any sense. We hold tighter tolorances on race engines and do better machining, use better parts and controll temps better. To me this makes for a perfect place to run tighter clearances.

[SWR]

Depends a whole lot on what "drag engine" you're talking of. Had a dragrace engine with 0.0026" rod clearances,and they lasted about a race,then they were dead (started knocking). Rebuilt it to 0.0013", they still run..and that's been a few years..

[MadBill]

On the other hand, if a high RPM drag engine is getting some big end bore distortion, 0.003" + clearances may be just the needed band aid to prevent the sides from pinching off the oil film...

[RW TECH]

I've referened an OEM development project that I worked on several times in this forum that slaughtered every championship & won everthing there was to win in dessert racing back in the late 90's going into the early 2K's. This included winning the Baja 2000, which was a 2,000-mile race in every climate/altitude extreme with peak engine speeds near 8-grand.

The crank stroke in that engine was 4.160" and neither rods or mains were ever set any looser than .0017". Rods were usually .0012" and mains were .0015".

This same configuration was fired up on the dyno, thrown to WOT/6500 RPM, and left there for several consecutive 8-hr. shifts.

We NEVER wounded anything in the lower end.


I've always found the oil temperature DECREASES when main bearing clearances are REDUCED TO A TIGHTER VALUE, thus a reduction of oil that gets the s**t whipped out of it when it hemmorages out from the bearing & all over the crank throws.

Unless you run a lot of flexible parts there isn't a real good reason to run bearings at loose clearances. If you're running a 4" stroke crank with 1.875" rod journals & 2.300" mains, then I'd say you're stuck running looser clearances to avoid tearing things up.

[jamie]

How about aluminum rods? Do they take less clearance because they expand when they heat up?

[RW TECH]

How about aluminum rods? Do they take less clearance because they expand when they heat up?

It'll be amusing to hear some of the backwards responses this one will draw..

[3V Performance]

I've referened an OEM development project that I worked on several times in this forum that slaughtered every championship & won everthing there was to win in dessert racing back in the late 90's going into the early 2K's. This included winning the Baja 2000, which was a 2,000-mile race in every climate/altitude extreme with peak engine speeds near 8-grand.

The crank stroke in that engine was 4.160" and neither rods or mains were ever set any looser than .0017". Rods were usually .0012" and mains were .0015".

This same configuration was fired up on the dyno, thrown to WOT/6500 RPM, and left there for several consecutive 8-hr. shifts.

We NEVER wounded anything in the lower end.


I've always found the oil temperature DECREASES when main bearing clearances are REDUCED TO A TIGHTER VALUE, thus a reduction of oil that gets the s**t whipped out of it when it hemmorages out from the bearing & all over the crank throws.
Unless you run a lot of flexible parts there isn't a real good reason to run bearings at loose clearances. If you're running a 4" stroke crank with 1.875" rod journals & 2.300" mains, then I'd say you're stuck running looser clearances to avoid tearing things up.

Your letting out speed secrets..

[RW TECH]

Your letting out speed secrets..

LOL!!!

Speed Secrets = Information that wouldn't be very difficult to establish with proper means to measure that those who either did measure or stumbled acrossed it by accident aren't willing to tell to other people.

[blwilliams]

Over the years I have learned that if the bearing is too tight, the crankshaft will make what ever room it needs. LOL
Personally I have never had a bearing fail from being too loose, on the other hand, re-read the first paragraph.
Just my .02
Like already mentioned, in a drag race engine, it is difficult to get you oil to temp and keep it there with all the sitting in the staging lanes.
I believe all the Pro Stockers like to run with hot (very light weight) oil and ice water in the radiator. As far as there bearing clearances go I can only make an educated guess.