[Dragncar]

Originally Posted by steve25

Hey gang let’s drop the notion that a anti friction coating can be used to tighten up a bearing clearance issue, it’s not made for that purpose!

The RA4 motors had a rod bearing clearance spec range of up to .003” like you say you have, so as others have said just run it.

If you feel you’ed like some added protection then run a Qt of Lucus oil supplement, it good practice in general anyway at least during the Summer months if you do not have a oil cooler

So, if you want to run a .001 coated bearing by your logic you should have .001 less than optimal clearance ?
I don't buy it.
Coated bearings are better than non coated bearings and clearance is clearance.
The oil does not know the difference.

[NeighborsComplaint]

Originally Posted by HWYSTR455

King bearings make +.005 bearings, but honestly, resizing the rods are a better option.

How would that improve the clearance between the bearing and the rod journal? Resizing is done to correct out-of-round condition. The bearing shell is a fixed dimension, only the thickness of the bearing material changes accounting for undersize and clearance.

[mgarblik]

I have seen +.002", .003 and .005" rod bearings available for some modern engines like the LS GM, some Chrysler stuff and some Ford engines with the "cracked rod, powdered metal " connecting rods. No other way to rebuild those when they are all messed up or have spun bearings. Because you can't cut the cracked caps, that is your only option other than replacement. Haven't seen these bearings available for any of the old engines, but they could exist I guess.

[Sirrotica]

You can get damn near any bearing size you could dream of for a sbc, but the only extra clearance I've ever found for a Pontiac is a -.001 for Ram Air rods, and only in a standard size journal, no extra clearance bearings, or undersized in .001 increments, as far as I've ever known in 50 years.

The moral to the story is your crank grinder better get it right the first time he cuts it, or you will be swapping different brands of manufacturers in to get where you need to be. I have even had to use and old bearing half, with a new bearing half to get desired clearance. There is a lot more leeway when you have too much clearance, as opposed to being too little clearance. When the crank heats up you're going to tighten the oil clearance up anyway, so better to have more room for expansion, than too little to begin with.

I've done a lot of Stratosteeak autopsies where there wasn't enough clearance to start with, resulting in too little room for an oil wedge to keep the parts from direct contact. Spun rod bearing, probably a broken rod, and flow through ventilation in the block, and pan.

[hurryinhoosier62]

Originally Posted by mgarblik

I have seen +.002", .003 and .005" rod bearings available for some modern engines like the LS GM, some Chrysler stuff and some Ford engines with the "cracked rod, powdered metal " connecting rods. No other way to rebuild those when they are all messed up or have spun bearings. Because you can't cut the cracked caps, that is your only option other than replacement. Haven't seen these bearings available for any of the old engines, but they could exist I guess.

Mike, we had +.001, +.002, +.003, +.005 and +.010 main bearings for aircraft recip engines because you could only grind the cranks .010 under as a last resort. In the few “cracked cap” rods I dealt with before I retired in 2011 I saw few that were actually spun; they tended to be more out of round than anything. I don’t trust that technology. The ONLY .001 +/- rod bearings I’ve seen for Pontiacs are the ones Butler carries and the ones for BBC rods used in Pontiacs with 2.200 rod journals.

[HWYSTR455]

Originally Posted by NeighborsComplaint

How would that improve the clearance between the bearing and the rod journal? Resizing is done to correct out-of-round condition. The bearing shell is a fixed dimension, only the thickness of the bearing material changes accounting for undersize and clearance.

Crush.

Big end tolerance is +- .0003, roughly, and can be 'played' with. How crush varies depends on the bearings/material.

True on the bearings for Pontiac 2.249/2.250 rods, I use 2.20 rods, my bad on the availability of + bearings.


.

[mgarblik]

Originally Posted by hurryinhoosier62

Mike, we had +.001, +.002, +.003, +.005 and +.010 main bearings for aircraft recip engines because you could only grind the cranks .010 under as a last resort. In the few “cracked cap” rods I dealt with before I retired in 2011 I saw few that were actually spun; they tended to be more out of round than anything. I don’t trust that technology. The ONLY .001 +/- rod bearings I’ve seen for Pontiacs are the ones Butler carries and the ones for BBC rods used in Pontiacs with 2.200 rod journals.

That makes sense. When your thousands of feet in the sky, tolerances, specs. and exact procedures are a life and death decision.

[hurryinhoosier62]

Originally Posted by mgarblik

That makes sense. When your thousands of feet in the sky, tolerances, specs. and exact procedures are a life and death decision.

What really kills is loosing an engine fifty feet off the ground. I’ve had two friends killed in aircraft crashes over the years. Both had engine failure fifty feet or less off the ground. To even grind an aircraft crank .010 requires removing the nitriding from the crank, grinding the journals then having the crank nitrided again before finish polishing.

[KEN CROCIE]

Had to look it up! from my 64 service man.!
Rod clearance WHEN NEW = .0005"-.0025".
Which implies . to me at least, .0005" wear would not be a problem.
in fact I have built street engines @ .0030" - .0035" with no problems, except being a little low oil pressure at idle. A change to 20/50 fixed it. Personally, I would run it.

[Jay S]

I didn’t see it mentioned, what rod bearings are they? What brand, which type.

I tend to allow a different range for different types of bearings.

Stock replacement aluminum bi metal type bearing .0015 to .003’, preferably .002” to .0025”

trimetal .002” to .0035, preferably .0025” to .003”.

Coating tri metal would be a great option at .003”.

Trimetal has a pretty thin aluminum overlay, doesn’t take much to burn thru it if something isn’t quite perfect with tight clearance’s. Stock type bi metal conforms and wears better with tight clearence’s, much thicker overlay. Not sure Clevite even offers bimetal aluminum type bearings anymore, king and seal power do.


I know of a 455 that has .0035”, seal power trimetal bearings, (FM) and has 40K of really tough miles on it. 15w40 oil. It just got put in a different vehicle and inspected, the bearings were pretty much used up. With the abuse it had, it fair pretty decent though.

[steve25]

I guess one can resort to using the special oil developed for the Pratt & Whitney Ram Jet engines that where used in the A-12 and the later SR-71 spy planes.

This oil was solid at 60f like wheel bearing grease and had to be at 85 degrees before it even started to flow at all , lol!

[hurryinhoosier62]

Originally Posted by steve25

I guess one can resort to using the special oil developed for the Pratt & Whitney Ram Jet engines that where used in the A-12 and the later SR-71 spy planes.

This oil was solid at 60f like wheel bearing grease and had to be at 85 degrees before it even started to flow at all , lol!

Uh, the J-58s used the same turbine engine oil as the rest of the Air Force’s turbine engines. It went into ramjet mode at speeds over Mach 2.5. It couldn’t be solid at 60F because the engines wouldn’t start. The SR-71s flew out of Great Britain for years. It gets a tad chilly in Great Britain in the winter.

[Cliff R]

I didn't see it mentioned or may have missed it, but you are checking them exactly 90 degrees from the parting lines, right?

For engines built here, I prefer to be on the mimimum spec vs the maximum........

[steve25]

There was what was called a start cart for each engine.
The cart had 2 Buick V8 engines that thru a special drive set up would spin the engine up to a certain rpm where they could be injected with a special fuel used just to get them up to there 3200 rpm idle speed.

Later versions of the start cart used 454 Chevy motors.

[Tim Corcoran]

Originally Posted by KEN CROCIE

Had to look it up! from my 64 service man.!
Rod clearance WHEN NEW = .0005"-.0025".
Which implies . to me at least, .0005" wear would not be a problem.
in fact I have built street engines @ .0030" - .0035" with no problems, except being a little low oil pressure at idle. A change to 20/50 fixed it. Personally, I would run it.

I would take anything this man says regarding Pontiac pretty damn solid advice.

[hurryinhoosier62]

Originally Posted by steve25

There was what was called a start cart for each engine.
The cart had 2 Buick V8 engines that thru a special drive set up would spin the engine up to a certain rpm where they could be injected with a special fuel used just to get them up to there 3200 rpm idle speed.

Later versions of the start cart used 454 Chevy motors.

There was ONE start cart per engine that contained TWO 401 Buick “nail head” engines coupled to one “generator” . Spent nearly 25 YEARS maintaining turbine engines of all types; turboprops(fixed and free turbine), turbojets, turbofans and turboshafts. ALL of them use one of the three types of turbine engine oil; all of them have the consistency of water because they are all synthetic and have to be able to run lubricate down to-60F. The fuel was JP-7, a super refined version of aviation kerosene that was incredibly stable. It was used for fuel, coolant and hydraulic fluid in the SR-71. It was ignited through a chemical ignition(triethylene boron) because a normal spark ignition would not ignite JP-7. 3600 rpm? Try much higher. Most turbine engines I dealt with “light off” at around 13-17% N1 (primary turbine speed). Many earlier turbojets (J-58 was identified as an after burning turbojet by P&W)had start speed as high as 61% N1. Primary turbines speeds, when measured in rpms, are in the neighborhood of 10,000-15,000 rpm at start up with operating speeds as high as 40,000 rpm. The TEB was injected into the J-58 at 3,200 rpm for the engines in the start set.

[Tim Corcoran]

Originally Posted by hurryinhoosier62

There was ONE start cart per engine that contained TWO 401 Buick “nail head” engines coupled to one “generator” . Spent nearly 25 YEARS maintaining turbine engines of all types; turboprops(fixed and free turbine), turbojets, turbofans and turboshafts. ALL of them use one of the three types of turbine engine oil; all of them have the consistency of water because they are all synthetic and have to be able to run lubricate down to-60F. The fuel was JP-7, a super refined version of aviation kerosene that was incredibly stable. It was used for fuel, coolant and hydraulic fluid in the SR-71. It was ignited through a chemical ignition(triethylene boron) because a normal spark ignition would not ignite JP-7. 3600 rpm? Try much higher. Most turbine engines I dealt with “light off” at around 13-17% N1 (primary turbine speed). Many earlier turbojets (J-58 was identified as an after burning turbojet by P&W)had start speed as high as 61% N1. Primary turbines speeds, when measured in rpms, are in the neighborhood of 10,000-15,000 rpm at start up with operating speeds as high as 40,000 rpm. The TEB was injected into the J-58 at 3,200 rpm for the engines in the start set.

What does this have to do with rod bearing clearance?

[Mr Twister]

I think North Korea just updated their jet engine playbook.

[track73]

I have in some cases when I wanted a half a thousanth less clearance took the rod cap and sanded it on a piece of glass with 600 wet or dry sandpaper until the machine marks were gone. Don't forget the clearence at the parting line is more to allow for the elongation of the big end during high rpm runs.

[hurryinhoosier62]

Originally Posted by Tim Corcoran

What does this have to do with rod bearing clearance?

Looks like steve25 decided to delete a few of his posts. Simple answer: there is ZERO turbine oil the consistency of grease, period. Likewise, no amount of “miracle oil” is going to “cure” bad machining on the rods or the crank. Mike gave what I consider to be the ONLY way to set the ID on the rod big end: have a .0005 tolerance.