3.0 Case Mains Evaluation

[2jmotorsports]

I am checking my 3.0L case mains and they are coming in as follows:

From flywheel towards pulley:

1: 2.5610
2: 2.5620
3: 2.5620
4: 2.5615

I got the gauge on the #5 main but I didnt have enough clearance to get the dial bore gauge "dial reversal" due to the gauge being too short and the dial being right up on #1 main. I had the nose bearing in place so I couldnt come in from the opposite side. My guess is that the rest are similar. Machine shop stated they were checked and are still STD.

I did three measurements roughly a third apart from each other on each main to check for out of round as well as to get an average reading. Id say each one was within .0005 of the other two.

So I am looking at the Bentley manual and it says the following:

Bores 1-8
standard.....(2.5590-2.5598 in.)
oversize......(2.5689-2.5696 in.)

I think I am closer to STD than oversize, so should I just use STD main bearings?
I am going to go with GT3 main bearings and I believe they come in 3 different STD sizes but I have no information on those specs. Anyone recommend what GT3 bearings to go with?

After getting bearings I plan on checking ID again with the bearings in place and probably plasti-gauge to be triple-sure.

Thanks in advance.

[DRACO A5OG]

I would go with STD mains.

For GT3 Mains (Yellow), contact EBS or order them here. Where ever you get them, mic them just to be sure.

[Flat6pac]

Just a point, the mains become tighter as the engine runs. The aluminum expands as the cross bolts remain cooler and steel thermal reaction is less than the aluminum.
Always looked like some slight deviation can be accounted for but a spun bearing on the main can't be corrected by recutting the centerline, as I found out last year.
Bruce

[2jmotorsports]

What are the choices? Red, blue and yellow? What are the thicknesses of these?

I have my crank and case mains measurements as well as the recommended clearances listed in the Bentley, so I guess knowing the available bearing thicknesses I should be able to make a decision.

[Flat6pac]

The colors compensate for crank cut in standard
The colors are color coded on the crank with dots.
The coding has to do with rods as that what it was on the engine I built.
Be careful because oil pressure is resistance to flow so you want the oil moving in and then out of the bearing shell. You can build too tight.
Bruce

[2jmotorsports]

Right. I dont necessarily want or think I need things any tighter than stock as this will be mainly a street motor. The thought behind the GT3 bearings was simply a "reliability upgrade" while we are in there.

[cgarr]

Watch your temps when checking I can turn an out of spec crank into a new one on a hot day! Lol


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[2jmotorsports]

Hmm. You have a point there. Ill recheck the case at 2 different temps and see what happens.

I know aluminum has a higher coefficient of thermal expansion than steel.

[DRACO A5OG]

If I may suggest, Confirm calibration of the Bore Gauge. I had to modify mine a bit to work properly.

[2jmotorsports]

Thanks Jim.

I had my bore gauge and micrometers professionally calibrated before I started the rebuild. I set a micrometer at 2.5590, zero out the bore dial, take my case measurements, then go back to the micrometer to make sure nothing has "moved".

I have not been taking temp into account though. Will check everything again and report back.

Thanks for the constructive feedback so far Gents!

[m42racer]

You cannot determine any sort of deviation between the crank and the bearing without first checking the case main housing bores and alignment.

There will be zero wear on the bearing outside diameter or the main housing bore unless there is some sort of movement. The wear will always happen on the inside diameter of the bearing. Nothing should be moving on the outside.

The main housing bore will make a huge change on the inside sizes as the outside is compressed some when it clamps the bearing in the housing and actually makes the shell round, or should do.

First make sure the bores are round and in alignment. Then fit the bearing shells and measure. The two most important clearances are the #1 and #7 bearing clearances as these provide the oil to all of the rods. #2 thro #6 are important but any add clearances in these bearings can be accepted. The manuals and factory specs are there to give guide lines, but you can "cheat" on some things if you understand what and why.

Check your journals for size and taper. Do the line bore check, if ok, re measure with mains fitted and do the math. Remember to torque the case bolts as if you were assembling the engine. All of them. Without knowing the journal sizes, its hard to say if the extra 0.001" is in the bearing only.
If it is and the case is good, then swap around the bearing shells and see if it gets any better. Move an upper shell to another lower one and see if anything changes. As I said, you can go a liltle bigger on the clearances on the mains that don't feed the rods.

The rods are the only bearings that come in 3 sizes of std. the red and blue bearings will give +/- 0.001" of clearance in the vert direction.

You do need to measure the #5,6 & 7 mains as these are typically the ones the most out of round. This is the end the crank moves the most. If the reach of your bore gauge is not enough, then fit up the case with the nose bearing and torque it all up. Then get a small diameter dowel pin and with the correct drill and reamer fit the dowel pin to the front of the case halves. There is room at the front on the casting. Then dissemble and fit up without the nose bearing with the dowel pin in place and re measure the front mains. Or borrow a longer reach gauge.

Throw the plastic gauge in the trash. You want to know if its correct, use the gauges you have already.

[2jmotorsports]

After doing some measuring with my old (OE) bearings back in the case with everything torqued to spec, I am finding my radial clearance to be around .0021"-.0026" which is on the large end of the allowable range of .0003"-.0028".

Doing some research on the GT3 mains it looks like the yellows are the nominal clearance, the reds are .0005" larger and the blues .0005" tighter.

I have managed to source the bearings at EBS but still unsure which color to buy. I dont know, for example, how the yellows compare to the STD regular bearings. Anyone have a link to what the measurements are on the GT3 yellows so I can pick the right ones?

Thanks in advance.