1G Measuring 6 bolt crankshaft

[Brandon Nicholson]

Hello there, I got a couple core motors from an old friend and got around to peeling one of them apart, I specked out the crank and am finding that the mains are .0001-.0002 out of the min spec.. it is cold in my house so maybe that could be causing it? The rod journals fall in spec but on the far end. My main question is if this crank is usable at all or not, it will be a balance shaft delete motor with stock pistons and rods w arp rod bolts.

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[1990TSIAWDTALON]

That looks within spec to me. Mains are between 1 and 4 ten thousandths and the rods seem to be sitting at 3 to 4 ten thousandths. I run my mains at .0015"-.0025" clearance and rods I like to keep under .003", preferably .002" clearance. Do the journals feel smooth? It looks like a decent crank to me.

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[We're on Boost]

Marty, what's that number 2.2832 that I see on your chart for the Main Journal diameter? Is that a typo?
But yeah, the numbers he measured look real good to me.

Here's the chart I see for rod and main journal diameters in the 1991 FSM, page 9-16:

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[1990TSIAWDTALON]

Marty, what's that number 2.2832 that I see on your chart for the Main Journal diameter? Is that a typo?
But yeah, the numbers he measured look real good to me.

Here's the chart I see for rod and main journal diameters in the 1991 FSM, page 9-16:

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I pulled it up on a Google search for 4g63 specs. If I measured it and it was the same and smooth journals, I'd have no issue with it. Polishing takes off a tad bit but you have to account for that. In the end, it is the actual final measurements that count, no matter what.

 

[We're on Boost]

No, I mean, that range from 2.2435 to 2.2832 for the main journal, that's a range of 40 thou! It's just plain wrong. The 2.2832 is wrong. The 2.2435 is ok.

 

[Brandon Nicholson]

That looks within spec to me. Mains are between 1 and 4 ten thousandths and the rods seem to be sitting at 3 to 4 ten thousandths. I run my mains at .0015"-.0025" clearance and rods I like to keep under .003", preferably .002" clearance. Do the journals feel smooth? It looks like a decent crank to me.

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Journals feel smooth but one light nick in the number one journal. I think a polish should take it out no problem I was more concerned about the mains being just on the end of the service limit. I believe a standard set of bearings should be fine though I just want to be sure every is correct for the build. I will have to measure the oil clearances once I get bearings

 

[DSMPT]

Assuming the measurements are accurate, it's still within the standard spec. When journals exceed the minimum spec, what you need to do is to use .025mm/.001" oversize bearings or/and mix it with the standard size bearings to adjust the clearance. Also polishing if necessary. A .025mm/.001" oversize bearing is about .0005" thicker than a standard size. In case if you would order the .025mm/.001" oversize bearing set, just don't get confused with .25mm/.010" oversize set, that's a common mistake.

 

[1990TSIAWDTALON]

It is also possible to polish a bearing if it is a bit to tight.

 

[We're on Boost]

I was more concerned about the mains being just on the end of the service limit.

I think that the numbers we've been looking at here are technically not "Service Limit" numbers. They are "Standard Value" numbers.
Service Limit numbers are much looser and they are given in terms of your measured Oil Clearance. Not the journal diameter.
It should be more clear if I show the entire page 9-16 from the factory service manual.
There you see that the Standard Value for rod and main oil clearance ranges from .0008 to .0020 inches.
But the Limit for rod and main Oil Clearance is 0.004 inches!
The Limit column is empty on the lines where journal diameters are given. Only Standard Value is given for those things.

"Looser is better" is kind of a motto with race engine builders.
Your "worst" main journal is 2.2431 which is only .0002 smaller than the smallest "Standard Value".
I think it's fine, as long as the journal is smooth and doesn't have more taper or out of round than it should, and from your sketches it seems you've already looked for out-of-round and that is way less than the .0006 they show on the chart.

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[donniekak]

The most important things are roundness, and no high spots. 4g’s have a good oiling system, just match viscosity of your oil to you clearances and usage.

Fwiw we ran .0045” on the rods and mains in a 1300+hp build and it worked great in a drag application with vr1 50 and dominator 60.

We ran the mains so big because the block and crank were flexing so much, they needed room to move. On inspection there were no signs of oiling problems.

In street apps I shoot for .0025”-.003”.