4.0 oversized bearings.

[vbrad511]

Hey all, I'll be taking some time off work next month to do some work on my '97. One of the things I'm planning on is pulling the motor to reseal the oil pan, and replace the lower end bearings. It's got a bit over 300k on the 4.0, and I'me wondering if I should use standard sized bearings. In other applications I've seen .002 oversized, and wondered if they're available somewhere for the 4.0, and if I should step up to them, given the miles on the motor. Yes, I know I should tear it all down and do everything, but I won't have the time for the downtime, as it's my work truck.
Thoughts?

 

[Uncle Gump]

Using .020 oversized bearings on a worn std. crank journals?

Sounds like complete disaster to me.

 

[vbrad511]

Using .020 oversized bearings on a worn std. crank journals?

Sounds like complete disaster to me.

Oops...I meant .002

 

[Uncle Gump]

Even then... never would do that.

I'd inspect and measure things first. Then get the correct bearings... if the crank is serviceable.

If the crank is worn to the upper limits of std. size... I'd still run std. bearings and use a high volume oil pump.

 

[Uncle Gump]

And just so we're on the same page...

Oversized crank bearings are typically

0.010
0.020
0.030

 

[19Walt93]

You want under size bearings, not over size. The cranks isn't worn bigger than when new.
Ford used to sell bearings in tiny under sizes- standard red was actually standard, standard blue was .001" under size, and .002 and .003" were both available. I'd mic everything before getting your bearings. The alternative would be buying standard bearings and plasti-gauging them. If there was too much clearance you'd end up paying for 2 sets. Failing that, if you don't have a way to measure the crank accurately and it looks good, just install new standard bearings.

 

[Uncle Gump]

Walt is correct... undersized.

Most of my engine rebuilding was with air cooled VW engines. Most engine cases were bored to straighten them up. So... those bearings were oversized and undersized.

I've never used any of those small increment bearings. But after you mentioned it... I think i did hear of them. How long has it been since they made those? Or am I way out of touch with common rebuilding practices?

 

[alwaysFlOoReD]

I'm way out of touch...
But I've heard of mixing and matching bearing to get the correct clearances. Eg: one half regular and one over(under) size.

 

[vbrad511]

You want under size bearings, not over size. The cranks isn't worn bigger than when new.
Ford used to sell bearings in tiny under sizes- standard red was actually standard, standard blue was .001" under size, and .002 and .003" were both available. I'd mic everything before getting your bearings. The alternative would be buying standard bearings and plasti-gauging them. If there was too much clearance you'd end up paying for 2 sets. Failing that, if you don't have a way to measure the crank accurately and it looks good, just install new standard bearings.

Great. This is what I'll do. I won't have the time to fully break down the engine and do everything I'd like to do to it. It's got a leaky oil pan gasket that needs replaced, so it's the perfect time to check the bearings too. Thank you

 

[SenorNoob]

Leaky oil pan gasket. Runs good otherwise with no noises? I'd grab the crank and try to rock it. If I couldn't see movement I wouldn't touch those main bolts.