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1993 Del Sol
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You are correct, its uncommon to just slap in oversized bearings and roll haha, unless you had prior knowledge of the crank being turned.

Machining or polishing the crank for new bearings is assurance the journals are straight and flat, and a standard rebuilding practice, because the new bearings going in will be very flat. Even if the crank seems flat, it could vary if its been used and abused before, meaning your measurements of oil clearance might show one reading in one spot, and another somewhere else.

Keeping things even and flat across the board is usually the goal when choosing oversized bearings. The machinist will cut the crank the right amount to stay within OEM spec oil clearance while using the oversize bearings.

Rule of thumb: if the crank has never been turned before, yet your oil clearances are way out of spec and requires the thought of oversized bearings to make up the slack, the crank needs to be turned, and the proper oversized bearings selected to achieve the proper oil clearance.

Just slapping in oversize bearings on a crank to bandaid oil clearances is exactly that, a bandaid, with no guarantee of flatness. It honestly should be turned at the machine shop, and oil clearances restored the correct way, unless of course you have prior knowledge of the crank being turned and it hasn't been used much.

My 2 cents :)
Great, I knew I wasn't crazy 18 years in the game. I had a friend who spun a rod and decided to just stick in oversized bearings at home, then called me complaining the block was making a really messed up noise lol.

As for the oil cooling I still want to hear his explanation on that.. Who knows? He might just know something we don't, I seldom dismiss an idea just because it seems foreign to me :unsure:
 

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Discussion Starter #22 (Edited)
You are correct, its uncommon to just slap in oversized bearings and roll haha, unless you had prior knowledge of the crank being turned.

Machining or polishing the crank for new bearings is assurance the journals are straight and flat, and a standard rebuilding practice, because the new bearings going in will be very flat. Even if the crank seems flat, it could vary if its been used and abused before, meaning your measurements of oil clearance might show one reading in one spot, and another somewhere else.

Keeping things even and flat across the board is usually the goal when choosing oversized bearings. The machinist will cut the crank the right amount to stay within OEM spec oil clearance while using the oversize bearings.

Rule of thumb: if the crank has never been turned before, yet your oil clearances are way out of spec and requires the thought of oversized bearings to make up the slack, the crank needs to be turned, and the proper oversized bearings selected to achieve the proper oil clearance.

Just slapping in oversize bearings on a crank to bandaid oil clearances is exactly that, a bandaid, with no guarantee of flatness. It honestly should be turned at the machine shop, and oil clearances restored the correct way, unless of course you have prior knowledge of the crank being turned and it hasn't been used much.

My 2 cents :)
The crank was taken to a machine shop and was polished and I'm assuming it was machined true. I thought by "turning" you meant that the goal was to remove material for oversized bearings. The machinist recommended I get oversized bearings on just the mains, but leave STD bearings on the rods. He said either run 10w-40 or 20w-50. The crank has about 50 miles on it since it's been polished, so would I be fine to put some oversized bearings in it?

As for the oil being cooled better with larger cleranaces, I read it on an enginebuildermag bearing clearances article. I didn't look into it too much just because I decided to do what the machinist told me to do.
 

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Discussion Starter #23
The crank was taken to a machine shop and was polished and I'm assuming it was machined true. I thought by "turning" you meant that the goal was to remove material for oversized bearings. The machinist recommended I get oversized bearings on just the mains, but leave STD bearings on the rods. He said either run 10w-40 or 20w-50. The crank has about 50 miles on it since it's been polished, so would I be fine to put some oversized bearings in it?

As for the oil being cooled better with larger cleranaces, I read it on an enginebuildermag bearing clearances article. I didn't look into it too much just because I decided to do what the machinist told me to do.
 

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As for the oil being cooled better with larger cleranaces, I read it on an enginebuildermag bearing clearances article. I didn't look into it too much just because I decided to do what the machinist told me to do.
I am in the camp of turbo builds should be looser and run heavy oil. The pressure should be maxed at idle cold. Wait until the pressure comes down under 40psi at 1000rpm before beating on it. I want to see 10psi of pressure per 1000rpm with up-to-temp oil.

I might be in the same boat as you right now. I'm doing a new build with about those clearances and I'm guess the oil pressure will be low. Oh well, hopefully everything comes together soon and I will find out.

Instead of running thicker bearings, you might consider having your rods cut and honed. You can actually make the ID of the rods smaller. You can't go much or you'll over crush the bearing. You'd have to discuss this with an engine builder.
 
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