7M bearing size confusion!

[CyFi6]

Trust me it took me a while to figure out the Toyota bearing system, it is a little funky. I had to ask a lot of the more knowledgeable members on here how to use it.
They are actually called undersize bearings, but I couldn't tell you how to get them, I have never needed them. Like I said if you decide you need to go undersize, you might as well use an aftermarket bearing.

I'm not 100% sure on the bearing prices off the top of my head, I ordered them along with a bunch of other things, I will check my receipt and let you know though. I want to say around $15 for the rods each and $20 for the mains.
A word of advice, when you get the bearings, if you are getting them from your dealership, upen the boxes and check them right there. Make sure all of them are OK and in the plastic shrinkwrap, I got a bearing from them once that was opened up and looked like it was dropped on the floor, had to take it back to return it.

 

[Backlash2032]

I only need one which is why I'm still debating getting the Toyota bearings. I pmed Jeff on the topic, so hopefully he replies quickly. Also, I will be ordering the bearings (if I decided to go toyota.. Im still on the fence.. then jumping to one side.. then climbing up the fence again.. lol) from Champion toyota

 

[CyFi6]

Jeff will help you out, pretty sure he knows how all this works better than most. If you need one undersize bearing, there is something wrong. Either someone machined something or you have measurements that aren't correct somewhere.

 

[Backlash2032]

I guess my only explanation is the number 6 journal was machined at one point.. Along with the number 6 main bore.. Which makes no sense to me.

I'll have things re-measured just to double check.. The main bearing bore is only .0002 off, so it could just be human/tool error, and I could see someone machining one journal on the crank. The journal is off by .0003. With these measurements it falls perfectly into the oversize slot on the table..

 

[CyFi6]

Keep in mind that an undersize bearing is used to correct for a crankshaft that has been cut. When main bearing bores are line honed, they are always brought back to the original bore size (they shave the cap down, then bore it round again to give a perfectly round bore that is the exact same size as it was from the factory). When a crank is cut, you end up with a smaller diameter, so you need to use a bearing with a thicker center wall to take up for the material taken off the crank. When you pulled the motor apart, what size bearing was in that spot? What did the wear look like?

 

[Backlash2032]

I believe it was a number 4 bearing there. Clearance was on the high side of being in spec.

But the thing is.. I'm using the crank out of the block the machine shop cracked, in a different block. Is it mere coincidence that that one journal matches up with the one in the block? This is so weird..

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[Backlash2032]

Bump.. I need to order bearings soon.

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[Backlash2032]

So. I figured out bearing sizes for all journals. I just threw the chart out the window and did the subtraction myself.

I still have two questions though. I have the rods at .0014. On all the rod bearings, I can use a #5 bearing and bring 3 to .0009 (spec is .0008-.0021), and 1 to .0010, and 2 to .0011. Should I do this?

On the mains, most of them are #5 bearings, but 3 are not. I could also close up the clearances on the mains by going with one size larger bearing. Should I do this? Or is it a bad idea to have mix matched clearances?

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[CyFi6]

I aimed for around .0015" on my rods, right in the middle of the range. One of my mains needed a #5 bearing, which put me at .0016", and because of this, I aimed for .0016" for all the other mains, to keep them even. You don't want one bearing on the tight end of spec and one on the loose end ideally.

 

[Backlash2032]

Okay! Thank you! Now I just need to know which part number is for the #1 main and I can put it my order!

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[CyFi6]

11071 is the front and 11701 are the others. Sorry forgot you asked that lol

 

[Backlash2032]

Its okay. Thank you, you've been a huge help! Hopefully my bearings will be here soon and there will be progress in my build thread!

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