Hello! I'm putting my 350 back together after machine work, and my initial measurements show that my rod bearing clearances may be too tight. The crank is .010" under on all journals, and the rods have been reconditioned. I ordered all of my bearings from TA. If my measurements are right, I may be about .002" too tight. Where can I get a .009" or .008" bearing?
.008/.009 bearings would be tighter. You would need .012 to do what you want. It's been long time since I've done much engine rebuilding but, back in the day you could get .001, .002, .003 undersize bearings so you could bring a slightly worn crank back in to proper clearance. If that didn't work you would need to have the crank ground to .010, which is what you've done. They make .010, .020,.030 undersise bearings but that's it! How are you measuring this? Have you tried Plastigage? Is the crank siezing when you torque the rod bolts? Check your bearings, they should have .010 stamped on the back, if not, they may be .020 bearings.
I like to check everything with plastigage as one last confirmation before I stick it all together. That should confirm what you mic out the clearances to be.
If crank was ground .010 and rods resized .010, it can't be .002 too tight. How did you measure? Mic the rod jrnl, bore gage the bearing with torqued rod cap. Use a .0001 dial gage.
I think you may be getting confused. If the rods and mains are .010 under, you get +.010 bearings. The big end of the rods being resized means they took a bit off the mating surfaces of the cap and rod, bolted them back together then machined the big hole back to stock specs. The rod big end has NOT changed from stock, other than it’s round again.
Yes, I do believe I was confused on terminology. But my inconsistency with my measuring tools (pictured) was causing the weird math. For instance, all of my rod journals on the crank mic'd out at 1.990, but I kept getting measurements of 1.990 or .19895 for instance inside of the rods with the bearings in and the caps torqued. I wanna blame that on the little "T" that I was using, as I can only eyeball with it. It's very hard to center and keep straight, especially when you have to lock it. I've ordered a dial bore gauge supposedly accurate to .0005" but until then I plastigaged my mains. They came out fine. I decided to try the #1 rod, and though it may have been cocked, it showed more clearance than my previous measurements regardless. I'm looking forward to what I see with the dial bore gauge.
OK, if some of your rod journals are too tight, you can polish them a little more to gain some clearance. Too tight is easier to fix than too loose without going undersized and starting over.
Chassis Service Manual specs are as tight as .0007 I believe. .0015 would be good. Better than over .002
The telescoping(or snap) gauges that you have are designed to be "rocked" in the bore. Basically, what you do is you loosen the clamp screw so that it barely holds the anvils in place. Place it in the bore at a very slight angle so that the anvils( or T) would be slightly larger than the bore and set the clamp screw to barely hold the anvils in position. Then, "rock" the gauge in the bore, which will then squeeze the anvils down to the smallest distance and the clamp screw will hold the anvils at that position. Then, you simply use your micrometer to measure across the anvil tips to get your dimension. They are self-centering when rocked in the bore this way. I will try to post a short video tomorrow on how to do it. With a quality set of telescoping gauges and micrometers, and a practiced hand, you can get very accurate and repeatable measurements(within a tenth or two of a thousandth), despite what a lot of people say. Hard to explain, but really easy to do, once you know how.
Having precision measuring instruments is a good thing to have, IF you know how to use them and interpret the readings, if not it will cause a lot of frustration. I have a few of those instruments and it still confuses me, my Dad was a design engineer for Alcoa here in Cleveland, he could spit out decimal or fractional equivalents without thinking twice, I guess I missed that gene
Made a short video. Will upload when I get home. Edit...Here it is... The key is to find a bore that you know what the diameter is and just keep practicing and get a "feel" for the touch you need. Practice, practice, practice. It's a lot tougher to get a feel for it with some lower quality import brand telescoping gauges. I've got an import set that just drove me nuts. I don't generally like Starrett stuff, but they have probably the best telescoping gauges out there. Pricey, yes, but worth it. Mitutoyo would be my second choice. LOVE the Mitutoyo micrometers and dial calipers. Then, measure your bore. Do it a couple times to get the repeatability. Make sure the screw is not too tight. If it is, you could scar up a soft bearing surface. It just needs enough tension to hold the telescoping anvils in position, but still allow them to move when you rock it in the bore. Setting up a dial bore gauge can be tricky as well. Even being a machinist for a number of years, we still have to check it a couple of times to get it right. Any questions, just ask.
