Machined crank confusion.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
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Machined crank confusion. Got my engine back from the machine shop. Started measuring my crank. They said it was just polished. After measuring my crank I’m consistently getting 2.0775 to 2.0774 on my Rod journals. I’m not experienced with this kind of work but am I wrong that 2.100 is the factory Rod journal size on an Ls crank? With my new bearings in my rods I am reading .0035 bearing clearance I want .0025. Am I missing something? Please help and thanks in advance.
TECH Apprentice
Joined: Aug 2018
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Got my engine back from the machine shop. Started measuring my crank. They said it was just polished. After measuring my crank I’m consistently getting 2.0775 to 2.0774 on my Rod journals. I’m not experienced with this kind of work but am I wrong that 2.100 is the factory Rod journal size on an Ls crank? With my new bearings in my rods I am reading .0035 bearing clearance I want .0025. Am I missing something? Please help and thanks in advance.
Well you know, I also have a 5.3 crank polished. The machine shop recommended this little shop and that's all the guy does there. I have not actually measured the crank journals or "mic'ed" it. 🤔
I'm assuming you are measuring with a dial bore guage the direct clearance? Can you get non-standard bearings to make your target clearance? You can mix-match different bearings to get there, but I don't recall what the rules are and you have to buy 2 sets.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
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Yes I am using a bore gauge. Like I said I’m a complete newb at all this stuff. I think if I use a .001 undersized or oversized not sure which…bearing it should work I’m just hoping someone with more knowledge can confirm that for me before I throw more money away hahah.
Got my engine back from the machine shop. Started measuring my crank. They said it was just polished. After measuring my crank I’m consistently getting 2.0775 to 2.0774 on my Rod journals. I’m not experienced with this kind of work but am I wrong that 2.100 is the factory Rod journal size on an Ls crank? With my new bearings in my rods I am reading .0035 bearing clearance I want .0025. Am I missing something? Please help and thanks in advance.
Last edited by grinder11; Jan 29, 2023 at 11:06 AM.
You are correct in assuming the crank should be 2.100. When polished, it might read 2.0999 to 2.0991ish. That crank has been cut. Might have happened to the owner before you, and the shop didn’t catch it? (Gasppp) You need to use an outside mic to measure that crank before you assume anything else. Even a Harbor Freight set will get you close enough to make it run a long long time.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
Likes: 8
Are you 100% certain the mic is reading accurately? Still, hard to imagine its .023" off!! Especially since you've bought standard bearings, I'm assuming, and you have .0035" clearance. I believe they sell .001" undersize bearings. That's where I'd look next. I'd say it sounds like the crank throws are ground undersize, but your clearance with the standard bearing sizes are too close for the crank to be -.020". My .02..
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Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
Likes: 8
You are correct in assuming the crank should be 2.100. When polished, it might read 2.0999 to 2.0991ish. That crank has been cut. Might have happened to the owner before you, and the shop didn’t catch it? (Gasppp) You need to use an outside mic to measure that crank before you assume anything else. Even a Harbor Freight set will get you close enough to make it run a long long time.
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Staging Lane
Joined: Jan 2020
Posts: 74
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I just rechecked zero and it’s perfect. Measured Rod journa #1 again and got 2.0775 unless I’m completely reading this wrong.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
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Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
Likes: 8
I was thinking that after you pass one of the .025 lines you then add the next number on the thimble at .00xx and add them. So I was starting with 2.075 + .0024 then + .0001 for the line up of the finest graduation. Should I be adding .024 not .0024 is that what I’m goofing up?
I was thinking that after you pass one of the .025 lines you then add the next number on the thimble at .00xx and add them. So I was starting with 2.075 + .0024 then + .0001 for the line up of the finest graduation. Should I be adding .024 not .0024 is that what I’m goofing up?
Thread Starter
Staging Lane
Joined: Jan 2020
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First short line past the zero is 2.025 then the taller line or midpoint is 2.050 then the third line makes 2.075 and finally the 1 which is 2.10. You came in short of the 2.10 by .024 due to the thimble reading of 20 then 4 lines past that which makes .024 so it looks to me like you're at 2.099. Does this make sense at all?
For a sanity check, just use a digital caliper. Reading a .0001” vernier micrometer can be confusing if you don’t use them all the time!
Getting accurate measurements to .0001” really takes the correct “feel”.
Getting accurate measurements to .0001” really takes the correct “feel”.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
Likes: 8
I had to leave the house. But I was getting really close to 2.558 as I recall I wasn’t having any second guess about the mains. Just confused as to what bearings to get to increase clearance because I was getting .0015 with my bore gauge and I’d like .0025.
Thread Starter
Staging Lane
Joined: Jan 2020
Posts: 74
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good idea I have a dial caliper I’ll double check with it when I get home.
No problem and glad to help. Just throwing that out there about the mains so you could confirm you were reading the tool correctly.