So I just was checking all my clearances for my 430 build. Crank was cut .020 mains and .030 rods. Clevite bearings from T/A, and everything looked until I got to the rod bearings. I checked 3 and stopped they are all checking out at .0007-0008. Rods were also resized with arp's. I think all the machining was done right except the rod journal size. Going to call the machine shop tomorrow but am looking at my options. I was thinking these are my options, .001 oversized rod bearings (if these are available??) looked online but no luck so far and T/A doesn't list these. I have to call them also. Or I can get the crank polished since I doubt .001-.0015 can be cut? What do you guys think?
Buick bearings are not available in oversize. I have seen bearings thicker than what they are supposed to be but I'd bet the rods are done too tight.
Don't recommend trying to polish even .0005" off the crank. First I would check and see if the rod housing bores are round. Take them back to the shop, have them torque them back up and "show you" on there rod hone gauge that there round. Find out if there on the high or low side. In your case you will need them to be put to the high side to get the most clearance if the crank is found to be on the high side. The rod nuts need to have proper clearance to seat properly on the rod cap. Sometimes there is not enough clearance for that size nut. You do need to see where they ground the crank to. Rod housing bore size; 2.3740"low - 2.3755"high Crankshaft rod journal size; 2.2490"low - 2.2500"high If the crank is high and the rod housing is low you could be at .0007"-.0008" Clevite bearing vertical oil clearance spec's are; 0.0007" - 0.0032" Unfortunately there are NO .031" rod bearings, never has been. I have had rod housing bores as much as .001" over the high side to get clearance. More questions your welcome to call me.
I hope this doesn't sound like a lecture, but it's wise to grind the crank last for this very reason. Pet peeve to see a machine shop quick to machine something to a nominal spec and the following problems left on you, at your expense. Grrrr.
How much faith do you have in your tools? Might be worth a quick sanity check with plastigage, or another micrometer.
The good thing about plastigauge is that it will give the absolute minimum you have and is quick and cheap!
As far as the crank journals, I was getting 2.2195-2.2198. So that sounds right for a .030 under rod bearing. I'll call the shop today and see what they can do for the rods. The cap was clearanced for the nuts, but I will have to measure the rod bores today. I'm using a "cheap .0001" micrometer set , but they have been very accurate for other builds. So at the least I know the clearance is accurate, being checked with a mitutoyo dial bore gauge. The shop sends out the cranks, as they don't have the machinery, but the crank seems to be done right...except for the razor sharp oil hole radius that gouged my #1 bearing when I checked crank runout
Just measured the rod bores, coming in at 2.374, Looks like they are on the low side. I'll relay this to the shop and see what they say.
So the shop said they will work on the big end to make the clearance. Is that the typical process? I would assume that would effect the bearing crush, and make it easier to spin a bearing. I've never had clearances needing adjusted in the past, so I'm a little unfamiliar with the work needed to make these adjustments.
That is a normal process as I expressed. I also mentioned how far past I have seen rod housing bores opened to. If they go to the high side you should have a little over .002
It would be a good idea to check your mics at the machine shop. He should have gauge blocks. I have no faith in cheap anything, especially precision measuring tools. You never want to say, "I should have". Been there done that!
I do have gauge blocks I check them with, they've checked out perfect every time. I think the biggest possibility of error is me not using mics enough to have a developed "feel". So how does the rod bore get "opened"? Like a honing process sort of? I've just never had to get adjustments done for clearances before and am curious what is actually done.
The type of mics isn't as important as their ability to repeat (and yours). All mics are periodically re-calibrated on a schedule in any prototype machine shop and after any suspect measurement or accidental rough treatment. Even the better brands need adjustment, including $1000 bore mics that have an extremely limited range or usefulness, CMM's have their limitations, etc.... The normal way nowadays is to grind the crank last for the very reasons you encountered. There's a range of measurements that determine your final dimensions, exacerbated by the fact that the bearing makers have outsourced production and consolidated similar p/n's. It's an acceptable fix to open up a rod bore. It's preferred to keep it tight for max crush.
So the machine shop is taking care of it at no charge! They're going to open the rod bore up a bit, and verified the clearance I was getting so they know where to go. Just filed a few rings tonight to what I was looking for, it shouldn't be long now!
I was just going to say make sure it turns over nice with no tight spots and check crank end play and rod side clearance as adding ARP bolts can offset the cap to the rod fwiw I shoot for .002-.0026 mains and .002-.0028 rods for high performance street
This is true but beware that plastigauge that has been sitting around may pick up moisture and as a result it will check tighter than actual.
Yup. Bearings are available in the "typical" undersizes: 0.010, 0.020, 0.030, etc. They're not available in 0.001, 0.011, 0.021, 0.031, etc. You might find SBC bearings in a one-thousandth oversize for folks with a worn crank they don't want to grind.
