bearing clearance math

Cant remember the math when computing bearing clearance using a dial bore gauge. must be getting old. The crank measures 2.199" and the bearing in the rod measures 2.202" using a snap gauge. I know this would give me .003" clearance, but how do you do the math for the bore gauge? I did 0 the bore gauge in the mic after measuring the rod journal and measured the bearing, but the math make no sense to me at the moment. Thanks

Set the outside mike at 2.2000 and set the dial bore gauge at .0000, then measure the I.D. of the rod bearing with the dail bore gauge and see if it shows on the - (minus) or + (plus )side of the zero. If it is on the plus side add that to the 2.2000, if on the minus side subtract it Let us know what you find out.
BTW, I like the old simple methods also to back up what you find with the new tools

ok, but why set the mic to 2.200 when the journal measures 2.199?

You can set it wherever you want , I used the 2.220 crankshaft rod journal diameter to use as a reference that way when the dial bore gauge reads +.0016 you know the bearing I.D. is 2.2016 If you set the dial bore gauge so 2.1990 is zero and you end up with +.0026 on the dial bore gauge you know you have .0026 bearing clearances, same results using a difference base to sart with, your choice IHTHs

ok, with mic set at 2.199. I pickup the dial bore gauge up and 0 the dial, then I inserted the bore gauge into the mic and it reads .027. I then 0 bore gauge again while in mic, remove bore gauge from mic and insert bore gauge into rod with bearing. bore gauge reads .026. so my bearing clearance is .026?

Dave is it .0026" instead of .026"?

I used the same method on my last two engines. I set the mic on each journal, then zeroed the bore mic and took the measurement.

sorry for the confusion here but i'm not sure. the gauge has increments of .0001. the gauge had .050 written on dial and goes to 10 and therefore every sweep would be .010. every number represents .001. i'm getting 2 full sweeps+ the 26, so if I read this right that would be .026. i'm thinking there should be some math here somewhere to get the end result.

You don't need two full sweeps to get the clearance.

Measure the crank. Set the bore gauge to the mic with one sweep and zero the gauge. Then stick in the rod 90* to the parting line and measure it. What it says is what it is.

the reason for 2 sweeps is I don't seem to have the correct anvil

what i'm measuring is .006 clearance. something isn't right with my measuring.

Oh crap you are at the tweener size.

In a pinch, you can use a snap gauge to measure the bore and then mic the snap gauge and do the math. Not as good as a dial bore gauge but it would get you in the ball park. You could then try and nail it down from there.

Look at the gauge again and see if it says .0005 instead of .050. If it is .0005 instead of .0001 then it reads like my Sunnen gauge does in 1/2 thousand increments instead of one thousands or one ten thousands increments like my Mitiyo gauge reads. I'm having a issue now with my 4 to 5 inch outside mike, it is reading about .0008 to small(SWAG,eye balling it) when I set it up with the 4 inch standard I don't see anyway to adjust and correct that mike so I may end up having to buy another 4 to 5 inch oudside mike. I don't use my Sunnen set up gauge to zero my dial bore gauges due to not trusting it

bore gauge does read on + side of 0 when inserted in rod bearing. Reads .0061, so either im reading gauge wrong or its inaccurate. Meatured bearig again with snap gauge and get 2.202 and rod jounal is 2.199. Ill try a different dial on the bore gauge tomorrow and see what happens.

Dave Do you still have the bore gauge zeroed to 2.199"? If you do set your mic to 2.202 and check the bore gauge again, it should read .003".

Can you post a photo of the dial on the bore gauge?

So you get three with a snap gauge and six one with a dial bot gauge?? Hmmmm. I'm more comfortable with your numbers from the snap gauge right now.


Weird.

me too. I believe every sweep of the needle is .010. The gauge says .050 range. If every sweep is .050 than i have about .003 with the bore gauge.

If it's a 0-.050" then the numbers on the dial face should be half the value shown.

What don't you have the correct anvil for? If it's the dial bore gauge how are you using it?

This gauge is reading in one thousands increments, not .0005, every has mark in between the big numbers is suppose to be one thousands, .0010. So one full sweep from zero to zero would be .100, one tenth of a inch. Me thanks something is not right here, some how
EDITED, it does say on the face that it is measuring in .0001,(ten thousands) not .0010(one thousands) increments The 0050 to .0050 saying would be one half, straight down, of the gauge reading from zero
No wonder your having the problems you are having
Stick with it, you will whup it
2nd edit.I would post pictures of my three different dial indicators reading in .0010, .0005 and .0001 if I knew how now ,but I don't anymore Sorry!

thats where my confusion is at. Increments of .0001, so there is 100 of those on the dial. That would be .010 per sweep. To me every number would represents .001. So where i 0 the bore gauge in the mic and insert it into rod bearing i read .0061 on the dial.

the mic is set to the rod journal diameter which is 2.199. Im using the next to smallest anvil. I only get .004 needle movement using smallest avil with all the spacers. I think the next anvil up gets me truer readings.

ok, heres something interesting. I measured the rod bearing with the snap gauge again and measured snap gauge with mic, I then 0 bore gauge in the mic with that measure(I think 2.225) and then inserted bore gauge in rod bearing and bore gauge reads .0095 reading gauge clockwise. I then measure rod journal with mic and 0 bore gauge in mic and then insert bore gauge in rod bearing and bore gauge reads .0061. if you subtrack (.0095-.0061=.0034)you get .0034. can you do it that way?
I also tried 3 others dial indicators and get .004 with two of them and .0038 with the other reading to left of 0.
If I read the shars indicator from the left of 0 or counter clockwise I get .0039.
so now my question is would .0035"-.0039" be too much rod bearing clearance? sorry to confuse anyone here. Thanks guys

My head hurts.

Perfect if you running blown alcohol with 70wt oil. .0025" is plenty. Depending on what your building.

LOL! I hear ya. I'm sick of it myself.

Snap gages are not precise enough for this. Put them back in the box. Correctly measure the journal with a mic and lock it down. Use the mic to set up the dial bore gage. Use the anvil that will spin the indicator half a turn or a turn. Clamp the mic down or in a vice. Rock the dial bore gage in the mic to find the square spot and zero the indicator. Drop the dial bore gage into the bearing bore and rock it to find the square spot (smallest dimension making certain you're on the exact centerline of the bore). The distance from zero is the clearance. All measuring tools should have a .0001 resolution and cost more than $19.99. Don't trust your tools or yourself until you can go through the procedure 3 or 4 times and come up with the same number to the .0001th. No calculator or math needed.

ok, enough confusion. I called the dial company(shars). they tell me if the needle is on the left side of the gauge while reading your clearance that you count counterclockwise from 0 and if needle is on right side of gauge you count clockwise. so at that I remeasured crank and being careful to not crank down on the mic with the clutch(just get the air gap out) I reset mic, re 0 bore gauge insert in rod bearing, read the left side of gauge I get .0033"-.0034". I think that's the most accurate I can get.
take a look at the pic of the gauge and you will understand.
rod bolts are tq 30ftlb and clocked 60* Thanks guys

No one said snap gauges are precise, but when the OP is questioning between .0026 and .026 then a snap gauge can help him find his way.

Sometimes you have to look at other options to get your numbers correct. No body said use a snap gauge to finalize bearing clearance. Damn.

That is a bit loose for my taste. A .001 under bearing would be nice. Or, if the rods are on the high side, you can size them to the low side, or a bit under and get it to .0026-.0028ish.

I think it's time to take it to your machinist so you really know what you have!
Maybe take your gave n if he's nice n has time he can school you how to read your gages

i believe the measures. The bearings are +.001 bearings. Ill just have to get another set. Standard bearings would put clearance at .0025 zone. I ordered +.001 because all the other engines i put together had tight clearances.

Let us know what clearances you find with the new bearings Is this a BB Chevy journal rod size? If so anything from .0020 to .0028 should work fine with non thick oil

ok. Be working in the basement. Do you think cold tools might show wide clearances.

As long as everything is at ambient it should be ok.


I worked in a shop that had a huge roll up door on the east end. During the winter, when the wind was blowing, the office retards would open that door and in a minute you could start to see ambient temp starting to tighten up the bores while I was honing the blocks.


Keep everything the same temp.

paid a visit to my machinest today. I took two rods with me with bearings torqued up to spec using angle method.I set my mic to a journal, 0 bore gauge and measured rod bearing at .0033 before I left the house. He measured .0033 with his bore gauge 0 ing it in my mic. so I am reading the gauge correctly and my gauge is accurate enough IMO. something he showed me though was the bearings have taper in them. .0033 in middle and .0036 off to each side. said to get new bearings, should not have any taper. as far as the .0033 rod bearing clearance, he told me not to get caught up in .0001 of an inch measures. he would run that clearance with heavier oil if that's what he had. these are King bearings, thought they were suppose to be perfect accuracy?

Vertical oil clearance is what matters, so the extra clearance won't hurt a thing. In fact, I'm not so sure even the best rods get out of round at higher RPM, regardless of bob weight.

I also disagree with running a heavy oil. There is ZERO reason to do it any more. Unless you are running alcohol or nitro. I'd get the right bearings and have the clearance .001 less and run a 30 grade oil.

all measures were vertical.

I ran .0035+ rod and main bearing clearances on my old 518 pump gas stroker motor, it would idle at 18 to 25 lbs at 650 RPM with 5W20Wt oil at 180F + oil temps, 30 lbs at 1200 RPM, 65 lbs at 6500 RPM
Your fine with .0035 clearnces on the rods I had to use the King rod bearings on the B1 motor I built last year to get the clearances oI wanted,(.0025+ to .0030) every other brand was to tight If your going to use a motor with 2.200 rod journal sizes and want to safely rev it up past 5500 RPM reguraly your way better off with .0030+ bearing clearances, no matter what weight oil, than having .0020 oil clearances

ok, I now have the new King standard rod bearings and I torqued one up in a rod and measured. .002". its looking like I will need the other .001" larger bearings which measured .0033". better too loose than too tight.

Dave,
Use one std shell, and one +.001 shell, and you should be right around .0026". It's common practice.

That's what I did on my mains.

ok, that's what i'll do. sounds good. what would be the proper orientation in the rod? thicker bearing in upper and thinner in lower?

Either way is fine, but if they have dowel holes, I like to keep them in the cap.

ok, thanks

The anvil is not your only means of adjusting. You can loosten the clamp that holds the dial indicator into the tube/handle of the DBG and move it up or down, then re-tighten the clamp. I like to put the zero at the top, then move the dial indicator up or down to get less then 1 revolution of the needle, stopping near the zero. Then do a final zeroing by turning the dial.
I know there is more than 1 way to skin a cat, but I always set the micrometer to the journal and lock it. Then I clamp the DBG in a vise (gently) to hold it with the movable point facing straight up while I use both hands to maneuver the mic over the points of the dbg. I press the fixed end of the mic against the fixed point of the dbg. Then I position the other end of the mic against the movable point of the dbg, and swing the handle end of the mic every direction to find the smallest reading and do the final zeroing of the dbg there. This way, as you sweep the dbg thru the rod bearing, the amount that the needle stops short of zero is your clearance. If the needle goes past zero, you have negative clearance.

Good luck!

thats how i 0 my indicator as well.