measuring main bearing clearance Q
 

When measuring for bearing clearance do I:

take the bore diameter with bearing torqued, subtract the pin diameter then divide by 2?

or skip the divide by two step? Thanks - Ryan

no dividing. measure the main bearing id with main torqued, measure crank journal. subtract little number from big number, hope you don't have to chase clearances too much. happy measuring!

Use a dial bore gauge and a outside mic,torque main bearings using correct lube in fasteners,measure crank with mic,set dial bore gauge off of mic to 0 ,then rock dial bore gauge inside bearing and see difference on gauge,this is absolutely the best way to measure bearing clearance,same procedure for rod bearings.BillC.

thanks, i was using the snap style then using a mic to measure that, i will find a bore gauge this week, even if i have to buy one.

using the mike and snap it looks like i was at.003 on mains and rods. this was at teardown (about 1500-2000 miles) with the F/M standard bearings. i will post more when i can trust my measurements. -RB

what Bill said. don't trust the snap gauge. you can't rock it in the bore like a dial bore gauge.

Summit Racing has what you need, thats where I got mine...

Be careful of the standard $100 style dial bore gauge. The hard ball on the tip of the anvil and plunger is so small that it can scratch/dig through the soft bearing surface. This will give you a false diameter and therefore a false bearing clearance.

Preferred would be a dial bore gauge with a more gradual radius on the anvil and plunger and a lighter spring pressure behind the plunger. Unfortunately this winds up being alot more expensive.

what he said. I bought a starret, which is the best I can afford. I think it was $300?. a local tool and die maker said he stopped selling dial bore gauges because he doesn't trust anything that costs less then 1500 bucks and not made in germany. gee thanks I said.

i ended up getting a fowler from enco, has not arrived yet but it was on the cheap end. i do however have a calibration lab here at work so i can have it checked for accuracy once it arrives. - RB

The accuacy is important, but the DBG is not "measuring" the diameter of the bearing bore, it's only telling you the "difference" in diameter between your zero (crank pin) and the bearing ID. Having a DBG that reads down to ten thousanths is nice too.

The bigger problem is that the tiny litle hard ball at the tip of the anvil and plunger, combined with stiff spring pressure behind the plunger can literally dig a trench in the bearing and give you a false clearance. It's not always much, but if your on the edge, it can bite you. They work fine for measuring the hosing bore in the block itself because the iron is hard enough to not be an issue.
Just be careful.

I recetly purchased a Central dial bore gauge. It's made in the US and reads to the 10 thousands. When I received it I took a 2-3" Starret mic, opened it to 2.500 and zeroed the bore gauge inside it. Then I opened the mic exactly .002 and rechecked with the bore gauge. It read exactly .002 so I figure it's accurate. The biggest PITA is trying to zero the bore gauge inside the mic as it takes a little practice.

thats a good idea, i just had my etalon 2-3" cal'd i will use that as my standard. Thanks - RB

I have a soft jaw hobby vise that I use to hold the mic when setting the dial bore gauge. Spend some time and get the feel.
What you learn when you start chasing ten thousanths (.xxxx") is that temperature and personal measuring techniques are really important. Then you have to step back and realize that your really splitting hares at that point and you need to give yourself a window of tolerance. It's a fun challenge!

Here are a few pics of the two Mitutoyo dial bore gauges that I use. The "511" series (bright finish) was a $100 ebay deal, while the "545" series (black finish) was a new purchase that a buddy and I split to ease the pain. Way more spendy, but still half of getting a basic Sunnen gauge setup. You can see how the 511 series, like most of the inexpensive gauges out there, has a very small steel ball at the end of the plunger (between the two guide wheels). The 545 series has a very gradual radius on the end of the plunger, and has about half of the preload spring pressure behind it. It glides over the bearing surface without leaving a trench behind.

Hope this helps!:)

Also "not a huge deal but if you wanna be anal" make sure the lill ball or anvil is facing up so gravity has no effect on your measurements and measure the bearings 90 degrees from the parting lines meaning straight up and down as this should be where your tightest clearance is fyi
I Want a Gage that measures all 5 mains at the same time to see how straight the mainline is, yes you can use a machinest straight edge and feeler guages but i want a more advanced tool but i also want a hand held sonic tester so i guess i can keep on wishing LOL

I bought a new hand held sonic tester on ebay a couple of years back,if I remember right it was about 100 quid($150). Yes it came from China,but it is bang on for accuracy and can be calibrated for virtually any metal.