It is time for late model block assembly and I would like to find information on
measuring the crankshaft clearance with a dial bore gauge. I do not want to use
plastic gauge. Step by step process instructions would be great. Specific to
Corvair engines only. Multiple sources are appreciated.

This video has been around for many years. It illustrates using the dial bore gauge on a Corvair. Hope it helps. Using Dial Bore Gauge - Corvair

For dial gage equipment, I recommend Grizzly magnetic unit.

Al
Georgia

DO YOU ALREADY HAVE THE CORRECT DIAL BORE GAUGE SIZE ?

Bob C aka Dryenko
Dobson, NC 27017

I deal with tight tolerance bore measurement everyday at work.
I'm in Quality Assurance , in a cylinder manufacturing business.

With a 2 point gage, you can basically make it whatever measurement you want, unless you are very good at the technique.
I'd advise practicing ..with most gages people have in their garage, no two people will get the same measurement on the same hole.


Eric P.
DeWitt, IA



Edited 1 time(s). Last edit at 03/14/2023 01:55PM by 1966-Corsa-GT-180.

And Pastigauge is not desired because? Time? Cleanliness? Accuracy?

Frank DuVal

Fredericksburg, VA

Tom Rahochik Wrote:
-------------------------------------------------------
> I do not want to use
> plastic gauge. .

I'm curious , have lots of time to read and willing to learn even at my old age. Please take the time to explain.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2023 KIA K5 GT/GT1 turbo-AKA ZIPPY II (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

FWIW: Even if you painstakingly measure the bores and mic the journals with high quality instruments, the accuracy of your result is limited by the the accuracy of two separate instruments and the amount of skill needed to get those measurements done correctly. If you get those right, it still makes sense to double check it with plastigage. If you get differing results between the two methods, it needs to be investigated why they differ. It’s a mistake in my opinion to overlook the plastigage. The bore gage and mic tell you what bearings you need to install to be in the ball park. The plastigage measurement gives you an “installed” value that you can’t get otherwise.

Also, having used measuring devices for tight manufacturing tolerances, there is a huge difference in obtainable accuracy in measuring brand new perfectly smooth parts versus parts that have wear from use. The more the part is worn, the more difficulty there is in finding an area to take a good measurement and applying the correct tool to get that measurement. If you are trying to measure a used crankshaft, take lots of measurements while looking for high and low spots, and out-of-round conditions. It is time consuming, but you will identify areas that you can’t see by eye. Same with the bore gage, lots of measurements and look for out-of-round. Practice with the gauges and work on your technique to gain repeatability in your measurements. Do yourself a favor and don’t skip the plastigage measurement. It’s an important part of knowing the status of your rebuild.

Craig T
Central NY
1961 Tramp (truck with a ramp)

Tramp61 Wrote:
-------------------------------------------------------
>... The bore gage and mic tell you what bearings you need to install to be in the ball park. The plastigage measurement gives you an “installed” value that you can’t get otherwise. ...

Which to me also asks the question if one doesn't have a very good, stock size crank where they can use the harder to find .001 and .002 bearings then they are going .010, .020, ... and can have the crank ground to the clearances they want. And even there one is still moving in .001 increments when they likely want some multiples of .00001 increments. One could use the .001 or .002 bearing and grind/polish to fit but to what exacting end?

Because the OP is asking how to effectively use the dial bore gauge it leads one to surmise that they have assembled few, if any engines. The intended use of the engine has not been stated. Is this a race engine? Are they going for long mileage between any subsequent rebuild? So, what exacting clearances are they shooting for, and why?

Is this a case of someone building one of their first engines, read or watched videos where the dial bore gauge is touted as the definitive means to measure bearing clearances and is following that advice? Or is this a case of a weekend driver that the high/low range of the factory bearing clearances and Plastigage as a measuring method are wholly adequate for the use? It seems there is more that needs to be known.

Something that has always been in the back of my mind is the singular main bearing that is offset. Even with a dial bore gauge one could get measurements that would "seem" in spec but how close to the journal is that offset if the clearances are being set on the tight side???

OP seems to have lost interest in following up. Would have also liked to hear the reasons not to use plastigage and the benefits of relying on the bore gauge. Was hoping to learn something.

Craig T
Central NY
1961 Tramp (truck with a ramp)

Sorry for the delay. Away on vacation. I made the assumption a mic and dial
bore gauge would be more accurate than plastic gauge. Per the above comments,
yes, I will now use plastic gauge. Are there any previous messages here in the
forum that can walk me through the process? And, is it possible that I may find
that one or two main bearings out of the four, may need a .001 bearing instead of
a standard one? (I do have a .001 set if needed) Thanks to everyone to guide me in the right direction....

Place one block half on bench so crankshaft can be placed in it. Place the four bearing halves in that half, and the other four halves in the other block half. Place the crankshaft into the black half on the bench.

Place a piece of plastigague across the crankshaft in three spots. Without moving/rotating the crankshaft, drop the other block half into position on the crank/block half on the bench. Very important to not move the crankshaft, as this will smear the plastigauge giving a false (smaller clearance) reading.

Torque block bolts. Remove block bolts. Separate the block halves, still not moving the crankshaft. Read the widths of the flattened plastigauge with the package it came in.

Instructions are in 1961 Shop Manual starting on page 6A-43, with illustrations. The online manual illustrations are useless.

Frank DuVal

Fredericksburg, VA

When you are satisfied with the clearances and start to do the final torque procedure, I whack the block corners with a dead blow after each stage to make certain the crank still turns easily by hand. If it binds back off the torque and start over. I guess not everyone does not do this, but it was recommended many years ago and works for me.

J.O.

65 Corsa Turbo Vert
79 Honda XL 500S
69 Honda CL 160 D
2010 BMW F 650 GS
2003 Bounder 36D
2023 KIA K5 GT/GT1 turbo-AKA ZIPPY II (wife,s car)
69 Newport Holiday Sailboat
Baja 150 dune buggy cart
Coleman HS 500 UTV
2016 KIA Sorento SXL Turbo

Bethlehem,Pa

Thanks for the procedure for checking main bearing clearance using plastic gauge. What color and thickness plastic gauge is recommended when measuring with
standard bearings? And, is plastic gauge available at most auto parts stores
like NAPA?

Tom Rahochik Wrote:
-------------------------------------------------------
> Thanks for the procedure for checking main bearing clearance using plastic gauge. What color and thickness plastic gauge is recommended when measuring with
> standard bearings? And, is plastic gauge available at most auto parts stores
> like NAPA?


Plastigage green for main and rod bearings, it measures .001 to .003 clearances and should be available at Napa and other parts stores