Dial Bore Gage

[87-F-250]

I'm using a Sunnen dial bore gage for the first time. I'm trying to see what condition my cylinder walls are in. I just honed them with a Flex-Hone. I also took the carbon buildup off the top of the cylinder with a bristle brush on the end of a drill.

Sunnen website (they have the operating instructions in PDF form)

The engine is a 7.3L. When I checked it quick with a caliper is was around 4.11 inches. What is the cylinder tolerances?

Also was looking for the crankshaft and other tolerances. Is there a section for this?

 

[flareside_thun]

If know one can get you answers I will copy it from my manual at school for ya. I'll be lookin at em anyways since they've got me rebuilding one.

 

[87-F-250]

Thanks flareside thun I appreciate it.

It would be nice to have one on hand.

 

[bike-maker]

I spent many a year running a Sunnen dial bore gauge.
If standard bore size (4.11"), the cylinders should have been honed to right at 4.1100"; piston clearance is typically built in to the piston.
Keep in mind, the gauge only goes about + or - .005" on the gauge from where you set it up; typical cylinder wear will be far more than that, which makes it kind of tricky to read. Set it up with about 3 revolutions on the gauge until it gets to your bore size, and then count the rotations on the needle and do some math to figure out where the bores are.
In order for the dial bore gauge to be setup accurately, you need a good micrometer, a standard to check it with, and all of your pieces (mic, standard, and block) need to be at the same temperature. Keep in mind we're talking about an instrument that is accurate to .0001" - that's one-ten-thousandth of an inch. Your garden variety calipers are typically inaccurate compared to a micrometer.
Crank shaft journals would be checked with a micrometer; rod journals and the crank bores in the block could be checked with your bore gauge.
The best place to realize the benefits of a bore gauge is in checking rod and main bearing clearances. You will know what the clearance is to the nearest tenth.........good bye plastigauge.
Hope this helps..........

 

[87-F-250]

bike-maker thanks for the information. I have a micrometer on loan too that was calibrated or checked for accuracy. But no standard or something called "measuring rings".

So cylinder wear will max out the measuring range of the gage? But there is a way to take individual measurements?

It might be better to talk about what I've got figured out about these instruments.

I know how to read a micrometer.

I selected the right Gage point no.6 (3.875 to 4.250-inch).

I screw the Gage point in to the gaging head and lock it in place with the lock nut.

I don't know how to set the 4.1100-inches on the bore gage? Do I take the micrometer and put it at the two points when the gaging head point is at rest.?

Is resetting the dial to 0 done by putting 0 over the indicator hand at the 9 o'clock position?

 

[bike-maker]

You're on the right track. Set your micrometer to the bore size (4.11"), lay the dial bore gauge on a work bench with the gauge face up, and use the mic to set the dial bore gauge. You usually will have to manually depress the bore gauge to get the mic to go over it. The screw point doesn't need to be bottomed out; you can adjust it to wherever you want to suit your needs - thus the locking nut. There should be 1 point on one side of the head, and three points on the other side; the middle of the 3 points does the measuring, and the outer 2 are there to keep the gauge centered in the bore.
It might be worth checking with some local machine shops if they could walk you through the process; it's really not that complicated, just hard as hell to convey in writing.
One thing I failed to ask; does this dial bore gauge have the lever on the back of it, just below the gauge, that retracts the little measuring fingers when pulled? If so, that's the industry standard for measuring cylinder bores. There's smaller versions that don't have the "retract" function on them; these have a smaller head and will therefore work better for smaller holes, such as rod journals.
Now with all of this said, when a machinist measures the bores on a block he's checking out, it's usually to see how little of a bore job will be required for a new set of over sized pistons. Unless the block has really low miles - like a race motor that gets torn down all the time, a machine shop will automatically plan on new pistons. With IDI's having the cavitation issues, combined with IH using a crapload of nickle in their cast iron (this means the blocks are hard and the bores wear really well), it would probably require a LOT of run time or serious abuse to require a rebore. I've only bored 1 IDI (8 sleeves) and multiple Powerstrokes and older IH gassers; this experience is why I have owned 3 of them. They are all seriously over built. Just looking at the cast iron parts, they appear to be pretty strong, but once you start machining on them, you realize what a high quality of metal IH uses. The connecting rods in a 392 IH gasser are probably just as strong as a 4340 steel Carillo rod for a big block chevy, even though they don't look as fancy.

 

[bike-maker]

Forgot to add, standards are just a little cylinder with a plastic sleeve over them - leaving the metal ends exposed for measuring - that are made to a highly precise length. So you take your 4" standard and make sure your mic measures exactly 4" on it.

 

[DeepRoots]

not to be a **** about this...... but I'm going to be.
1. Honing takes material off the walls. If using the same pistons, the clearance between piston and cylinder WILL be greater.
2. Honing follows any cylinder irregularity. Thus if the bore is out of round, you are just enlarging that.
3. Read up on torque plates. Don't believe me? measure everything with that bore guage, bolt the heads back on to spec and remeasure from the inside. Note the differences.

If I were interested in making a long lasting IDI, I would either A. Get a 6.9 bored and honed properly. B. Sleeve a 7.3 and bore/hone as needed.

Best of luck,
Drew

 

[bike-maker]

1. I think the flex hone he's referring to is the kind with all the ****** balls on it. These don't really enlarge the bores; their purpose is to reestablish a "cross hatch" . The crosshatch is where the oil is retained in the cylinder, keeping the rings lubricated.
2. A good cylinder hone does not really follow irregularities (not the kind any of us would have laying in their garage). The proper equipment uses 2 rigid stones in combination with 2 additional scrapers that is rigid enough to stay in a perfect cylindrical shape. Not so with a ****** ball hone or cheaper version.
3. Torque plates do make a difference. I've personally honed a cylinder before with out a torque plate, then dyed it, bolted on a torque plate, and made a light pass to see the difference. It isn't a matter of distorting the entire cylinder. What happens is anywhere a head bolt is in close proximity to the cylinder, a section of the cylinder pulls out, towards the bolt. So it doesn't make it oval, or bigger, or smaller; it gives it worbles. On a high horsepower engine, using a torque plate is a definite advantage; I'm not sure that our old IDI's make enough horsepower (or cylinder pressure for that matter) that a torque plate is going to have a very significant effect on ring seal.
4. I agree with your idea on building a long lasting IDI. But they last long enough, I doubt I would ever invest in rebuilding one; just go buy another used one. Put new rings and bearings in, and run it for another 300k. If I was going to spend a bunch of money on one, I'd transplant a DT in my truck instead.
5. I don't think you're being a ****, deeproots.

 

[87-F-250]

Thanks for your input. Check out the video on distortion. Trying to keep the machining costs down by not bringing in the block. I'll be getting new pistons, performance cam from typ4, rings, and bearings. Turbo connecting rods and head and main studs.

Thanks for patience I'm a slow gradual learner.

So when I put the micrometer between the two points should I leave the gage head point fully extended or does it need to be slightly depressed so it can flex out?

Or do I leave the gage head point fully extended and then set the distance by screwing in the other point and locking the nut?

I just want to see where I'm at for a reference. So I know how good a cylinder needs to be.

I'm using the Flex-Hone but I have a cheapy 3 stone hone too. How important is it to get the carbon ring off at the top of the cylinder?

 

[bike-maker]

You could do it either way, actually. The further depressed the gauge head is when you set it up, the further past your bore size you will be able to measure. The carbon ring would be nice to get rid of, but as long as you get the big chunks, you should be fine. You will never get it to look like a fresh bore unless it is , in fact, a fresh bore. Use the flex hone (every machinist I ever worked with called them a ****** ball hone) to get some scratches in the cylinder wall for oil retension. You're shooting for about a 30* angle on your cross hatch.

 

[RLDSL]

Man, if going for a first time with a bore gauge, that thing has to be about the most confusing contraption I've ever seen .I imagine it's accurate once you ever get the blamed thing figured out . The one I have is so stinking simple a child could figure the thing out ( good thing or I'd be in trouble

 

[flareside_thun]

I realize some people may not agree with this but if you're that worried about the micrometer, get yourself a GOOD digital caliper.....

 

[bike-maker]

I realize some people may not agree with this but if you're that worried about the micrometer, get yourself a GOOD digital caliper.....

If measuring a used cylinder bore, then yes. Just don't try it with more delicate things like bearing clearance.

 

[flareside_thun]

Agreed.....