Measuring Cylinder Bores-A bunch of questions and some pics

[Gyrhead]

Just a quick prenote here:

In the past, I always sent my motors to the machine shop without ever measuring things to see where it stood relative to clearances and dimensions prior to sending it. I guess ignorance was bliss. Perhaps I showered a few too many machine shops with money that should have remained in my pocket. Knowing that this motor came from a great running SVO with 140 PSI per hole but a blown turbo and deciding to take the opportunity to get a look at the internals before bolting it all back together, here we are:

After degreasing the block and painting (just to keep things clean and rust free after hot tanking) I measured the bores. I used 3.7795" as my starting ref point, knowing that the motor would be likely be slightly worn from the low end of the spec (3.7795-3.7825)
Despite not having a 4" mic available, I used my vernier to set the measurement the best I could.

I then zeroed my Chinese bore gauge (hey it works) at 3.7795", trying to keep the anvil square till I zeroed it. I realize there is some degree of Kentucky Windage here!

I then measured at 45 degree intervals in the bore and both 1/2" down from the ridge (there is none tho) and down to the bottom of the bore for taper. All the while rocking the gauge for maximum dimension.

I noted that all cylinders were consistent at 17.5 thousands overbore from the upper range of the spec in all directions One was 17 thou. Taper was within the .010 service limit.


Before I panicked, I measured the NOS small journal Lima blocks I have and they all consistently measured out at at 5 thousands over the 3.7795".

So could I infer that my bores are 12 thousands above spec?

If I were to infer this, what would it mean?

Would it be time for an oversize set of rings or perhaps a bore and new slugs. God I hope not. I see that off-the-shelf rings are at .50mm-1.0mm or 20 thousands, so those might not work.

I'm just not that comfortable with reading the spec data and don't know enough to know where the service limits are.

Sorry for all these technical questions...But it's good learning. At least for me.

[MikeFleming]

Couple notes. First off when you have the bore gauge in the cylinder, you rock it back and forth to get the LOWEST reading. I suspect you just typed it wrong.

Next you will never get accurate readings using those calipers. And you shouldn't care either. Use the bore gauge merely to determine out-of-round, taper and hour glassing. Find the max variation from some known value and only write down the variations (since you can't accurately set the gauge, there's no point is writing down absolute numbers other than to subtract lowest from highest and finding the average).

Once you determine if the bores are "good enough" (obviously a subjective term), - assuming the bores are acceptable - then move on to determine the piston-to-cylinder clearances. You should already have some 12" feeler blades in assorted sizes (0.0020, 0.0025, 0.0030, 0.0035, 0.0040, ...). Measure each piston in the bore with the appropriate blade. Put the blade in so it covers all of the bore. Insert piston, holding it by the rod, where the skirt is completely inside the bore (maybe 1" down from gasket surface. Hold piston steady while removing the blade. Change blades until the blade feels tight, but still moves. Close enough. Take copious notes. BTW - that's piston WITHOUT rings - you're measuring skirt-to-wall clearance.


Taper was within the .010 service limit. That is a Ford warranty limit - if it's less than that, it's good enough as far as the customer is not getting e new engine under warranty.

YOUR limit (well, my limit) should be significantly less, say 0.0035 MAX out-of-round, taper or hour glassing. If ANY reading is 0.0035" variation from lowest to highest in the same bore, it needs to be re-cut to straight and round, imho. New bores, properly machined will be within 0.0005".

Shoot for a piston-wall clearance between 0.0035 and 0.0045". Less is too little for a forged piston and more than 0.0045 will make piston slapping noses when cold.

Set your ring end gaps to: 0.015", second 0.015", oil 0.030". Remember when file fitting moly rings always file inwards so as to not chip the moly coating off. If youhave some brre size variaitons, be sure to measure/set the ring end gap at the smallest bore location.

I have pics somewhere.

[brsvo]

First off you need to get a micrometer (and a standard) the calipers you have are not up to this type of work. You stated the bores were .017" over did you measure the pistons? Total clearance is what counts. Measure the bottom and half way up the skirt not the top of the piston. (Take the largest measurment) The piston top has far more mass and expands further when heated. The factory may have put in .010 over slugs for some reason. I don't have the spec's in front of me so----. Wow Mike you typed that out faster than what I typed please disreguard this post!

[MikeFleming]

The factory may have put in .010 over slugs for some reason. I don't have the spec's in front of me so----. Factory pistons are labeled in metric sizes: 0.25, 0.50, 0.75 and 1.00mm oversizes. In addition to two different sizes of standard bore.

None of the factory pistons are available anymore (except perhaps fpr some personal NOS stashes).

[brsvo]

Your correct as usual but .25 is still .0098425" if we were getting picky!

[Patrick]

Heaven forbid that we introduce the term "cam ground piston skirts" in to this mess.

[Gyrhead]

Once I thought about this, I realized I was missing half the equation. I did not provide any info on the pistons. They are Ford Casting number E3ZE-6110-C4A. Couldn't cross ref this to the Ford book. Pistons are 6108, not 6110 and I had no luck in my OHC 2.3 section. Google was a bust-out as well, however there is a guy on FeeBay selling a set which he states are standard bore with no markings.

Upon inspection, the crowns are marked (stamped) 0.51 which as we learned is mm, not inches and loosely translated to 0.20". The marking is near the outside of the dome. I wish I could turn the casting number though. Pistons tops are pretty oily after 5 quarts burned thru them when the turbo let go.

I suspect this motor was rebuilt by Ford at some point as we have already seen that the crank has been ground to .020" U/S

I suspect once all is said and done, the bores and piston clearances will be OK.

I do understand, I'm not measuring anything, per se...just comparing readings. I borrowed a 4" micrometer to set the bore gauge properly and we'll see where we go.

I will also measure the piston to bore clearances as discussed. Guys, Thanks for taking the time to write it up. Mike, you're right.. LOWER.

From my snowmobile building experience, all non-chrome or Nikasil bores get a light ball honing to restore the cross hatching. A thorough wash follows! Should I do this here?

[Patrick]

I suspect this motor was rebuilt by Ford at some point as we have already seen that the crank has been ground to .020" U/S
...

Ford didn't rebuild the engines. They had "Factory Authorized" rebuilders.

There are prbably more numbers on the top of those pistons somewhere.

[MikeFleming]

Upon inspection, the crowns are marked (stamped) 0.51 which as we learned is mm, not inches and loosely translated to 0.20". 0.020". Needs that extra zero.


From my snowmobile building experience, all non-chrome or Nikasil bores get a light ball honing to restore the cross hatching. A thorough wash follows! Should I do this here? Those silicon ball hones? I wouldn't bother. You installing new rings? Moly-faced top ones? leave the bores glossy and shiny - maybe clean them a wee bit with a fine ScotchBrite pad and lots of soap and water. Nothing rougher. Then dry and oil. Moly facings like a VERY smooth bore to seat to.

Do you have access to a torque plate and an old head gasket? Would be best to measure the bores (and piston clearances and ring fitting) with it torqued in place - along with the main caps torques.

[Gyrhead]

Quick set of questions (in italics):

What is the standard piston diameter in inches? The Ford book lists "Coded Red" and "Coded Blue" and three thousands oversized (.003"). I don't know what this means. I measured all my pistons as follows; And yes, I purchased a 3-4" micrometer to do it. No more calipers!!!

Piston 1: 3.787"
Piston 2: 3.792"
Piston 3: 3.789"
Piston 4: 3.789"

I measured per the book at piston pin bore centerline 90 degrees to pin.

Remember how these pistons were marked 0.51 on the crowns? I took this to mean 0.0020, or twenty thousands oversized. Without knowing the standard piston size, I cannot confirm this. Therefore I cannot buy my ring set yet.

Oh, yeah..meant to tell you guys... piston skirt to bore clearance is around .0035"

Also, my new crank came in, machined .0010 for mains and rods per the box I visually inspected it confirmed the undergrind measurements and the chamfers were nice and smooth. the casting numbers were correct and the bearing surfaces were nicely micropolished. I installed the matching main bearing shells and thrust bearings as noted and dropped the crank in dry (no spinning) and Plastiguaged all mains. All were between .0020 and .0017 (if I had to guess, since the plastigauge doesn't measure that fine).

I know the book would prefer .0008-.0015" with an allowable of .0008-.0026"

Do you guys think this will be too tight?

I then assembly lubed the mains and torqued the crank in using the two step process to 90 ft lbs and measured thrust clearance. This came up to .006" on both sides. I cannot find the spec in the Ford book, but perhaps I am looking under the wrong caption. I suspect it is referred to as free end play limit of .004-.008.

Am I right?

I also set my magnet dial indicator on the balancer end and the flywheel end and measured for out of round or "warp" for lack of a better term. the crank rolled nicely with no drag and end runout was less than .0002" total (plus and minus) while rotating the crank 360 degrees.

Is there a book specification for this?

I'm no engine builder, so thanks for the help.

THESE ARE MY WIFE'S FINGERNAILS BTW...

[MikeFleming]

What is the standard piston diameter in inches? 3.780, then +0.0005 for the red/green OS versions, then +0.0030", then .025mm, 0.50mm, etc. BTW - I've never seen the red/green or +0.0030" available via a service replacement part.

Note that the piston is ALWAYS smaller than the bore and displacement is based on ring swept area, which is the bore.


Remember how these pistons were marked 0.51 on the crowns? I took this to mean 0.0020, or twenty thousands oversized. I would also take that to mean +0.020 (0.51mm) or ~3.800". Find a machinist to check your micrometer before reaching any conclusions.


Oh, yeah..meant to tell you guys... piston skirt to bore clearance is around .0035" This is very good.


All were between .0020 and .0017 (if I had to guess, since the plastigauge doesn't measure that fine). Yes, it's just a sanity check. Make sure the Plasti-stuff is FRESH. As it ages, it gets harder and doesn't smoosh as well.


I know the book would prefer .0008-.0015" with an allowable of .0008-.0026" The .8-1.5 thou spec is proper for a fresh engine using 5/30 engine oil. 2.5-3.0(thou) would be proper for 20/50 oil. So 1.7-2.0 is fine for 5/30 or 10/30.


Do you guys think this will be too tight? [/quote[ See above. Looks perfect to me.

[quote] This came up to .006" on both sides. ... free end play limit of .004-.008. Both sides? Not sure what that means. 6 thou is fine.


Is there a book specification for this? For runout of the outer face of the crank pulley? Not that I've seen. For runout of the flywheel friction surface? Yes. Inany case .2 (thou) is great.


THESE ARE MY WIFE'S FINGERNAILS BTW... My compliments to the wife for keeping her nails clean and polished.

[Patrick]

So you don't want to post up a pic of your wife's smiling face?

[Gyrhead]

She wasn't smiling while holding "those oily, dirty things..eek...my nails"

[Gyrhead]

Fleming, I forgot to zero my micrometer, I did it, then ran up the street to my buddy's shop to confirm:

I was off a bit in measuring the slugs.

No 1: 3.7945"
No 2: 3.7948"
No 3: 3.7959"
No 4: 3.7965"

Guessing these pistons are indeed .51mm or .002008" oversized.

[MikeFleming]

Guessing these pistons are indeed .51mm or .002008" oversized.
0.02008" oversized

Fixed. Decimal point placement is important.

[Gyrhead]

Dammit.....I hate decimals