Polo-94Z28

*I decided to move this to the advanced forum section to see if any other builders had some info/comments.*

I have measured my oil clearances for my new motor in 3 different ways.

-Plastigage
-Journal with a mic, bearing shells with a mic, and bearing housing with a bore gage.
-Bearing ID with bearing installed and caps torqued properly.

Plastigage said .004" total so .002" all the way around. That seems fine.

Using properly calibrated and certified mics and bore gage I get numbers that don't add up. (yes everything is clean, calibrated, and tightened properly, measured at the same temp and same respective time)

I mic the crank rod journals (Eagle 4340) they are 2.0992" - 2.0993" across the board. The rod bearings (Clevite H-Series) measure .0627" - .0626" for all 16 halves. If I measure the rod journals themselves (torqued via bolt stretch gage) (Eagle 4340 H-Beam, ARP L-19 Bolts) to .0075" stretch. Set the mic to 2.225" and lock it. Set the zero on the rod bore gage and I measured it. I get 2.2245" - 2.2250". If you add up the numbers...

2.2245
2.0993
-0.1254
---------
-0.0004" on the minimum side

2.2250
2.0992
-0.1252
---------
0.0006" on the high side ... either way it sucks


But If I stick the bearings in the rods, stretch em bolts, set the gage to 2.0993" and measure I get .0018" - .0019" of positive room over 2.0993" zeroed.

I am using the correct mic to measure the bearings, a half spherical pipe mic.
I am allowing pretty much zero of my body heat transfer to the instruments.

In conclusion... what gives?!

Mousebuilder

Wow, something dont sound right, first off disregard plastigage. Second I would 3-way it, just an idea. You can't get more accurate than that.

Polo-94Z28

Yeah I don't use plastigage to actually build and engine, just more or less check that everything is the same size, no over/undersized bearings etc. Which it showed me anyway. And by three-way I'm assuming you mean measure the bores, bearings, and journals in 1/3 rotation from the centerline? I do 90* to the split, and then close to the split for a check. Journals I do 90 then 90 of that as well for out of round and then taper as well. Didn't have any problems with any of those.

I'm gonna go through the whole process again tonight (for about the 4th time) and see if something is getting mixed up... gonna grab a fresh pair of eyes too... that helps

Thanks.

Mousebuilder

Well, that one way to three way, the other is to mark 90deg on the crank, and put it together. Bearing and all, then with a dial indicator, and a custom made bracket. ( if ya dont have one, or know how to make it your kind lost on this way to check clearances) Use a rubber tiped bar to move the crank on all axis's opposite the dial-indicator. My old man can explain it better, i just know how to do it, so please forgive me if i dont make sense.
Basicly to check side play, you would set up your indicator on the right side of the crank, with the indicator pin on the crank, then using the bar, you would push on the other side of the crank, exactly opposite the Indicators pin. you do this in 45deg increments.
wow, i am even confusing myself. If someone else here knows what i am talking about, and can explain it better please do. I gave my self a headache.

Polo-94Z28

So basically (if I am understanding you correctly) you want me to check the 'endplay' of bearing clearance. By forcing the crank to move and measuring the movement with a dial indicator every 90* of crank rotation? I see that as another method, but it doesn't quite explain as to why I'm getting the differences I am. (not that I'm trying to badtalk your methods).

Thanks.

Mousebuilder

ya, i dont explain it well. Its just a error proof way of checking the clearances. My father taught me how todo it. Unfortuantly i am not as elequent in my explanations as he is.

SStrokerAce

Ok the way I do it....

Mic the crank journal. Then setup the bore guage based on that size, so it's zeroed out at the journal size. Then have the bearings installed in the rods and them TQed up. Then you get a pure clearance reading.

Basically you want to shoot for .0020-.0025" clearance.

Bret

Mousebuilder

Ya what he said works great.

remind me to get the old man to write down how to do his dial thingy so i can explain it without it sounding like i am smoking crack..

1racerdude

Do it with one of these and ya will never go wrong. The ID fit is automatic.

They are spendy if ya don't do a lot of engines. I used a dial bore guage for years but grew VERY tired of setting it up,Sooooo I got some of these and can measure anything from the lifter bores to the cyl bores.

67RSSS6SPD

Yup this is the best way to do it.No need to worry if the Mic is calibrated this way,Just lookig at the differance between the 2 readings.

OldSStroker

Remember installed bearings are not round on the inside. They are bigger across the rod at the split line. This helps generate the oil wedge and also allows some safety when the running loads distort the inside shape of the big end of the rod. Most folks measure 90 degrees to the split line to determine the minimum bearing diameter to figure minimum clearance.

On an oval bore, a 3-point measurement using 120 degree points won't give you as accurate a reading as a dial bore gage with measuring point 180 degrees apart. These usually have guide rollers adjacent to the moving point, but they don't enter into the measurement.

Now 3-point ID gages are pretty good for bores that are supposed to be round, but they lie to you about rod and main bearing bores. Picture an exaggerated oval bore with the major axis being the split line, and the minor axis being the diameter you really need to know. Look at what you get with a 3-point measurement with one point 90 degrees to the split line. Tell me if you are measuring the actual minimum size or larger or smaller.

The 120 degree 3-pointers aren't very good for determining the shape of the hole either, unless the hole is 3-lobed. Most aren't. We measure a lot of holes in our precision manufacturing business, and we do not use the 120 degree gages, as easy as they are to operate.

Oh yeah, measure the inside of the installed bearing shells and the journal and do the math. Anything else and you are fooling yourself. Also remember that .002 clearance is something less than that from metal to metal. It would be .001 if the journal stayed in the middle of the oil wedge, which it doesn't.

FWIW, how do the insides of the rod or main bearings get out-of-round if the bearing bores in the rod or block are round, which they should be after honing?

Some very high-end engine builders like F1 have considered Diamond Like Carbon (DLC) coating (Casidiam is one brand of DLC) the rods and crank journals in order to eliminate bearing shells. For DLC coated surfaces to work, they must be as smooth as 0.5 Ra or smoother. A polished crank journal is about 5.0 Ra or ten times as rough. You can get things like round pins and round holes that smooth if you spend enough time and money, but consider generating the 0.5 Ra on the slightly oval shape that the inside of an installed shell bearing gives, and is needed. My information is that that problem probably hasn't yet been solved.

My $.02

1racerdude

If ya measure the installed bearing with one leg of the intramike at 12 O'clock it never gets into the "larger" area of the brg and ya don't have the problem without the brg installed so all ya got to do is put it in the hole and don't have to pay attention to how it is clocked.
The intra mike's measurement read the same as the dial bore guage (I have a Fowler) when checked with each other but the intramike is a whole lot less trouble especially on the rear main and the one foward to that when the engine is on a stand.
Ya don't have to reset it to different sizes just get the right span intramik. My set will cover .800 to 4.400 and ya can measure anything from the lifter bores to the cyl bores. Most will not spend the money for the set(3500) IMO it was worth it.

AFAIK the bearings are made that way and we use to put shims in between the rod cap and rod to get that sizing when resizing the rods, before the brg manufacturers started making the bearings thinner at the parting line.

MachinistOne

I do it the same as Bret. Mitutoyo mic's and Sunnen dial bore guages.

Mindgame

You're right OS.

I have an old Starrett dial bore gage (2 point) that I check bearing clearances with. 90* to the parting line I get one measurement... 45* to the part I get another which is how I was taught to check for eccentricity.

Curiously enough, I just checked a new bearing in a properly sized rod with bolts stretched to spec... at anything other than 90* to the parting line I get a larger diameter measurement. Which tells me that the bearing is indeed eccentric, arriving at a maximum thickness 90* to the part. I get +.0004 at ~60* to the part with King aleculars.

-Mindgame