Platigage and bearing clearances

[Bob Johnson]

I have read lots of opinions on how to check main and rod bearing clearances. There is something that confuses me. It is generally agreed that there should be 0.001" of clearance for each 1.0" of bearing diameter. On a B engine the main bearings are about 2". That would result in a bearing clearance of 0.002". The confusion, for me, is the following. Should the bearing be 0.002" larger than the crank journal? For example, bearing 1.999" and crankshaft journal 1.997". Or is that clearance a 0.002" gap all the way round the journal. Which would make the example bearing 1.999" and the journal 1.995"?

With regard to Plastigage. I have read conflicting instruction. Most say use one piece across the journal. There were also instruction to place two pieces across the journal 180 degrees apart. The first method would give an 0.002" difference (0.001" overall gap) between the bearing and the crank. The second would give a 0.004" difference (0.002" overall gap).

I have tried both and the 0.004" difference (0.002" gap) appears to be too much. The crank can be moved up and down producing a rattle noise.

What do you guy think?

Bob Johnson

[SeaSlugs]

Originally Posted by Bob Johnson

I have read lots of opinions on how to check main and rod bearing clearances. There is something that confuses me. It is generally agreed that there should be 0.001" of clearance for each 1.0" of bearing diameter. On a B engine the main bearings are about 2". That would result in a bearing clearance of 0.002". The confusion, for me, is the following. Should the bearing be 0.002" larger than the crank journal? For example, bearing 1.999" and crankshaft journal 1.997". Or is that clearance a 0.002" gap all the way round the journal. Which would make the example bearing 1.999" and the journal 1.995"?

With regard to Plastigage. I have read conflicting instruction. Most say use one piece across the journal. There were also instruction to place two pieces across the journal 180 degrees apart. The first method would give an 0.002" difference (0.001" overall gap) between the bearing and the crank. The second would give a 0.004" difference (0.002" overall gap).

I have tried both and the 0.004" difference (0.002" gap) appears to be too much. The crank can be moved up and down producing a rattle noise.

What do you guy think?

Bob Johnson

plastigauge you use one strip, it creates a high point so to speak that gets flattened when things are tightened/torqued. then remove the journal and see how far it got flattened - thats your clearance.

to check for roundness yes use it 180* apart but do one strip at a time - do one side get a result and record it, get the plastigauge off 100% clean, then do the other side, get a result and record it - ideally they should match but most likely they wont unless it was fresh bored. take an average and adjust shims accordingly

[Dodge]

The bearing should be .002 larger than the crank as in you r first example. The second example is .004 which is too much and why you would have the slop up and down.
Just use one piece of plastigauge too measure the clearance.

[Jim Brierley]

As sea slugs says. You are looking for total clearance. If doing it in-car, put a little upward pressure with a jack under the crank so you get a true reading. .0015 is fine for a B that is not raced.

[Art Newland]

I just went through the process, use a small length of plastigauge, like .25 inch or so. Lay it length-way in line with the crank and away from any openings in the bearings. Put the cap on and torque it properly, don't spin anything! Take the cap off and measure the squished plastigauge. Look for between .001 to .0015 clearance. I'm sure there are other opinions.

[SeaSlugs]

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Originally Posted by Art Newland

I just went through the process, use a small length of plastigauge, like .25 inch or so. Lay it length-way in line with the crank and away from any openings in the bearings. Put the cap on and torque it properly, don't spin anything! Take the cap off and measure the squished plastigauge. Look for between .001 to .0015 clearance. I'm sure there are other opinions.

yea i forgot to mention the no spin part with plastigauge present...ideally you would do it in 4 places to see how eggy the journals are but 2 is good enough for these low rpm engines.

Isnt there a go-nogo method using a piece of tin foil?

[Art Newland]

Also might mention to be sure to completely clean the P-G off the cap and journal. Yes I've read of the tin foil method, also just taking out shims until it locks up then put one back in, and even more crude than that. These engines seem to tolerate a lot! If it's not really lose and knocking it's self apart, you're probably good to go.

[SeaSlugs]

Originally Posted by Art Newland

Also might mention to be sure to completely clean the P-G off the cap and journal. Yes I've read of the tin foil method, also just taking out shims until it locks up then put one back in, and even more crude than that. These engines seem to tolerate a lot! If it's not really lose and knocking it's self apart, you're probably good to go.

yea, im betting though the closer you are in spec the longer you can go before you have to re-adjust so unless you like adjusting bearings id recommend getting it to .0015 the first go around haha.

[FRANK PKNY]

Bob I have been a self proclaimed mechanic since 1959. I have tried the Platigage route, found it unreliable on Model a engines. I will give you a very brief idea of how I check my bearings. Pull the cap and inspect if the Babbitt appears intact , set the transmission in neutral , spark plugs out of engine, place in hand crank. turn the engine over, it should feel rather free , not lots of resistance, Take off one (Peel off) sliver of shim stock, from each side of the cap. bolt When your happy with one bearing loosen it up then the cap up tight and turn the engine over by the hand crank. If the engine is still free same amount of resistance repeat the procedure till it feels too tight, loosen the cap and put back one sliver of shim. I some times use Prussian blue on the cap to see how well the bearing is fitting. I have goon so far as to scrape the bearing on the high spots, but this is rather difficult if the engine is in the vehicle. You then need to loosen that cap and go on to the next one, same procedure for all rods and mains. You will get a feel for the resistance, just make sure your not over tightening the bearing surface. A good tight fit you can barely move the rods back and forth on the crank shaft. I know I'm opening a can of worms here. But this is the way it was done in the shops years ago. I learned from an old-timer when I was a teenager. Of course the bearing surface of the crank shaft needs to be in good condition, if it's not Again this is a judgement call if it's just a tad bit rough a temporary fix would be to use a strip of sanding material to polish it up, but at this point you would be best to go for rebuilding. Oil pressure is your friend, if there is a lack of it, your in trouble even though your rods are splash oiled. This is my way I'm sure others will pipe in. I have driven Model T's and A' many thousands of miles, With engines adjusted in this manor. The old Dykes Motor manuals have this procedure written in them. You can find one on the web or at swap meets, I just gave one of mine to a youngster intrested in mechanical stuff. JMHO Frank

[bettlesr]

When I had to change a piston on my original engine in the car when I bought it ('28 block), I checked all the bearings with plastigauge. I can only assume that the engine had been rebuilt earlier with the wrong type of babbitt. The plastigauge was intact and there was a groove in the babbitt where the plastigauge had dented it. Around a year or so later, the engine got a bad knock and had to be towed home. When I pulled the pan down, all the babbitt was in the pan.
After this, Schwalm's got the job of building me a HP engine in a '31 block

[Dollar Bill]

Originally Posted by SeaSlugs

Isnt there a go-nogo method using a piece of tin foil?

S/S, this is what I have in my notes for the Go - No/Go foil method you mentioned:

Use a piece of heavy duty aluminum foil which is .002 thick. The regular is .001 and may be folded if that’s all you have. You want a piece as long as the bearing surface and ½ inch wide.

Lay this in the cap along with the shims and tighten it up. Now see if the motor will turn with the foil in place using a 6 inch lever in one of the crank balance holes.

Add/remove shims to obtain rotation with .001 and binding with .002.

[Tom Wesenberg]

I use a micrometer to check the crank for egg shape. I've never used plastigauge to check for egg shape journals, but have used it and the foil method to check for oil clearance. Hold the P/G is place with a drop of oil along it's length.

BTW measure the crank at 90* apart to check for egg shape.
180* would be the same as the first measurement.

[Kohnke Rebabbitting]

Originally Posted by bettlesr

When I had to change a piston on my original engine in the car when I bought it ('28 block), I checked all the bearings with plastigauge. I can only assume that the engine had been rebuilt earlier with the wrong type of babbitt. The plastigauge was intact and there was a groove in the babbitt where the plastigauge had dented it. Around a year or so later, the engine got a bad knock and had to be towed home. When I pulled the pan down, all the babbitt was in the pan.
After this, Schwalm's got the job of building me a HP engine in a '31 block

Mr. Bettlesr,

The reason that Plastigauge indented your Babbitt is because you used the Plastiguage dry.

When you do not use the lube, the dry surface will not let the plastigauge slide, or spread out, and so when the Plastigauge has to go some where, so it goes in the Babbitt, instead of spreading out for a true reading.

Never read the Babbitt, always read the crank.

One thousandths per inch should always be used in setting bearing clearance, that is Minimum. The high side should never be more then a one half thousandths more.

If in this case, using a Model "B", a 2 inch crank, when hot, will swell right at .002.

So where is your oil clearance? You have none. So what happens when the bearing has to open its self up. It isn't going to be the crank wearing smaller, it is the crank pushing its self free, and the Babbitt is being moved to struggle, and twist its self loose.

Model T's have a 1- 1/4 inch crank, when broke in, depending how hard, run with 2 to 3 thousandths clearances.

Model A's with a 1- 1/2 rods run about 3 to 3-1/2.

[Mike V. Florida]

This long version of the foil method;

http://www.fordbarn.com/forum/showpo...2&postcount=14

[H. L. Chauvin]

Hi Bob,

As to "What do you guy think?

Never used foil or metal shims in over 59 years, & never used the modern Plastigage Crap introduced by United Kingdom in 1948.

My Dad born 1902, Gramps born 1867, Great-Grand-Gramps born 1836 and Great-Great-Grand Gramps with his steam boats, (the Paragon and the Teche), born 1813, & all of us always adjusted bearings successfully without the plastic crap which came out after people lost hand and eye coordination and developed horrible hand writings, developed 5 thumbs, could not "see" level or square , and/or round objects, and could not "feel".

If theses same Plastigage dependent guys ever tried to built boats with hand planes & hand saw and planks, they would have all leaked and sunk .... so they had to use Plastigage crap to adjust bearings and later buy aluminum boats or fiberglass boats.

Ten years ago on my 1930 Town Sedan, for bearing adjustment , I still used the "feel" method ............ much later recommended by Henry Ford for Model T's in the 1920's in his Model T Ford service Manual.

But just one opinion based on Babbitt bearing adjustment perfection from our ancient steam boat engine book written in 1848; <Les Machines a Vapeur>.

[Bob Johnson]

H.L.

Would you please explain the "feel" method. I am very interested in learning how to do it. I have to use Plastigage because no one has taught me a better way.

Thanks
Bob

[Jim Brierley]

I race the Model B engines, and use a little more clearance than for touring. I have gone 153 MPH on a full-babbitt engine, B rods. I'm still running the same block and C crank on the same babbitt mains. I use .0025-.003" clearance and full pressure oiling. Red-line is 6,000 RPM, using a Cook OHV cylinder head. I believe in using Plastigage. To each his own!

[40 Deluxe]

Originally Posted by Jim Brierley

I race the Model B engines, and use a little more clearance than for touring. I have gone 153 MPH on a full-babbitt engine, B rods. I'm still running the same block and C crank on the same babbitt mains. I use .0025-.003" clearance and full pressure oiling. Red-line is 6,000 RPM, using a Cook OHV cylinder head. I believe in using Plastigage. To each his own!

Can't argue with success!

[Terry, NJ]

What I believe H.L. is saying is to do (From Experience) what others require measuring devices and methods to accomplish. In other words, I knew a guy who was all surprised when a printer could tell the difference in type sizes (1/77 of an inch IIRC) by sight. Heck! Thats bigger than 1/100th or .010. I' myself could easily feel .002 when I was working in the trade. In some cases .0005. You just sort of know after a while. That's the critical thing, knowing after a while! I doubt if anyone could do it after thirty years as a insurance adjuster. It takes time to develop that feel well enough to rely on. Even now. I wouldn't trust myself doing it (Too many candles on the cake) Stick to micrometers and plastic gauge! Hey, H.L. If I were to replace a Garboard Strake, would I have to pull it out of the water?
Terry

[H. L. Chauvin]

Hi Frank,

Per part of your Reply no. 9.,

"I know I'm opening a can of worms here. But this is the way it was done in the shops years ago. I learned from an old-timer when I was a teenager."

I learned a similar very "simple" method as a teenager 59 years ago by mechanic Dad who was born in 1902.

Appears many on this Forum have no clue and even cannot imagine that in 1931 on Ford's no. 20,000,000th car, Babbitt on these cars were later adjusted at least approximately 3 times which would equate to 60 million "successful" Babbitt adjustments made "without" Plastigage. With more Fords after 1931, even more difficult for some to imagine.

Maybe Babbitt adjustments by 1931 could have been performed by mechanics and also owners with about a 1931 education level of at least 3rd grade ..... but just guessing ......

I remember riding in my Uncles boat in 1947, powered with a Model B engine with a Police head accompanied by 2 downdraft carburetors ..... no marine transmission .... his particular boat had 2 speeds ..... screaming at wide open & stop ...... absolutely no Plastigage in 1947 ..... he ran it and raced for over 12 years problem free.

I could write how this simple method was done years ago, but I can imagine what would happen.

Many experienced mechanics on this Forum may wear glasses & hearing aids, but I sincerely doubt if many lose their feelings.