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Farmall & IHC Tractors Discussion Forum
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Crank bearings

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CNKS

01-11-2005 10:00:41




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I am currently checking the crankshaft on my 460. Two questions: 1. Is it ok to use new bearings (inserts) on an old crankshaft without having it ground, if the roundness is within limits? 2. This question is immaterial if the answer to #1 is no. Two of the main journals are out of tolerance, how much I don't know as I have to purchase the next size plastigage before I can measure. How much, if any, less clearance will there be if I use the new inserts on the old crank? Two of the journals are not within the recomended range, but may be inside the maximum allowed. Recommended is up to 0.003, maximum is 0.006.

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Opa A

01-11-2005 17:25:06




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
Measuring clearance with worn bearings and plastigage will not tell you whether the wear is in the crank lournal or the bearing shell. If the bearings are original they will have the wear as they are much softer than the crankshaft. Someone may have already replaced the bearings and then you would have to suspect more journal wear. Most bearing manufactures stamp the bearing date in the back of the shell, as well as dimension, STD, 0.010, etc, this can be a good indication of service life. I've often done 3 to 4 bearing rolls in one engine before the crank needed work. Measure the crank, and if the results are within specs (specs may already be a standard undersize) and you can't feel any grooves with your finger nail I'd just install new bearings and run it. I remember doing an engine in a Case W14 loader and the guys that work on the all the time advised me that if I had the crank turned 0.010 under it would break within 500 hrs, (only engine I've ever seen with that weak of crank). Just the same I don't like to undersize a crank unless needed.

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Opa A

01-11-2005 17:31:21




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 Re: Crank bearings in reply to Opa A, 01-11-2005 17:25:06  
By the way you are correct in plastigaging with the engine upsidedown, for the mains you don't want the weight of the crank helping to crush the plastigage. When you check clearance on final assembly, check with no oil on the upper bearing shells as the oil will hold the crank away from the bearing shell and show less clearance than there is. Once you are done checking all the main bearing clearances, lift the crank out again and lubricate the bearings, reinstall the crank and check endplay.

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superih

01-11-2005 16:05:40




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
It doesn"t cost that much to have a crank turned!!



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CNKS

01-11-2005 12:54:36




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
I took it apart because of low compression on two cylinders, checked wet and dry and it's mostly rings. Going to have the head redone and put in new pistons and sleeves, might as well check the other stuff while I'm at it. The block and head are going to be checked for cracks, flatness, etc and hot-tanked. I need a new camshaft and lifters because the old one is worn out of spec on all lobes. I was just experimenting with the crank to see if it needed to go to the machine shop. It probably does, but I was curious if new inserts would solve the clearance problem if the thing was round and not garfed up too much. The roundness will be checked with a micrometer. If round I have heard it could be simply polished if it was otherwise ok. I am checking the clearance of the bottom inserts with the engine upside down in an engine stand -- I suppose gravity affects that too?? -- lot easier than doing it laying on my back. The service manual shows the engine upside down. I also know that the new stuff needs to be plastigaged too, this is only an estimate.

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Randy SE-MN.

01-11-2005 14:19:53




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 Re: Crank bearings in reply to CNKS, 01-11-2005 12:54:36  
A wise old owl by name of Lee at C&G taught me how to re-clearance the bearings on my "50 M with strips of paper...and by god it worked. I"m sitting at 70 PSI hot. I"ve built more engines than I"ll live to be years old, being almost 30 years in automotive, I"ll not forget this one soon...Randy



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Andy Martin

01-11-2005 14:04:45




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 Re: Crank bearings in reply to CNKS, 01-11-2005 12:54:36  
With the engine upside down you should put the plastigage in the rod bearing, not the cap.

If the crank looks good and the machine shop passes it then by all means going with the bearings that fit, 001" under or whatever is the thing to do. A good machine shop should steer you right.

We put a Case backhoe together last year with rods a little loose (0.003) and so far so good. Works every day.

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El Toro

01-11-2005 11:03:55




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
If all the journals were worn the same and the shaft was nice and smoothe I would probably use the new inserts. Since you have some worn more than the others I would have crank measured at a machine shop and see what they recommended. Undersize bearings are probably available if the shaft needs to be ground undersize. I've used .002" undersize when the shaft was slightly worn and only needed to be polished. You do not want to have to do this job twice. Hal

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captaink

01-11-2005 10:55:14




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
Answer to # 1. If the crankshaft is within tolerance when measured with a micrometer, and it is smooth without grooves or dings in it, it is fine to put in new bearings. When you measure with the micrometer, you will then know if you need standard, 0.001, 0.002 or 0.003 undersize bearings. More than that, and you should consider grinding the shaft. You can not tell if a crankshaft is good by using plasti-guage with an old bearing. The old bearing may be worn which will throw off the reading. Plasti-guage is only useful with new bearings to check to make sure you have the correct clearance between the shaft and the bearing.

Answer to #2. See plastiguage comment in #1. Old bearings probably are worn and will not give a reliable reading on the crankshaft. Only a measurement with a micrometer will give you an accurate story. When in doubt, take the crank out and take it to a machine shop and have them measure it. Work bearings or worn journals on the crankshaft will allow excess oil to escape and lower your oil pressure. While it is true that the engine ran with wear in it, you obviously took it apart for some reason, and are concerned about rebuilding it correctly. You need to decide how deep your pocket book is compared to what and how much the tractor will be used to see if spending the money is justified.

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Andy Martin

01-11-2005 11:34:17




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 Re: Crank bearings in reply to captaink, 01-11-2005 10:55:14  
In addition, you mentioned out of roundness. You can only measure out of roundness with a micrometer. With plastigage be careful always to put it on the bottom bearing. If you put it in the top bearing, gravity can depress it some and make the fit look better than it is.

The bearings should say if they are undersize on their backs. Check them.

Even a cheap micrometer will give you good enough readings for a crank if you know how to use one.

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gene b

01-11-2005 10:11:45




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 Re: Crank bearings in reply to CNKS, 01-11-2005 10:00:41  
There are bearings avail 3thous over from some suppliers you mite have to check around for a supplier. For light duty it is not that important as you aint running 3000rpms in a tractor pull. It ran now with some wear didnt it. Same old **** how much money do you want to spend and is it worth it. If you are going to spend a 1000 mite as well trade for something else and then have the same problems just goes on and on. Mite even want to get some 1thous shim stock and use on the caps in case the 3thous are too tight. The plasticguage will tell the story.

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