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More crank bearings

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CNKS

01-11-2005 18:19:12




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Perhaps the question I asked below should have read "how can I tell when a crank needs to be reground?". My assumption, right or wrong, was that if I used plastigage between the old inserts and the journal, and if the clearance was boderline, as a couple are, that new inserts would decrease the clearance to an acceptable level. I can't see how the clearance could be MORE with new inserts. All this assumes that the crankshaft is within spec as to both roundness and journal diameter, and is not grooved or nicked--I am not sure of this and will probably take the crank to a machinist anyway, that does not mean the machinist has to do anything. Another question is, if the crank is slightly out of round, but still within spec, will it cause excess wear on the new insert, which in theory, is a perfect half circle? Sorry for the questions, but rather than take the engine including the crank to someone and saying, "here fix it", I would like to know what's going on.

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El Toro

01-12-2005 17:46:59




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
I think Lee covered the crankshaft measurements
very well. A machine shop will degrease that shaft and then will determine whether it needs to be ground in a very few minutes.

You also need to take the block and have it degreased and new cam bearings installed and have the bearings and lobes measured for wear. They usually recommend a new cam. This is all related to having good oil pressure. Too many postings to read. Hal

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lee

01-12-2005 18:56:13




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 Re: More crank bearings in reply to El Toro, 01-12-2005 17:46:59  
if the engine has cam bearings, they will likely be destroyed by a caustic hot tank cleaning. These are best replaced anyway. Some engines
the cam just runs in the block. In this case the block should be checked on size.



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CNKS

01-12-2005 19:15:00




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 Re: More crank bearings in reply to lee, 01-12-2005 18:56:13  
I told the machinist I wanted new cam bearings and he said he had to pull them before hot-tanking anyway, he will put the new ones in. Cam looks pretty bad to me.



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lee

01-12-2005 13:39:54




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
This is my take and I'll have to say I did not read all that below word by word. An engine is an engine to me, tractor or automotive, so I don't look at old tractors as though quality of work should be anything less than say for a daily driver automobile. The plastigage is just a means for checking or verifying an assembled journal or rod bearing clearance in lieu of a more elaborate process requiring the proper measuring tools. Plasigage must be used without oil as it will dissolve in oil. Typically an outside micrometer calibrated on size and good to a resolution of .0005 (.0002 for closer work) should be used to determine the journal diameter measurements. First off the crank must be clean and a thorough visual inspection made to evaluate the ground journals for surface finish, nicks, scratches, etc.. It goes without saying it will be near impossible to measure a beat up crank precisely. Assuming it looks and feels real good, several readings would be taken on each diameter to locate the high and low readings, subtracting to get out-of round. On a very good journal the difference may not be discernable ie., the journal is round. At least two readings would be recorded on paper at the high and low spots usually 90 degrees apart. Sometimes more readings are taken and recorded at equal spacings around depending how anal the machinist may be. After all the measurements are taken and recorded an assesment of the condition of the crank and how much to grind it can be done against the specs. Cranks tend to wear out of round or to have surface finish problems so I would look at surface finish and out-of round very close against specs. If surface finish is a problem the crank should be ground. If out of round (i won't quote a spec) beyond spec it needs to be ground. As stated above it is difficult to get good measurements if surface finish is poor. It helps to know what a good journal looks and feels like.
This sounds like a lot, but with experience a guy can evaluate a crank rather quickly.
Moving on. Ideally a dial bore gage is used in a similar fashion on the assembled mains with the bearing shells in place or on rod big ends with bearing shells in place to determinie the inside diameter of the assembled bearings. If all is round as it should be the assembled clearance is determined by subtracting the appropriate inside and outside diameters. The dial bore gage step is often time skipped at a shop. They may have a crank ground at .010 under and buy the appropriate bearings. Plastigage is then used to determine the fit-up conditions. Since the crank was ground they can easily verify it for round and proper size. So plasitgage can be a fairly easy check for clearance at assembly in a case like this. I'll stop here. I hope it makes some sense. The problem with your question is it cannot be answered in short form. Even this long write-up does not do justice.

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CNKS

01-12-2005 14:47:03




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 Re: More crank bearings in reply to lee, 01-12-2005 13:39:54  
At least you said plastigage dissolves in oil. The machinist said he doesn't do any assembly, assuming he does good work (probably does as the tractor dealers send their work to him), I still need to know how to use the plastigage properly, which I believe I do now. As I asked below, if done dry, the dry measurement on the paper scale must compensate for the lack of oil in the in the upper journal, since the crank is should bottom in that journal because of no oil, doubling the clearance. All this is immaterial, since I'm not doing the grinding, as long as I correctly measure the clearance with the plastigage -- thanks!

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brtx

01-12-2005 16:09:31




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 Re: More crank bearings in reply to CNKS, 01-12-2005 14:47:03  
cnks plastigauge has to be used on a dry surface because you are measuring clearance for oil flow.any oil on the surfaces will give you a false reading.lubricating bearings on assembly can be done with a pressure tank filled with oil.connect a hose to the oil galley then put air to the tank.this will lube all aspectsof the oil system.never run your tank empty and you can fill your oil pan at the same time.when you are reafy to start remove the coil wire and let the engine free wheel till toue have oil pressure on the gauge.ready to fire then.my 2 cents

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lee

01-12-2005 15:50:31




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 Re: More crank bearings in reply to CNKS, 01-12-2005 14:47:03  
Sounds like you will assemble with engine out of tractor and crank case up. Don't put the rear rope seal or any other seals in. This is a mock up to check mains clearance using plastigage. Keep things clean. Clean all the mains bearing saddles. Lightly oil. Place the bearing shells lightly oiled. Place the crank lightly oiled. Place the bearing shells in the caps lightly oiled. Oil the bolts. Bolt the caps on without plastigage and torque to spec to seat the bearing shells. Turn the crank over a little it should be free. Remove the mains caps. Wipe the exposed crank journals and cap bearing surface clean of oil. Use thinner or alcohol to remove all oil. Place the plastigage per instructions on package. Place the caps and torque to specs. Don't turn the crank. Remove the caps. Check the plastigage clearance. The plastigage will likely stick to surfaces. It doesn't need to be cleaned off completely. It will dissolve in oil. The clearance spec is the total clearance with the crank bottomed in the mains saddles. Lots of guys would just assume the shop did their job correctly but I would do this plastigage check. It's a bit of work but worth knowing you got what you paid for, proper bearing clearance. If this were done from underneath the tractor the crank must be forced up and held up in the saddles.
The same can be done on the rods. Torque the rod bolts carefully so as not to crush the plastigage artificially.

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CNKS

01-12-2005 17:30:32




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 Re: More crank bearings in reply to lee, 01-12-2005 15:50:31  
Thanks, I probably would not have remembered to seat the crank before using the plastigage. I now have everything apart and an empty block ready to take to the machinist. Crank looks ok, but of course the measuring will tell the story. Some of the bearings look worn to me, a couple unevenly worn. Engine sleeves and pistons are scored, so will replace.



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lee

01-12-2005 17:59:40




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 Re: More crank bearings in reply to CNKS, 01-12-2005 17:30:32  
remove all the oil galley plugs. Document in some way how many there are and where they go. Do this, if you can, some may be difficult to remove, before you take it to machinist for hot tank cleaning. I would not depend on the shop on these plugs. You will want to clean the galley
drillings and put the plugs back after you get it back.



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lee

01-12-2005 17:04:50




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 Re: More crank bearings in reply to lee, 01-12-2005 15:50:31  
this link may help in using it.

http://www.dana.com/perfectcircle/Plastigage.htm



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CNKS

01-12-2005 17:52:58




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 Re: More crank bearings in reply to lee, 01-12-2005 17:04:50  
I notice the link indicates how to determine the taper, or difference in clearance at the edges of the bearing and also indicates that approximate out of roundness can be checked by checking in two locations. Reading between the lines, this to me indicates that it can be used for checking clearances of old bearings, although it is not a substitute for a micrometer. After reading it is obvious that I have not used it absolutely properly, will do so when I reassemble. The rest of you that responded might look at the link, also, it is from the company that makes plastigage.

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Opa A

01-12-2005 11:02:24




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
I don't know if you've seen my comments from yesterday, they're posted. Just one more thing. If the crank has already been ground by a reputable machine shop they will have stamped the undersize dimension they ground to somewhere on the crank. Your questions are interesting, and your answers to other questions in these discussion boards have always been insightful and have helped give direction in the resoration of my "A". Thanks.

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CNKS

01-12-2005 12:09:31




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 Re: More crank bearings in reply to Opa A, 01-12-2005 11:02:24  
I've read everything, thanks. I don't disagree with any of it, just looking for explanations. The crank has standard bearings, so I doubt if it has been ground at all. The bearings look pretty well scored in places, crank does not look bad, grinding will take care of that. It and the block are going to the machine shop. Block and head hot-tanked and checked for cracks. Going to let machinist install sleeves and cam bearings, and either order or tell me what crank bearings I need. Then I will do the rest, as he doesn't do the final assembly, I don't like paying labor anyway. The camshaft needs to be replaced, according to my measurements, I will ask the machinist to verify that. Compression low on all cylinders, wet test indicates rings, two cylinders are considerably lower than the other four. All this on a supposedly good running engine. But, I'm not putting old parts back in, after going this far.

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Aces

01-12-2005 08:31:41




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
CNKS You should do the plastic gage with the shaft and bearing dry because you are trying to find the clearence between the bearing and shaft. And I would gage the old bearings to get and idea how bad the wear is. New bearings of the same size should never give a larger gap. One should never assume the bearing in the box is what the box says, check the bearing to see it is marked as what one wants. Part of the confusion here is that you can not put over size bearings in and engine, if the shaft is warn and and different bearings are needed you put in under size bearings. Say you have a 2" shaft, first you will have standard bearings, then IH had .002 under size, in some cases they had .003 under size. If .003 under size don't do the job you have the shaft ground. So if the shaft is ground you take off material you don't add, so now the shaft is 1.990" if you need to go .020 then the shaft is 1.980 under the orignal 2", so we put in under size bearings not over size, because it is the diameter of the shaft that determons the size of the shaft, the bearing does not determon the size of the shaft. So we have standard and under size bearings.
The best way in an old engine to determon the condision of the shaft is with a micrometer it will tell you if the shaft is out or round with out needing to know the diameter of the shaft. To know if the shaft has been ground you will need to know the original size.
Hope this is some help.

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CNKS

01-12-2005 12:31:40




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 Re: More crank bearings in reply to Aces, 01-12-2005 08:31:41  
I don't know where the "oversize" came in as I didn't intend to mention it. Except, I was asking that if I could determine wear by plastigage with the old bearings on the crank; a few said no, I asked why not, that I couldn't see how there could be MORE clearance with new bearings (of the same size, that's what I meant anyway), and if the old ones were slightly worn, the new ones would then take care of the problem PROVIDED the crank was ok. You just indicated I could check the old bearings, which I have already done. The rod bearings are ok, at least two crank bearings are borderline. Doing it dry -- the oil film between the bearing and crank keeps it lubricated, centering the journal between the bearing halves. Perhaps the plastigage scale on the wrapper takes that into account, and with no oil the 0.003 (or whatever)dry measurement with the crank bottomed on the part of the bearing on the rod, is actually 0.0015, with the oil there? That's what I was asking. Anyway, the crank is going to the shop--Thanks!

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CNKS

01-12-2005 07:15:08




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
Thanks for the responses. I am retired, have 2 acres and 6 tractors. I do this as a hobby, yes a very expensive hobby. The questions I asked were not to see what I could get by with and do a minimum job, but to increase my rather limited knowledge (as you can tell by the questions) about tractor engines. I know not to put standard bearings on a reground crank. The work, if any is required (apparantly there is) will be done by a machinist. I am merely trying to learn by asking questions. The two mains out of tolerance are the two center ones. The crank will be measured and checked for roundness. I will do that myself just out of curiosity, then let the machinist do it. I still don't understand why plastigage should not be used on old bearings, just as a ballpark measurment to determine wear, as long as the crank is still throughly inspected, and polished or ground whichever is needed, and the correct inserts installed later? Perhaps someone can answer that SPECIFIC question. Two other specific questions. When using plastigage, are the journals/bearings supposed to be lubricated or not? What I am currently doing is removing the bottom cap (the engine is upside down in a stand) wiping the oil off the top (bottom) of the journal and wiping the bearing. The connecting rod part of the bearing is untouched. Does this give an accurate reading? When installing the correct bearings on a properly prepared crankshaft, is lubrication needed? Again, with the engine upside down, and the bearing surface and journal where I put the plastigage clean, with the connecting rod surface clean, doesn't the correct torque push the crank into the unlubricated rod journal, and double the reading?? Or if I do lubricate the whole journal, how do I know I have the right amount, or does the excess lubricant get squeezed out when torqued? Sorry to prove my stupidity, but the consensus on this forum is that there are no dumb questions (although there may be dumb questioners).

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scott#2

01-12-2005 08:32:14




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 Re: More crank bearings in reply to CNKS, 01-12-2005 07:15:08  
CNKS,

I dont know much about tractors but I know about precision engines. Plastigage is primarily used for checking the grind job and bearing quality, to insure a accurate bearing oil clearance. I have had cranks come back that would not give a consistant reading across the journal. (bad dressing job on crank machine wheel) There are just too many variables in using plastigage on old/used parts to get a ballpark figure, especially since the ballbark is quite small when it comes to oil clearance. Block bores, rod bores, bearing quality (from different manufactures), bearings worn uneven, out of roundness, crush factors torque values, cleanliness on and on and on. I have even used different manufacturers bearings on the same engine when setting the bottom end up and often get different results. Plastigage is such an accurate way of measuring clearances that there is absolutly no room for variables or mistakes. Drop an eyelash anywhere in there and the reading is flawed. Dryer lint, cigarette ash, any contamination will give false readings. All readings should be taken with dry clean surfaces. This means block bores, main bearings (both sides), rod bores and their inserts (both sides). No oil, no nothing anywhere. If a journal is out of round or just round and worn to a smaller diameter, no amount of torque will push it down into the bearing for an accurate measurement. You only ues assembly lube (moly) on final assembly.

Hope this helps,

scott#2

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CNKS

01-12-2005 09:42:02




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 Re: More crank bearings in reply to scott#2, 01-12-2005 08:32:14  
Thanks, the crank has standard bearings, so I "assume" it has not been ground. The machine shop will do the work, and get me the proper bearings. They will then be plastigaged during assembly. As I said the reason for my measurements is to get an idea about what is going on. Apparantly my measurements don't mean much. Just trying to learn the system.



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EricB

01-12-2005 06:35:56




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
CNKS
Reading your question about tolerence being more with new bearings brought the thought that, perhaps the crank had already been turned and oversized bearings used. Thus new original bearings would fit poorer than old oversize. Be careful! International has put out technical corrections on a number of crankshafts and warnings not to turn. I had a B250 with a turned crank and broke it.
I have never changed a crank or bearings without matching both surfaces. Mind you, those were racing cars but then a good job is a good job.
Its also a big job. I'd be tempted to do it right.

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scott#2

01-11-2005 20:37:38




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
Cranks need to be ground whenever you feel uncomfortable putting it back together the way it is. I dont know the wear limits on the journals, but if you want an engine to run HARD all day, the bottom end needs to be precise for obvious reasons. Shims can be used at times but unless its a "hard" brass or other material, over time it can "beat out". If it were me and I wanted a work horse that I didnt have to think about, I would grind/replace if possible. If its on the wear limit and wasnt doing much HARD work, I would let it go. An out of round journal will increase wear, especially if you have more than one. A loose, rotating mass will eventually beat the bores in the block out of round as well. Then an align bore is in order. Yet another expense. You can pay now or pay later. There are fine lines between new, ok and broken. New and ok about .003 - .006" as you say (limits). Ok and broken/spun can be as little as .00015".

Its a tough decision.

scott#2

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brtx

01-11-2005 20:04:55




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
cnks mike the crank.that will tell you if ita out of round.new inserts will only decrease pressure if they have too much clearance.like putting standards on a ground crank.were the 2 inserts that were out of clearance beside each other?if thats the case you may want to get the line bore checked.there may have been a bearing failure in the past.on 855 cummins we always had the line bore checked.if its out of alignment it may end up stating to wear the new inserts the same way.just a thought.good luck

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riverbend

01-11-2005 19:37:02




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
How about one more opinion ? It ran with the worn bearings. It will run fine with new bearings, and it will have better oil pressure.

I foolishly thought that I had mis-measured the journals on my H when I rebuilt it. They were only a thou or so undersized.... When I checked it with the new, standard shells, the clearance was 0.004". Pretty disappointing.

I bought a roll of 0.001" copper shim stock from McMaster Carr and shimmed up both sides of the mains and rods. It measured 0.002" all the way across.

When I took it apart, only the lower shell had been shimmed. I know, but I thought that somebody had shimmed up worn shells. It ran like that for 10 years. On the transplanter, it had to run so slow that it would stall out. Other times when the disk went deep in the sand coming up a hill, it lugged down until it died. I took it apart because the valves were shot.

The tractor worked fine this summer. I am a little more careful not to lug it so much anymore. It still has to run at idle to pull the transplanter, but now it makes more power and does it easily. The oil pressure reads half a gauge, hot, at idle with 10W40.

If the journals are smooth, I would not worry about reusing the crank as is. I never had the crank reground on my Norton and it will touch 7000 rpm. It has gone 35,000 miles so far, and if it breaks (knock on wood), I could be 1500 miles from home.

If you need some thin shim stock, let me know, I must have enough to do 5 engines. Be careful when you trim around the oil holes. It worked better to put the shim stock on cap or the block rather than on the back of the bearing.

Greg

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Bob

01-11-2005 18:53:13




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
You can get UNDERSIZE inserts, such as .002", if the crank is not too grooved or out-of-round.

When the crank is worn excessively out-of-round, the problem you run into is that you still need adequate oil clearance between the crank and bearing, at the LARGEST diameter of the crank, but yet there will be excessive clearance at the worn part of the crank, possibly leading to "knock" and early bearing failure.

If you have the engine all apart anyway, and are buying new bearings already, ask a machinist you trust to check out the crank. If it needs grinding, you should be able to get it done for $60.00 to $150.00, and do the overhaul RIGHT.

Saving the cost of a grind, while it's all apart already isn't going to look very cost-efective if you put it back together, and have a knock, or low oil pressure.

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CNKS

01-11-2005 19:05:31




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 Re: More crank bearings in reply to Bob, 01-11-2005 18:53:13  
Thanks --I'm not necessarily trying to save the cost of a regrind, I'm just trying to learn something that may be useful both now and later. That's what this forum is for.



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Josh In Indiana

01-11-2005 18:52:15




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 Re: More crank bearings in reply to CNKS, 01-11-2005 18:19:12  
CNKS, How are ya this evening.
You ask, "how can I tell when a crank needs to be reground?" If it were me I would run my fingers over the crank and feel if it is groved or not. I would also look to see how it is wearing. Like if it is more wore on the sides than the center or vice versa. If there are already inserts there then chances are that someone has been there before and ground the crank and put those inserts in. Its just a guess. Depending on your use of the tractor could influence your decision. If it is out of round, meaning egg shaped then I would definetly have it ground. If its not out of round and not wore bad I would have my machinist find me a set of inserts to put in that would bring it back up to clearances and run it. Those cranks are pretty hard and they can take alot. Sorry for getting a little long winded.

Good luck,

Josh in Indiana

P.S. Those inserts should have a number on them. e.g. 5 or 10 thousanths. that is how thick those inserts are. Look up to see that the righg gap is and then that will tell you if someone has been there before or not

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