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Bearing Clearances - NAA

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Ramrod

09-15-2004 12:14:55




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What kinda bearing clearances should I see (using plastigage) on the Main and Rod Bearings? I figure on checking that just to be sure the right size stuff is installed.

Thanks,
Ramrod




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Ol Chief

09-15-2004 19:59:11




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 Re: Bearing Clearances - NAA in reply to Ramrod, 09-15-2004 12:14:55  
Icannot help you with the clearance spec. on yourNAA.HoweverI have worked on reciprocating gas, diesel and steam engines from 20 HP and up to 2500 horse.Also lots of steam turbines all sizes up to 60,000 HP with shaft speeds up to 9,000 RPM.In nearly every case the general rule of thumb is .001 inch clearance per inch of shaft diameter.I will not say that there is no deviation from this approximation and certainly one should adhear to mfg.specs. if available.If and when you get the spec.compare it to the rule of thumb and see if I am close by approx.Go figure.

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Ramrod

09-15-2004 17:44:47




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 Re: Bearing Clearances - NAA in reply to Ramrod, 09-15-2004 12:14:55  
I'm overwhelmed by the support offered here, THANKS! I'm looking at 20 over bearings on rod and crank, but the mic will confirm that, and yes I do have the tools to measure it properly, but on this tractor, I just can't take chances, due to what I've found the last wrench did to the old warrior. This time out, it will get the best I can offer to make up for past sins commited against him. I'm constantly surpeised at what I find as I tear down and inspect, so I've come to the conclusion not to take anything for granted. I will mic and plastigage, using the specs given to me here, and pray that the threads hold. If they don't, I figure they woulda give up soon anyhow, so I'll just fix that too. This tractor will run another 50 years after I'm done with it, I really hate to do things twice, so I usually make sure I've done my best the first time out.

Thanks guys,
Ramrod

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ZANE

09-15-2004 14:24:52




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 Re: Bearing Clearances - NAA in reply to Ramrod, 09-15-2004 12:14:55  
The way I do it is to read the size of bearing by looking at the bearings that came out of the engine and then buying that size to replace them with. If the crankshaft has been reground while you had it out be sure to insist that the machinest corrictly mark the crank to the new sizes and X out any old sizes on the crank. Then buy the size he has marked.

New bearings are made to exact tolerances (If made in the USA) and you do not have to worry yourself about wheather or not they are going to fit if the machinest did his job.

Besides you probably will do more harm by using plasti gauge than not using it simply by putting more wear on the threads of the rod bolts and the main bolts. You do realize that threads can become turned over and not give a correct torque reading if used too many times????

The only time that plasti gauge is good to use is if you are installing rods or mains on an engine that the bearings are poured babbitt. Even then if the machinest or mechanic used the right amout of smoke and soot for his clearance you don't need plasti gauge.

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Hobo, NC

09-15-2004 16:39:28




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 Re: Bearing Clearances - NAA in reply to ZANE, 09-15-2004 14:24:52  
After ya had to do engine work fer a paycheck ya get to know the feeling ya have when the clearence is eather rite or wrong, one of them wiggle and jiggle things ya do when ya intall a crank. ya even learn that theirs no warranty on a crank kit after ya fire the engine up so ya even check their work fer'em ( is that a deal or what yer the quality controll Xpert and yer not on the pay roll) seen that two many times, only payback is it goes back and you loose a sale cuzz i'm getting a kit from a nutter supplyer. In the last few weeks i have had two engines that had the wrong bearing. I can't see how anybody could miss a .010 bearing on a .020 shaft, one was a N motor, even had the pistons in bac'erds a oil pressure relief spring that was so stiff ya could not move it with yer fingers. gotta admit i did get bit on a crank that was .0005 under, did a ring job in the chassie on a 72 chevy motor home that had 50k and i know it had never been into, was gonna use the old bearings but could not find 1/2 of one of the rod bearings, off I go get a set of STD rod bearings and it runs 100 miles befer it goes to knocking and spinns in the rod.
Then some wonder why the labor rate is so high in a repair shop, cuzz the buck stops here. like some said, sometimes ya eat the bear and sometimes it eats you. I do not use plastic gauge cuzz i have the tools to check the crank and bearings but iffin you don't have the rite tools it would be the next best thing

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Rob

09-15-2004 13:32:33




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 Rick sounds right in reply to Ramrod, 09-15-2004 12:14:55  
This guy has posted a lot of info but for your number he seems to have put down a typo.



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Rick H. Ga.

09-15-2004 12:55:58




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 Re: Bearing Clearances - NAA in reply to Ramrod, 09-15-2004 12:14:55  
Ramrod, I don't have the FO-19 manual in front of me at the moment but if my memory serves me correctly the clearences are rather tight like under .003 (3 thousands of an inch).

I used plastigauge on my Jubilee crank and got about .001 clearence on both rods and mains. I had my crank turned .010 under on both rods and mains. I hope mine is not too tight. The assembly turns over OK with the help of a socket and ratchet on the pulley bolt but is hard to turn by hand. I had the same situation on my 8N engine when I rebuilt it (hard to turn by hand). The 8N rebuild cranked eaisly and has run great ever since. I hope the Jubilee does the same. HTH. Rick H. Ga.

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Hobo, NC

09-15-2004 13:51:04




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 Re: Bearing Clearances - NAA in reply to Rick H. Ga., 09-15-2004 12:55:58  
The rope seals is why it turned hard, if it was the bearings it would not have held up. Would pay to install the crank with out the seals and see how it turns then remove it and install the seals, or just use plastic gauge.



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gahorn

09-15-2004 17:06:32




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 Re: Bearing Clearances - NAA in reply to Hobo, NC, 09-15-2004 13:51:04  
Plastigage is OK, I guess, but there's nothing better than the proper tools. MIcrometers tell the real story.
If you don't have the correct tools, I'd suggest the same thing as Zane....simply look at the pn's of the bearings you just removed and replace them with the same. Bearings wear faster than cranks (they're softer), and if an engine has run fine/long time with the removed size....then it'll do it again and again.
Make damn sure when you remove rod and main caps that you install those caps exactly in the same order/position/orientation as you removed them or you'll be sorry.
And if you don't want to deal with low oil pressure when that rebuilt engine is hot, ...then replace ALL the bearings...rods AND mains...and rebuild/re-bush that oil pump too. A common oversight on rebuilds is to ignore the piston-pin bushing. Check your old one for clearance/fit/tightness. If you find it tight, then fine, but be sure you clean out the oil passages in it with a soft wire (copper or brass). If it's got slop you better replace it. Take it (your rods/pistons/pins/bushings) to a machine shop if necessary to have them pressed out, pressed in, reamed, etc.)

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Rob

09-15-2004 17:25:53




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 See there's the rub... in reply to gahorn, 09-15-2004 17:06:32  
Don't know the history of a lot of these engines; don't know how long or how well it's run with the bearings in there. You can't even figure the last guy replaced everything. I know I've repaired engines without rebuilding them, depends on the problem and the budget.
I have a 2N out there that has always (5-yrs I've known it) had low pressure but the rope seals aren't leaking at all. Makes me think something wasn't done right the last rebuild because I expect to see the seals leaking on a worn engine.
I might end up getting parts miked but I figure plasti-gage will tell the tale. I should know this weekend or next week.

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ChrisH

09-15-2004 19:01:11




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 Re: See there's the rub... in reply to Rob, 09-15-2004 17:25:53  
Hi fellers. In my old 2n, the camshaft was the loose fitter. Even with new bearings and rebushed oil pump, the camshaft is what it is--no bearings--just the shaft running in the bored block. Anyone know how to "tighten up" the clearance? Knurlizing, maybe? Anyway, I think that's the reason for a lot of low pressure claims. Chris h (IA)



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Rob

09-15-2004 19:58:45




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 I think you're right. in reply to ChrisH, 09-15-2004 19:01:11  
I've seen some discussion about that camshaft, oil pressure, and retro-fitting bearings. I don't know anything about knurling. Sounds like a way to go though; a lot cheaper than retro-fitting bearings.



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