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Ford 9N, 2N & 8N Discussion Forum


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11-07-2005 08:58:46

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First off, I'm not an engine guy so please bare with me. I'm in the process of overhauling the engine. Everything has been taken out expect for the cam shaft and the exhaust valves at this point. The crankshaft appears to be in good shape (according to me) with a little bit of raise in the middle of each the main, rear, and front bearings. The question is, should I go ahead and have the crankshaft turned, polished, or what? And if is is polished, should I replace the bearings. Same goes for the rod bearings. The reason I took it apart is that it smoked extremely bad, enough to keep the mosquitos away for weeks at a time after running the tractor. Any help would be appreciated. I know I've stepped into a big undertaking, but I'm having a lot of fun (so far) learning.

PS...I'm planning on buying a piston and sleeve kit and was holding off buying one before I knew about the bearing.

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11-08-2005 08:01:16

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
If you reuse bearings you are not rebuilding the motor in my book. You cannot eyeball normal wear on a crank journal - anything visual is SERIOUS damage. You must measure accurately with a micrometer.

If the engine needs rebuilt you are going to spend significant time and a fair amount of money. So pony up the additional couple of hundred bucks needed to have an automotive shop clean and resurface all the wearing hard parts. That means new pistons, sleeves, and bearings, wrist pins and bushings, etc. Reground crank, cam, and valves and seats. Block professionally cleaned and magnafluxed and decked as appropriate. Anything else is a false economy that will likely cost you far more in the long run if you are going to keep the machine for your own use.

As the saying goes - "you can pay me now or pay me later". Later almost always includes interest.


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Paul K in IL

11-07-2005 19:52:55

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  

I would never even consider putting old rod and main bearings back in an engine. Take the crank to a good machine shop that does a lot of them and tell them to clean it up and match the bearings to the journals. If it comes back with bearings taped to the journals make sure you install the bearings in the same journal they were on when you got it back. Some shops turn all the journals to the same size and some don't. If they don't want to get the bearings for you make sure they tell you how much undersize they ground the rods and the mains.

Also we ALWAYS plasti-gauge all rods and mains before we put the engine back togather. Much better to find out you have the wrong bearings before you put the oil pan back on.

Good luck.

Paul K.

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Wade Currens

11-07-2005 19:22:14

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
Im rebuilding my 8N engine as well. I had a machine shop check mine it looked good to me no real scars or scratches but was worn down under the normal measurements. It had to be turned .010 on the mains and rods. After I put it back together it seemed tight. So after talking to a friend who is a real mechanic not a parts replacer such as I, he said to plastiguage it. When I did the clearences were good but I found a nick on a rod journal that has already cut into the copper of the bearing. So after all that make sure are very careful not to hit the journals with the studs or rods themselves. Cover the studs with some rubber tubeing caps. Also can anyone tell me if the rope seals will make an engine seem tight when put together? Just my two cets from a fellow parts replacer!

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11-07-2005 18:23:00

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
Corry, take a close look at the bearing inserts. They tell a story about the crank. If the insert linings are worn smooth and even then you can figure your crank is in pretty good shape. If the linings are torn, heavily scratched or pitted, or worn on one side then you have warning signs of a problem you need to track down. You can expect to see more wear in the center of the cup than on the ends.
Take the crank in to a machine shop and have them give it a look-see. If your bearings are in good shape then don"t let them tell you the crank needs any more than polishing. Let the shop see the bearings. I might polish a good crank with some emery cloth but I know some about it.
No matter what, you should use plastigage before final assembly, even if a machine shop has done the work and provided the bearings. Plastigage is cheap and easy; instructions on the package and a primer in the FO-4. You need to know the clearance range to measure (like 0.001-0.004) to get the proper Plastigage. There are three colors (clearance ranges).
With <$10 of plastigage you can measure each journal every 90* to get round, taper, and clearance if that"s what you want to do. You need 4 packages of the plastigage (12" each)...I think a box has 4 packages. Or if you got a mic you can do that but you will still need a package of Plastigage for the final assembly.

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11-07-2005 13:25:54

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
Excellent advice thus far. Keep in mind that with the crank and/or bearings worn more oil is thrown off the crank. Usually the oil rings can not handle that, especially in an already worn engine. The result is smoke - lots of it, and usually oil-fouled plugs. (Experience = 25+ years in automotive machine shop and more in knuckle-busting farm equipment dealer's repair shop.) Love those N-series Fords!

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11-07-2005 12:33:04

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
Corry: Rick is absolutely right - have a reputable machine shop check the crankshaft & do whatever needs to be done to get it in spec. Otherwise you are spending $$$$ on parts & labor for a engine job that will not last. GA Jim

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RIck H. Ga.

11-07-2005 09:31:19

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 Re: Crankshaft in reply to Corry-8N, 11-07-2005 08:58:46  
The condition of the crank is determined by measuring the ware of the journals with an accurate micrometer. You can do this yourself if you have the tool and know how to use it; and, have a shop manual to tell you what the ware tolerances should be.

When I rebuilt my 8N engine, I had the crank checked and polished and the rods resized (checked for roundness and ware) by a professional machine shop.

I have been told by a good mechanic that if you can run your fingernail over the journal and it catches on a grove or scar of some kind, it needs polishing, at a minimum.

Good luck with it.

HTH Rick

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