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jamesjedi's Avatar
 
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Measuring Bearings and Scratching the Bearings

I see that the bearings are very soft and easily scratched, as is the crankshaft. Has anyone got a method to reduce the scratching/marks while measuring? I just mic'd the nose bearing for a comparison and see that it has left a very small mark.

Possibly a very small amount of oil?

I imagine the answer is obvious, however it is worth asking.

Thanks,

James

Old 08-08-2019, 05:38 AM
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Plastigauge

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Old 08-08-2019, 07:48 AM
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I see some do not believe it is accurate.
Old 08-08-2019, 08:28 AM
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Bearings

If you use a ball style mic or a dial bore gauge with the ball points and as little preload as possible you are only going to leave a trace that you touched it and that's not going to bother it. Plastigauge is better than nothing but not much, if your going racing on Sunday and it's Saturday night and no options maybe.
Mike Bruns
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Old 08-08-2019, 08:44 AM
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You can buy Teflon tips for your bore gage. These help some, but you will always have some markings. Quite normal and do not worry.
Old 08-08-2019, 08:46 AM
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As Mike said.
Old 08-08-2019, 08:48 AM
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I measure the journal with a mic, the bore with a bore gauge, and the shell thickness of the bearing with a ball mic. The bore gauge can be a bit harsh on bearings but with the ball mic you can be a bit more careful.

BTW there is a procedure in the factory manual for aligning the #8 end of the cases along the split prior to taking the bore measurements at that end of the case.
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Old 08-08-2019, 09:48 AM
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Thanks for all the replies! I will work on the above points. I truly appreciate it.
Old 08-08-2019, 01:15 PM
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Quote:
Originally Posted by Jonny042 View Post

BTW there is a procedure in the factory manual for aligning the #8 end of the cases along the split prior to taking the bore measurements at that end of the case.
I'd like to learn more about this. Any links?
Old 08-08-2019, 04:27 PM
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James - the crankshaft is soft, and easily scratched? Where did that come from? I perceive the crank as being about as tough as you could imagine, especially on the nitride surfaces of the journals.

Try to drill and tap the crank plug holes so you can make cleaning the insides of the crank easier next time, and tell me how many taps you break. I've avoided that by just taking the crank to a crankshaft shop for cleaning and resealing.
Old 08-08-2019, 06:39 PM
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Quote:
Originally Posted by mikedsilva View Post
I'd like to learn more about this. Any links?
Not a lot of detail.....
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Old 08-08-2019, 06:49 PM
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Good luck trying to do it as above.

We have ground inserts each measuring the main housing size that go into the case in place of the #8 bearing. The case halves are then bolted together and we insert a dowel pin to hold the case halves in place. Then the case halves can be line bored with the dowel pin holding. There is little tool pressure when line boring, but the cases could still move if not dowelled.
Old 08-08-2019, 08:33 PM
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Quote:
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Good luck trying to do it as above.

We have ground inserts each measuring the main housing size that go into the case in place of the #8 bearing. The case halves are then bolted together and we insert a dowel pin to hold the case halves in place. Then the case halves can be line bored with the dowel pin holding. There is little tool pressure when line boring, but the cases could still move if not dowelled.
I did it with some difficulty but it wasn't that bad. You just zero the bore gauge with the measuring tips on either side of the case part line, then rotate just enough so that they are on the other side of the part line. Any different from zero on the bore gauge is misalignment. You are basically checking the #8 journal for out of round and correcting it with a mallet before you cinch down all the case bolts to perform your measurements.

I can see if you built a number of engines and time is money, you'd invest the time in a means of aligning the case such as Neil has.I was going to bore out an old #8 bearing but the lathe I have access to wouldn't hold it in the 3 jaw chuck so made do with the factory way.

Back to the subject of measuring the bearings, this is the anvil mic I bought. Like any relatively cheap tool you'd want to check it for accuracy and make allowances but in my case when I checked it against my mitutoyo 1" mic they were in agreement to within a fraction of a tenth of a thou. Close enough for the large clearances on these motors. You could run tighter clearances (and use a thinner oil) if you wanted but it seems the bearings that are easily obtained will give you clearances better suited to 10W40 or 20W50 etc.

https://www.ebay.com/itm/1-Dual-Ball-Anvil-Micrometer-Pipe-Tube-Round-Carbide-Tip-Wall-Thickness/231361340781?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
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Old 08-09-2019, 04:21 AM
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Can anyone chime in with any evidence one way or another, if such minuscule scratches make a difference one way or another?

People have taken out bearings that have had serious wear and were fine...

Porsche bearings have marks on them too, where they are measured...

I do sometimes wonder if these issues are seriously over thought...
Old 08-09-2019, 12:00 PM
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Neil Harvey answers it in a post above.

Old 08-09-2019, 01:46 PM
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