Crank Journal Bearing Size Question - Alfa Romeo Bulletin Board & Forums
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post #1 of 20 (permalink) Old 07-12-2019, 10:33 AM Thread Starter
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Crank Journal Bearing Size Question

I'm rebuilding a 2L engine and am looking for some advice on bearings.

The crankshaft main journals measure out between 2.3605" to 2.3607", which is in the band for "Standard Blue" journals. When I look to buy a set of bearings, they are all listed as either "Std.", "0.010 over", etc.

My question is whether this measurement for the new bearings ("Std.", "0.010", etc) is against the "Standard Blue" or "Standard Red" journals.

Thoughts?

Mike
1969 GTV 1750
1966 Super
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post #2 of 20 (permalink) Old 07-12-2019, 10:46 AM
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The blue and pink color bearings are no longer available. Just the standard size, unless it needs to be ground, then the adjusted bearing size would apply.

1966 GTA replica, 1967 Duetto, 1987 Quadrifoglio
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post #3 of 20 (permalink) Old 07-12-2019, 01:07 PM Thread Starter
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Originally Posted by classicalfas View Post
The blue and pink color bearings are no longer available. Just the standard size, unless it needs to be ground, then the adjusted bearing size would apply.
Please excuse my ignorance as I'm new to this with Alfas, but I still don't understand. My question is which one is standard? My manual lists red & blue and neither of them is defined as "standard".

Mike
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post #4 of 20 (permalink) Old 07-12-2019, 01:32 PM
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Not ignorant. Crankshafts are ground with tolerances, + or -, When ground just under the size, instead of scrapping the crank, Alfa issued slightly smaller bearings to compensate. Crankshafts from the factory had a blue or pink paint mark on one of the counterweights to distinguish the different sized journals and which appropriate bearing to use. These are no longer available from the factory but some oldtimer might have some factory NOS bearings stashed away in his garage or basement. When assembling the motor, dial bore gauge the journal with the bearing shells in, then check the diameter of the crank journal with a mic. The difference will be your clearance, if too tight, the crank could be polished by a crankshaft grinder. If you don't have any of the special measuring tools you can use Plastigage. Its a thin strip of wax that you place on the crank journal then assemble the bearing caps. Then disassemble and check the squished wax against a chart that it come with, that will be your clearance. Usually fairly accurate.
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post #5 of 20 (permalink) Old 07-12-2019, 06:32 PM
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Std. or standard means an unground crankshaft

Hi Mike

You wrote ".....they are all listed as either "Std.", "0.010 over", etc. Those are terms that bearing manufacturer's use. "Standard" means a bearing that fits around a crankshaft that has not being machined / ground down.

"0.010 over" means the bearing fits a crankshaft that has been ground down "0.010 inches"

"Blue" and "Red" bearings might have been available from Alfa in the day, but have been NLA for decades.

Hope this helps
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post #6 of 20 (permalink) Old 07-12-2019, 06:56 PM Thread Starter
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I'm probably over thinking it, just trying to figure out what "standard" means since the current bearings are all sized referencing "standard".

Mike
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1966 Super
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post #7 of 20 (permalink) Old 07-13-2019, 02:21 AM
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If the bearings that came out of the motor are stamped Standard or STD, the crank has never been ground and is the factory size.

1966 GTA replica, 1967 Duetto, 1987 Quadrifoglio
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post #8 of 20 (permalink) Old 07-13-2019, 02:50 AM
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We might also add that 2 litre cranks were factory hardened, an extra expensive step in the process. And a reason not to want to scrap the crank. Other earlier cranks and some later where not hardened. Cranks are ground then hardened then polishished and sometimes change dimensions during hardening.

Your, crank because of the hardening likely is in good std condition.

Both red and blue are standard. Just very slight variation in size as classicalfa says.

While at it, Consider drilling out the aluminum oil way plugs, cleaning all the oil ways and threading the oil ways for set screw plugs. There are some tricks to know doing this. Search for it. Unless this has already been done by a previous owner.

Ken
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post #9 of 20 (permalink) Old 07-13-2019, 02:54 AM
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Quote:
Originally Posted by Alfa69GTV1750 View Post
Please excuse my ignorance as I'm new to this with Alfas, but I still don't understand. My question is which one is standard? My manual lists red & blue and neither of them is defined as "standard".
They are both standard. What are the markings on the bearings that came out. Red, blue, std???

Ken

Ken Geiger, Toronto
1965 GTA, RHD, Stradale
ex- 1965 GTA, RHD, Corsa, Trans/Am 66-72
1964 Sprint GT, B-Sedan in 70's
1970 Giulia Super (CDN Spec)
1976 1600 GTj (Italian Spec)
1966 Harley Sprint (Aermacchi) 250
2000 Catalina 320, Hull #765 Northern Dream
2001 BMW Z3 3.0i
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post #10 of 20 (permalink) Old 07-13-2019, 05:25 AM
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Quote:
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We might also add that 2 litre cranks were factory hardened, an extra expensive step in the process. And a reason not to want to scrap the crank. Other earlier cranks and some later where not hardened. Cranks are ground then hardened then polished and sometimes change dimensions during hardening.
Ken
For the 2L NOS std bearings come in blue or red/pink to suit the blue or red/pink crank as mentioned.
I've had a 1300 crank hardened(nitrated) as it grows in size (changes dimensions), then micro polished it back to get the std bearings to fit.
Ken's comment I think he means when the crank was 'made' the cranks were ground then hardened then polished, not to confuse it to what I would do to repair it which may be possible for the 2L crank to first case hardened it again (nitrated) as it grows in size (changes dimensions), then micro polished it back to get the dimensions you want.
Don't forget not all the bearings are the same on the 2L (or 1750) cranks, 'trap for young players' especially when you start grinding the crank, check your parts manual first.
Steve

Last edited by Steve105; 07-13-2019 at 06:20 AM.
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post #11 of 20 (permalink) Old 07-13-2019, 08:04 AM Thread Starter
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The crank was bought individually.

Mike
1969 GTV 1750
1966 Super
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post #12 of 20 (permalink) Old 07-13-2019, 08:22 AM
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Have a machine shop inspect the journals, usually if you can feel a scratch or a groove with your finger nail the crank needs to be ground undersize .010”. If the journals are nice and groove free the standard size bearing would be appropriate.
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post #13 of 20 (permalink) Old 07-13-2019, 11:32 PM
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Have a machine shop inspect the journals, usually if you can feel a scratch or a groove with your finger nail the crank needs to be ground undersize .010”. If the journals are nice and groove free the standard size bearing would be appropriate.
Really! wise up people, think 'less is more'. Cranks deserve more thought and patience. The less you grind a crank the more you extend it's lifespan. It's not 1976 or 2016 for that matter where you can stumble across a NOS crank in a shipping container full of factory spares! I'm sure there maybe a few machine shops that have idle capacity in machines and people waiting to cut your precious crank down by .010' if they say so!

If you can't tell me which bearings are different on a 2L crank how are you first going to tell the machinist, and second how will you check they did what they are suppose to do?

So here is my strategy I use to avoid unnecessary grinding of my cranks
1. Measure the crank a few times
2. Work out if the crank journals are in the range for blue or red std(You have)
3. Look at the surfaces of the crank, if fine ,just nitrate it again and micro polish it to come back to specs for the bearings you will use.
4. Look at the surfaces of the old bearings
5. Get some bearings NOS blue and red or reproduction, buy all three sets(cheap really in relative terms) if you factor in the cost of the engine build i.e. parts and labour and longevity you are chasing for your engine (i.e. to last another 50 years, because you want to of course!): you can on sell the other bearings not used.
6. Fit the bearings for the correct clearances for the application you will use the engine for. If the reproduction set is too loose, work out if you need the blue or red NOS ones and get them fitted.
7. Don't forget not all the bearings are the same along the crank!

In Australia there are new laws so as to protect consumers, even if you as the consumer supplied some of the parts like bearings to the engine builder.
If you do choose to have your crank ground and later find one of the bearings has seized or your crank has snapped and destroyed your engine well?
Steve

Last edited by Steve105; 07-14-2019 at 12:47 AM.
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post #14 of 20 (permalink) Old 07-15-2019, 06:26 AM
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I'm not sure who would buy a set of bearings that have been split apart, some taken from this batch and from that batch, I certainly wouldn't. You grind the crank if needed, renitride, straighten, then polish. If you want to get super critical and your building a race motor you dial bore gauge the ID's and grind to your desired diameters for your tolerances your trying to achieve. If bearings need to be a little heavier you have them coated by Calico Coatings. https://www.calicocoatings.com/index.php Done! Its not that difficult.

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post #15 of 20 (permalink) Old 07-17-2019, 05:30 PM
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If the crank journals are within spec for size and roundness (TIR) I would buy new standard size bearings, check with Plasticgage and go. I am assuming this is a street engine. Yes, the Plasticgage could appear somewhat hokey, but from my experience it measures real clearance
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