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Discussion Starter #1 (Edited)
Just picked up my crank from the 20/10 grind, magnaflux and balance. Here is the spec sheet from the shop.... I must admit these numbers dont mean a lot to me except for looking at them against their target tolerance.... Anybody have any insight on whether this was a good call? Initial spin doesnt look much different than the final one to me.
 

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Richard Jemison
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Balancing a 4 cyl crank.

Typically paying for balancing a 4 cyl Alfa crank is a waste of time and $$ as they are very well balanced at the factory.

Looks like your`s fit that statement. Differences in the first & last are "ghost" numbers. Doubt they did any weight changes.

In fact these cranks have insufficient counterweights to cover light rods and pistons above 7000 RPM.
Lightening is not a good idea.

At best only round the leading and trailing edges of the counterweights. After that, balancing might show some correction needed.
 

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Discussion Starter #3
Thanks RJ, that is kinda what I thought looking at the numbers. Live and learn. They magnafluxed it though and I just wanted to be sure. I'm impressed at how balanced it was comparing the 2 spins. I just got done weighing piston/pin combos, all the motronic pistons were identical weights. I'll start assembling tomorrow. Is there a blueprint sheet for tolerances or do I need to dig through the shop manual to find them?
 

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If this is Motronic, it's a 2000? I thought it was not recommended (or that easy) to grind nitrided 2000 cranks.
The Centerline tech listings give bearing sizes, clearances, etc. So do the old Shankle and AR Ricambi catalogs tech sections.

Andrew
 

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You have a special radii you have to reinstate when you grind your crank.
If your mechanic or grind shop don't know about it chances are you won't either until your crank snaps at that spot if you don't reinstate the radii when you re-grind your crank!

The radii needs a special bearing!, so there are bearing and installation issues.

I would advise any one who is going to have a ground crank installed don't until you have confirmed it's radii is reinstated as per factory recommendation and listed on your spec sheet(photos)/receipt. Plus photos of the special bearing being installed in the correct place!

If your engine is already built you may have to pull it down and check you have the correct radii on your crank as well as you have the correct bearing for it!

Those who build engines for a living may want to help explain it to us and where and what the radii is. Of course only some engines have this issue.

There are clues in the parts manuals, and I have evidence on the NOS factory bearings I have.

Regards Steve
 

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Discussion Starter #6
Interesting. Cant wait to hear the responses and knowledge on this one!
 

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You have a special radii you have to reinstate when you grind your crank.
Non Alfa Romeo specialists don't know about it and you won't either until your crank snaps at that spot if you don't reinstate the radii when you re-grind your crank!

The radii needs a special bearing!, so there are bearing and installation issues.

I would advise any one who is going to have a ground crank installed don't until you have confirmed it's radii is reinstated as per factory recommendation and listed on your spec sheet(photos)/receipt. Plus photos of the special bearing being installed in the correct place!

If your engine is already built you may have to pull it down and check you have the correct radii on your crank as well as you have the correct bearing for it!

Those who build engines for a living may want to help explain it to us and where and what the radii is. Of course only some engines have this issue.

There are clues in the parts manuals, and I have evidence on the NOS factory bearings I have.

Regards Steve

It should be standard machine shop practice to check the radii from the factory and/or check the specifications for the particular crank. All this information is available, it's more a matter of if they bother to do it.
From 1750 upward the rear-most radius in #4 rod crank journal is increased for superior fatigue resistance. The bearing shell requires a larger edge bevel to clear it. ALL REPLACEMENT BEARINGS made in the last 40 years have the larger bevel for the increased radius on all bearing shells in the box, so don't panic, you really can't go wrong. Only the early O/E 1600 rod bearings have almost no edge bevel, so when the bigger radius 1750 first came along, they provided ONE pair of shells with the bevel for #4. These bearings have long been superseded. The only ones you are ever likely to find are in old original Alfa spare parts boxes & I still have numerous sets haunting the back of the shelves.
LOTS of 1750 & 2000 cranks have been reground in the past by lazy machine shops who have not done the larger radius,
but I've yet to see a failure attributed to this. In fact the ONLY BROKEN cranks I've ever seen have been standard factory 2000 with the larger radius, but they have done LOTS of hard track work. Still it is better to HAVE the correct radius & surly they would have failed sooner with a smaller one. I have found quite a number of 1600s with fatigue cracks when I magnaflux crack-tested them. Generally at #3 or 4. The factory used to recommend ntriding these for racing to increase fatigue life.
1300 & 1600 all have the small radius all over. Nitriding all cranks is highly recommended as done to 2000s & 1800s.
These nitrided cranks with good oil change services will in a road car go 200/300,000km without needing regrinding.
Our own 2000 Alfetta sedan has just clocked over 380,000 on its stock factory fitted crank & original main bearings ( I changed the rod bearings at 230,000km after an oilway plug dropped out)
Anyway, nothing unusual in any of this, just regular engine building common engineering sense. Don't be put off by people who try to make out everything is some great & mysterious puzzle to work out. I do about 30 Nord cranks per year.
Regards,
Vince.
 

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The 74 GTV I just rebuild, we tossed the crank and used a better 0/0 one due to grooved rod journals. The bearings in it had, as discussed, narrower bearing material on the steel backing to account for larger filet radii. The new ones going one were off-the-shelf from Jon Norman, King I think.

Andrew
 

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From my collection of NOS bearings, I think the time line of bearing bevels was only one conrod bearing in the set had the bevels for Alfa Romeo OEM.
Then the after market bearings varied from a bevel on only one side of all of the bearings, to steps(not bevels)/bevels to both sides of all the bearings.

For #4 rod crank journal if you are installing the bearings that have the bevel/step on only one side, there is an installation issue with these if they are put in back to front, so the bevel/step is not above the radii of the con rod.
I'm not sure about what is on the market at the moment with 2019 reproduction bearings if they have bevels or not.
Regards Steve
 

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None of this is rocket science, #4 rod should have the same side to side play/end float as all the other rods once bearing shells installed & bolts tightened. IF any of the rods make the crank hard or impossible to turn, OR you don't have side play then you need to investigate: 1, that you have the rod in correct way. & 2, that the bearing has bevels/steps for radius clearance.
All new production bearings for years now are made with the clearance bevels on all shells.
Another interesting point: late T/spark 75/164/155 cranks have the large radii all the way along on all journals, so all bearings have to fit these anyway.
 
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