4-1/8” crank

Re: 4-1/8” crank

Tim Ayers said:
Wait, the tang on both halves of a two piece locked-in type of bearing does not do anything in helping it to stay in place? Once seated on the crank journal, it would need to be pushed inward in order to release itself from the tang slot, no?

When you spin a locked-in type of bearing in a motor, that is a mechanical failure. The halves sit on top of one another when the rod cap is connected to the main portion of the rod body.

How can't the tang not help to keep the bearing shells from spinning?
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All the tang does is locate the bearing shell side to side for installation so it does not rub the crank fillet on installation..On some race engines we run .040 clearance from the edge of the shell †o the fillet.
The crush in the rod and main saddle holds the shell from spinning.
 
Re: 4-1/8” crank

Pete said:
All the tang does is locate the bearing shell side to side for installation so it does not rub the crank fillet on installation..On some race engines we run .040 clearance from the edge of the shell †o the fillet.
The crush in the rod and main saddle holds the shell from spinning.
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Interesting. All this time I thought it was the crush AND the tang that held the bearing in place. Learn something new every day!
 
Re: 4-1/8” crank

And on aluminum rods, you usually PIN the bearing . . . to prevent it from rotating when the rod gets hot and the aluminum expands. Extra safety measure that most/many aluminum rod manufacturer's use.
 
Re: 4-1/8” crank

'The crush in the rod and main saddle holds the shell from spinning'.

So, if the tang is merely for locating the shell, why is it that the rear main bearing, which can quite conceivably be located by the thrust faces, has tangs?

I believe the tangs are an aid to prevent bearings from spinning.
 
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Re: 4-1/8” crank

Brian said:
'The crush in the rod and main saddle holds the shell from spinning'.

So, if the tang is merely for locating the shell, why is it that the rear main bearing, which can quite conceivably be located by the thrust faces, has tangs?

I believe the tangs are an aid to prevent bearings from spinning.
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"Brian" raises an interesting point! DD

.
 
Re: 4-1/8” crank

Brian said:
'The crush in the rod and main saddle holds the shell from spinning'.

So, if the tang is merely for locating the shell, why is it that the rear main bearing, which can quite conceivably be located by the thrust faces, has tangs?

I believe the tangs are an aid to prevent bearings from spinning.
Click to expand...

Brian:

Interesting question.
 
Re: 4-1/8” crank

Brian said:
'The crush in the rod and main saddle holds the shell from spinning'.

So, if the tang is merely for locating the shell, why is it that the rear main bearing, which can quite conceivably be located by the thrust faces, has tangs?

I believe the tangs are an aid to prevent bearings from spinning.
Click to expand...

Definitely need the crush but the tang helps. The bearing can't spin until it shears the tang.
Bill
 
Re: 4-1/8” crank

There is another thing the tang does on some engines, it forces the assembler to put the shells in the right orientation (given oil holes) - typically on the rear main.

Now we all know the answer is "it depends" . . . on the engine, on how the bearing halves were made, top vs. bottom, etc.

Like Pete mentioned, the location of the shells is very important - especially on race cranks with heavy fillets on the journals. The last thing you need is for the bearing shell to slip to the side, lose oil clearance and burn . . . and you'd not even know it happened until you ran the engine.
 
Re: 4-1/8” crank

If anyone has ever seen a "spun" bearing, that is all the evidence that is needed to prove that tangs do not keep a bearing from spinning.

It's the crush that holds them, once the crush has hammered out, nothing will hold them from spinning in the housing. It's also important, that the big end of the rod, is in spec.

If the rod bearing is narrow enough to clear the crank fillet, it's not hard to install them, you just make sure the bearing is on the inside edge of the rod but, not out side of it, touching the other rod, on that journal. Always check the rod side clearance, to make sure.
 
Re: 4-1/8” crank

frnkeore said:
If anyone has ever seen a "spun" bearing, that is all the evidence that is needed to prove that tangs do not keep a bearing from spinning.

It's the crush that holds them, once the crush has hammered out, nothing will hold them from spinning in the housing. It's also important, that the big end of the rod, is in spec.

If the rod bearing is narrow enough to clear the crank fillet, it's not hard to install them, you just make sure the bearing is on the inside edge of the rod but, not out side of it, touching the other rod, on that journal. Always check the rod side clearance, to make sure.
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That's my point. The mechanical failure caused the tang to fail as well, no?
 
Re: 4-1/8” crank

Tim Ayers said:
That's my point. The mechanical failure caused the tang to fail as well, no?
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Exactly. That little tang is no match for a bearing that is going to fail due to lack of lube,overload,lack of crush,etc. I rebuild diesel engines every day for a living and we see it all the time. We've built oddball stuff and removed bearing tangs when it wasn't practical to cut notches for them...no issues at all.



Terry
 
Re: 4-1/8” crank

bbrocksr said:
When the bearing welds itself to the crank the crush isn't going to help either.
Bill
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This has been a very informative discussion and bbrocksr's comment made me realize how silly my initial belief was.

Makes total sense now that crush and not that fractional tang holds the bearing in place.

Learn something new every day.

Thanks, all!
 
Re: 4-1/8” crank

Noticed the 'new' crankshafts are around $1000, and good used Merc's sell around $400. Newc
 
Re: 4-1/8” crank

Newc said:
Noticed the 'new' crankshafts are around $1000, and good used Merc's sell around $400. Newc
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I was going to mention this. It would seem that the combination of consuming a good Merc crank and the machine work involved would make an aftermarket crankshaft a more economic solution. There is the satisfaction that comes with cooking up something like this and making it work, though.

BTW, "Newc", I haven't seen a good used Merc crank priced at $400 for the last 20 years. Are things better out where you are?
 
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