Eagle Cast cranks - QA?

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Hmm...I'm a bit out of my depth here , but what I understand is this:

A crank is index ground to correct the distance of each of the rod journals from the axis of the crank - correct?

So I assume that by turning the journals down on a very slight offset from their current location, this moves their "center" slightly so they are all positioned at the correct distance from the central axis of the actual shaft - Im hoping this is correct?

So the .035th is the total variation of all the journals respective from the central axis. (Ie one might be 10th, another 10th and another 15th out)

What Ive been told is that they can be brought into correct alignment by taking varying amounts of between .015-.020th of each rod journal.

I guess this is where i find out if ive got the story mixed up...LOL!
 
Moparmal said:
Hmm...I'm a bit out of my depth here , but what I understand is this:

A crank is index ground to correct the distance of each of the rod journals from the axis of the crank - correct?

YES(caps to tell the answers apart...)

So I assume that by turning the journals down on a very slight offset from their current location, this moves their "center" slightly so they are all positioned at the correct distance from the central axis of the actual shaft - Im hoping this is correct?

YES

So the .035th is the total variation of all the journals respective from the central axis. (Ie one might be 10th, another 10th and another 15th out)

What Ive been told is that they can be brought into correct alignment by taking varying amounts of between .015-.020th of each rod journal.

THIS IS WHERE I GET a little confused. I have a very hard time believing there is a throw that is .0175 (1/2 of .035") out either long or short. Has this crank been chucked up in a crank grinder, or is this a V block type measurement on a bench? I would want to see it on the grinder with an Arnold gage on it before I said go ahead. two or three thou, yeah, seen that before, especially in stock cranks. But way past ten? That's a hard pill to swallow.
Click to expand...

Maybe it's just my doubting nature...
 
Ah I see - OK, I'll verify what I was told, maybe I missunderstood.

The machine shop has a second to none reputation where its being done, they do a heap of circuit track race car stuff for all the pros over here (Our = of Nascar).
 
While I am starting to understand what you've been talking about, it does get your head spinning a bit.

I'll have to check the speed shop tonight when I go there and ask about mine.

I have it at home now, it's been balanced, and the block and pistons are at the machine shop being prepped.

But I did go out to my shop and check the box. It's an Eagle forged crank, and it's made in China :thebirdm:.
 
Moparmal said:
A crank is index ground to correct the distance of each of the rod journals from the axis of the crank - correct?

So I assume that by turning the journals down on a very slight offset from their current location, this moves their "center" slightly so they are all positioned at the correct distance from the central axis of the actual shaft - Im hoping this is correct?
Click to expand...
That would take care of the stroke index, but there's also the swing index (relationship between rod journals such that each piston is timed to its valves in the same way as the other cylinders). This was my motivation for the craptastic diagram somewhere above.
 
doktor_x said:
That would take care of the stroke index, but there's also the swing index (relationship between rod journals such that each piston is timed to its valves in the same way as the other cylinders). This was my motivation for the craptastic diagram somewhere above.
Click to expand...

Thanks Doktor - I guess you'rereferring to the piston/valve phasing which is also effected by the position of the rod journal?

Im afraid i don't know any more on the measurements - but the machinist said it was fixable so its not the end of the world.

- If I can get some more detail I will.....once I shed this stinking head cold!! LOL!!

Sky bolt - The piston connects to the rod which connects to the crank rod journal.

All the piston/rod assemblies should be the same length.

If a rod journal is "out", then the total length is effected.

If the length from the centre of one rod journal is further "away" from the crank centerline, this means that this piston will not be in the same position for a given spot in the crank rotation, as all the others.

(Like a 4 spke wheel with one spoke too long or short)

This means two things:

1 - The piston attached to the effected journal aon't necessarily reach the same height in the bore, because the placement of the rod journal effects the total distance between the centre of the big end, and the centre of the piston pin.

Also,

2 - if the positon of the rod journal is not exactly at 90 deg to the next one, it also effects the timing of the sweep of the pistons. The piston attached to the effected crank journal will "throw" or move up slower or faster than the rest - like an out of balance Hula Hoop.

So the piston won't be in the right place when the cam opens the valve.

Probably the best way to think indexing is that it "degrees" the crank, rods and pistons so they all travel the same speed and arrive at the same place.

But because the problem is caused by the journals poisiton on the crank - it has to be done with machining and not changing the position of a timing chain cog.
 
Moparmal said:
Thanks Doktor - I guess you'rereferring to the piston/valve phasing which is also effected by the position of the rod journal?



Sky bolt - The piston connects to the rod which connects to the crank rod journal.

All the piston/rod assemblies should be the same length.

If a rod journal is "out", then the total length is effected.

If the length from the centre of one rod journal is further "away" from the crank centerline, this means that this piston will not be in the same position for a given spot in the crank rotation, as all the others.

(Like a 4 spke wheel with one spoke too long or short)

This means two things:

1 - The piston attached to the effected journal aon't necessarily reach the same height in the bore, because the placement of the rod journal effects the total distance between the centre of the big end, and the centre of the piston pin.

Also,

2 - if the positon of the rod journal is not exactly at 90 deg to the next one, it also effects the timing of the sweep of the pistons. The piston attached to the effected crank journal will "throw" or move up slower or faster than the rest - like an out of balance Hula Hoop.

So the piston won't be in the right place when the cam opens the valve.

Probably the best way to think indexing is that it "degrees" the crank, rods and pistons so they all travel the same speed and arrive at the same place.

But because the problem is caused by the journals poisiton on the crank - it has to be done with machining and not changing the position of a timing chain cog.
Click to expand...

Subscription to thread deleted.
 
Moparmal said:
Probably the best way to think indexing is that it "degrees" the crank, rods and pistons so they all travel the same speed and arrive at the same place.
Click to expand...
That's probably the best description that I've ever run across. I tend to think in a fashion that strongly resembles 3D modeling. It works out beautifully within the confines of my skull, but most of it is lost in translation to text and/or static images.
 
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