How accurate is factory crankshaft timing, before and after turning? ? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-22-2010, 06:54 PM
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How accurate is factory crankshaft timing, before and after turning? ?

And how accurate is a typical factory before turning? 2442 as an example.
How many different types of crank machines are currently in use in relation to the built in ability to keep or adjust timing?

What machine is recommended today? Are there crank guys on the forum? We have three in our area, one guy considered an artist. Hundred miles away a couple of more of that caliber.

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Old 09-22-2010, 08:48 PM
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What timing???
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Old 09-22-2010, 08:53 PM
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Indexing is the term used most, I believe.

A good crank man can do things to salvage a crank that might otherwise be scrapped, in some cases the grinder can correct for inaccuracies brought about by tolerances or prior work done by a lesser tech or machine.

It really depends on several things: what do you have to work with to start with, and what is it that you want to end up with.
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Old 09-22-2010, 09:08 PM
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Quote:
Originally Posted by 68NovaSS
What timing???
He's talking about the throws in relation to a centerline, the position of the centerline of the throw in relation to 360 degrees and also the diameter of the throws. For instance, on a SBC 350 crank, as you look down through the centerline of the crank from the nose, if you consider the first throw as North or 0 or 360 degrees, the second throw will be at the East position or 90 degrees. The next throw will be West or 270 degrees and the last throw will be South or 180 degrees. So, each throw has to be machined at the correct position in relation to a circle and the centerline of the throw has to be the same distance from the centerline of the main bearings on all throws and all throws have to be the same diameter without sloping larger or smaller one end of the journal to the other.

Cobalt nailed it more clearly with "indexing".
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Old 09-22-2010, 10:12 PM
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I've always called index.. Factory cranks can vary greatly as to proper index and stroke..

Just depends on how many thousands of cranks that machine kicked out before maintainence and how close they were being checked..

My ex-father in law was a plant manager for Chevrolet in Flint, Mich. and you would be amazed at what got passed when quotas were high.

Index can be off several degrees, either way. A good regrinder can usually correct this. I have had a few cranks over the years that BARELY corrected with a .010 grind.. I've also had to "cheat" a bit on a few on stroke correction to get a good .010 crank..

As for crank grinder machines. There are many brands and sizes. Use/size depends on a shops particular requirements..

Most of the experienced crank grinder operators in this area are gone.

I have a Storm-Vulcan and The shop has a AMF (Denmark). Either will do a 4ft. crank..
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Old 09-22-2010, 10:42 PM
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Quote:
Originally Posted by BOBCRMAN@aol.com
I've always called index.. Factory cranks can vary greatly as to proper index and stroke..

Just depends on how many thousands of cranks that machine kicked out before maintainence and how close they were being checked..

My ex-father in law was a plant manager for Chevrolet in Flint, Mich. and you would be amazed at what got passed when quotas were high.

Index can be off several degrees, either way. A good regrinder can usually correct this. I have had a few cranks over the years that BARELY corrected with a .010 grind.. I've also had to "cheat" a bit on a few on stroke correction to get a good .010 crank..

As for crank grinder machines. There are many brands and sizes. Use/size depends on a shops particular requirements..

Most of the experienced crank grinder operators in this area are gone.

I have a Storm-Vulcan and The shop has a AMF (Denmark). Either will do a 4ft. crank..
Term "INDEXING" is more proper than journal timing. First time I heard it , was from a Woods a long time ago. Old man called the procedure "indexing the journal timing".
Subject came up because I'm having offset grinding done frequently. Going from 2.1 journals to 2", or from 2" to 1.888" or less.. Lots of advantages in it......stroke and timing are INDEXED<<set to my own blueprint.
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Old 09-23-2010, 02:26 AM
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It seems a little like pouring concrete at least to me; compared to motor cycles with press fit journals.. Now that makes me wonder how close it is was from the factory. If you only had one or two journals that were off a little, could you or would it be worth it even to grind just those down enough to compensate and make it even with a thicker bearing and then just use two different size bearings? It seems like the alignment status of fresh ground crank could be measured easily enough ... I would think using the balance machine lathe and some dial indicator gauges and it seems I saw a pic of a setup like that for the snowmobile engines. It also seems like they would be sposta measure its trueness after grinding but I bet that some don't. Kawasaki KZ-Z1 have press fit, I bet lots others as well, not just two strokes. The serious guys weld em when they get them where they want them because they don't trust the factory press fit especially under higher than factory hp. I do know from experience on the triples at least, that they do slip because you have to set all three sets of points to where the piston actually is in mm btdc not the degree of the crank, and sometimes it is off a little bit. Makes me wonder if that wouldn't work on 900 kaw too because of the hemi heads. Gauge was expensive like 180$! But I had to get one to get the ignition timing correct. While it seemed to make a pleasant difference on my gt750 in the way it ran and idled, the gauge came with adapter pins and different length pin tubes that will screw into the spark plug holes of most two stroke bikes (at least according to the manual) and that has let me time my moped and husky too. It justifies the cost to me then, even if I only time a few of my friends bikes.

All I really just wanted to say that I think it would be kinda cool if we could just adjust our cranks with some kinda bronze hammer or something like some the motorcycle type engine machine shops do to make it right but I had fun working up to it with that paragraph...
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Old 09-23-2010, 01:15 PM
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I worked at a certified Ford engine remanufacturing plant for exactly one year, I was a cylindrical grinding specialist and did all the hydraulic rams and GM locomotive blower regrinds after chrome plating.

My Sunnen equipment was right next to the crank refurb line where they hired guys with little experience or qualifications to do the crank regrinds, it was horrible work since they were ground dry and literally done in 1 minute per journal...dusty dirty work compared to the nice shiny chrome close tolerance stuff I did. Their equipment was extremely worn and in poor shape as a result of the high turnover

One day I wander over while waiting for more work and asked one of the older guys how they indexed the journals, I never seen them do it so I was curious. To my surprise they dialed in off the original journal and undersized them from there, no stroke measurement, no indexing...nothing.

I talked with the manager of that area and asked him why they wouldn't check the journal indexing and at least the stroke dimension, it was on the drawings! I was met with a blank stare and he said "why bother, no one can tell the difference and when we last tried it our reject rate went up 300%."

So there you have it, those factory engines we rebuilt could have strokes or crank indexing anywhere those cast iron and forged cranks twisted too. I don't doubt he was right on anyone being able to tell and unless the crank was bent it never got a second look.

BTW we straightened the automotive cranks with a 20lb deadblow hammer between solid metal vee blocks, the industrial engine cranks were done on a 50 ton press...pretty barbaric! LOL!

It ain't rocket science, and I doubt you could tell unless you were checking the deck which isn't going to tell you the indexing anyway.
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Old 09-23-2010, 02:21 PM
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Quote:
Originally Posted by 4 Jaw Chuck
It ain't rocket science, and I doubt you could tell unless you were checking the deck which isn't going to tell you the indexing anyway.

That is what I was afraid of on the factory cranks.. Great story tho.

Checking the deck in relation to the crank degree with a degree wheel would tell you for sure right?
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Old 09-23-2010, 02:34 PM
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Just out of curiosity, I fired up AutoCAD and drew a 3.75" crank throw and 5.7" rod at TDC, and then drew them at 3 degrees BTDC and 3 degrees ATDC. I then measured the difference between the little end of the rod at the three points (3* BTDC, TDC and 3* ATDC). Anyone want to take a guess at how far the top of the piston moves during that 6* swing of the throw?
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Old 09-23-2010, 02:59 PM
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Quote:
Originally Posted by XNTRCI-T
Just out of curiosity, I fired up AutoCAD and drew a 3.75" crank throw and 5.7" rod at TDC, and then drew them at 3 degrees BTDC and 3 degrees ATDC. I then measured the difference between the little end of the rod at the three points (3* BTDC, TDC and 3* ATDC). Anyone want to take a guess at how far the top of the piston moves during that 6* swing of the throw?
I'm not doing the math right now but offhand I'd say less than .002".
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Old 09-23-2010, 03:07 PM
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Dirty Biker -- It'd sure get you close.

Think about it . . .a 4 inch stroke (easy number to work with) has the rod journal on a 2 inch radius. If it was off 1 degree, that'd be about .034 out of position. Takes a lot of grinding to correct that. Maybe some of it could be done on other journals, and all if worked to take best advantage of the available stock, but if you ground two journals eccentricly to correct for a .034 indexing error, you'd need to grind at least .034 off the diameter of each to correct for this error. That's if the error is only one degree. If another journal is off 1 degree in th eopposite direction . . . . now you're grinding .068 off of two journals.
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Old 09-23-2010, 03:28 PM
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I can't edit my post above anymore. I mistated what I did... I drew a 3.75" stroke, which is 1.875" throw.
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Old 09-23-2010, 04:01 PM
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I sent a crank off to get turned a month ago or so. It came from a vortec engine that some guy ran out of oil and was a steel crank and figured it was worth turning. Machinist thought 10/10 would be plenty to fix it because it didn't look too horrible. I have seen worse that only went 10/10. Had to do 20/30 because the throws weren't true to where they should be. he also called it "indexing" and explained it the same way. Each throw should be exactly 90* from each other.
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Old 09-23-2010, 04:23 PM
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Cranks aren't usually going to have errors measured in degrees, rather in minutes and seconds of degrees. A minute of arc is = 1/60 of a degree, etc..
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