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Author: Subject: Measuring up for main replacements
coyoteboy

posted on 16/11/15 at 01:23 PM Reply With Quote
Measuring up for main replacements

So I've stripped an engine I'm working on (blown ringlands) and I'm looking at mic'ing up the crank to check for what shell sizes I need but:

1) None of my tools have accuracy suitable. Even the £300 set of external micrometers, while having resolution of .001mm, have an accuracy of 0.05mm.
2) Stock crank dims are 54.985-55.001mm, oil clearance of 0.015-0.033mm (which is VERY tight!).

Measuring with verniers I get 54.85 (clearly outside of spec), measuring with lower res external micrometer I get 55.01mm (clearly outside of spec). I'm more tempted to believe the micrometers but it cant' be above original spec. I'd also doubt it's that far below original spec because there's no obvious wear on the journal (lovely and smooth, no lips) but I've also no idea if it's been ground before but it doesn't match any standard oversize grind either. Part of me is tempted to just drop in standard shells and measure clearance to check but there's a good chance it'll be miles out from stock clearance.

Thoughts?





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Nickp

posted on 16/11/15 at 02:15 PM Reply With Quote
Any markings on the shells? ie 010 +10.....?
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owelly

posted on 16/11/15 at 03:16 PM Reply With Quote
Use http://plastigauge.co.uk/





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coyoteboy

posted on 16/11/15 at 05:26 PM Reply With Quote
No markings, and plastigauge relies on you having already bought the shells, which defeats the purpose.





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Nickp

posted on 16/11/15 at 06:09 PM Reply With Quote
quote:
Originally posted by coyoteboy
No markings, and plastigauge relies on you having already bought the shells, which defeats the purpose.


If there's no markings then you can be 99% sure they're STD

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DIY Si

posted on 16/11/15 at 06:14 PM Reply With Quote
Refit the existing shells, assuming you haven't binned them, with plastigauge and then check the part number on the bearings would be my first move.

Or, I'd take the crank to a machine shop and see what their kit says.





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owelly

posted on 16/11/15 at 06:36 PM Reply With Quote
Are you micrometers calibrated? Do they come with standards to check? I know you say they're not accurate enough but it's possible to 'feel' the right dimensions if you see what I mean?! Can you use the standards to set the micrometer at a set dimension and then use the Plastigauge with the micrometer?





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coyoteboy

posted on 16/11/15 at 08:13 PM Reply With Quote
Yep they are calibrated and match their standard bang on but if their manufacturer quoted accuracy is worse than the oil clearance, how the nuts are you meant to ever know it's right?!

I'm basically stuck with reassembling with the original bearings and assuming they are std, or buying new shells and trying it out. I could take it to an engine builder but a) it's a matter of pride and b) I'm not sure how they would be in any different a situation either. I can't find tools with the accuracy required and I'm pretty sure most builders won't have them either. Or be wanting to waste time on a freebie measuring.





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perksy

posted on 16/11/15 at 09:05 PM Reply With Quote
As NickP said 99% certain they are standard if they aren't marked on the back

The mains don't take that much stick, its the big end journals that do most of the work

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coyoteboy

posted on 16/11/15 at 09:10 PM Reply With Quote
Hmm yeah but, assuming that's right, it still doesn't tell me if I have wear on the journals and therefore need a regrind Bit annoying!





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Nickp

posted on 16/11/15 at 09:13 PM Reply With Quote
quote:
Originally posted by coyoteboy
Hmm yeah but, assuming that's right, it still doesn't tell me if I have wear on the journals and therefore need a regrind Bit annoying!


Do the shells look worn?

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perksy

posted on 16/11/15 at 09:16 PM Reply With Quote
Usual practice is use the micrometer and check for ovality (check at various points around and across the journal)
Visual check first of course

Even if your micrometer was out a little it would still show an ovality error

Using the 'ratchet' on the mic is the supposed standard way of using it, but as said above just about everybody i've worked with does it by 'feel'

Unless there is surface damage I'd be surprised if they were worn excessively
If it had been ground previously then over sized shells would be fitted and marked on the rear of them

[Edited on 16/11/15 by perksy]

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paulf

posted on 16/11/15 at 09:23 PM Reply With Quote
When I worked for an engine reconditoner we used normal basic micrometers checked against a standard at each end of the range. It is dependent of feel when measuring something very precisely but im sure that your crank will be standard as it would be very easy to vary by a few tenths of a thou either way.
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coyoteboy

posted on 16/11/15 at 09:28 PM Reply With Quote
Shells at the timing end are screwed.
Main wear
Main wear


Shells at the fly end are almost spotless.

Journals at both points measure identically with no visible scoring/wear/roughness.

I've been trying by ratchet and by hand just feeling for a bite. There's no ovality that I can sense in the mains, slight in the big ends but barely perceptible (i.e. 3 at each of two points 90 degrees apart "feels" slightly larger on the mic, but is below the 0.01m resolution by some way.

The only mark on the rear is "D2J" and a logo which doesnt' seem to tally with any manufacturer I can see (closest to federal mogul) and the code reveals nothing anywhere online, certainly doesn't match the OEM manual codes. Posted to a forum about the engine one person seems to be fairly sure it's an OEM shell but that's all.





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