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Hi all,
I've taken apart the B20E I eventually want to put into my 122. As told in another post, it's a 8-bolt crankshaft, which I heard is stronger (really?). After a thourough inspection, it appears that one main bearing and the corresponding rod bearing (is that how you call the machined part of the crank on which the rod gets hooked?) are slightly marked. I can feel with my nail that a tiny spur has been made into the metal of the shaft: same feeling as if one single sand grain had gone halfway around each bearing. There is no stain or anything (no heating, I presume). A few persons have told me: "put everything back in, it'll work just fine". I'd like to hear your experiences with installing a non-perfect crank (with its original bearings, of course). Any short term trouble (i.e. before 100'000 miles?)
ALternatively, I have acces to another shaft which is supposed to be perfect (need to check) but it's a 6-bolt. Will the rods of the 8-bolt fit this crankshaft? Then I guess I should keep the bearings that came with the 6-bolts: will they fit as well?
THanks for your ideas and feedbacks! Séb
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If you are doing a complete rebuild then by all means take it to the machineist and ask their opinion... A small fret can sometimes be "polished" off instead of a full re-grinding. Have them put a generous filet on there if they grind them.
The 8-bolt is not necessarily stronger than the 6-bolt but the parts will not interchange. The big happiness of the 8-bolt for the enthusiast is you can use the B21 pistons in a later rebuild for a nice pep-up.
If you are only "freshening" the motor then the crank will likely be OK. Use new bearings, however, as using old ones is a waste of time money and effort.
"Mikeing" the journals with a caliper will not give you very good accuracy and a micrometer with a pointed mandrel will do a much better job (pointed for the groove, flat or round is OK for "general diameter" and round necessary for inside diameters.
I tend to use plastigauge instead. On dis-assembly (or anytime after dis-assembly) I clean the bearing surfaces, apply a strip of plastigauge and re-assemble. Torque down and then dis-assemble again to measure the strip. I do the same on assembly to ensure all is well.
Mike!
--
Mike!
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I would examine the bearing shells that came off the suspect journals.
It strikes me as odd that the mark only goes halfway around because it would
go all the way around if it had been run with a piece of grit in the bearing,
or the piece of grit would be embedded into the bearing.
It could have been damaged in handling.
You should mike both the crank and the bearings (use a tube mike with round
face to mike the bearing shells, and go EASY so you don't put a dimple in the
shell. Especially mike where the marks are to determine if there is raised
metal there. If the shells are full thickness or within 0.001" and you don't
see anything embedded in them, and the crank mikes the correct size with no
raised or flat spots, I'd conclude it is handling damage and OK to use.
The machine work is expensive, maybe more than what you could find another
crank for, and always carries the risk of a screw-up. Likewise a smaller
bearing journal is not as strong as a full-size one. Stiffness goes as the
square of the radius.
--
George Downs Bartlesville, Heart of the USA!
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Hi George and thanks for this input, you rise a good point here by saying there might be something stuck in the bearings. I guess the best thing I have to do is bring the whole stuff to the shop to have them look at it, they'll know better than I will. Your message is still a bit unclear to me though, as my English teacher never told me what "to mike means". From what you describe, I can draw a rough picture, but I haven't found the word in my eng.-french dictionnary. Could you provide some light, maybe a picture of what the proper tool is supposed to look like (or web resource)? Thanks in advance, your help is, as always, highly appreciated!
All the best and greetings to the heart of the USA ;-)
Séb
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mike (noun) = micrometer (caliper, usually) (in this case)
mike (verb) = measure with a micrometer (caliper)
--
George Downs Bartlesville, Heart of the USA!
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OK, got it! Cambridge online dictionnaries gave me only "micropohone". Didn't make much sense ;-)...
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Hi George and thanks for this input, you rise a good point here by saying there might be something stuck in the bearings. I guess the best thing I have to do is bring the whole stuff to the shop to have them look at it, they'll know better than I will. Your message is still a bit unclear to me though, as my English teacher never told me what "to mike means". From what you describe, I can draw a rough picture, but I haven't found the word in my eng.-french dictionnary. Could you provide some light, maybe a picture of what the proper tool is supposed to look like (or web resource)? Thanks in advance, your help is, as always, highly appreciated!
All the best and greetings to the heart of the USA ;-)
Séb
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An engine rebuild is a pretty big job, but most of that job is removal of heavy parts, disassembly, and reassembly.
If your crank is not perfect. And I mean perfect or better, I'd spend the money on some machine work and bearings while you have it apart.
And yes, I'd agree that it'd probably run fine if you don't, but why not do the job right since you're almost there
--
-Matt '70 145s, '65 1800s, '66 122s wagon, others inc. '53 XK120 FHC
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I agree with Matt... at least have a machine shop evaluate the damage.
No, rods for 8-bolt and 6-bolt cranks are different sizes and will not interchange.
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Thanks, folks, I'll follow the wise way... Cheers, Séb
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