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Post by buster on Nov 2, 2021 18:34:04 GMT
with current great debate going on about nick's cm400, its inspired me to get on and build my 250 engine back up. I actually robbed quite a few parts off this motor for the 400thing build but I'v been quietly acquiring the bits and pieces I needed (at prices I'm prepared to pay, tight git ) and I think I have everything except for a stator (bought one on ebay for £20 but needs rewinding). so after all that encouragement for nick to have a go, I'll probably blow it with the initial parts list. worth noting that in my opinion this engine is pretty low mileage (crank shells are in really good shape, phew cos they're all black) so this is a bare basics build. the new bits and that little lot came to £185.28
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Post by buster on Nov 6, 2021 21:28:15 GMT
so to begin clean the 40 odd years of grot off then doing a bit of exploratory measuring I hit a snag, checked the rod bearings, ones ok, ones not. no big deal as they are available. problem is I also checked the main shells in the casing and two of them are no good , even worse they're black shells . so three possible options, find a crank coded ccc or aaa, find some NOS black shells or buy some NOS blues and have the crank ground . I have only one word, bugger and thats bugger with feeling
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Post by johnfcbn44dx on Nov 6, 2021 23:18:15 GMT
One single pair of Black Shells? and your sorted? Two shells 13315-414-003/4 ?
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Post by johnfcbn44dx on Nov 6, 2021 23:50:41 GMT
Just looked in the tin, I sold two NOS once I thought I had an order for another 4 replacements from Japan, but they came back 3 days later saying they could not supply them, I had not updated the spread sheet...
So I have two used black, one shell is marked over a 2mm width, but majority / mostly not wiped, the other seams ok, will check in daylight though I have two further used shells that may be black, but I've not got a mic to measure them.
But I'll start searching for NOS Black again!
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Post by andy1kenobe on Nov 7, 2021 11:12:02 GMT
If anyone can find black shells it'll be you John.
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Post by johnfcbn44dx on Nov 7, 2021 12:06:37 GMT
Black used
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Post by johnfcbn44dx on Nov 7, 2021 12:20:17 GMT
Unknown colour / unsure It does seem black is difficult to find on the 250s but it seems to be Brown on the 400s that is difficult.
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Post by buster on Nov 7, 2021 12:30:31 GMT
on the face of it john they look ok, would you be prepared to sell them?
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Post by buster on Nov 7, 2021 12:36:44 GMT
a further option here, I'v just had a head scratching session (much measuring and swapping round of shells, then checking with plastigauge) and one set of shells will do. it may even be that I can get away with a set of blues (just bought a pair NOS on the off chance). measuring the crank (mag wheel end) with a micrometer seems to show that its reasonably true (yes thanks I know a micrometer isnt the tool for checking but I dont have any V blocks or a dial gauge) it also seems to be at the smaller end of the tolerance. plastigauge will tell the true tale when they arrive
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Post by johnjones on Nov 7, 2021 13:49:31 GMT
Diameter of unworn central channel area of the crank, and the worn area of the shell supporting area, how is the difference.
You must have clearance for the oil so the shaft "rides" on the oil, at pressure. This I know you know.
A "Mike" is the excepted measuring tool/instrument for diameter checks/measurements. A surface table, vee blocks, dti and magnetic mounting would be nice, but expensive needing a warm dry clean booth or building, not a damp shed with its own climate like what I have to endure, but I can dream....
It's a main bearing with the crank having good endfloat control, so no real bugbear with taper and ovality...how is the centre main journal.
It's usually the flywheel side big end that has issues...
It's good using plastigauge but any "rotation" will smear and give a false reading unwhat, but you know this.
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Post by johnjones on Nov 7, 2021 14:07:52 GMT
Will a main bearing wear oval ?
Yes...
So measure north south, and east west, and other positions, and tabulate.
This I know you know.
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Post by buster on Nov 7, 2021 14:36:31 GMT
problems here have probably arisen (slightly) from the fact that this is a secondhand set of cases (matching crank bridge) they are marked ccc as were the originals but I dont know the history of them any more than that. the c marking means theres no scope to 'bore' the casing (do a's or b's even exist?) as you say JJ the mag/flywheel end is the one that suffers but it does seem pretty true as does the centre and indeed the other side, theres much worse looking cranks on ebay at the mo (in my opinion junk or boat anchors if your an american).
makes me partly wish I was still working in QC for an engineering firm (could lay my hands on great measuring gear, and had all their own calibration blocks/bars etc) but not to worry. I'll see what the plastigauge says with a set of blues.
I can see the north/south measurement but east/west? the shells are elliptical in nature and surely would give an oddball reading east/west?
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Post by johnfcbn44dx on Nov 7, 2021 14:49:46 GMT
on the face of it john they look ok, would you be prepared to sell them? I'll try and post both pairs tomorrow, if you could do a comparative check on the unknowns with the mic, see if they are the same as the known black shells. If you pm you address, (I'll have it already but my filing system is a shambles...) I've still plenty time to hunt more black shells.
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Post by johnjones on Nov 7, 2021 16:12:12 GMT
The journals, n and s, e and w...
The bearing shells in situe and torqued, measured with an internal Mike....
Are you using the Haynes shell selection matrix, the honda manual matrix or the one from CMSNL ?
The bottom shells get most of the load/wear...top for big end...
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Post by buster on Nov 7, 2021 16:39:37 GMT
The journals, n and s, e and w... The bearing shells in situe and torqued, measured with an internal Mike.... Are you using the Haynes shell selection matrix, the honda manual matrix or the one from CMSNL ? The bottom shells get most of the load/wear...top for big end... I know what your saying, dry build no crank, but I dont have an internal micrometer either I'm using the haynes table. the shells themselves have all been mixed up, I would have kept them in exact order but the original top case/bridge didnt survive the strip down. I'v honestly never known a mag wheel bolt in so tight, it says a lot that I bought it off a breaker with the mag and stator for £75, he obviously couldnt shift it either
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