Crankshaft main journal wear


Post Reply
jetts68
New Member & Happy To Be Here
New Member & Happy To Be Here
Posts: 24
Joined: Sun Feb 05, 2023 8:07 am
Location: Ireland
Location: Ireland

Crankshaft main journal wear

Post by jetts68 »

Hi all I have measured the wear on my main and big-end crankshaft journals as follows.
M= main journal B= big-end journal

M1 35.974 . 35.975 . 35.976 . 35.976
M2 35.976 . 35.976 . 35.976 . 35.976
M3 35.981 . 35.981 . 35.982 . 35.982
M4 35.984 . 35.984 . 35.984 . 35.984
M5 35.984 . 35.984 . 35.984 . 35.984
M6 35.976 . 35.976 . 35.976 . 35.975
M7 35.976 . 35.976 . 35.976 . 35.976

B1 35.982 . 35.981 . 35.981 . 35.982
B2 35.986 . 35.986 . 35.986 . 35.986
B3 35.986 . 35.986 . 35.986 . 35.986
B4 35.975 . 35.975 . 35.976 . 35.976
B5 35.984 . 35.984 . 35.985 . 35.984
B6 35.986 . 35.986 . 35.986 . 35.986

I have measured each journal at 4 points left and right sides of the bearing area and 90° from the first two measurements. The surface condition of the journals is good in relation to scoring and visual damage. So my question is, looking at the measurements of M1 journal would you risk regrinding the crank or go with a pair of AA blue bearing shells the crankcase bearing id is 39.012 on that bearing. The old shells on that bearing had signs of uneven ware and the shells on B1 where warped. The crankshaft had a bow of 0.09mm at M4 journal and a bow at M2 journal of 0.04mm when I straightened the bow at M2 the bow at M4 reduced to 0.03mm. The crankshaft now runs true across all main bearings at 0mm ±0.01mm. I suspect at some point the engine may have hydro locked on cylinder one as the conrod on cylinder one is a C 3 stamped rod and all the rest of the rods are C 1 coded rods. I haven't measured the conrods yet for straightness as I'm waiting for my local engineering shop to machine up a conrod big-end spigot to measure off of. Look forward to your opinions and suggestions.
Last edited by jetts68 on Sun Mar 12, 2023 6:11 pm, edited 1 time in total.
daves79x
ICOA Technical Director
ICOA Technical Director
Posts: 4778
Joined: Sun Oct 01, 2006 8:05 am
Location: Knox, PA
Location: Knox, PA

Re: Crankshaft main journal wear

Post by daves79x »

C is the rod weight code, so the correct rod was used. 3 is the reference for the bearing size. Do weigh all the rods though. I can't remember the oil clearance range, but the difference between the thinnest and fattest bearing shells is not that much. Select the correct replacement shell for the crank and case codes, Plastigauge it and see if you are within the standard clearance range. I'll bet you will be.

Dave
CBX-tras
ICOA Member
ICOA Member
Posts: 498
Joined: Tue Feb 16, 2010 1:29 pm
Location: Clinton Twp, Michigan
Location: Clinton Twp., Michigan, USA

Re: Crankshaft main journal wear

Post by CBX-tras »

+1 to what Dave said. You'll be fine.

The motor has 7 mains, you only show 6. Or, am I missing something?
jetts68
New Member & Happy To Be Here
New Member & Happy To Be Here
Posts: 24
Joined: Sun Feb 05, 2023 8:07 am
Location: Ireland
Location: Ireland

Re: Crankshaft main journal wear

Post by jetts68 »

You are correct left out the 7 main.
Post Reply