Topic: Crankcase - crankshaft clearances

[Kevin400F]

I'm preparing to rebuild a CB550 engine, and have several used bottom ends from which to select the best components.  Honda spec for crank bearing clearance is 0.0008" to 0.0018", with a maximum service limit of 0.0031".  There are four different bearing "color codes" to choose from, depending on the crank journal diameter and bearing seat bore in the case.  I have a bunch of used bearings in good condition, and if you assume all the bottom ends have their original bearings/cranks and you go by the "theortical" required bearing based on each of the coding combinations, there are bearings of each size variant....D-yellow (thinnest), then C-green, B-brown and A-black (thickest). 

When I dry-fit the crank using plastigage and say, a D bearing and find the clearance on the high end of the tolerance, say 0.0025", can I substitute a good USED (and therefore likely to be slightly larger than when new) C, B, or A bearing as needed to bring the clearance down within (or closer to) the spec range?  Do the bearings have enough split-line clearance to allow use of an A bearing in a crankcase bore that was originally fitted with a D bearing?

My budget precludes ordering all new bearings from DSS or Honda (just thought I'd toss that out there to head off the easy answers).  Gurus please step up and provide feedback from the "been there, done that" perspective.

Thanks in advance,

Kevin in warm, sunny Texas

[bryanj]

All the sizes of shell will fit all the holes, its the thickness of material on the shell that is altered, use what you have as long as the bearing surface is good, dont forget you have the same problems with the big end shells DO not mix n match rods from different engines unless the weight code letter is the same

[Kevin400F]

Thanks loads for the feedback, Bryan!  Yep, I'll be running through the same evaluation process with the rods, and all the rod size and weight codes are plainly visible so I've at least got an indication of which shell was originally installed in each.  But, the Plastigage will tell the tale, and I'll swap shells around as needed to get the optimum clearances.

Cheers,

Kevin

[dusterdude]

i dont mean to scare you kevin,and god knows im a plastiguage guy myself,but the new hot rod magazine has a tech article about using mics or plastiguage.they mic`ed and/or plastiguaged a crankshaft and the plastiguage clearance came up way too tight,kinda makes ya wonder.

[bryanj]

With plastigauge what they dont tell you is to torque up first with NO gau. ALSO make sure the hole the shells fit to is DRY and SUPERCLEANge rod to "settle" the shells then CAREFULLY dismantle so you dont disturb anything, fit a piece of gauge rod and re-torque

[MRieck]

i dont mean to scare you kevin,and god knows im a plastiguage guy myself,but the new hot rod magazine has a tech article about using mics or plastiguage.they mic`ed and/or plastiguaged a crankshaft and the plastiguage clearance came up way too tight,kinda makes ya wonder.

I just read that articl too. You are right.

[Kevin400F]

Good info on the potential watch-outs when using Plastigage.  I can see how you could get a "smaller than actual" reading if the precautions Bryan described aren't observed.   Dirt behind the shell, or the shell not being properly seated in the case to start with would squish the Plastigage to a greater degree, giving a false reading.   I need a good excuse to buy a 1-2" micrometer anyhow, and will check clearance using both methods.

Cheers,

Kevin

[MRieck]

Good info on the potential watch-outs when using Plastigage.  I can see how you could get a "smaller than actual" reading if the precautions Bryan described aren't observed.   Dirt behind the shell, or the shell not being properly seated in the case to start with would squish the Plastigage to a greater degree, giving a false reading.   I need a good excuse to buy a 1-2" micrometer anyhow, and will check clearance using both methods.

Cheers,

Kevin

You'll need a bore gauge too. Nowhere near as expensive nowadays as they were 20 years ago.

[scunny]

bump
interested to see how you got on with the mix and match of bearings