Topic: Replacing CB750 Crank and Rod bearings

[Kamal]

I just want to get some seasoned engine builder's opinions and experience on replacing bearings, where you get the parts from, and how much they were. Currently, Im looking at $8 and $10 per bearing shell.

I am re-assembling a motor and am torn on whether to replace the bearings while I'm in there.  The bearings look good, measure up a little on the loose side.  This was a race motor, I don't believe it had too many miles on it.  Its prolly about a 90hp motor.  Its got Carillo Rods, bumpy cam, porting, and is an 811cc motor.  I won't be racing this motor, just running it hard on backroads and whatnot.

Do you think these bearings will hold up?

[holysmokes]

this is the time  to replce bearings, chains or tensioners

if you are uncertain of longetivity, replace

honda will have bearings in stock, bearings go by colour

a couple hundred dollars will replace both mains and rod bearings easily

any honda dealer or from service honda

[MRieck]

I just want to get some seasoned engine builder's opinions and experience on replacing bearings, where you get the parts from, and how much they were. Currently, Im looking at $8 and $10 per bearing shell.

I am re-assembling a motor and am torn on whether to replace the bearings while I'm in there.  The bearings look good, measure up a little on the loose side.  This was a race motor, I don't believe it had too many miles on it.  Its prolly about a 90hp motor.  Its got Carillo Rods, bumpy cam, porting, and is an 811cc motor.  I won't be racing this motor, just running it hard on backroads and whatnot.

Do you think these bearings will hold up?

You want to run the Carrillos at .002. I've got some green (C) con bearings coming this week....I could give you a good price on 3 (I need the rest).

[Big Jay]

If you need the chart to pick the rod bearings, e-mail me at  tech@aperaceparts.com with a fax number, and I will send it to you.

Jay

[bryanj]

If its got non Honda rods the chart wont work unless you got superacurate measuring kit

[Jerry Rxman Griffin aka MuthaF'er]

If its got non Honda rods the chart wont work unless you got superacurate measuring kit

Why? If you plastiguage them and get correct clearances why would there be an issue?

[Big Jay]

If its got non Honda rods the chart wont work unless you got superacurate measuring kit

The chart has big end bore sizes. Just take them to a machine shop ( with the rod bolts torqued) and have them measered. Get the measurement out to four places and you are all set.

Jay

[Kamal]

Some time ago I spoke with Mark McGrew from M3 racing, here is what he told me to do:
----------------------------------------------------------------
Hello,

The crank is probably "straight" as far as size goes, as I have not had
one
with different sizes for ten years. No markings is normal, so just
"mike"
the crank with a metric michrometer (or have a machine shop do it) and
the
journals all should be 36.00 mm's.

Carillo rods are always 36.00 mm [I think Mark meant 39mm] on the dot, so no worry there. You
should
mike 'em to see what the ID is. Remove all bearings, clean, bolt and
torque
to 52 foot pounds (yes, 52!)...and then use an inside mike to
measure...just
to be sure. Again, should be 36mm.

Cases are all "B" so go to the book and you need either yellow or green
bearings.

Let me know if you don't have the book for the color codes. ie: Honda
shop
manual.

M3
---------------------------------------------------------------------------------------------

I just used an inch dial caliper to measure my journals, and calculated the conversion, which showed between 35.96 and 35.99, so needless to say, those are inaccurate measures...I do need to get a Metric Micrometer and do the measures again. 

Is there a way to tell which bearing it is by the number stamped on the bearing? Or do the different color bearings have the same number stamped on them?  If memory serves me, there was one odd bearing shell in the current set with a slightly different code.  I'd like to figure out why theres an odd shell even if I am measuring and going from the ground up.

Thanks Big Jay, I do have the bearing chart in my copies of the original honda manual.  Thanks for your input MRieck, and everyone else for their input so far.

[bryanj]

ike must be "lucky" i have two cranks in my garage with different pin sizes and all the cases i have seen recently have at least one journal hole with a different letter. The hole sizes will never alter in the cases but the rods can stretch very slightly, if the pins have worn the crank is shot anyway and yes having done all the math plastigauge is the best way to go but if you have bought all the shells it may cost you a fortune.

If you have the time and patience buy two of the "slackest" rod shells and case shells then do a plastigauge check with multiple assemblies and work out the correct sizes from that

[Kamal]

Hello everyone,

I have some measures for these engine parts now that I got some metric measuring tools.

Every crank pin and journal measures out to 35.98 mm. This figure is slightly smaller than the chart allows for.

The rods are 39.00 mm and the cases are stamped BBBBB.

According to the chart, I need Browns for the cases and Greens for the rods. But since my pins seem .005 smaller, I wonder if I should go a step thicker on the bearings, to Black/Brown instead of Brown/Green?  The bearings that are currently in place are both a dark color.

Does this sound about right to people? Any suggestions?

[Kamal]

Hello everyone,

I have some measures for these engine parts now that I got some metric measuring tools.

Every crank pin and journal measures out to 35.98 mm. This figure is slightly smaller than the chart allows for.

The rods are 39.00 mm and the cases are stamped BBBBB.

According to the chart, I need Browns for the cases and Greens for the rods. But since my pins seem .005 smaller, I wonder if I should go a step thicker on the bearings, to Black/Brown instead of Brown/Green?  The bearings that are currently in place are both a dark color.

Does this sound about right to people? Any suggestions?

[RRRToolSolutions]

Use plastigauge to measure the clearances. I just bought a stick for less that $5 and had enought to do all 9 journals. Clean the bearings, clean the journal, cut the gauge, torque to specs and remove and read the width of each stripe - and you're ready for ordering.

Be careful torquing those Carillos to 52. I just bought a new set and mine says "Do not exceed 45 lbs" You've after bolt stretch of .005~.007 and mine occured at 35 lbs on the dot.

Regards,
Gordon

[Big Jay]

Use plastigauge to measure the clearances. I just bought a stick for less that $5 and had enought to do all 9 journals. Clean the bearings, clean the journal, cut the gauge, torque to specs and remove and read the width of each stripe - and you're ready for ordering.

Be careful torquing those Carillos to 52. I just bought a new set and mine says "Do not exceed 45 lbs" You've after bolt stretch of .005~.007 and mine occured at 35 lbs on the dot.

Regards,
Gordon

Yes. We do 42lbs. Don't do 52.

Jay

[MRieck]

Use plastigauge to measure the clearances. I just bought a stick for less that $5 and had enought to do all 9 journals. Clean the bearings, clean the journal, cut the gauge, torque to specs and remove and read the width of each stripe - and you're ready for ordering.

Be careful torquing those Carillos to 52. I just bought a new set and mine says "Do not exceed 45 lbs" You've after bolt stretch of .005~.007 and mine occured at 35 lbs on the dot.

Regards,
Gordon

Yep...35lbs right around where I've the proper stretch. And when you think about stock CB bolts torqueing to 14lbs.... I'd also recommend cycling those rod bolts a couple of times with 3 stage torque.

[rhinoracer]

According to the chart, I need Browns for the cases and Greens for the rods. But since my pins seem .005 smaller, I wonder if I should go a step thicker on the bearings, to Black/Brown instead of Brown/Green?  The bearings that are currently in place are both a dark color.

I wonder the same thing, does one go to the dealer and ask for colored bearings? Are they actually painted? I'm not kidding, I've only seen the used bearings in my engine and they don't have any colored id marks and the stamped codes don't match anything I can figure out

[Jerry Rxman Griffin aka MuthaF'er]

After you Plastigauge and have determined what clearance you actually have you pick your bearings using this clearance. Each bearing is assigned both a color code and a part number. If I were you I'd definitely take BOTH to the Honda dealer. Too many parts dewds (and I use this term accordingly) that don't know their ass from a hole in the ground when it comes to old bikes. I haven't bought bearings lately but if I remember correctly the edges have the color on them. I haven't seen a cross reference for the codes stamped on the bearings. 

[Kamal]

Hello Everybody,

So, I have the final measures from clearancing the bearings on this race motor, and wanted to run the results by some of the experts here.

For the crank bearings, they were between .025 and .038 mm on the green Plastigage

For the rods, I got a little looser measure, no looser than about .051 mm (.002") for the rods.

Is there really any reason to change out these bearings, which look and measure perfectly fine??? Do bearings fail due to other reasons besides dimensional wear, such as metal fatigue, etc. The Honda book says not to replace unless they measure out of spec. But, we do have a society bent on fixing things that aren't broken. I'm curious to hear people's opinions.

[bryanj]

If the bearings are abused the white metal can "peel" but if there are no signs of damage there is nothing to worry about. If bearing surfaces are an even gray colour with no scores just re-use em