Topic: Busted Main Bearing

[Turbogrimace]

So I screwed up one of my main bearings while specing the tolerances.  It slipped out of the groove that holds it in and I tightened it down.  its now got a slight bend in it and its unuseable.  What is the best method to replace this fella?  Do I have to replace all both half pieces?  I believe it's a B case bore with a B shaft.  Unfortunately my micrometer isnt accurate enough to mic them out right now. 

Since I didnt turn the crank when it was torqued down, do you think there is any damage to the crank?  Also, there is now a slight indentation in the case where the position notch on the bearing pushed into the aluminum.  Is this an issue, or can i just replace the bearing and roll with it?

Thanks a lot fellas.

[bryanj]

You can replace just the one half, I would be astonished if the crank was damaged.

As to the bore in the case the ally where the tongue was may be raised around the dent and it will need carefull dressing with fine carborundum paper (wet and dry is what its called over here in UK) BUT make sure ALL residue is removed before rebuild.

Somewhere in the book is a spec for the shell thickness which may be easier to measure just do the undamaged half as it will be the same grade

[fuzzybutt]

You can replace just the one half, I would be astonished if the crank was damaged.

As to the bore in the case the ally where the tongue was may be raised around the dent and it will need carefull dressing with fine carborundum paper (wet and dry is what its called over here in UK) BUT make sure ALL residue is removed before rebuild.

Somewhere in the book is a spec for the shell thickness which may be easier to measure just do the undamaged half as it will be the same grade

+1 just make sure to put the ball type anvils on the mic

[754]

Carefully work down the area that  got bruised on the case. you may wabt to get a machinist to help you.

the trick is to remove high spot without removing other material. more a job for stoning or very careful scraping.. using blueing will help.

 proceed carefully or you end up with a tight spot or a loose spot..

[Turbogrimace]

It's mearly a dent in the case behind the bearing.  Is it ok to run it like this?  Its not putting any more pressure on the bearing area.  Just a little bit less support to the shell.  A verrry little bit less.

Thanks for the previous advice.

[bryanj]

The edges of that dent WILL be raised and need stoning back carefully

[Turbogrimace]

Great, I will look into that.

Where is a good place to purchase the new bearing shells?

[Turbogrimace]

Does anyone know of a good place to buy a micrometer with interchangeable anvils and spindles?  Digital would be nice to haha.

[bryanj]

A digital vernier would be ok and the shells are HONDA only

[Turbogrimace]

Unfortunately I cant find a set of calipers that are accurate to a thousandth of a millimeter.  Thats what the specs call for to determine the bearing sizes.

[mystic_1]

Most people use Plastigauge, which if you're unfamiliar is small piece of deformable plastic, you place it across the bearing and then install the crank.  Torque the cases together but don't rotate the shaft.  Now unbolt again and remove the crankshaft, then measure the width of the squished plastic.  This tells you how much clearance there is between the current shells and the crankshaft.  If that clearance is too large, buy thicker shells to bring the tolerance back into spec.

Assuming your parts are original and that this is the engine's first rebuild, you can determine the size of the existing shells by using the codes stamped into the crankcase and crankshaft.

Check out Honda Service Bulletin #14 (HSB14) in the Technical Library section of the website.

mystic_1

[bryanj]

It's the accuracy problem i have been quoting for years, on the line Honda use "air" gauges which pump a regulated pressure through a plug or ring and note the pressure drop which can be callibreted to millimeters clearance and thus size.

If you are measuring the pin it could be worth finding a good local engineer and getting all the pins measured so you can compare what he/she gets to the other ones you have and relate that to the one you need. Unless the crank has been lightened the marks are there but take some seeing as they are lightly etched