Topic: Need advice with engine bearings!

[JHansen]

Hi,

Hoping someone can shed some light on the mystery of ordering Honda engine bearings...

I am rebuilding a 76 CB400f and I need to order engine bearings. What measurements do I need to take to help me determine what bearings to order? I've inspected the orgional shells and cannot find any color markings on them. I have checked the clearances between the bearings and journals with plastiguage and all are between .0015" and .002". This is my first engine rebuild and I am having some trouble intrepreting the bearing chart in my Clymer and Haynes manuals. Hope this is enough background info. Let me know if you need more info. Motor had 31,000 miles when it was torn down due to a non functioning (seized, with a broken adjuster bolt, since repaired) cam chain adjuster mechanisim.

Thanks in advance for any help anyone can offer! Please help me get me screamin CB back on the road!

[oldbiker]

Let me say first that I don't know what the correct clearance as given by plastiguage is, however from my experience I would think that 4 readings that are similar as yours are would seem to be OK. The Haynes manual says maximum clearance permissable is 3.2 thousanths of an inch.
As for the charts in the manuals:- Measure the journal diameter and write it down (call it A). Measure the bearing housing inside diameter, write it down and call it B. Now refer to the chart. Look along the top row and find the column that corresponds to your readin 'A'   Go down that column till you find the row that corresponds to your reading 'B'  In that intersection you will see a letter and/or a colour. That is the reference colour of the shells you require. Theoretically you should do this process for each bearing separately.

[JHansen]

Thanks alot oldbiker!

When I measure the bearing housing inside diameter, should I do this with the bearing shells inserted in the cases or without?

I appreciate the help!

Cheers,
John

[low-side]

There should also be markings next to the crank journals and crankcase bores that can be matched up in order to get the correct bearings as long as the crank isn't badly worn.

[Dennis]

However oldbiker says that max clearance is .0032", you say that you are measuring .002 or less, why bother?
What is the appearance of the shells?
If they look good and are well within wear limits, why would anyone go through the trouble and expense of replacing parts in very good condition?
am I missing something here?

[JHansen]

Dennis poses a good question... because the clearances are within tolerance. I'd like to know what you gyus think.

The bearing surfaces do not look new.(duh) The look pitted in some areas. The machine shop were I took the barrels to be bored out said that pitting was small bits of metal that had loged into the soft surface of the bearing shells. (both the crank and cam journals suffered very mild score marks, the shop thought they would be allright.) The machine shop indicated that this was probably a result of infrequent oil changes and reccommended that they be replaced. I have every intention of using the engine all the way up to 10000 rpm when finished with it, and I'd hate for the motor to fail because of bearings when I'm already in there now.

However, I'm happy to entertain the notion that I'm being overly paranoid here. Please advise.

Cheers,
John

[Dennis]

The machine shop indicated that this was probably a result of infrequent oil changes and reccommended that they be replaced.

Now this puts it into a whole different perspective! Doesn't it?

[oldbiker]

Take your measurement of the housing without the shells in place. If you look at the tables, you will see there is an allowance of about three mm for the thickness of the shells. I think your present shells would be OK if they are not scored or damaged but if you decide to replace them while you already have the engine stripped down then dont forget to break them in over the first few hundred miles. Also if you fit new shells, be sure to clean them thoroughly of grease before fitting. A light smear of oil is all that is necessary. Best wishes, John.

[bryanj]

And that smear of oil is on the bearing surface only NOT ON THE STEEL BACKING

[bryanj]

Further I have found that with the measuring equipement available to most people it is impossible to be accurate enough to use the Honda bearing tables. Originally air gauges accurate to 100th of a Thou were used and without those forget it. I have always rebuilt using the tightest tollerance (black usually) shells and run the motor in for a few thousand miles instead of a few hundred with oil and filter changes every 500 for a while.