Just got bit by the tight cam bearing bug

[EngineerDoug]

Hello all,

Just got my 383 block back from the machine shop, bored 0.040" over. Spent the morning cleaning it and getting it dry. Installed the cam bearings with no issues - everybody is lined up just right. I go to slide in my new cam and find it is really tight. I didn't even manage to get it slid in all the way, but then again I did not want to use too much force. It is late in the day and I don't want to start rushing things, so I have set it aside.

I have read about core shift, machining tolerances, and camshafts being less than straight - this is not a big surprise. Please outline the steps or things to check so I properly work my way through this issue. The last thing I want to do is rush in with a scraper before I have done my due diligence.

Thanks!

 

[mentor70]

in some cases, you may have just slightly mushroomed the cam bearings with the tool, and maybe a light chamfering can get you going. the tight bearing tolerance would have to be checked with bore checking tools that good machine shops should have.

 

[dieseldazzle]

Piece of cake just use a bearing scraper on where the interference is when you pull it out and see the witness marks. Done this on several motors

 

[miller]

Still have your old cam? If so, use it as a guide for the new cam bearings. Make sure the old cam is fairly clean, especially the journals. See how easily the old cam will install, get it in place, and rotate it back and forth.
The journals will 'mark' any high spots on any of the bearings, or if there's an alignment issue. Then you decide if to use a bearing scraper on those spots.
Once the old cam installs easily, and rotates easily...then try the new cam.
Be sure not to get too rough, and damage the bearings. All your doing is using the old cam as a tool, and guide.

 

[dvw]

I've scraped plenty of cam bearings. Installing the cam is the first thing I do in case they need to be fitted. Scrape a little test scrape. Now when I'm installing bearings I start with the rear and front, check with cam, install another , check and so on. This way you can find the offending bearing easily.
Doug

 

[dieseldazzle]

I've scraped plenty of cam bearings. Installing the cam is the first thing I do in case they need to be fitted. Scrape a little test scrape. Now when I'm installing bearings I start with the rear and front, check with cam, install another , check and so on. This way you can find the offending bearing easily.
Doug

Exact same way I do it and op, understand scraping the bearing is an acceptable practice. It is difficult to wrap your head around at first I know being a "bearing" and all

 

[EngineerDoug]

Thanks for the tips. I did manage to get the shaft fully in the block, which showed me some shiny spots on the bearings. Number three in particular was tight. I didn't scrape it, but I did Scotchbrite these areas. I then flushed the bearings with solvent thoroughly. The cam is now installed, and will easily turn by hand with the cam sprocket - with gooey assembly lube on the journals. Would you call it good at this point?

 

[Mark B]

As long as you are sure all of the scotchbrite bits have been removed. That stuff is nothing more than sandpaper with nylon holding it together. Nothing worse to have roaming around inside your fresh engine.

 

[Cranky]

I have a home made bearing installation tool and so far so good with it. I hate those universal cam tools. Seems you end up with problem bearings with them more often than not.....

 

[moper]

Yup - scrape away... Don't use any abrasives - scrape them.

 

[Fran Blacker]

This will make you cringe. In the early 70's Camaro Craft did a two part article Hoover talks Hemi's. He said if the cam is to tight cut a groove in the cam journals install the cam and turn it to scrap the bearings.

 

[Kern Dog]

This will make you cringe. In the early 70's Camaro Craft did a two part article Hoover talks Hemi's. He said if the cam is to tight cut a groove in the cam journals install the cam and turn it to scrap the bearings.

Nothing wrong with this procedure. I took a stock 440 cam and put diagonal grooves on each journal. I filled the grooves with axle grease before slipping it in. I rotated it a few turns, pulled it for cleaning, adding more grease....Did this until it spun easily.

 

[ykf7b0]

I used emery cloth on the high spots of my cam bearings. Still working great 15 years later.

 

[Fran Blacker]

I used emery cloth on the high spots of my cam bearings. Still working great 15 years later.

I believe cam bearing are babbit. Sanding them you can embed abrasive in them. Hey 15 years can't be all bad.

 

[ykf7b0]

A hard 15 years with an occasional hit of nawwsss.

 

[EngineerDoug]

Hmm, after reading the comments about Scotchbrite I think I will backtrack. Not much work to pull the cam, replace the bearings, and scrape as needed. I'll flush the block with some more solvent just to be sure. My biggest paranoia about this build is cleanliness. I've been as diligent as possible about keeping everything clean, but this scotchbrite move was probably a mistake. Better safe than sorry - I did not know that abrasive particles could embed themselves in the babbit.

Thanks.

 

[miller]

Better safe than sorry - I did not know that abrasive particles could embed themselves in the babbit.

Think he meant with the sanding cloth, not the scotchbrite...there's several dif grades of scotchbrite, too.
You don't need to pull those bearings, unless you just need the practice! As long as the holes are lined up with the oil ports, leave 'em in. Hint...cam bearing are the first thing you should put in a bare block, nothing else until they are 'fitted' to the cam. Pull the cam itself back out, and carefully clean the bearings, AND oil ports.
Only then, your ready to put the cam in for good.

 

[Fran Blacker]

Yes scotch brite is better. Cleaning with solvent will leave dirt behind. I used soap and water and compressed air to dry. Solvent doesn't have soap. My father was in dry cleaning business and he explained to me the object of soap was to suspend dirt to be washed away. Other members with more experience in engine building could add to this. Some sort of soap is needed to carry away dirt.

 

[EngineerDoug]

So is the consensus that scotchbrite will still leave abrasives behind, but proper washing with soap and water will wash them away?

It does sound like, given the choice between scraping and scotchbriting, the former is preferred to the latter. I'll have to give some thought to whether I install new cam bearings or leave them in. I do have my old camshaft that could be grooved to serve as a reamer.

Thanks for the input.

 

[ykf7b0]

• I have to wonder if emery cloth (or scotchbright) is proven to be a killer of camshaft bearings. The 70+ life long Mopar engine builder who recommended the emery cloth to me has used emery cloth his entire life and never had a cam bearing to fail. That's all the proof I need to feel ok with using it on cam bearings. Do what you feel comfortable with but I'm beginning to believe this is being overthought. I don't even remember washing the bearings afterwards.