New block, tight cam, fix?

The cam was run in my megablock, so apparently the new aluminum block is the problem. I could take it back to the machine shop, but if there is a way to fix this in my shop would be better. My first move is to get out my dial bore gauge and start mesuring bearings and cam in both blocks.

Are they babbit bearings like stock? On my one stock block the cam would go in but not turn with new bearings. Brushed the bearings in Dykem, then took off the tight spots with a bearing scraper.

Very common problem, a good shop should fit the cam before returning the block to the customer. A bearing scraper or an old cam with diagonal cuts on the journals can be used to size the bearings.

Yes….i’ve had to do this on more than half of the engines I’ve done. Not hundreds….but not 2 either.

A bearing knife, a bearing scraper, is your friend on a lot of stock BB Mopar blocks with new cam bearings
I was told that the factory align hone or align bored all of the cam bearings in BB back in the day
I've had to scrape more of them than not with new bearings, maybe 30 % are okay
I now install one bearing at a time and check fit the cam for each bearing If it is tight rotate it so you can see the high spots and scrape them until it spins freely It may take several scrapings to get them like you like them
That is a pain but a lot faster than having to determine which bearing, bearings are tight and need scraping with all of them in the block

Most OEM iron blocks have tight tunnels and some of the shops would hone the tunnels for proper bearing fit or crush priorto bearing installation. Since it's not OEM iron and assuming you're looking at a sleeve-type bearing, I would measure the tunnel bores prior to installing the bearings, just my 2 cents...

Because of where you are at now, John's idea is the easiest fix. Just use a whizzer wheel on your air grinder and an old camshaft and cut those little grooves (mine are straight) in the cam. Then stand the block on it's bellhousing and using oil and a drill and cut the bearings to size. Having said that, now I use Cab's way and do the bearings one at a time, test fit, and use a bearing scraper (or the side of a flat head screwdriver) if needed.

I have used some fine emory cloth to sand on the bearings a bit. Might be some useful information for you here. https://www.youtube.com/watch?v=WfBY8VfZa6A&ab_channel=Nick%27sGarage

Thanks guys. Will check and see with a dial bore gauge, dykem, what ever it takes to figure it out. Then find a cam core,,,,,,,,

I remember having this issue with my new KB block and new cam. I was horrified when my old engine builder (godspeed) brushed some blue stuff on the bearings, turned the cam and scuffed off the high spots with what looked like an old penknife ! We are still running the same block and cam 11 years later

That’s exactly how I do it. Blue the bearings, find the high spots and bearing knife the high spots out and send it.

Question:
How much material do you estimate is being scraped off by whatever scraper you are using ? A few 10-thousanths ?
So the bearing bore is no longer EXACTLY round, a teeny bit egg-shaped ?

My old Machinist use to line bore the cam tunnel and then locktite the bearings. You could spin the cam with one finger just like it was on roller bearings.

You need to remember that the lifters are not pushing straight down, they are making the cam rock back and forth in the bottom 1/3 of the cam bearings
If the bearings are the stock type soft Babbitt the cam will make them fit into them

It’s not just the bores being tight on the block but core shifting around because of the heating and cooling cycles on a used block. Sometimes the new cam can be a little bigger as well. I can remember the last time I installed cam bearings and the fit WITHOUT using a bearing knife on the bearings. I use some scotch brite cloth on the bores afterwards to smooth up the bearings before final fit.

During a cam swap I found one cam bearing spun and the others looked horrible. After installing new durabond cam bearings the old cam would not even come close to going back in, so I used the "cam cutter" suggested on this forum.

The first pass removed a large amount of material from the 4th bearing and a small amount from the first bearing.

I used the scotch bright pad on the drill with WD40 to smooth out the surface of the cam bearings... I am not sure if that helps or hurts but it made them "feel" much smoother. I probably don't want to know what sort of stuff the scotch bright pad embeds in the babbitt,

After about 30 more passes I got to this point. Note: After I got the cam to go in and rotate smooth I pulled the entire engine apart, deburr, hone, clean, new rod bearings main bearings.... etc...

Just had the same problem in a 383 block. Motor had a Isky cam and fit fine. Comp Cams, cam would not fit. I compared journals in size. The Comp cam was .001 larger on every journal. I put it in the lathe and polished every journal down .001, slid right in. If its a Comp cam check the journal sizes.

The BMP aluminum block does not come with cam bearings.
The shop that machined my bores, etc installed new Clevite cam bearings for $75. The cam fit perfect.
He told me the factory Mopar blocks had cam alignment minor issues, but most of the new aftermarket blocks don't have any issues with the cam bearings.

I found that the Durabond chill bearings fit real well, most of the time
They are the only cam bearings I will use now

I have had to clearance the bearings in my 440 build the last time and this most recent rebuild. The 383 in my other car needed it too. I'm getting to where it would surprise me if a cam fit without any additional work.

All the issues start after the factory cam bearings get replaced.

That’s because all the production engines had their cam bearings machined on the ID AFTER installation.
Same thing for automatic transmission bushings.

They could hold tighter concentricity with this method.

This process is still in place to my knowledge.

I can understand how there can be a sizing/alignment issue in an OE block after the bearings get replaced........ because of the procedure being used by the factory for the finish sizing.

But there’s really no excuse for a $5000+ aftermarket block having the issue.
The cam bores should be in alignment and to size........ and so long as the cam is straight and sized within spec....... the cam “should” slip right in.
I’ve used 3 of the previous generation BM/Mopar aluminum blocks and those had no problems with the cam fit.

I pulled the cam, put in another cam, and it glides freely. So i checked the diameters of the new cam. They were all spot on with the other cam. So i tried reinstalling the cam that was tight. I cleaned the journals, put 20w50 oil on it, and it turns freely! I am scratching my head, and have to figure it was the type of assembly lube I used when I originally put the cam in? I used Lucas assembly lube, and it was tight on install, but after sitting for months, it got thicker? I couldn't turn cam with my bare hand, but after going to 20w50 it is snug, but I can turn it with fingertips.

I gave up using the old Torco brand red assembly lube after they got bought out back a long time ago.
The motor runs on oil, correct? So why not use that to assembled them on all the bearings, pistons and piston wall surfaces
I do
I prime all my motors and spin them over by hand or on the starter with all the spark plugs out before starting them to make sure they are well lube with the engine oil they will live on: up: