[Formulajones]

I've had this very scenario on a couple of Pontiac engines. What happens over time, in the cases I've seen, is the cam bore is out of alignment and the cam wears itself into one or more of the bearings. So those bearings tend to mushroom around that cam journal.

Then when you go to pull the cam out, it's stuck and needs a little persuasion, usually prying with a screwdriver through the lifter valley. Sometimes the bearing comes out with it, or sometimes it just pushes the cam through the mushroomed part of the bearing and brings out bearing material with it.

In either case, it's usually a cam journal alignment issue. Sometimes this can be addressed after bearings are installed with a light cleanup, making sure the cam spins freely by hand before proceeding with assembly, but in more severe cases the bore may need touched up by a competent machinist.

For some reason I only run into this with Pontiac blocks.

[hurryinhoosier62]

Originally Posted by Formulajones

I've had this very scenario on a couple of Pontiac engines. What happens over time, in the cases I've seen, is the cam bore is out of alignment and the cam wears itself into one or more of the bearings. So those bearings tend to mushroom around that cam journal.

Then when you go to pull the cam out, it's stuck and needs a little persuasion, usually prying with a screwdriver through the lifter valley. Sometimes the bearing comes out with it, or sometimes it just pushes the cam through the mushroomed part of the bearing and brings out bearing material with it.

In either case, it's usually a cam journal alignment issue. Sometimes this can be addressed after bearings are installed with a light cleanup, making sure the cam spins freely by hand before proceeding with assembly, but in more severe cases the bore may need touched up by a competent machinist.

For some reason I only run into this with Pontiac blocks.

Compared to other blocks, Pontiac cam bores aren't supported as well.

[HoneyHush]

I put my 68 400 together 2 years ago. I took it home from the machine shop, scrubbed it down, greased the cam up and started to put it in. I usually put the cam in first because it’s easier and then install the crank. I got the cam all the way in to the very last bearing and thump, it rubbed the bearing really hard. You could push it in all the way but the cam was really hard to turn. Packed up and went back to the machine shop and after a few arguments and 2 more sets of bearings I took it to another shop after this one said “oh just run it it’ll free up”. The next day the new shop called and I picked up my block. Cam went right in and zinged around. The first shop had simply burred the edge of the bearing saddle and was too lazy or unintelligent to sand the burrs off and it was cocking the bearing up and closing it up some. May be the same exact situation in your case. May just need new cam bearings and some attention to detail. That’s the first thing I thought when I saw your cam discolored back there. Hope this helps

[footjoy]

Well the cam bearing oiling holes were full of bearing material. I showed the pictures to the guy who built the engine. Long story short I dropped the engine off at his shop yesterday.

He is not sure what happened but he will look into it

[tom s]

Have him blue the bearing bores and run the bar through it.He might be surprised!My guy was!Tom

[dataway]

In general ... is it more likely the cam is bent than the bores that far out?

[Formulajones]

There has been a ton of bent cams recently it seems. The cams I've bought within the last year (2 rollers and 2 flat tappets) all had to be straightened.

Even with that said, the 3 I did for Pontiacs still didn't spin very well in the block and had to have the cam bores in the block addressed.

[tom s]

Cam was straight,Number 1 and 4 were off 1 thou.One was on the bottom and 4 was on the top.The cam would turn with 2 fingers in the block before it was line bored.FWIW,Tom

[track73]

FWIW. I had a problem installing the 041 cam that's in the engine now. I struggled to get it into the 4th bearing. I checked the cam with a straight edge and it was fine. I put in a new bearing with similar results. I knew he engine block was baked and blasted for cleaning. I ran a brake hone through the journal and saw that the edges were shinny but the middle was untouched. I ran the brake hone until edges were even with the middle duched with WD-40. I proceeded to wash the block put in a new bearing and the problem was eliminated.

[NeighborsComplaint]

Was the cam actually stuck i.e. wouldn't budge when pried by the timing gear with the cam still in position? Or stuck as in pulled it free of the cam bearings and dropped it and couldn't realign it with the cam tunnel (bearings)?

[hurryinhoosier62]

Originally Posted by tom s

Have him blue the bearing bores and run the bar through it.He might be surprised!My guy was!Tom

Tom, I’ve seen 6.9/7.3 IDI diesel blocks with substantially more material in the cam tunnel than Pontiacs have distorted cam bores. It is amazing how little material removed it takes to straighten the bores.

[Dragncar]

I knew a guy once who had a tight cam bearing on a chevy. He took a old cam and made 2 thin cuts across the journal that was tight with a cut off wheel. Put the cam in and "shaved" the bearing until it spun free enough.
I would not do it on a engine I cared about, but it worked.

[hurryinhoosier62]

Originally Posted by Dragncar

I knew a guy once who had a tight cam bearing on a chevy. He took a old cam and made 2 thin cuts across the journal that was tight with a cut off wheel. Put the cam in and "shaved" the bearing until it spun free enough.
I would not do it on a engine I cared about, but it worked.

It CAN, but it’s NOT the correct way to solve the problem. Why folks do not check cam bore alignment eludes me. It’s a fairly simple procedure.

[TedRamAirII]

Originally Posted by hurryinhoosier62

It CAN, but it’s NOT the correct way to solve the problem. Why folks do not check cam bore alignment eludes me. It’s a fairly simple procedure.

Easy to check. How easy to correct?

[Formulajones]

They run a bar through it much like they do for the main saddle I believe.

Doesn't take much. They are usually off .001" like Tom mentioned but that's enough to bind up the camshaft, and sometimes in different directions which is worse. And if run that way, will mushroom the bearings on those journals and make it tough to get the camshaft out.

[tom s]

I will post a pic of my #4 bearing when I get a chance.Tom

[hurryinhoosier62]

Originally Posted by Formulajones

They run a bar through it much like they do for the main saddle I believe.

Doesn't take much. They are usually off .001" like Tom mentioned but that's enough to bind up the camshaft, and sometimes in different directions which is worse. And if run that way, will mushroom the bearings on those journals and make it tough to get the camshaft out.

Precisely. What I did was to set up the block on a Berco BC-5 and “zero” the indicators.,When I sat up the cutter, I would set it for a spec between the minimum and maximum range. This usually removed the area of distortion WITHOUT losing the press for bearing retention.

[Formulajones]

Originally Posted by hurryinhoosier62

Precisely. What I did was to set up the block on a Berco BC-5 and “zero” the indicators.,When I sat up the cutter, I would set it for a spec between the minimum and maximum range. This usually removed the area of distortion WITHOUT losing the press for bearing retention.

Excellent explanation. Thanks for that

[455Grandville]

Originally Posted by hurryinhoosier62

X 2, Mick. This is WHY I always check cam bore alignment. Just because a block is made of cast iron does NOT mean it doesn’t distort over time.

Uh huh. Years ago my cousin and I machined a 351w for a guy who never paid or came back for the block.. We stored it upright for years and when we found a buyer, we inspected it and found dimensions had changed a fair amount.

[455Grandville]

Originally Posted by hurryinhoosier62

Tom, I’ve seen 6.9/7.3 IDI diesel blocks with substantially more material in the cam tunnel than Pontiacs have distorted cam bores. It is amazing how little material removed it takes to straighten the bores.

Yea, you’re just dusting them.