BBC cam journal
12-05-2009, 07:41 AM
#1
Pro
Thread Starter
BBC cam journal
Building a Gen 6 BBC, bought a new 502 block fitted with cam bearings. My new cam wont quite fit, it appears the cam bearing to journal clearance is too tight. An older cam fits but only just and its still tight to turn once in.
Its not practical to return cam or block to supplier and Ive already fitted crank and pistons.
Would taking a whisker off the cam journals be a practical option?
Its not practical to return cam or block to supplier and Ive already fitted crank and pistons.
Would taking a whisker off the cam journals be a practical option?
12-05-2009, 08:27 AM
#2
Pro
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I think TBH that's going to have to go back to the supplier or your machine shop.
If the new cam wont fit and even an old cam still binds then you've got a major issue with the cam bearings that only a re-strip and exam will sort out.
I know it's not what you want to hear but it will be quicker/safer in the long run.
If the new cam wont fit and even an old cam still binds then you've got a major issue with the cam bearings that only a re-strip and exam will sort out.
I know it's not what you want to hear but it will be quicker/safer in the long run.
12-05-2009, 08:29 AM
#3
Le Mans Master
Member Since: Sep 2001
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Building a Gen 6 BBC, bought a new 502 block fitted with cam bearings. My new cam wont quite fit, it appears the cam bearing to journal clearance is too tight. An older cam fits but only just and its still tight to turn once in.
Its not practical to return cam or block to supplier and Ive already fitted crank and pistons.
Would taking a whisker off the cam journals be a practical option?
Its not practical to return cam or block to supplier and Ive already fitted crank and pistons.
Would taking a whisker off the cam journals be a practical option?
Likely cause: ends-edges of cam bearings are very slightly mushroomed when bearings were driven into block. Reach in there & feel for it (sorry crank-pistons gotta go). If that's it, get yourself a good, sturdy & sharp knife. Reach in there and scrape a slight chamfer on edges cam bearings.
Alternative approach: possible your local machine shop may have a tool that will fit thru cam bearing bores and slightly ream bearing edges.
While you're at it ... suggest double-check those oil-holes in cam bearings are aligned with holes in cam tunnel.
12-05-2009, 09:31 AM
#4
Drifting
Remember GM line bores the cam tunnel with the bearings installed, Try to by a replacement block from as the come with bearings installed.
We trial fit a cam and bearings before we do any work to the block as we do find about 3 or 4 a year that need to be line bored and we have alot of other shops that find this issue after thay have the lower end to gether and can't get the cam.
I hope this is not the case try another set of bearings to see if it cures the problem.
BBC's seem to be the worst one for alignment problems.
We trial fit a cam and bearings before we do any work to the block as we do find about 3 or 4 a year that need to be line bored and we have alot of other shops that find this issue after thay have the lower end to gether and can't get the cam.
I hope this is not the case try another set of bearings to see if it cures the problem.
BBC's seem to be the worst one for alignment problems.
12-05-2009, 10:32 AM
#5
Le Mans Master
Remember GM line bores the cam tunnel with the bearings installed, Try to by a replacement block from as the come with bearings installed.
We trial fit a cam and bearings before we do any work to the block as we do find about 3 or 4 a year that need to be line bored and we have alot of other shops that find this issue after thay have the lower end to gether and can't get the cam.
I hope this is not the case try another set of bearings to see if it cures the problem.
BBC's seem to be the worst one for alignment problems.
We trial fit a cam and bearings before we do any work to the block as we do find about 3 or 4 a year that need to be line bored and we have alot of other shops that find this issue after thay have the lower end to gether and can't get the cam.
I hope this is not the case try another set of bearings to see if it cures the problem.
BBC's seem to be the worst one for alignment problems.
12-05-2009, 07:40 PM
#7
Le Mans Master
It's almost certain that one or more of the cam bearings just weren't put in quite straight. It happens. I've never seen "mushroomed" cam bearings and if they're that way then the shop beat the Hell out of them to get them in and they should come out.
The shop should always check the bearings with a cam before they let the block leave the shop. It's sloppy work any way you look at it
The shop should always check the bearings with a cam before they let the block leave the shop. It's sloppy work any way you look at it
12-09-2009, 05:27 AM
#11
Pro
Thread Starter
I havent got the crank out yet, planned to tonight, but the wife has got me checking a report for her.
Incidentally this is a NEW block so cam bearings would have been installed by GM not a workshop. Fortunately my local machine shop is happy to look at it once it comes apart. I found 2x 2.5" bearing shavings once the cam cam out. If it it only needs an edge cleaned up I'll try that myself.
Incidentally this is a NEW block so cam bearings would have been installed by GM not a workshop. Fortunately my local machine shop is happy to look at it once it comes apart. I found 2x 2.5" bearing shavings once the cam cam out. If it it only needs an edge cleaned up I'll try that myself.
12-09-2009, 07:23 AM
#12
Safety Car
Very common both sbc & BBC.
Likely cause: ends-edges of cam bearings are very slightly mushroomed when bearings were driven into block. Reach in there & feel for it (sorry crank-pistons gotta go). If that's it, get yourself a good, sturdy & sharp knife. Reach in there and scrape a slight chamfer on edges cam bearings.
Alternative approach: possible your local machine shop may have a tool that will fit thru cam bearing bores and slightly ream bearing edges.
While you're at it ... suggest double-check those oil-holes in cam bearings are aligned with holes in cam tunnel.
Likely cause: ends-edges of cam bearings are very slightly mushroomed when bearings were driven into block. Reach in there & feel for it (sorry crank-pistons gotta go). If that's it, get yourself a good, sturdy & sharp knife. Reach in there and scrape a slight chamfer on edges cam bearings.
Alternative approach: possible your local machine shop may have a tool that will fit thru cam bearing bores and slightly ream bearing edges.
While you're at it ... suggest double-check those oil-holes in cam bearings are aligned with holes in cam tunnel.
Take it down with a small round file on the edge or a knife as suggested. You have nothing too lose if the bearing gets messed up. They will be coming out anyway if they're that bad. Most builders have had to do this at one time or another.
12-19-2009, 08:58 PM
#14
Pro
Thread Starter
After taking all the internals out found cam journal was wearing on one side of a couple of centre bearings. machine shop used a bearing scraper to tidy it up. Now I have to put it all back again.
