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Old 04-20-2003, 05:24 PM
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Post Cam Bearing Question.

Working on a 350 SBC that was given to me by a customer, I`m doing a rebuild on it, and I noticed when I was cleaning the oil holes with a brush, that the cam bearing holes are in alignment with the main bearing holes, I`ve looked at every other block I have, none of them line up, I`ve never seen them installed at the machine shop in alignment. this engine was fresh rebuilt when the customer got it, he installed it and it was knocking, I found no spun bearings. would this cause a oil pressure problem? the bearings look new, so I was going to reuse them, but I wanted to find out first if there installed wrong. Thanks.

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Old 04-20-2003, 06:20 PM
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DV, I have seen alot of machine shops install cam bearings this way. Its not the best way to install them but it will not cause an oil pressure problem. All big block Chevys have the cam bearing holes lined up with the main bearing holes. You might check under the rear main bearing cap. There is a small oil line plug on the oil filter side that might be missing. If this plug is left out it will cause low oil pressure. Good luck,
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Old 04-20-2003, 06:53 PM
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Was the cam scored ? Here's some info on bearings, I hope it will help you a little, sound's like you groove behind the bearing.
On blocks without grooves behind the cam bearings, care must be taken to insure that oil holes line up between the bearings and block. Where the block has a groove behind the bearing, the bearing should be installed with the oil hole at the 2 o'clock position when viewed from the front for normal clockwise camshaft rotation. This will introduce oil into the clearance space outside of the loaded area and allow shaft rotation to build an oil film ahead of the load. With a drop of oil in the bearings you should be able to turn the cam easily with your fingers, and should have no perceptible clearance (slop) in the bearings. Stronger bearings will not wear in rapidly to make their own clearance like softer materials. Minimum clearance should be .002" for stock engines and .003" for high performance. Optimum clearance range for high performance applications is .003" to .004". Because of the stack up of tolerances on the block, shaft and bearing it is impossible to control clearance to this range in the manufacture of the bearing alone. Clearances must be measured at installation.
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Old 04-21-2003, 07:42 AM
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DV, In our shop we install the cam bearing holes at the 4 oclock position for #2,3,4. The #1cam bearing has two holes in it and should be aligned at the 4 oclock and the 8 oclock position. The #5 bearing should be installed at the 3 oclock position to help oil the cam and distributer gear. A camshaft has a constant load on it due to 16 valve springs holding it down. The vertical oil clearance is all at the top. At the 2 oclock position there is a lot of clearance! This may cause low oil pressure at idle. A camshaft should have a minimum clearance of .002-.004 according to Clevite engine bearings. If your motor has a Knocking noise, it would be a good idea to measure all rod and main bearing clearances. The thrust bearing on #5 should be checked also. If all checks out good then look at the piston pin clearance and the piston to wall clearance. Also check your fuel pump pushrod clearance. They can make more noise than you can imagine and is normally the last place people look for an engine noise. Good luck!!!
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Old 04-21-2003, 12:21 PM
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Thanks for the help guys. I had never heard this engine run, and I don`t know who built it the first go round, I`m useing a different crank and rods. I`ve got the bottom end mic`d and the clearence is right at .003, I just wanted to make sure about the cam bearings, whoever did build it the first time put sealant on the outside of the freeze plugs, they also reused the stock timing chain which was completely worn out and real slackish. the customer told me he didn`t know who built it, he got it with a vehicle that had got it from someone else. he also told me it knocked bad. I`ve replaced almost everything, and next i`m gonna check the cam clearence. Thanks again guys for the help.
DV
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