I am new and came for help on Gen V 7.4 Liter Cam bearing problems after rebuild

T

tulsatoolfool

Member
When I search on the internet for engine problem solving I end up here and decided to join. Rainy morning in the Tulsa area. Appreciate the knowledge and kind banter on the posts.
I had a Chevrolet 1995 7.4 Liter VIN N rebuilt stock. It has an Isky 256 cam in it so lift is .492 and duration is 202@.050. I used Driven break in oil BR30 at start up for break in of cam and lifters. Changed oil and filter and ran break in oil again for 500 miles. Then changed to HR2 10w-30. Oil pressure was okay to begin with. It has a stock M77 oil pump. Added an AllStar mechanical oil gage to get accurate readings. Around this 500 mile mark I could start the engine and have around 30psi at idle and watch it decline to about 10 as the engine warmed up and killed the engine at that point. The engine had King engine bearings installed. The rebuilders test stand showed oil pouring from the middle three cam bearings. Everything else looked good. So a set Durabond cam bearings were installed. After a few hundred miles of driving I have 10psi at idle and 22psi is all it will make. Tore engine down and cam bearing babbitt rubbed/flaked off on same bearings as before at different clockings about 1/2 way around. Main bearings look good and measure in tolerance. No debris in oil pump check valve.
Please advise on steps to take to find the problem.
 
well my first guess would be that the cam core is bent and/or the cam core bearing surfaces are not concentric or smooth,
simply based on its the center three cam bearing taking the brunt of the damage. but Id certainly verify the oil passages were free of abrasive crud from the previous bearing damage and all the oil passages were carefully cleaned and the cam bearing oil passage entrance's matched the blocks oil passages.
personally Id dis-assemble, remove all oil passage plugs,then clean the oil passages out flush the oil passages with solvent and a rifle bore bronze brush and reassemble and install oil passage plugs only after verifying the cam bore bearings are line honed, and bearings installed with a visual check the oil passages are clear,
Id also check the cam bearing oil clearances, to verify they are in the correct range, and coat the bearings with moly assembly lube prior to can shaft install, yeah a huge P.I.T.A. time consuming and costly, but it may prevent a repeat failure.

CHEVY BIG BLOCK VI

Top 10 Reasons to Build Gen VI Big Blocks (NOTE NOT MARK V) http://garage.grumpysperformance.com/index.php?threads/block-prep.125/ http://garage.grumpysperformance.com/index.php?threads/installing-splayed-caps.7267/#post-68837...
garage.grumpysperformance.com

Gen 6, 454 Rebuild(long)

This will be mostly a stock rebuild but being out of the loop for so long im sure i'll have some questions as i go along. Lots of pictures and hopefully you all will have some suggestions! The goal is to end up with a reliable engine that performs better than stock My block is at the machine...
garage.grumpysperformance.com
 
You must log in or register to reply here.
Back
Top