"I have a 350 out of a 71 corvette rpo
L-48 the engine had almost 50,000 miles on it when I got a hold of it and being a kid I decided to install a cam while the engine was out I chose comps xe268h-10 while I had the engine open I noticed it was really clean the cylinders still had a crosshatch there was no signs of any problems so the next week we installed it in my 69 Chevelle Malibu everything went fine through cam break in although valve train was noisy which I later read was quite common with this cam but at the end of cam break in I reached for the key to shut her Down and at that moment something let loose and she started knocking pretty bad so I shut her down immediately I tore the engine down this summer while I'm out of school and we could not find a problem so I took it to a my machinist who builds race motors Steve Smith and he mic'ed everything out checked the wrist pins found nothing Wong with the lower end then he looked at the heads and saw a ton of carbon build up which we also noticed when I tore it down so Steve suggested it may have been a price of carbon . Anyone else have this problem before? Well we decided to hone, ring and bearing it while its out hopefully will run fine now"
I doubt a chunk of carbon large enough to cause a sudden loud knock would form and break loose in a fairly new engine, but what I have seen frequently as a cause is stamped rocker pivot balls locking up and breaking loose due to lack of proper lubrication,or valve springs breaking or rocker studs pulling loose, and that can sound like a loud rod knock to some people, Id also suggest checking for spring bind with the stock valve train clearances yet an aftermarket cam installed, in short Id take a close look at valve train geometry and clearances, look for broken parts and check piston to valve clearance, before assuming it was carbon causing the issue you describe, a comps xe268h-10 cam may not look that much larger than stock but its large enough to cause several clearance issues like bent valves, if you don,t bother to check all the valve train and piston to valve clearances, in a stock engine, in some cases and simply installing that cam and finding the engine rotates with a breaker bar without binding after its installed is NOT checking clearances, its a great way to find out how expensive being lazy and not checking can me!
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L-48 the engine had almost 50,000 miles on it when I got a hold of it and being a kid I decided to install a cam while the engine was out I chose comps xe268h-10 while I had the engine open I noticed it was really clean the cylinders still had a crosshatch there was no signs of any problems so the next week we installed it in my 69 Chevelle Malibu everything went fine through cam break in although valve train was noisy which I later read was quite common with this cam but at the end of cam break in I reached for the key to shut her Down and at that moment something let loose and she started knocking pretty bad so I shut her down immediately I tore the engine down this summer while I'm out of school and we could not find a problem so I took it to a my machinist who builds race motors Steve Smith and he mic'ed everything out checked the wrist pins found nothing Wong with the lower end then he looked at the heads and saw a ton of carbon build up which we also noticed when I tore it down so Steve suggested it may have been a price of carbon . Anyone else have this problem before? Well we decided to hone, ring and bearing it while its out hopefully will run fine now"
I doubt a chunk of carbon large enough to cause a sudden loud knock would form and break loose in a fairly new engine, but what I have seen frequently as a cause is stamped rocker pivot balls locking up and breaking loose due to lack of proper lubrication,or valve springs breaking or rocker studs pulling loose, and that can sound like a loud rod knock to some people, Id also suggest checking for spring bind with the stock valve train clearances yet an aftermarket cam installed, in short Id take a close look at valve train geometry and clearances, look for broken parts and check piston to valve clearance, before assuming it was carbon causing the issue you describe, a comps xe268h-10 cam may not look that much larger than stock but its large enough to cause several clearance issues like bent valves, if you don,t bother to check all the valve train and piston to valve clearances, in a stock engine, in some cases and simply installing that cam and finding the engine rotates with a breaker bar without binding after its installed is NOT checking clearances, its a great way to find out how expensive being lazy and not checking can me!
related info
viewtopic.php?f=52&t=6237&p=19552&hilit=burnt+rocker#p19552
viewtopic.php?f=52&t=401
viewtopic.php?f=52&t=7716&p=29797&hilit=broken+valve+spring#p29797
viewtopic.php?f=52&t=181
viewtopic.php?f=44&t=6669&p=21369&hilit=locating+noise#p21369
viewtopic.php?f=52&t=399
viewtopic.php?f=44&t=6669&p=21352#p21352
viewtopic.php?f=87&t=4687&p=20859&hilit=tear+down#p20859
viewtopic.php?f=50&t=5893&p=18037&hilit=reluctance+pull#p18037
viewtopic.php?f=50&t=609&p=26934&hilit=reluctance+tear#p26934