89GMCJOHN
I'm Awesome
Lengthy post but I want to give details to help guys out ...I just got done putting a 274 cam in my newer 350 - 5.7 shortblock (2k miles on it ) in my carburated 1989 Shortbox. After this cam change At COLD idle I would get an intermittent nasty deep sounding knock. Like a normal tap tap tap tap then a knock ......normal tap tap tap tap tap knock cadence . It pretty much goes away away after the engine was at operating temp for the most part . I have 60 psi at idle running my melling z28 pump SVHP. l It sounded like lower end - bearing type knock to me - so I thought I hurt it and it needed bearings . My very experienced racing buddy came over and said no that sounds like an intermittent sticking lifter hitting the cam to me because he thought it was coming from the front of the motor .
I came across a GM TSB for roller motors exhibiting cold knock that said you need to use a specific FRAM or GM filter with an anti drainback valve in it . I bought it and it didnt work AT ALL to get rid of the knock . NO IMPROVEMENT . BUT I did notice it held oil pressure ALOT longer in the block after you turn the key off. Hastings LF279 is what I bought which flows almost 5x the volume of the Fram PH5 I had in there and has the anti drain back valve I found out after alot of research . I will personally never run a PH5 again. The TSB goes on to say if that filter doesnt fix it drop a FACTORY recalibrated prom in that reduces idle spark to reduce cylinder pressure at idle and get rid of the knock. Alot of guys complain about the knock but just live with it and apparently it doesnt hurt the 5.7 motors longevity much.
Hmmmm I thought - since I am carbed and I run no computer and a mechanical HEI maybe its my idle vacuum advance which I didnt have hooked up on the previous cam - build . When I swapped the new cam in I also inadvertently connected the full vacuum advance port on my Demon carb to my distributor then simply adjusted the idle jump down.
I can tell you 110 percent when I disconnected the vacuum advance from my HEI and cold start it now - it doesnt knock a single stinking time at idle , off idle , accelerating etc. NOT A SINGLE TIME . It didnt knock when previously connected however going down the road under acceleration etc. AGAIN IT ONLY KNOCKED AT IDLE .
So I can tell you guys if anybody is having an intermittent roller motor knock disconnect / plug your vacuum advance if you are running one and try starting it that way and listen for the knock to go away. I can sit there while its idling , connect the vac advance hose knock knock , disconnect it - silence connect it knock etc.....if someone would have told me that was the cause I would have called BS and said no way it would be suffering from preignition etc and wouldnt cause that particular D E E P knock sound. Again it doesnt sound like spark knock - it sounds like a single sharp bearing knock . I may connect it to carb ported vacuum later on to see if that is ok but for now its disconnected and silent and Im happy ......FWIW
I came across a GM TSB for roller motors exhibiting cold knock that said you need to use a specific FRAM or GM filter with an anti drainback valve in it . I bought it and it didnt work AT ALL to get rid of the knock . NO IMPROVEMENT . BUT I did notice it held oil pressure ALOT longer in the block after you turn the key off. Hastings LF279 is what I bought which flows almost 5x the volume of the Fram PH5 I had in there and has the anti drain back valve I found out after alot of research . I will personally never run a PH5 again. The TSB goes on to say if that filter doesnt fix it drop a FACTORY recalibrated prom in that reduces idle spark to reduce cylinder pressure at idle and get rid of the knock. Alot of guys complain about the knock but just live with it and apparently it doesnt hurt the 5.7 motors longevity much.
Hmmmm I thought - since I am carbed and I run no computer and a mechanical HEI maybe its my idle vacuum advance which I didnt have hooked up on the previous cam - build . When I swapped the new cam in I also inadvertently connected the full vacuum advance port on my Demon carb to my distributor then simply adjusted the idle jump down.
I can tell you 110 percent when I disconnected the vacuum advance from my HEI and cold start it now - it doesnt knock a single stinking time at idle , off idle , accelerating etc. NOT A SINGLE TIME . It didnt knock when previously connected however going down the road under acceleration etc. AGAIN IT ONLY KNOCKED AT IDLE .
So I can tell you guys if anybody is having an intermittent roller motor knock disconnect / plug your vacuum advance if you are running one and try starting it that way and listen for the knock to go away. I can sit there while its idling , connect the vac advance hose knock knock , disconnect it - silence connect it knock etc.....if someone would have told me that was the cause I would have called BS and said no way it would be suffering from preignition etc and wouldnt cause that particular D E E P knock sound. Again it doesnt sound like spark knock - it sounds like a single sharp bearing knock . I may connect it to carb ported vacuum later on to see if that is ok but for now its disconnected and silent and Im happy ......FWIW
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