Pushrods too short = misfire?
03-15-2014, 06:00 PM
#23
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Same suspicion, thought I'd revive this Hey All,
New to the site, but not new to twisting wrench's - I've been searching threads on an issue that we've been having with a fresh build on a 383 chev SB so I thought I would turn to you professionals - so thank you in advance as this may get lengthy...
And yes, I know that this is an LS1 site, but this is the best group of information as far as engine works go that I have found so you, are the chosen ones... I think that you'll be able to chime in on it based on basic principals.
So here goes-
The recipe:
1987 4 bolt Main 388 Stroker
Eagle balanced 3.75 cast steel crank
Eagle 5.7 Con Rods
Keith Black 9.9:1 hypereutectic pistons
Comp 270 .480 intake .498 Exhaust degreed 108
Stock Hyd lifters
Eldelbrock Alum E-Street 64cc heads
Eldelbrock RPM Air Gap intake
Roller Rockers 1.5's
So here is the issue - and yes, I left out pushrod length, that I will divulge in a moment as I think it's the culprit, but want your opinion...
Issue:
excessive knock in cylinder one, exhaust lifter
sounds like excessive lifter noise
can adjust value (tighten) by 1/8th turn, noise goes away for 30 seconds or so and then gradually comes back to where it was
if I adjust out the noise by tightening adjuster until it's gone, hangs the valve open and we get next to zero compression.
This by the way, only takes about 3/4 turn from zero lash to hang valve open.
checking the pushrod length, it currently has 7.74's and upon some research, the head instructions call for 7.90's so we are .106 short...
Quite a bit at almost a quarter inch by definition...
Nice lumpy cam drowned out by taptaptaptap. and not quiet like the sowing machine I see referenced. please shoot me.
Previous to rushrod investigation, lifter replaced thinking it was done so that elimates that, we have good oil flow out the top of the pushrod so I would say that eliminates ovalized lifter bore I would say, plus - this engine has less than 500 miles on it since the build / line bore from the machine shop. So I would HOPE that is good.
I have 7.9's on order but won't arrive until Monday due to a shipping delay-
Think I am on the right track?
As a side note, number 2 will dry foul the plug after a while - running normal heat range, I have no idea if that is a hint or not - leaning towards a possible valve misadjust - for the record - adjustment is 1/2 turn past zero lash on all with the exception of number one exhaust that is adjusted all the way just shy of compression loss and still has the noise.
Thanks for the direction, I could really use it-
any questions please ask, I tried to cover it all info wise but am sure that I left something out that could help-
New to the site, but not new to twisting wrench's - I've been searching threads on an issue that we've been having with a fresh build on a 383 chev SB so I thought I would turn to you professionals - so thank you in advance as this may get lengthy...
And yes, I know that this is an LS1 site, but this is the best group of information as far as engine works go that I have found so you, are the chosen ones... I think that you'll be able to chime in on it based on basic principals.
So here goes-
The recipe:
1987 4 bolt Main 388 Stroker
Eagle balanced 3.75 cast steel crank
Eagle 5.7 Con Rods
Keith Black 9.9:1 hypereutectic pistons
Comp 270 .480 intake .498 Exhaust degreed 108
Stock Hyd lifters
Eldelbrock Alum E-Street 64cc heads
Eldelbrock RPM Air Gap intake
Roller Rockers 1.5's
So here is the issue - and yes, I left out pushrod length, that I will divulge in a moment as I think it's the culprit, but want your opinion...
Issue:
excessive knock in cylinder one, exhaust lifter
sounds like excessive lifter noise
can adjust value (tighten) by 1/8th turn, noise goes away for 30 seconds or so and then gradually comes back to where it was
if I adjust out the noise by tightening adjuster until it's gone, hangs the valve open and we get next to zero compression.
This by the way, only takes about 3/4 turn from zero lash to hang valve open.
checking the pushrod length, it currently has 7.74's and upon some research, the head instructions call for 7.90's so we are .106 short...
Quite a bit at almost a quarter inch by definition...
Nice lumpy cam drowned out by taptaptaptap. and not quiet like the sowing machine I see referenced. please shoot me.
Previous to rushrod investigation, lifter replaced thinking it was done so that elimates that, we have good oil flow out the top of the pushrod so I would say that eliminates ovalized lifter bore I would say, plus - this engine has less than 500 miles on it since the build / line bore from the machine shop. So I would HOPE that is good.
I have 7.9's on order but won't arrive until Monday due to a shipping delay-
Think I am on the right track?
As a side note, number 2 will dry foul the plug after a while - running normal heat range, I have no idea if that is a hint or not - leaning towards a possible valve misadjust - for the record - adjustment is 1/2 turn past zero lash on all with the exception of number one exhaust that is adjusted all the way just shy of compression loss and still has the noise.
Thanks for the direction, I could really use it-
any questions please ask, I tried to cover it all info wise but am sure that I left something out that could help-
Last edited by justachevyguy; 03-15-2014 at 06:52 PM.
03-15-2014, 06:33 PM
#24
hptuners or efi live also.
Just add to the thread, I run 7.3 pushrods with an 04 zo6 cam. Everyone told me 7.425. 7.4 was too long and 7.35 also. I have about 45 on the preload with the 7.3's and its much better. No milling had been done to the l92 heads or the lq9 block with ls7 lifters.
Just add to the thread, I run 7.3 pushrods with an 04 zo6 cam. Everyone told me 7.425. 7.4 was too long and 7.35 also. I have about 45 on the preload with the 7.3's and its much better. No milling had been done to the l92 heads or the lq9 block with ls7 lifters.
