jwmbishop Posted July 1, 2010 Report Share Posted July 1, 2010 We are all pretty familiar with the sound of an exhaust leak - that poosh poosh exhaust sound. My kids truck started making that sound - at first he could could hear it only under hard load (I could not - I wear hearing aids and think that particular freq is isolated out). However it grew louder and started doing it at mild load and now even at idle. At that point I could hear it. I changed header gaskets and #8 was burnt badly while all the others were still nice white paper. Got it all back together and noise is still there - completely within the exhaust (can hear it even at the tip of right pipe). First thought was burnt ex valve - comp test gives 150 on all cyls and 7 spark plugs are equally cinnamon with #8 just a tad darker (but not black) - and these are well built heads. It is not down on power (or if it is is very slight where we can't feel it - 383 with lots of cam), and is under 2000 miles on build. I know it was broke in right - I have done hundreds of break-ins. (that sounds funny - I am NOT a crook!) This weekend I will throw a dial indicator at it to make sure I don't have a wiped nose on the ex lobe - kinda doubt it as I have never seen a wiped exh without a backfire - and hyd lifters are forgiving of the variance from base circle (unless its dumping its oil press) - but what else could it be? Trying to cover all bases with the simple stuff before I pull it and tear it down for a visual. So far I know to check for cracked dist cap/rotor, crossed or burnt plug wires (new Moroso Blues - no one has had em off), broken rocker/bent push rod, valve spring (no lash tick) and vacc leak (even tho plug was dark - and 850 rpm vac is steady at 12 not pulsy - nor changed from original tune). I am using the Accell HEI ign mod with rev limiter - could this go bad and effect only one cyl? Any other simple things to look for? Link to comment Share on other sites More sharing options...
PAPA Posted July 1, 2010 Report Share Posted July 1, 2010 Crack in the header? Link to comment Share on other sites More sharing options...
tps48 Posted July 1, 2010 Report Share Posted July 1, 2010 Maybe the suface of the header is a little warped,not bolting flat to head. Especially if flanges are mild steel. Link to comment Share on other sites More sharing options...
CuttingEdgeRacing Posted July 2, 2010 Report Share Posted July 2, 2010 Crack in the header? +1 Probably on the underside of the flange/tube Link to comment Share on other sites More sharing options...
jwmbishop Posted July 2, 2010 Author Report Share Posted July 2, 2010 Why would a cracked header or flange leak cause the gasket to burn or darken the plug? Link to comment Share on other sites More sharing options...
PAPA Posted July 2, 2010 Report Share Posted July 2, 2010 Why would a cracked header or flange leak cause the gasket to burn or darken the plug? It was just a suggestion. Those little "Grimlins" will drive you crazy. Let us know what you find. Link to comment Share on other sites More sharing options...
jwmbishop Posted July 2, 2010 Author Report Share Posted July 2, 2010 THATS IT - I refueled the thing after midnight! Link to comment Share on other sites More sharing options...
jwmbishop Posted July 10, 2010 Author Report Share Posted July 10, 2010 wiped nose. #8 exh has .030 less off seat travel than #6. Obviously hearing the result of no overlap (early close), poor evac (less time open) and excessive cyl pressure (late open). Oh well this time I will go with a little less cam - it was too much for the street anyway -eliminate the torrington and use a regular tapered cam (this was a custom square ground cam). Link to comment Share on other sites More sharing options...
racer61 Posted July 13, 2010 Report Share Posted July 13, 2010 wiped nose. #8 exh has .030 less off seat travel than #6. Obviously hearing the result of no overlap (early close), poor evac (less time open) and excessive cyl pressure (late open). Oh well this time I will go with a little less cam - it was too much for the street anyway -eliminate the torrington and use a regular tapered cam (this was a custom square ground cam). out-tricked yourself. If i had a dollar for everytime ive out-tricked myself. I might be able to afford my bad judgement. lol Link to comment Share on other sites More sharing options...
jwmbishop Posted July 13, 2010 Author Report Share Posted July 13, 2010 I refuse to acknowledge how many times I have outsmarted myself. Like I said - 1st time I have seen a wiped #8 (which for some reason is the most common) that did not produce a backfire when opening the throttle. I think it's because it is not progressed far enough (.030 is not really that much!) as I am really sensitive to this build (the first engine I ever blueprinted for ME) and paid close attention. I was sure hoping for something far simpler. The cam is a $300.00 (cam only) Schneider custom grind. I have used 100's of their cams (just not in the past 15 years) and the only 3 wipes I've seen were from not using enough of the assembly\breakin lube (or not getting full oil splash very quickly after start up). Neither applies here - wondering if they followed Crowers lead in nitriding depth reduction to lower manufacturing costs. Crower cams have always wiped easier than schneider (or at least used to). I'll send it back to Jerry and have him let me know what happened. We were expecting 400Hp and 430 FtLbs somewhere around 5500 - but the dyno ended up at 435/490 @ 4800 (and the curve started coming on at 1250 rpm - best idle at 1050). Oh well it was really not very street-able as empty it would fry the tires just burping it off idle too hard (but man did it pull a 4500lb trailer like nothing) - so dropping to a smaller cam will not make me cry (too much). edited to add: Or a roller! Link to comment Share on other sites More sharing options...
jwmbishop Posted July 19, 2010 Author Report Share Posted July 19, 2010 Hear that? The sound of me doing a happy dance! the cam is undamaged - the lifter split the pushrod cup and was not holding the correct geometry - the push rod being off center at the lifter end changed the effective profile. One new lifter and a gasket set and we are back on the road. Link to comment Share on other sites More sharing options...
racer61 Posted July 21, 2010 Report Share Posted July 21, 2010 - the push rod being off center at the lifter end changed the effective profile. uuuhhhh, does that mean its broke? Link to comment Share on other sites More sharing options...
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