1973 455, forged 10.15:1 cr, 2000 miles since rebuild and put new exhaust on and noticed that it sounded "muddy" out of the driver's side bank. I did a leakdown test and all cylinders were around 15% except #5 showed about 50%. all leakage on all cylinders were into the crankcase and not through the valves or head gasket. cam checked out fine as well. any ideas???
Hate to sound like I am being sarcastic when I'm not trying :bglasses: but the piston in that hole DOES have rings on it? 50% leakdown with the air leaking into the crankcase sounds like a significant mechanical issue. There are only three paths directly to the crankcase from the cylinder: 1) Past the rings. The ring end gap is too big, there is a broken ring or rings. 2) Through the piston due to cracks or broken parts. 3) Through the cylinder walls due to cracks or breaks. If I had to guess, I'd say there are problems with the rings in that cylinder. In any case, I wouldn't run it again. ou: :af:
It does have rings in it and they were custom fit to each cylinder. I'm guessing that i have a broken ring. The big Buford is coming out saturday and i will post what i find. Thanks for the reply.
(4) Head gasket. Fingers crossed hoping it's that simple; it's another potential leak path into the crankcase if leaking towards the top area of the deck's sealing surface. If so, there will be some visible evidence around #5. Devon
Oops! Good point DW! I didn't think about the head gasket leaking and letting pressure go under the intake. uzzled: Hope it's that easy and just a defective gasket. ray:
I had the intake off when I had done the leakdown test and the air was clearly coming out from the bottom of the cylinder. I just removed the head and everything looks great. it looks like I'll be getting the engine hoist out tomorrow. thanks and stay tuned....
On my last new engine build I had a dead cylinder with zero compression while I was diagnosing a miss. Checked under a valve cover to find a bent pushrod and, ultimately, a broken lifter. It was one of those reminders to ALWAYS look for the simplest possible solution first.
Pulled the motor, found nothing EXCEPT my top 2 ring gaps were lined-up on cylinder #5. Now what? should i separate them 180* apart and stick it back in or should i run a ball hone in that cylinder and put a new set of rings in that cylinder?
from memory, somewhere around .020" top and .022" 2nd ring. all the cylinders have the same gaps. all other cylinders are fine
Also found the source of the "muddy" sound. pulled the cam and measured the lobes. first here are the new cam specs: 225* .318" intake lobe lift (.493" valve lift) 235* .335" exhaust lobe lift (.524" valve lift) TA dual springs 120# and 300# open as measured specs today: .316" intake lobe lift (.318" new) .296" exhaust lobe lift (.335" new) (.459" valve lift vs .524" new) the exhaust lobes have a "flat" spot on the lobe tops. time for a new cam. maybe i should stay under .500" lift.
