Not sure if this worked or not but here is a photo of the piston. the valve had a 3/16" aluminium coloured mark on it so it must have kissed a couple of times after bending too
X2! last 400 pontiac i built had BBC rockers that screwed right in. the guys i worked with were pontiac racers from way back and insisted i make this change or i would be sorry. seems pontiacs don't do well with cam upgrades unless the rockers are done also.
Don't know about QC on new and reground cams today, and this may not even apply here, but in years past I've seen a few lobes not in sync or out of phase with the rest, cylinder to cylinder. I learned this one on a big block Ford that ****ed a couple exhaust valves and I couldn't figure why I didn't have as much piston/valve clearance on a couple cylinders as the rest. Once I zeroed my degree wheel, I went ahead and checked every cylinders lobes to make sure they were in phase with what I had just set up for #1. Again, I don't know about today's cams, but years back, some aftermarket cams were junk. Side note; I had a major leading brand name cam once that the bolt hole for the cam gear was so far off center, I was unable to use it in a Chrysler that had a cam driven Hilborn pump. Company refused a warranty claim on that one as well. Check, check, check.............. Tom S. in Tn.
Thanks for the clarification on the pushrod length Traditional Racing. That part completely slipped my mind when I posted earlier.
Sounds like the pushrods are too long and Yes you need a set of polylocks to make the valvetrain adjustable. if you can afford it I would get a set of screw in studs installed and convert to pushrod oiling as those hollow rocker studs were problematic even in stock engines. Hope this helps, bud
Just wondering what i should put in for studs? 3/8" top or 7/16"?how long? if i do this can i go back to stock pushrods? Any suggestions on rockers? if i use roller rockers do i need shims? found a set of scorpion roller rockers @ summit $225/set polylocks included. anyone have any comments on these? will they require shims and pushrod guides? i just spoke to the machinist and he says my press in studs are the bottleneck type and the hole is already 7/16" (he says they look original too) what do i use to put 7/16" studs in? helicoils?
i just spoke to the machinist and he says my press in studs are the bottleneck type and the hole is already 7/16" (he says they look original too) what do i use to put 7/16" studs in? helicoils?
helicoils is your best bet, cheaper too than setting them up for 1/2" holes, but that depends on the machinest and what he would charge
http://www.summitracing.com/parts/MRG-924G/ For the polylocks http://www.summitracing.com/parts/MRG-924G/ For the studs I'm not an expert, but have had alot of old pontiacs through the years I believe 61-66 389 and 421 pushrods are the same lenght and the later 350-400-455 pushrods are different. I"m a little curious about the valves used, If I recall the stock 64 389 4bll engine had 1.88 intake valves (a bit hard to find) while the high performance ones had 1.92's Did he subs***ute something else? My gut feeling is the wrong pushrods, Hope this helps, Bud
I got the valves in a rebuild kit i bought (they're elgins i think). The machinist said he used a checking pushrod to get the proper length for the p/r's. I am starting to lean towards helicoiling and screw in studs. and what the hell, throw in a set of scorpion roller rockers (poly locks included!) and drive on!!! i gotta spend another 250 on new cometics why not blow another 250 on rollers! wife's gonna kill me
When the valve kisses the piston, it bends the shaft so it can lock it into the guide. It is always difficult to determine what happened first.
I worked on a 366 Chevy truck engine that a was traded in by a farmer. They hadn't changed oil and wore some lobes off the cam. The dealership put a new cam in it and it had a miss so they sold it cheap because they thought it had a bad piston. When I checked it there was no compression in one cylinder. I pulled the valve cover to check the valve lash to make sure the valves were closing. When I rolled it over, the intake valve opened and closed but the exhaust valve started to open right after the intake closed. The exhaust lobe was ground wrong. I removed the exhaust rocker and then I had compression. I changed the cam and it ran great. New doesn't mean it's good.
I have to ask has any done a mock up and used modeling clay to check piston to valve clearance ? .100 is what you want in most cases . the other stuff has been mentioned already . Rod too long ? piston out of spec ? pin hole too high ?
I can't remember where i read it but, i read somewhere that the max lift in this engine is .510. my intake is .462 so i have .048 right off the bat if my ***umptions are correct.
Jim Hand's book, "How to Build Max Performance Pontiac V8s" is well worth the money of $14 at Amazon. It explains all of the parameters with nice drawings and pictures.
Update: The positive valve seals were determined to be the culprit. valves were to dry and stuck. Back to o-ring and deflector shields. Gonna get jim hand's book from chapters soon. Full roller heads now. Just gotta slap em on confirm p/r lengths and we will be rolling again!
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