Hey Guys, just putting a question out there. I just got my 64 gp runnin after a complete rebuild and bent the exhasut valve ever so slightly. Exhaust valve lift is .480 (some info says max is .510). Push rod is bent and there is a small kiss mark on the piston. engine ran for ten min after the valve bent. removed valve cover and push rod was no longer under rocker arm and arm was off to the side. What could cause this? Cam is a comp 275deh dual pattern cam. i also put on .051 thick cometic mls gaskets to lower compression and gain clearance. 1 thought is that the valve guide pinched the valve when it got hot and the valve never returned from full lift before piston reached tdc. This thought has some merit as the valve closed a little more as the head cooled down. Also the rocker arm nuts were tightened all the way down. Is this common? Orig arms, everything else is new (springs, valves pushrods, lifters etc.). I always ***umed with the old rockers that you should tighten them till they stop clicking but there is no more thread left to play with. Someone please correct me if i am wrong. Thanks everyone. If you need more info to help ***ess the issue ( i know it is hard to do without seeing it) let me know.
Anyone? Head is at the machine shop today and need some ideas for discussion. Wondering if there wasnt enough tension onm the pushrod and perhaps it moved making increased valve lift. any techy's wanna field this one with past experience or wisdom?
Hmm, pushrod length? As stated above i should have some thread left on the rocker arm studs when tightening them down no? There is no positive stop below the rocker like on roller rockers just the end of the thread cut to stop the nut. Perhaps my pushrods do need to be a bit longer. Which would be good because the machine shop bought the p/r's. Thanks
<TABLE cl***=SpecCard width=760><TBODY><TR><TD cl***=RedHeading>Specifications</TD><TD> </TD><TD cl***=style21> </TD><TD cl***="SpecLabel Intake">Intake</TD><TD cl***="SpecLabel Exhaust">Exhaust</TD></TR><TR><TD cl***=SpecLabel>RPM Range:</TD><TD cl***=Spec><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBRPMRange cl***=SpecBox value="1500 to 5800" readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBRPMRange> </TD><TD cl***=SpecLabel>Valve Lash:</TD><TD cl***="Spec Intake"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBValveLashIntake cl***=SpecBox value=Hyd. readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBValveLashIntake> </TD><TD cl***="Spec Exhaust"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBValveLashExhaust cl***=SpecBox value=Hyd. readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBValveLashExhaust> </TD></TR><TR><TD cl***=SpecLabel>Valve Timing:</TD><TD cl***=Spec><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBValveTiming cl***=SpecBox value=0.006 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBValveTiming> </TD><TD cl***=SpecLabel>Duration:</TD><TD cl***="Spec Intake"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBDurationIntake cl***=SpecBox value=275 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBDurationIntake> </TD><TD cl***="Spec Exhaust"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBDurationExhaust cl***=SpecBox value=277 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBDurationExhaust> </TD></TR><TR><TD cl***=SpecLabel noWrap>Lobe Separation: </TD><TD cl***=Spec><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBLobeSeparationAngle cl***=SpecBox value=110° readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBLobeSeparationAngle> </TD><TD cl***=SpecLabel>Duration @ .050" Lift:</TD><TD cl***="Spec Intake"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBDuration050Intake cl***=SpecBox value=219 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBDuration050Intake> </TD><TD cl***="Spec Exhaust"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBDuration050Exhaust cl***=SpecBox value=228 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBDuration050Exhaust> </TD></TR><TR><TD cl***=SpecLabel noWrap>Intake Centerline:</TD><TD cl***=Spec><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBIntakeCenterline cl***=SpecBox value=106° readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBIntakeCenterline> </TD><TD cl***=SpecLabel>Valve Lift:</TD><TD cl***="Spec Intake"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBValveLiftIntake cl***=SpecBox value=0.462 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBValveLiftIntake> </TD><TD cl***="Spec Exhaust"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBValveLiftExhaust cl***=SpecBox value=0.48 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBValveLiftExhaust> </TD></TR><TR><TD cl***=SpecLabel> </TD><TD cl***=Spec> </TD><TD cl***=SpecLabel>Lobe Lift:</TD><TD cl***="Spec Intake"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBLobeLiftIntake cl***=SpecBox value=0.308 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBLobeLiftIntake> </TD><TD cl***="Spec Exhaust"><INPUT style="WIDTH: 135px" id=ctl00_ContentPlaceHolder1_CamSpecsDetails21_TBLobeLiftExhaust cl***=SpecBox value=0.32 readOnly name=ctl00$ContentPlaceHolder1$CamSpecsDetails21$TBLobeLiftExhaust> </TD></TR><TR><TD cl***=ValveTimingHeading colSpan=2 noWrap>Valve Timing @ 0.006 Lift:</TD><TD cl***=style21> </TD><TD cl***=style31> </TD><TD cl***=style32> </TD></TR><TR><TD style="TEXT-ALIGN: center" colSpan=5><TABLE border=0 cellSpacing=0 cellpading="0"><TBODY><TR><TD cl***="VT Exhaust"><TABLE cl***=ValveTimingExhaust cellSpacing=3 cellPadding=3><TBODY><TR><TD> </TD><TD cl***=ValveTimingHeading>Exhaust</TD></TR><TR><TD cl***=ValveTimingText>Closes</TD><TD cl***=ValveTimingLabel>24 </TD></TR><TR><TD> </TD><TD cl***=ValveTimingText>ATDC</TD></TR><TR><TD cl***=ValveTimingText>Opens</TD><TD cl***=ValveTimingLabel>72 </TD></TR><TR><TD> </TD><TD cl***=ValveTimingText>BBDC</TD></TR></TBODY></TABLE></TD><TD cl***="VT Centerline">106 </TD><TD cl***="VT Intake"><TABLE cl***=ValveTimingIntake cellSpacing=3 cellPadding=3><TBODY><TR><TD cl***=ValveTimingHeading>Intake</TD><TD> </TD></TR><TR><TD cl***=ValveTimingLabel>31 </TD><TD cl***=ValveTimingText>Opens</TD></TR><TR><TD cl***=ValveTimingText>BTDC</TD><TD></TD></TR><TR><TD cl***=ValveTimingLabel>63 </TD><TD cl***=ValveTimingText>Closes</TD></TR><TR><TD cl***=ValveTimingText>ABDC</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLETig?
I believe that they may be saying that your pushrods might be "too long". I'd have to ask how much homework you have done on rebuilding and modifying Pontiac 389 engines. How much research did you put into the parts selection for the valve train? Unless the machine shop did get a guide too tight the problem probably lies with having valve train parts that aren't compatible with each other. That could include high valve lift with no valve reliefs, wrong length pushrods, springs that bind with the amount of valve lift, rocker arms with a higher ratio than what the rest of the setup was designed for.
I looked for a very long time for a cam which would fit inside this engine. I ordered a rebuild kit that included pushrods but the machine shop told me i needed different ones. I guess the question is . . . if the pushrods were too long or ratio (stock) was wrong, why didn't i blow every valve? Is 3000rpm enough to get valve float? the valve kissed the piston so lightly it it only put a shiny spot in the valve relief. Will this be a concern at higher rpm? (max 4500 rpm). As to pushrod length... (cuz i'm a bit new) if i had a pushrod that was longer than another but, rocker arm tension to the ball of the pushrod was the same for both, would this make a difference in valve lift. I would think the rocker stud nut would be at a different height but .480 of valve lift would still be .480 of lift. Like i said I'm new at this.
Update: It was actually the intake valve that touched the piston. And it has less lift than the exh valve. Machine shop thinks it may have been lubrication issue or not enough preload on the lifter/pushrod. He replaced the regular valve seals with positive valve seals and removed the caps on the springs. Is there any concern with doing this? The guy says that is how it is done with most hi-perf engines. The cometic mls gaskets have been heat cycled 6-8 times now, is this something i should replace? i am looking into pricing another one. Any commments would be greatly appreciated.
Generally, and I repeat GENERALLY, a longer p/r is needed with a performance cam. So you are correct in that ***umption. Let me explain and hope to shed some light for you. When I answer posts like this, I tend to get VERY layman in terms and verbage, so dont be offended, its just how I explain. O.K. When you increase the lift of a cam you increase the size or hieght of the cam lobe. You could say the distance from the center of the cam core increases to the top of the lobe. Now, as you increase this lobe height, and increase the lift off the valve, you start to close in on the diameter of the actual cam bearing journal size. Very large lift cams would actually have lobes bigger than the journal size- but wait. If the cam manufacturer did this, you could not physically get the cam into the engine because the lobes wouldn't fit past the bearings. So to cir***vent that, they will reduce the size of the " base circle " of the cam. The base circle is the area of the cam behind or under/opposite the cam lobe. Now with the base circle diameter being smaller than original, the cam grinder can increase the lobe size and you are still able to get the cam through the bearing bores. That leaves a new problem, when the valve closes and the p/r is on the base circle of the cam, there will be a large gap or excess clearance that MUST be made up. The engine would not only be very noisy, you would probably spit out the p/r's while thr engine is running or trying to run. This is where the longer pushrod comes in. With the stock length p/r, when the valve is closed, it is trying to follow the cam base circle and you have the rocker arm tip now moving off the valve tip. This is the term " geometry " you might have heard. So to correct the geometry you need the correct length p/r. TR
What are you referring to caps on springs? Who ***embled the heads? What is the installed height? What retainers did you use? I don't think it is push rods as comp spec's on the net doesn't note not to use stock push rods. Need more info Tig.
Traditions has a great explanation. I've had a difficult time getting people to believe that they need longer pushrods. What might have happened in this case is the push rod might have been short enough to come out of the lifter or rocker arm pocket or both and catch on the lip so it was effectively longer.
You need to make your valvetrain adjustable. Factory is 20 ft lbs on the rockers and your done. Most factory cams were around .410 lift. At least something similar to the comp cams roller tip 1.52 rockers and some 3/8 nuts. Screw in arp studs would be evan better but alot more work since there pressed in studs right now.
Bingo! The "torque to 20 ft. lbs" only applies to factory cams/valve train. Anytime you change the cam to non-factory specs, you MUST change the rocker arm nuts to the adjustable style- either a poly lock or SBC/BBC style, depending on rocker stud size. Seems like the 389's had a shorter pushrod than the '67- up 350, 400, 428, 455 engines did. Might want to check w/ Ace at Pacific Performance Racing in California, Butler Racing in Tenn., CVMS in Virginia, Pontiac Dude in Florida, or go to PerformanceYears.com and ask about the valve train issues.
Also, I don't believe your heads have screw-in studs... odds are great that you popped the rocker stud loose from too much lift, which allowed the pushrod to jump out.
Thank you Engineman, to the O/P, the cups you mentioned are known as oil deflectors or shields. When you install a Viton or Posi type of valve stem seal you remove these and the o-ring type seal from the valve stem. These cups would keep excess oil from running down the valve stem into the guide and past the valve and keep the oil from being burned in the combustion chamber. Installed height is the " valve spring installed height ". The specs for a valve spring will include a closed pressure rating as well as a open pressure rating. To insure these specs are met and to insure the spring doesn't bottom out or coil bind, the manufacturer establishes a installed height for the spring. There are several other reasons for this critical dimension too. Many factors can be contributed to pushrod length, and it is the responsibility of the person ***embling the engine to check and correct this. TR
Also, the difference between your .480 vs .510 (actually .512) lift is the rocker arm ratio 1.5 vs. 1.6
Traditions, you are correct about the reduced base circle vs. cam core diameter, but that cam uses a fairly stock lobe. It's smaller than some of Pontiac's Ram Air grinds, duration wise, but 'slightly' larger in lift- slightly. I've run 301 adv. duration cams from comp w/ standard pushrods in Pontiacs- never an issue. I'd still check the rocker stud for pull out.
Installed height valve on seat is 1.600" 117 lbs. Height at open 1.100" 232lbs. coil bind at 1.000".Installed= 1.600" -intake lift=.462" Installed minus lift=1.138" coil bind 1.000" Looks like.138" away from coil bind.This is okay on paper you must see what what have with your combo.These numbers are used for checking purposes.Supplied by Comp. Installed height is the dimension from valve spring pad to the underside of the retainer where the spring seats.Taken as a reference when ***embled supplied by the cam mfg. The one rocker stud is out because something had to give a little due to interference with piston to valve clearance.Those spring covers you refer to are used in stock engines from the factory for oil shedding. Did you purchase new retainers from Comp cams?Sounds like you may not have.Retainers from comp are for dual springs which is what you have.If you bought new springs?Your engine I believe came with single springs and a dampener.If this is so you need to confirm what retainers were used.As there is a good chance that stock retainers won't accommodate dual springs.Its hard to make a more concrete ****ysis without being hands on or a few pictures as a guideline for thought.Hopes this along with your dilemma. My2¢ Tig
I never know what I'm going to find. Even if the parts are sUpPoSeD to fit, I like to check a lot of stuff. It's not real hard. Then I know. http://www.iskycams.com/camshaft.php A few strips of clay on the pistons, then rotate the engine to see how squished they get is fast and cheap. Dan T
Dumb thought on this - still have the press-in rocker studs? Any chance when the piston hit the valve it could have loosened that stud a bit? Probably remote given it looks like the push rod is what gave out on it, but I think I'd check anyways for the few seconds it will take.
You guys want to hear something weird? My buddy had a trans am, 400 pontiac, he stuck a big cam in it and pulled a stud. Well, we had a few beers and I said, hell, I wonder if BBC studs would screw in there and we could use BBC rockers also. Sure as hell we tapped the head put ONE BBC screw in stud on it and a BBC rocker and went to town. Ran fine! Just another story from when we didn't know any better. LOL.
My machine shop guy tells me he had to go with different pushrods to maintain good valve train geometry. He is thinking lubrication issue to the valve. he says the positive seals may be to blame and is thinking we should go back to original valve seals and deflector shields. Any thoughts? he feels the 275deh cam is not aggressive enough to require fully adjustable valve train. Apparently the original studs do the rocker oiling and the rocker ball is designed for this.
engine builder says the stud is out but can not confirm if it came out before or after the valve touched the piston. Says valve was "welded" in the guide
Sounds to me like maybe the guides are too tight. You do need a small amount of clearance for the valves to heat up and expand. A lot of people are running the positive stem seals so I highly doubt that was the problem.
You NEED an adjustable valve train with just about anything past a stock cam , just change to an aftermarket rocker arm.
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