I installed a set of PRW roller rockers 1.5 ratio on a stock set of 318 heads. I am having a problem with the rockers on the intake valves hitting the spring retainer before it contacts the valve stem. the intake valves have a shorte amount of the stem protruding out of the top than the exhaust.

question.

can i change the valve spring retainers to something that will expose more of the valve stem (any part number suggestions would be great). Will that change valve spring pressure enough to make a difference?

or can i just add valve lash caps to trick my rockers into thining that the valves stems are taller.


I am kind at a loss here, has anyone lese run into this problem?


P.S. I was running stock steel stamped rockers, oredered the new stainless steel rollers from prw , along with new shorte pushrods to allow for proper adjustment.


Thanks for any advice

Luke

 

Sounds more like a rocker arm geometry problem. I have never heard of them before. How did you decide the pushrod length? I have an adjustable pushrod that I use to determine the correct length of the pushrod. When a machine shop checks spring pressure they add shims underneath the springs to correct the spring pressure. That causes more or less of the end of the valve stem sticking out.

 

I measured pushrod length by using an a adjustable pushrod after toruqing to specs the rocker onto the head.

I am not sure what you mean by valve train geometry, the rocker shafts ar fixed so there is really no way that the rockers can be either up or down or front or back so the geometry is really set by the manufacturer, am i correct?

the set i ordered is made specifically for the application i have, but for some reason the valve stem that is exposed above the retainer on the intake valves is shorter than on the exhaust valves, thus by the time the roller contacts the valve stem the base of the rocker has already contacted the spring retaining washer, i am not sure if that makes any more sense.

 

I understand what you mean, I used a Comp Cams 744-16 retainer with their 901-16 spring and that depth changed for the better. Not completely sure if this retainer fits a stock spring without some measuring or hand fitting. You could check your stock one against their advertised dimensions.
The geometry of shaft rockers mostly relates to how the roller moves across the valve stem through the total lift. This can be affected by valve stem height, rocker (true) ratio etc. If you go with a lash cap you may need a different length rod so the rocker adjuster is not turned in too far.

 

That makes sense. I was gone all weekend so today will be the first time in a couple days i will get to work on it i am going to take some measurments and get a little more info as to what i am working with(spring size wise and all)

So you used the com retainers and it gave you more of the valve stem exposed?

Thanks

 

Not really more stem exposed, the OEM's are flat with a square edge, the others are tapered toward the edge with very little edge. This gives a bit more room under the rocker near the shaft. This is on a 302 casting head.

 

Ok i understand now. I got in there tonight and was able to clearance a couple of the rockers that were the problem, part of me thinks it is that just a couple of these rocker arms are cast a little larger than the others, otherwise everyone of my intake valves would be hitting , but that isn't the case, only a couple of them are.

my other thought is what if someone who owned the heads before me had the pedestals machined and that is why i have a clearance issue. if the pedestals were machined down just a little bit it would lower the overall height of the shaft makeing clearance of the rockers an issue.



i am hoping that clearancing the couple that were an issue and setting the valves right takes care of it.

i will let you know what i find out

thanks

Luke

 

Luke here is a good read.

http://www.mopartech.net/showthread.php?t=8434

 

Thanks for the article that explains a lot. i looked last night and couldn't find any Mopar specific rocker shaft shims. all i found was some for fords, and i don't want any blue oval parts in my car if i can help it.

Do youguys know of a specific mopar pedestal shaft shim kit.

Thank s

Luke

 

http://chucker54.stores.yahoo.net/rocshafshim1.html

 

sweet thanks. i will let youknow what i find
out

 

Ok well i got everything hooked up and set and started turning over the engine and i cant get it to start.

thinking it had something to do with the new rockers i put my old ones back on and still nothing.

i check for spark and i am getting 12 volts to the coil with the ignition in the run position. when i turn the ignition switch to the start position and crank the motor i get about 8 volts and barley a noticeable spark.


I ran a hot lead straight from the positive side of the battery to the positive side of the coil and the thing fired and ran almost before i turned the key. I am not so hot when it comes to electrical stuff but that would tell me that my ignition switch is not working correctly right?

any thoughts would be great

Luke

 

Check your ballast resistor first...easy to do on ohms.

 

If this is your wiring: http://www.mymopar.com/downloads/1965/65BelvedereB.JPG

The Brown should have 12v at start then to coil.

The Dk Blue should have 12v at run then through ballast resister 8v to coil.

Basically needs more voltage at start as the start motor "steals" voltage from the ignition circuit.

 

Sorry , forgot to mention i am running a pertronix ignition with no ballast resistor, as per the installation instructions, and the car was running great.

I ave a factory manual and looking at the harness diagram i have been mapping it out ,

What i have found.

pulled the ignition switch i read 0 ohms when i check the switch from the bat to ign1, and ign 2 port
i even went as far as to hook up the battery side of the switch and turn the key to the start position while checking the ign. 2 port and i get just under 12 volts.

not sure why i am getting only 8 at the coild

resistance in the wire? why so suddenly?

sorry for not giving you guys all the info first.

 

Well i thought it might be the ignition witch but i was wrong so now i am going through the harness and checking connections. i fund an article that said if you are drawing more than .2 volt to the starter when cranking that your positive battery cable is bad and should be replaced. half of me thinks that my starter is bad because it doesn't wind down the way it usually does after you crank it.


I HATE ELECTRICAL STUFF !!!!!!!!!!!!!


I don't want to just keep throwing parts at this thing, but my factory manual says that if the reading on volt meter is over .3 volt when you run it between the starter post and the positive battery terminal that your started is most likely bad.

Any tips and tricks are most appreciated at this point.

 

Sounds like your on your game. Any poor connection will create resistance which generates heat and a voltage drop after that connection. What I do is "hopscotch" which is clip to a good ground start at 12v then move down that circuit before and after each connection point. The 12v should be present at each as you move along, when you see a voltage drop you have found a bad connection. Many times in old cars and my work a poor connection or switch will not show a poor resistance "ohms" reading, but show up only when you apply current.

 

it is weird i have 11 volts in the run position , but once i turn the ignition to the start it shoots down to 8 .

i am going to replace the positive battery cable because that is cheap and i am still running the stock one, then go from there.

Thanks

 

EUREKA!!!!!


Well i need some validation here maybe am still wrong but you guys tell me. so before i had 11.5 volts at the run position. when i crank it i would get 8.5 volts, not enough to fire the car.

so i pulled the leads running to the starter and when i turn the key to the start position i get 11.5 volts so that tels me that the starter/ positive battery cable is pulling to much voltage and robbing my coil of the neede volts to give me good spark.


does that make real sense or just Luke sense unfortunately not always the same thing.


Thanks

 

Check your battery then. Could be bad.

 

I am getting 11.5 volts off of t battery and that is after it has been sitting for three weeks and been cold cranked about 100 times, trying to diagnose this thing

it a yellow top optima

 

11.5 isn't good...try charging it and sell if it retains a charge of 12 vdc or higher.

 

FIRST ALL THANKS FOR ALL OF THE GOOD ADVISE.


HERE IS WHAT ENDED UP SHAKING OUT. THE STARTER WAS BAD , THAT WAS ROBBING MY VOLTAGE FROM TO THE COIL IN THE STARTING CIRCUIT. ALSO THE ROCKER ARMS ON THE PASSENGER SIDE ENDED UP NEEDING TO BE CLEARANCED (QUITE A BIT) SO THAT THEY WOULD NOT HIT THE VALVE SPRINGS. FOR SOME REASON UNKNOWN, THE VALVE SPRINGS/ VALVE POSITION ON THE PASSENGER SIDE HEAD ARE POSITIONED IN TWORDS THE CENTER OF THE MOTOR MORE THAN THE THE DRIVER SIDE, MAKING CLEARANCE AND ISSUE. ONCE I TOOK THE ROCKERS ON AND OFF ABOUT 100 TIMES I FINALLY GOT ALL OF THEM CLEARANCED CORRECTLY THEN SET AND THE MOTOR FIRED RIGHT UP NO PROBLEMS.


THANKS AGAIN FOR ALL OF THE HELP

LUKE

 

Good job and thanks for the update.