Pretty pictures + tech question re: head

[stockymcstock]

Okay so i just got my RB25 head back from the workshop.

it had 12 rooted valve guides (some asshat had bashed them out with the wrong size punch) so 12 new custom ones were made up from CA18 guides which have the same ID and OD but are a bit longer. hence, 4mm or so was machined from the end of them to bring them back to the correct length.

all 24 valves were re-seated and the spring assemblies re-installed.

there are NO differences in the heights of the inlet and outlet lifters.

so.... WHY THE HELL DO SOME OF MY VALVES HAVE DIFFERENT LIFT?!?!?!

the cams are installed correctly, torqued correctly etc. only SOME of the valves do this, there's five sets of valves which show the problem, but not all on the same cylinders, and on both inlet and exhaust sides! see photos:

sorry i couldn't get a good shot of the problem, but you can see how the two exhaust valves in the 2nd picture are different heights at full lift, wtf?





so what is going on here guys...?

[Jim]

hydraulic lifters? some have probably bled down while it's all been off the car.

[stockymcstock]

while i was in the shower just then i had that thought too..... yes they are hydraulic.

the discrepancy is quite large, like 2mm difference in some of the lifts, could they be so far off that this has happened? i hear if you store em upside down they can get air in them somehow, so what do i do to fix it? take em out, throw a G-clamp on them and tighten it up?

[Jim]

OHC hyd lifters will take up about 2 or 3 mm of slack depending on the type so yes it could well be the problem. The only way to pump them back up is nto apply oil pressure to them. Some types like in the SOHC 2S corona and (in particular) camiras are a right bastard of a thing and will actually hold the valves open until they bleed back down, meaning the car has no compression when you first put it back together.

the lifters in rocker arms like falcon, magna and I believe your motor will just be noisy until it gets oil pressure and has it for a few minutes.

best bet is to talk to the place that did the head for you. if there's a real problem you want to make sure they know about it BEFORE the head goes back on.

[stockymcstock]

sweet - i'll ask the guy and see what he says. i beleive they will pump back up like you said after a few seconds/minutes of running so it could be all right. they seat perfectly and everything, overall the head looks bloody fantastic, so i'll ask the man and see what he says.

[Rollin]

if you do just put it on, i would turn the motor over slowly a few times by hand to make sure nothing goes "chink" before starting it...but it should be ok to just wack on and start.

[AdrianSSS]

Neill you are 100% correct -



That certainly IS 24 valves of sexuality :D

[Jim]

so what did he say? fitted it yet?

[stockymcstock]

turned the head over, turned each of the cams over a number of times and the lift difference has all but gone away. didn't go back to ask the guy, too busy converting the goddam car to manual. 16 hours of the worst pain of my life.

block comes back next week and i'll assemble it all and see if it's free-running. i reckon it will be..... just. maybe not at 7000rpm though.....