Engine Build #3: Top end

S3700155Now what in the hell is this? well, after i got the bottom end of the block assembled and went through my dial-in to set my camshaft and timing, it was time to start on the heads. on the oldsmobile v-8 cylinder heads, both the center exhaust posts of each head feed the exhaust crossover to the intake. good for cold weather/ not good for performance. Chevy cylinder heads would also use either one or both center exhaust ports for the same purpose, but it was not as severe as on the olds heads.  there are numerous ways to block these off using block-crete, epoxy, and there is also some kind of a goofy zinc alloy you can use(which can melt). the way i do it is melt down some scrap aluminum and pour it through the exhaust post openning until it fills just below the exhaust port on the back side. i melt the aluminum in a blacksmith’s ladle and use the rosebud on the acetylene torch for heat.  now it isn’t contoured at all for peak flow and there is a reason for this. if you contour it into a nice bowl shape, the edges of your plug will erode and flake causeing it to end up just like you see it anyways. the best i have found in doing this is to create a wall/plug of aluminum at the back of the exhaust port pocket and leave it. these are factory heads mind you.

 in this day and age if you want serious performance :buy aftermarket cylinder heads and say screw it. more often than not it is cheaper than jacking around fixing up factory heads. but here again, i am just seeking to improve a pair of factory heads a bit not re-invent the wheel.  on chevy heads for derby engines i have done this with good results, but just welding a plug into the intake seems to do about as much good on a chevy small block.

 Now the next step in fixin up my heads was to go throughS3700157 the valves.  Since i am on a budget i elected to do what i call a polish valve job, which is actually a service technique i learned in trade school from an old fart diesel mechanic i had as an instructor. basically you take lapping compound you can get at any parts store and spin it with a power drill instead of that ridiculous stick with a suction cup. i don’t have all day to mess with that shit. as you can see in the photo i have a quick-chuck style power drill. you put 3 or 4 dots of valve gringing compound on the face of the valve, stick it in as so and spin it with the drill at low speed; lifting and applying light pressure in 2 second intervals. you want to go low speed and yo don not want it to bark loudly or screech as it grinds. this causes vibration which will ruin the cut. after you grind, clean em off and check your valve action. your valves should pop closed and sit flush to the valve pocket. if it doesn’t that you may have bad valves or need to have everything sent to the machine shop. also while you’re at it, check your valve guides for excessive side play. if they are real sloppy your valves can stick open.

what you are doing by lapping the valves to the valve seats of the head is mating the two surfaces together to improve the seal of the valves. it also works to clean the carbon and other odd deposits off the seats. it is a cheap ass way of fixing up your cylinder heads rather than completely ignoring em after you go through the bottom of the block. this IS NOT an alternative to a valve job from the machine shop. regrinding the valve seats and valve faces completely is the right way to do this. a 3 angle valve job is also an excellent idea but i don’t really see the benefit of it unless you are going to be doing other port work on your heads and try to flow some serious cfm’s.

once you get your valves in order, it’s time for springs. although you can shim your springs according to wear, i always replace valve springs when i am replacing the camshaft. the valve spring tension must match the cam lift requirements otherwise you will have problems. i also replace my keepers every time. your retainer are a toss up. i elected to keep my rotators since they were factory. on chevy heads i usually omit the rotators in favor of solid retainers on both intake and exhaust. once you install your springs, take a rubber mallot and tap the springs to make sure the keepers seat fully into the retainers. you would rather have em shoot across the garage instead of comming apart and dropping a valve into your new engine!

it’s time to bolt on your heads. don’t get into a hurry here.  this is where the chevy and the olds engines really went two different directions. on your SBC’s, it can be as simple as bolting em on and setting your valve lash. on the oldsmobile: the rocker arms are not adjustable. actually they are a piece a shit. the aftermarket adjustable stuff isn’t much better it is usually re-fucked ford parts. so before you torque make sure your valvetrain will not bind- especially with an aftermarket camshaft.

for a non adjustable valve train: assemble your heads to your engine block with hand tightened head bolts. do not torque. put in a couple of push rods and a few rocker arms. check to make sure your valve lash is going to be spot on. you may need different pushrods or even convert to an adjustable valve train to make your camshaft work. you want a bit over zero lash for a hydraulic camshaft to preload the lifter(check your factory spec). converting to an adjustable rocker arm set up may or may not require some major machine work depending on what kind of heads you have to convert to an adjustable set up. this is why you don’t torque your heads until you know for sure.

if it looks good then roll it to maximum lift on both the intake and exhaust valve to check for valvetrain bind. now there are numerous ways to check for your valve clearance to the pistons and/or rocker arm bind.  the most unique way i have seen is using play-doh on the piston faces while swapping in solid lifters for checking. you then roll the engine over slowly and disassembe to check your pattern of valve to piston clearance in the play doh. .

 on a hydraulic lifter set up, an aggressive camshaft can be binding the valvetrainS3700161 during assemble and never know it as the lifters are collapsing as your spin the engine on the stand.  it will bind after start up and snap the front of the camshaft once you build enough oil pressure to pump the lifters fully. this can be due to either the valves hitting the pistons from incorrect piston: cam timing combination, valve spring coil bind, or the rocker arms are not slotted far enough and they bind on the pivots. a simple check is to stick a big pair of channel locks on the rocker arm at max lift of the valve and pull the rocker arm down until you have play on the push rods. this also checks for coil bind on the valve springs. i would not be doing the channel lock method on a race engine with aluminum rocker arms. this is a simple check that works well for a cheap build like this.

NOW, once you have ensured you valvetrain is going to be alright. torque your head to specification and assemble your valvetrain. start at the center of the head and work your way out. i torque the heads on in 3 stages: like 20-45-85 ft/lbs, have a sip of beer in between stages to give the head gasket time to crush.

i like to use the mr gasket head gaskets for oldsmobile they seem to hold up better over the fel pro. it’s also cheaper. for SBC, i tend to shy away from the metal head gaskets- especially on derby engines. even when using the ultra-copper i have had gasket sealing issues with stamp steel head gaskets. i had better results with the cheapo summit head gaskets for SBC over the stamp steel fel pro gaskets. it didn’t matter if it was a light or heavy casting heads either.

there ain’t much left to do on the olds at this point , but you chevy guys(and anyone else with an adjustable valvetrain) have to set valve lash. on these is do what is called the companion cylinder method. you basically take your firing order and chop it in half. so 1-8-4-3-6-5-7-2, 1 would be in the same position as 6, 8 the same as 5, and so on and so forth. this is how most engines for automotive work.

look at your rocker arms. you want to set your valve lash at or close to TDC compression of that cylinder that you are on to ensure you are not part way on a lobe. so to start, you bar the engine over looking at the rocker arms on #6. when the exhaust is just about finished and the intake rocker starts to move: you are at or near TDC of number 1 cylinder and can set your valve lash on both intake and exhaust of #1.

once set, you go about a 1/4 turn on the crank and watch the rockers on #5 to do the same thing as # 6  having both rocker arms in motion: this will center #8 at TDC compression and you can set both of those valves for lash. you just work your way down the line and should make 2 complete revolutions on the crankshaft ending up back at TDC#1 compression when finished.

the main reason i like doing it like this is because with aftermarket camshafts can be ground all over the place. so it may seem like you are on the bottom of the lobe and you really aren’t- causing lost performance from incorrect lifter preload.

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