Head disassembly question or two

[jerry]

i bought a used head complete with valves et al. my goal is to disassemble it and go through the learning process at the same time.

it's my understanding that when dealing with the bottom end the rods and pistons are matched to a specific cylinder.

wrt the head, is it necessary to keep track of which particular cylinder the bits were originally installed? i.e., do i number each rocker arm, intake, exhaust valve, etc?

i don't have the nice OEM tool to depress all the valve springs at once. what have folks used to?

[ryanOC]

i think i kept all the rockers/valves/etc ready to be put back where they came from when i did mine

just use some masking tape and a sharpie to keep track

[wurlyvalve]

"it's my understanding that when dealing with the bottom end the rods and pistons are matched to a specific cylinder. "

Not really. It should be, on race cars they are. For example, where I work we fill the combustion chamber up with 'safety clean' using a burrette and measure the volume of the chamber to 0.1cc. We run our pistons 20thou down the block (don't use head gaskets) for squish - so a plastic dish is sealed over the top of the block with the piston at TDC and we measure the 'down bore' volume. Then knowing the down bore volume and the combustion chamber we remove the piston and have a 'sacrifical lump' on the top of the piston machined down to equalise the total volume - and hence compression ratio across all cylinders. Hence we get equal squish and equal compression. On a road head one tends to deck the block to get level, skim the tops of pistons to achieve identical squish clearances, then 'cc' the heads and equalise by opening up the smallest chambers to match the biggest - then re-skim to regain desired compression.

Short answer, heads are not specific to bottom ends on road cars.

Might have missunderstood the question. Wrt keeping pistons etc to block. Again, ideally you'd match piston dia with bore dia. Errr, one should do but....

For balance purposes weigh piston, gudgeon pin and rings. Equalise the rod and big end bolt weight. Bolt the rods together small end to small end and balance them by taking weight off the big end. And vice versa for the little end (I encourage reading David Vizards tuning BL's A series engine for excellent description of rod lightening and balancing). Match the big end dia for the journal dia. Don't believe the hype about balanced bottom ends. Vizard has documented examples showing no hp changes to the engine, and increased max rpm limits the order of about 50rpm before terminal failure. However he did notice extreme improvements in vibration levels.

"wrt the head, is it necessary to keep track of which particular cylinder the bits were originally installed? i.e., do i number each rocker arm, intake, exhaust valve, etc?"

It is simpler to. You don't have to. But setting up will take longer. Keep each valve with each cylinder and with the original head. You can swap around but you'll then spend longer lapping the valve in. This 'wears' the seat down and recesses the valve deeper into the combustion chamber hurting low lift flow - hurting high rpm power/torque. Rockers can be moved around also, but check the roller etc is in full contact with the valve tip. With conventional pads if they have worn a lip is created - should the cam (ie because a sportier one has been fited) push the rocker further the lip digs into the tip and pushes the valves sideways rather than down wearing the valve guide out quicker. Rocker locating springs really don't matter. Although if you have spacers fitted they will be matched to the shaft/rockers to give a nice 10thou side float and won't be able to be mixed around (BMW heads have springs as std). The valve springs can be mixed up as you like on a road car. Not so on a race engine as the seat pressure (another reason for not wanting to lap your valve too hard) will be determined by the valve spring cap to spring base gap and the free length/spring rate of your spring. Also a race head will have been measured up for valve crush.

In short, try not to mix stuff up.

"i don't have the nice OEM tool to depress all the valve springs at once. what have folks used to?"

Brute force, ignorance and a bloody big hammer. The rockers levered up one by one and the cam gentle tickled through the head with a hammer. My rockers shafts were a swine to remove. They weren't all that worn, but do watch for the bits that the rocker bushes are in contact with as they wear the shaft on one side, this creates a lip that catches as the shaft is pushed through the head.

To give an idea of how hard my shafts were to push through. I heated the head up around the rocker posts with a gas torch, put the head on our 30ton hydrualic press ---- and we blew the seal in the press!!!!! Ended up with the head on the bench, getting it toasting hot with a gas torch (we melted the rocker locating springs clean off the shaft) and hammering a punch onto the end of the shafts (the punch was so hot we had to wear welding gloves to hold it whilst we hammered. But I have been informed my head was more stubborn than most (removed form an engine that head been left outside unused for numerous years).

Cheers,

Glen.

[jerry]

thank you for your in depth discussion. your post will be printed, archived and digested slowly, as my brain allows.

[DukeRimmer]

It is traditional to keep the valve parts separate and in order using a plank with eight holes drilled and numbered. Rocker shafts have always pressed out easily for me (must be good karma?). My cam removal spring press is home made but it works. Have fun with it and let me know if you need any small parts to complete the project. I've disaassembled many, and assembled few.