I got a request today to talk someone through a bigblock cylinder head assemly. While not an expert I have done this many times and while it sounds like alot of work it takes only an evening to install the valves and springs right.
Thought I would share this with anyone would wants to try it themselves. I would certainly help anyone who needs advice or someone jump in if I overlooked anything.

I can certainly talk you through it but you will need a few tools. The big one is the spring compressor. Do you have one? If not you will have to rent one.
You will have to make a little tool. The card with the cam will tell the installed height. It is probably 1 7/8th or 1.875. I take a piece of bronze welding rod and make a piece with radiuses ends or rounded ends exactly this length. Then I take the lift say .580 add .060 for safety for a total of .640. Now subtract the .640 from the 1.875 and you get 1.235. This is the length of the second rod. I then join the 2 rods together with another piece about 3 inches long. Join the 2 rods in the middle roughly on a 45 degree angle with the 2 precise lengths paralled. All this is rough but the rods are exact. Solder them together to form a tool in the shape of a Z but the joining rod not touching the ends but connected near the middle. One end has the installed height and the other the open plus saftey value.
Now take a spring and retainer and put it in a vise and squeeze the spring totally closed. Measure from the end of the spring to under the retainer. This is the collapsed size of the spring. Again add .060 to it for safety. This value must be under the 1.235 height you got for the open value of your gage.
Also get a collection of shims from a speed shop and try to make an agreement to take back any un-used shims.
Now install a valve in the head with the valve seal in place. Be sure to use the plastic cap on the valve to protect the seal. Install the retainer with keepers and pull up on the retainer and insert the large end of the gage you just made. It should fit. If too loose add shims until it is just a snug fit. If the gage is too long you are in trouble and need a higher installed height. Look into different keepers or retainers.
Now that you have the installed height properly set remove the gage and push down on the retainer until it bottoms on the seal. Try the gage now and it should not fit. It should be too long. Another way is put the smaller gage in place while pushing down and there should still be clearance between the seal and the top of the retainer.
If anything doesn't work as I have said please get back to me so we can discuss the problem.
I might have overlooked something or you need to adjust something,
Do this for every valve, don't skip any. I have seen all but one valve have the necessary clearance but one was out and it dropped a valve.
Good luck
Norval

 

humm... wow... You got me all confused now norval. Reason is, I have heads that are assembled and am currently removing the valves to do some porting. It was all clear and simple in my head...the process of removing a spring was easy, compress the spring, remove the 2 retainer halves and voila...same thing to reassemble it. But now...I just read your post and I don't understand a word of it...and it has to do with assembling heads. Am I forgetting something?!

 

Lohkay. Didn't mean to confus you and if you are just taking your head apart and putting it right back together fine , but if you are building a high performance motor with new valves, springs , retainers and high lift cam throwing the parts together without proper checking for spring bind and retainer to seal clearance is asking for trouble. All cams also come with degreeing cards. On these cards is the recommended springs and their installed height. This is critical. Installed with too much height and they are not at their recommended pressure and if installed too tight you could run into coil bind and that is disasterous.
Anyone building a high performance motor should be checking. Even assembled heads bought over the counter should be spot checked.
This is a very high cause of failure when installing cams and just saying it will fit. It can be the cause of flat spots on your cam.
Check

 

I see. It was my intention to buy a new solid roller cam (my previous was hyd. flat)....so is this something I'll have to look into? I thought the install height (spring compression?) was standard cause I can't think of a way to change the height...The retainers always end up at the same spot on the valve no? Maybe by changing retainers?

 

Keepers can be bought with extra clearance and so can different retainers. If the valves are sunk a little into the head the installed height is too high then shims must be used under the spring. I have had to buy different keepers and retainers for doing the exhaust and different for the intake.
If you install that new solid roller cam you have to check. Don't take it for granted that your guides are short enough or the seals aren't too high. Nothing is really standard. I keep 4 different combinations in the shop at all times to solve these problems. Also my big block stuff fits my mustang. Springs, keepers, retainers are interchangable between the 454 and 302-351. Isn't that the pits?

 

the most improtant think to do when assy. heads is to use camsaft breakin compound on the valve stems and guides because if you use positive(teflon) valve seals very little oil will get to the stems for quite a while and never use positive seals on the exhaust valves because the exhaust need lots of oil or they will seize in the guides. :chevy

 

This is a great thread! Lots of good information because I have my heads at the machine shop right now having them enlarged for my new, larger valves. A question on lubricants for valve stems. My brother has some lead lubricant that he always uses on valve stems. Has anyone else ever heard of this? He swears by it.

 

if you are installing larger intake valves in a stock chevy head you must open the combustion chamber next to the valve or your air flow will be less than with the smaller valve because the side of the chamber blocks the flow because the valve is closer to it.

 

clem: I'd like to hear more about this not using PC seals on exhaust valves. I've never heard of it before, and I just assembled my heads today, hopefully I don't have to take them apart again.

 

since the exhaust valve does not see vacuum like the intake valves the oil does not get drawn into the guide and it even sees positive pressure which will keep oil out of the guide. i always use umbrella seals on the exhaust for this reason. if you use all teflon PC seals on the exhaust i would ream them out with a valve guide reamer to open them up a little. :chevy

 

Quote:
(I'd like to hear more about this not using PC seals on exhaust valves. I've never heard of it before, and I just assembled my heads today, hopefully I don't have to take them apart again.)

David,Don't worry.You are good for the go.The seals will wear in rather quickly.With you Iconel exhaust valves and the good guides you have you are in great shape.Also the lube will get caught in the upper part of the PC seal and lube for quite some time.The ehaust centerline of your cam will not create excessive heat any way.

When building a smog casting like a 781 or 049 in my opinion it is not a good thing to stack up the shims under the valve spring where the exhaust valve rotater was.This allows the spring to walk around and puts undue stress on it creating much heat and fatiging the spring for the possible early retirement of it.Spring cups are made for this very purpose.I use them on the intake as well and have the heads machined down to avoid using any shims at all.

When using new springs a spring pressure checker should be used as all will not be exact.If you want for example 135 seat pressure after springs has heat cycled a few times they will loose a bit.Usually 5-7 lbs.So my advice is to set that example at 140-145 seat in anticipation of the loss of pressure after cycling a few times.
It is not as much seat pressure as it is open pressure on the nose of the cam.Do what it takes to get the open pressure where you want it as long as the seat pressure stay within reason.Within reason meaning to prevent the valve from bouncing off the seat when closing.
Mant variables from cam to cam as in lobe design and variable of building a BB vs Small block due to the difference in the weight of the vavle train. So more or less it is one motor combination at a time as for optimum results.




[Modified by mountainmotor, 8:32 PM 3/14/2002]

 

if you are building a engine for drags or street the oil to the exhaust seals are not a problem but if you are building for endurence,circle track or boat racing where G forces come into play the oil can be pulled away from the valves for period of time you need oil to the exhaust guides. the first time the chevy V-8 ran at indy they kept sticking exhaust valves in engines because of the G forces in the corners. this is where the oil spray bars came from.

 

Norval,

A question on the valve lift. The numbers given on the cam card are for the cam, right? So do I multiply that by the rocker arm ratio? Or is the lift given on the cam card the actual valve lift?

 

Norval,
A question on the valve lift. The numbers given on the cam card are for the cam, right? So do I multiply that by the rocker arm ratio? Or is the lift given on the cam card the actual valve lift?


I don't know. On my comp cam card it has both. It gives the cam lift and lift after the 1.7 rockers. If you see lift figures like .343 this is cam lift so multiply it times the rocker ratio so you would have .343 times 1.6 or 1.7 = .583 valve lift. Look at the card and decide if this lift is reasonable. If it is around .500 this is valve lift. If it is in the .3-.4 range this is cam lift and needs to be multiplied.
Sorry I can't be more exact.

 

Makes sense. Mine is .520 (I) / .510 (E). Must be valve lift.

Thanks.