General Question about Cylinder Heads casting process

[boostedsohc]

So I have run into a small dilemma but it might be OK.

So the SOHC 6G72 engine has cylinder heads comprised of 1 camshaft per head and 2 rocker sliders spring loaded with camshaft caps in the middle and end. Typically on say, the DOHC 6G72, the camshaft caps are line cut, drilled, and tapped for camshaft dowels. When this process happens, there could be slight variations in the line cut process and when mixing up camshaft caps (have heard a lot of people mixing them up) then the camshafts can bind because the cap bore now has a protrusion that binds the camshaft. On the SOHC however, is this the case? Every SOHC head has the same camshaft cap position, rocker sliders, springs, etc.

My scenario is that I picked up a second set of heads without the camshaft stay hardware, springs, rockers, lifters, etc in the heads. My plan was to use this hardware on the new heads. I was advised by the engine builder that we need to check to see if the cam fits because he is thinking the line bore on the camshaft caps will be off in comparison to the old heads. Is this really true? Or do I have nothing to worry about? If it comes to line boring, I will do it for sure.

I guess I have heard that they recommend keeping all of the heads hardware with the same head, which is fine, but in theory, I think the SOHC defeats this because the camshaft cap hardware is standard spec in every sense including spacing. What's your take on this and if there are any pros in here, that would be helpful.

[Ondonti]

You won't find much support for swapping cam caps that were machined as an assembly and not held to tolerances for the purpose of being swappable. Why would someone build high tolerance caps when they still have to cut the grooves in the head? Big waste of money.

If you got a head without caps and paid money for it, sorry.

[boostedsohc]

You won't find much support for swapping cam caps that were machined as an assembly and not held to tolerances for the purpose of being swappable.

What are you saying then? I can't do it?

What happens when you get new cams? Obviously the camshaft manufacturer must meet the specifications of the bore of the cam caps, am I right?

People don't buy cams and have to have the camshaft caps machined by a shop before they use the cams.

[tryingbe]

Are you trying to put new camshaft in or are you trying to put new cam caps in?

[Vigo]

Well you already said you were willing to do the line boring. If thats the case then you can make it work by throwing dollars at it. IF the heads are stock, untouched heads without cam caps, it would still be cheaper to toss them and buy a set WITH cam caps and not pay for line boring. Everything else about the heads is interchangeable other than the differences between slider and roller cam followers. You obviously wouldnt want to mix and match those parts, but you could run the full setup of slider or roller and it will work fine.

[boostedsohc]

I'm not sure you guys are following. All of the cam hardware is the same between a 6G72 SOHC and another 6G72 SOHC, my question is will the cam caps line up? My suspicion is yes it will, my concern is will the bore for the camshaft be the same between the heads if you moved the hardware from one head to the other? I would assume that it would, however if it doesn't, line boring is the resolution. That's my curiosity...

I will add that finding SOHC Heads that don't have cracks in the quench areas is hard to obtain. It took me a few months to find a set that weren't cracked.

Is there anyone that has any experience with reusing cam hardware from 6G72 SOHC head to another 6G72 SOHC head?

[86Shelby]

As for swapping caps; I've helped do it. I don't know the longevity of the engine though.

While I was in tech school during the engine rebuilding/machine class, a friend had damaged one of these V6 heads to the point it wasn't useable. We found a spare head at the school but it was missing the cam caps. The things we did to get it to work...well I don't recommend it. First, a few thousandths were milled off the cam pedestals on the head. Second, we milled a few thousandths off the caps. The school had no line bore machine and the quotes we got from a nearby shop that had one was more than what a refub head cost. So three of us held the head as straight as possible and we used the rod honing machine to hone the cam bores. That sucked trying to hold that head as straight as possible, pushing & pulling it along the honing bar, lube getting splashed everywhere and dripping down our arms onto the floor. What a mess. The hone didn't reach all the way through the head, so we had to repeat the process on the other end; oh joy. Thankfully all the BS worked. The cam spun freely and the bores were nearly dead-on to what the other head measured. A few weeks later the engine fired up and ran like a top.

[boostedsohc]

Well I am not saying the cam caps are mixed up in terms of order, just from one head to another was my question. I doubt that the bore would change at all, I was just concerned that the caps might look different even though the bore was fine. I guess time will tell. I pickup everything from the machinist tomorrow if all goes well with testing the cams and the aftermarket cams in the heads.

[Dr. Johny Dodge]

if you take the cap from one and put it on the other you will most likely not have a round hole where the cam goes

like swaping the crank caps or rod caps

the holes for the shafts are only going to be exactly round if the parts were maried to each other before the boreing / honeing bar came along

elsewise you will end up with a oval or squished circle which will cause you binding as the shaft , whatever it is , tryes to turn

knowing how the hole for the shaft is made is the answer to the question

[turismolover22]

Id assume since any SOHC and DOHC that has removeable caps are line bored, the onlyway to assure you have the correct alignment is to keep all the hardware from each head when you do parts swapping, cams, rockers, etc.This is the reason milling the head on an 8v due to warpage isnt always the answer. Sure the head gasket surface is now flat, but since it is now "permanently" warped everywhere else you will have misaligned cam bores.

[crusty shadow]

the cam caps are machined specifically for each head and each cam tower location. you can not mix and match caps without having to line hone the cam bores. it doesnt matter if its the exact same type of head or not. like stated above the cam caps are matched to the cam tower exactly like a rod cap or main bearing cap or you will have to line hone the head- no exceptions no matter what. having the head line honed will cost you about 3 times more than what it would cost to just pull a pair of complete heads out of the junkyard.

[boostedsohc]

I am going to play it by ear, I will know more tonight if the cams drop in or not.

[Sundance 6g72]

Im not sure what all is going on here but.... I have used cams from different heads in my heads without problems. I have always stuck with the same cam caps for reasons discussed above. Its just a good idea. Im sure you might find some cam caps that work fine and maybe some that are tighter or looser than others. As a general rule you run with what came with the heads.

[boostedsohc]

Just to quell all of your fears, the heads worked out perfect.

We dropped the cams in and used the camshaft hardware from my other SOHC heads on the new heads and assembled. The camshafts spin freely with little to no effort and the journals did not scratch or marr. So no line boring was required.

[crusty shadow]

have you checked the clearance between the cam journals and the cam towers? just because it spins over doesnt mean its correct. too much clearance on one cam tower and you will have low oil pressure across the head and you will wipe out the head, cams and all the valvetrain hardware.

[boostedsohc]

have you checked the clearance between the cam journals and the cam towers? just because it spins over doesnt mean its correct. too much clearance on one cam tower and you will have low oil pressure across the head and you will wipe out the head, cams and all the valvetrain hardware.

Yes, the machinist checked the clearance and said it's within spec and has just enough clearance to spin free but not too much clearance to move around inside the bore.

[Ondonti]

Im not sure what all is going on here but.... I have used cams from different heads in my heads without problems. I have always stuck with the same cam caps for reasons discussed above. Its just a good idea. Im sure you might find some cam caps that work fine and maybe some that are tighter or looser than others. As a general rule you run with what came with the heads.
Yes I actually remember someone could not get their camshaft to turn when they mixed up the caps. To think they are interchangeable by keeping them in the same arrangement is wrong. I don't know how somebody would actually measure and claim it was okay. In reality its a wait and see. Turning cold is different then when things heat up and move around. Good idea? Not at all. I would also not line bore a stock head since it changes the location of the camshaft which slightly changes cam timing. Waste of money for a stock head.

If you did this kind of stuff on a customers car that would be a terrible choice. Doing stuff like this on your own car is fine since you automatically take responsibility for it. I don't understand why it is thought that DOHC or SOHC makes any difference. Cam caps are cam caps. They are bored as an assembly. We all should understand that they won't bolt down the same on each cylinder head and therefore bores will not be perfect cap to cap, and boring machines will not sit down the same in each head just like they won't cut exactly the same in each head. Sometimes you can do things wrong and still land within tolerances.
Regarding the condition of the journals, I have some very nasty looking cylinder heads as far as journal condition goes and I just ignore it. I wouldn't worry about scored journals on the cam either as long as there are no obvious high spots that will actually chew up the aluminum. If there were I would just knock down those high spots.

[Vigo]

Not getting a good impression from this thread. Seems like OP came in, asked a question, didnt like the answer, and decided the people responding didnt understand what he was asking.

I understood what you were asking. The head and cam caps are machined as an assembly and cam caps are NOT interchangeable between heads unless you just get lucky, which you or may not have, since you havent put any miles on it.

I agree with Brent. If it's your own car, by all means take a chance and find out. I do that, Brent does that. But if it were someone else's car, or if you were paying someone to do it for you, you would want to end up with a head that had the original set of cam caps to work with. As i said, on a set of stock heads, it's cheaper to just get another used head with caps, then it is to try to fix a head with mismatched caps.

But in the future, you will probably never have to deal with this again because presumably you wont pick up spare heads that are missing critical parts, and you wont mix and match cam caps, so it will never be an issue again unless these mix-n-match heads end up failing.

[Rrider]

I swapped cam caps before on a non TD, no machining or honing.. and the clearances were way out of spec large. Motor still ran fine, but it was noisy.

[boostedsohc]

Not getting a good impression from this thread. Seems like OP came in, asked a question, didnt like the answer, and decided the people responding didnt understand what he was asking.

I understood what you were asking. The head and cam caps are machined as an assembly and cam caps are NOT interchangeable between heads unless you just get lucky, which you or may not have, since you havent put any miles on it.

I agree with Brent. If it's your own car, by all means take a chance and find out. I do that, Brent does that. But if it were someone else's car, or if you were paying someone to do it for you, you would want to end up with a head that had the original set of cam caps to work with. As i said, on a set of stock heads, it's cheaper to just get another used head with caps, then it is to try to fix a head with mismatched caps.

But in the future, you will probably never have to deal with this again because presumably you wont pick up spare heads that are missing critical parts, and you wont mix and match cam caps, so it will never be an issue again unless these mix-n-match heads end up failing.

I am satisfied with the answer that I was presented and I have one more question then.

If the cam caps are machined and each head has different specs, then why is it that cam manufacturers can make a cam fit every head of that engine type? If this logic of the assembly is line bored after the cam caps are cut is true, then that means before you install cams from the manufacturer that you should have the journals micced and have the heads line bored. I haven't really heard of too many people have their heads line bored for their custom cams. I understand that 90% of the time the cams are regrinds, but cams can be off just like cam caps from another set of heads so hence my constructive argument.

I rotated the cams a few times with the hardware attached and the cams rotate fine with no grooves.

[Vigo]

If you drill 1000 heads with the same boring bit, then all the holes should be the same size, and the same camshaft should fit in all of them.

The differences are where EXACTLY that whole was drilled in relation to the rest of the head. There are small differences there. That's why you can't always mix and match caps. The half-moon cut in the cap might end up being slightly offset from the half-moon cut in the head, and all of a sudden you don't have a perfectly round hole anymore.

[135sohc]

Camshafts are one piece and can be made with enough repeat precision that they don't need to be custom fitted for every cylinder head.
A mass produced casting has core shift and when it is multiple different pieces coming together no two are going to be identical, hence they are a 'machined matched pair'

[Rrider]

The half-moon cut in the cap might end up being slightly offset from the half-moon cut in the head, and all of a sudden you don't have a perfectly round hole anymore.

Right, looking back I'm pretty sure the motor I did the cap swap on had peanut shaped holes for the cams. But back then I had no idea. The head on the motor was bored slightly lower than the cap donor head.

[crusty shadow]

you need to forget about the camshaft, all the valvetrain hardware- those parts are not the concern. they will be machined to a specific specified size at the factory- for all intents and purposes you need to consider them exact copies of an original part.

cylinder heads along with all other parts that are cast will have production variances due to the casting process. those parts are cast in a mold made of sand. a worker takes a "plug" and then assembles that by hand and packs sand around it in the casting box. things like core shift, which worker was assembling molds that day etc will all affect the final dimensions of the part. things like lifter bores, spring pockets, cam towers will all have variances in dimensions due to those factors during the casting process. you need to consider a cast part a copy of a copy of a copy.
the longer the production run goes on the more variances there will be you have to consider each cylinder head as unique as a fingerprint. none of them are dimensionally the same the cam journals on the head may be in the same places, but the cast part of the head that they are machined out of will have subtle variances. one cam tower might be a couple thousandths taller than the one next to it, or slightly wider or slightly shorter etc. the line honing process is the only way to ensure those journal surfaces are perfectly in line with each other.

if those cam caps from a different head do happen to work then you messed up by not buying a lottery ticket instead because you got god damn lucky.

[boostedsohc]

you need to forget about the camshaft, all the valvetrain hardware- those parts are not the concern. they will be machined to a specific specified size at the factory- for all intents and purposes you need to consider them exact copies of an original part.

cylinder heads along with all other parts that are cast will have production variances due to the casting process. those parts are cast in a mold made of sand. a worker takes a "plug" and then assembles that by hand and packs sand around it in the casting box. things like core shift, which worker was assembling molds that day etc will all affect the final dimensions of the part. things like lifter bores, spring pockets, cam towers will all have variances in dimensions due to those factors during the casting process. you need to consider a cast part a copy of a copy of a copy.
the longer the production run goes on the more variances there will be you have to consider each cylinder head as unique as a fingerprint. none of them are dimensionally the same the cam journals on the head may be in the same places, but the cast part of the head that they are machined out of will have subtle variances. one cam tower might be a couple thousandths taller than the one next to it, or slightly wider or slightly shorter etc. the line honing process is the only way to ensure those journal surfaces are perfectly in line with each other.

if those cam caps from a different head do happen to work then you messed up by not buying a lottery ticket instead because you got god damn lucky.

That is exactly what the engine machinist said!