changing valves, info please

[Hondo]

Got at least one bent valve for sure, wondered if the corresponding cam has to be removed to change a valve, or can a valve be changed with the cam in place in the head?
Are valve guides replaceable? Real OEM shows a "valve guide" part number which is replaceable, but the part is discontinued. When a valve bends, is that guide automatically shot? Can a used guide be salvaged from another head?
Does the M42 cam require the special tool, or some other procedure for removing a cam so it doesn't crack? I've seen pelican parts DIY where they take the tension off the cam by placing rope inbetween the valve and valve guide, enabling the cam removal w/o as much danger of breaking cam.

[colin86325]

Got at least one bent valve for sure, wondered if the corresponding cam has to be removed to change a valve, or can a valve be changed with the cam in place in the head?
Are valve guides replaceable? Real OEM shows a "valve guide" part number which is replaceable, but the part is discontinued. When a valve bends, is that guide automatically shot? Can a used guide be salvaged from another head?
Does the M42 cam require the special tool, or some other procedure for removing a cam so it doesn't crack? I've seen pelican parts DIY where they take the tension off the cam by placing rope inbetween the valve and valve guide, enabling the cam removal w/o as much danger of breaking cam.

If you bent a valve, you're going to have to remove the cylinder head.

Aftermarket valve guides are available. Depending on how the valve is bent, it is quite possible that the guide is damaged.  Re-using guides is not a good idea and they are pretty affordable new.

It's a very good idea to use the cam tool when removing/installing the head--but many have done so without the tool.
M42 cams are hollow, so if you start at one end without evenly untightening nuts in a balanced manner, yeah you can crack a cam in half.

The rope trick you mention is for changing valve seals, springs, or retaining hardware.
 

No offense, but I hope you plan on taking the car to a mechanic, as some of your questions make me worry if you were to attempt the work.

Cheers,
Colin

[Hondo]

Naw, don't worry. I'll be doing it allright, but not before I do the tranny job in the 88.
I thought people would assume I pulled the head first. Common sense and all. I was more curious about whether I could change out the valve without removing the cam, because the tool is like $1,400 or something, isn't it? I sure won't be buying that, it would be cheaper to replace the engine. The rope between the valve and valve seat is supposed to take enough pressure off the cam that it can be removed without breaking the cam.  I've read the evenly untightening the cam caps won't prevent cam damage.
On the guides, believe it or not a bmw tech said the guide probably could be used but I doubt it. The main question is, are the guides pressed in, or is the head cast and machined? If the guides are pressed in I can take one out of a donor head.

[nicknikolovski]

Like colin86325 said, to take the cams out, just loosen the cam bearing bolts.                                        

Refer to this picture

Start from the middle, loosen the first bolt a quarter of turn, then go in a similar sequence as if you were doing a cylinder head, however loosen each bolt 1/4 of turn only before moving onto the next bolt. This ensures even distribution of pressure on the cam so that it doesn't bend and break.

Also ignore the red circles, they're just the lifters.

[peerless]

You know at first I wasn't sure what the hell you where talking about regarding the cam and the rope. But that makes since after I thought about it. Interesting, but unnecessary. Just be careful and take it slow. I have removed and installed a few of them so far without any problems.

Regarding valve guide replacement. I have some good news for you. Since the head design is 'cam over bucket' the valve has no side loads whatsoever. So very very little wear. Just bending the valve does not automatically ruin the valve guide. I have done 2 M42 heads, one had all 8 intake valves bent and the other had 4 exhaust valves bent, didn't have to replace any guides.

And yes the guide is pressed in and no you can't reuse a used one. The reason being is that you will most likely damage it upon removal. But if you feel confident enough. The problem is that if you mushroom any part of the guide during installation and don't catch it the valve could seize when the engine warms up. I have seen happen before on other cars so I speak from experience.

Good Luck with it.

Naw, don't worry. I'll be doing it allright, but not before I do the tranny job in the 88.
I thought people would assume I pulled the head first. Common sense and all. I was more curious about whether I could change out the valve without removing the cam, because the tool is like $1,400 or something, isn't it? I sure won't be buying that, it would be cheaper to replace the engine. The rope between the valve and valve seat is supposed to take enough pressure off the cam that it can be removed without breaking the cam.  I've read the evenly untightening the cam caps won't prevent cam damage.
On the guides, believe it or not a bmw tech said the guide probably could be used but I doubt it. The main question is, are the guides pressed in, or is the head cast and machined? If the guides are pressed in I can take one out of a donor head.

[Hondo]

You know at first I wasn't sure what the hell you where talking about regarding the cam and the rope. But that makes since after I thought about it. Interesting, but unnecessary. Just be careful and take it slow. I have removed and installed a few of them so far without any problems.

Regarding valve guide replacement. I have some good news for you. Since the head design is 'cam over bucket' the valve has no side loads whatsoever. So very very little wear. Just bending the valve does not automatically ruin the valve guide. I have done 2 M42 heads, one had all 8 intake valves bent and the other had 4 exhaust valves bent, didn't have to replace any guides.

And yes the guide is pressed in and no you can't reuse a used one. The reason being is that you will most likely damage it upon removal. But if you feel confident enough. The problem is that if you mushroom any part of the guide during installation and don't catch it the valve could seize when the engine warms up. I have seen happen before on other cars so I speak from experience.

Good Luck with it.

Regarding the guides, what you say makes sense too.
Aluminum is pretty soft. I'm thinking a tool could be made from a good valve, the stem would probably keep everything straight, but the valve seat-end of the valve would have to sit absolutely perfectly flat on top of the guide, (machine the "tulip" flat) and that end would also have to be machined slightly undersize of the guide diameter, so the guide could be pushed though the head, (by pushing on the valve tool). If you use a press to push it out, perhaps it would not mushroom.
My dad is a machinist, i'm sure he could cut a valve to make it work.
From what you are saying though, the guides should be OK. Thats one piece of good news.