So after figuring out that I need to make my own tool to replace a valve spring without removing the head, I have designed and am building one that will use the studs from two of the cam bearing caps as stable points and then presses the spring down. Figuring that it works ok, would there be any interest in me posting pictures of the tool for others to make? I figure that as rare as valve spring breakage is on these cars, it still must happen sometimes, and to have to remove the head to fix it is just silly when nothing else is bad. So yeah, give me any opinions on this....tata, and thanks again for all the helpful info on diagnosing my car's engine issues.
Nate Gundy
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'86 240DL, M46, K cam, 25/21mm sways

"So yeah, give me any opinions on this"
I'd try to remove the old spring first.

I haven't replaced a spring, but looking at Haynes, it looks like you need to remove the camshaft. Since (I think) you know how not to remove/install a camshaft, try doing it the other way.

Once off, pull out the follower/shim bucket. Since the spring is broken, you may not need a spring compressor (or to jam rope in the cylinder). Remove the spring keeper and lift out the spring parts. If the piston is up the valve shouldn't fall all the way in.

You can then re-assess the situation to see if you need a spring compressor tool to put in the new spring. eg. You may be able to compress the new spring on the bench and tie it compressed with strong twine?

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1980 245 Canadian B21A with SU carb and M46 trans

Yeah, I will have to remove the cam which I just put in a few months ago, but that's not really very difficult. I've finished making the tool now anyways, and it only cost around 25 bucks canadian to make, including 7 bucks for some JB weld, so it's not really a huge investment. I don't think that it would be very easy to pre-load the new spring and then be able to release that pressure once the spring went into the car...I just can't figure out how there would be enough clearance in there. However, those are good suggestions and I shall look into them anyways. Thanks,
Nate Gundy
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'86 240DL, 260K miles, M46, K cam, 25/21mm sways, and now failing engine...

Yes definitely post. If someone goes to the work of figuring something out, it would be a waste to us as a whole to loose that knowledge.

A side thought here; how are the valves held closed while the spring is depressed? Sometimes air pressure is used via an air hose adapter to the spark plug hole.

the trick I'm going to use, since I'm on a low budget and have no air compressor, is to fill the cylinder with nylon rope and then compress the cylinder enough to hold the valve up there...should do the trick, and I've heard of others doing this before.
Nate Gundy
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'86 240DL, M46, K cam, 25/21mm sways

I say.. Yeah post some Pics.

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'75 Jeep CJ5 345Hp ChevyPwr and two motorcycles: it wasn't Volvos safety , it was Longevity that sold me