.... Damn, I totally missed all the discussion about the Typ4 cam, decompression etc.
Over on FtE, I have a thread about my '88. I've tried for a couple of /years/ now to get my Typ4 cam to work(the first engine I threw it in was probably a bit high on the valve spec - the pistons were hitting the valves so much that it made /no/ power. And no, you couldn't really hear it.
Put a stock cam back in? It ran just fine. Tried like three times to get it to work on that motor, back and forth.
I also ran into an issue with the next motor, which I had fully rebuilt by a local shop. That just got a stock cam. After a few thousand miles, it started to tick.
A few more thousand and I found that the #1 exhaust guide was completely gone.
Upon disassembly I found that the passenger side head had not been recessed to spec. /every/ valve had hit, some worse than others.
The driver's side was within spec, and there was no valve marks on the pistons. Imagine that!
When rebuilding from that, I had got a set of 'decompression' gaskets from a guy on the forums over there - three layers of thin steel with two layers of Victor Reinz material in between A good .110" thick. Tried to use the Typ4 cam, and while there were no clearance issues... it just didn't want to run right. Lots of white smoke.
Ended up putting the stock cam back in... and found the same issues, but less. It would at least run cleanly with the stock cam(note: adjusted injection timing on both cams).
I ran that for a couple thousand miles, until the gasket started to leak. Despite having /lots/ of copper-coat on all the steel surfaces, it was getting lots of bubbles in the radiator.
Note that I suppose I should have retorqued the studs - I was running ARP studs initially torqued to 120 ft-lbs, but never touched them again(stock gaskets don't require it).
One head(that had apparently been where the leak was) had a bit of a crack on the underside. I didn't have another handy, so I just threw it back on with stock gaskets.
Surprisingly enough... No leaks as far as I can tell.
And it ran *much* better than with the decompression. Far easier to start, no 'smoking until it warms up' etc.
That ran for another few months, during which I installed a bigger turbo, got it maxing 30+ PSI of boost... and then the engine threw a rod one cold morning as I was starting it up(day after black friday).
At which point it's sat, waiting on some time and money...
I'll note that even now, the radiator is perfectly full. Still no water leaks, even with the oil pan having some nice big holes in it!
Out of all this, I have come to the conclusion that:
1. I don't trust rebuilders. If you have to have a machine shop do work, double check it yourself! Cheap micrometers and calipers are good enough, and really cheap.
2. IDIs /do not/ like decompression. Stock gaskets are great, and shouldn't be messed with.
If you can find extra-thick one layer gaskets, great... But I wouldn't trust any layers of metal not to leak over time.
3. Recess the valve seats for extra clearance. Near as I can tell, the seats have plenty of material, and it should be trivial to recess them, say, .030" without impacting function.
4. IDI valve guides need lubrication - all of the heads I've seen have some guide wear.
I've also found that simply /not having/ the valve stem seals... does not cause smoke or noticeable oil loss.
Next build won't have any guide seals - better to burn a little oil than to wear the stem.
Also, considering both sides are under /pressure/(from the turbo) and not suction as in a gasser... getting enough lubrication may still be hard.
