TBI Exhaust Valves, cast stems?

[1990Z71Swede]

Picked up a pair of low milage 193 Heads.
The seller told me he had a bit of an "oopsie" when taking them of the block.

Apparently he missed the head and hit a valve when tapping the head, trying to free the head gasket. To his surprise the valve brooke clean off

They seem super brittle, as if the stems where cast iron.

That can't be right...can it?

Also, I need a new exhaust valve
There seem to be a few different ones out there.
What fits the 193 heads?

 

[Hipster]

Picked up a pair of low milage 193 Heads.
The seller told me he had a bit of an "oopsie" when taking them of the block.

Apparently he missed the head and hit a valve when tapping the head, trying to free the head gasket. To his surprise the valve brooke clean off

They seem super brittle, as if the stems where cast iron.

That can't be right...can it?

Also, I need a new exhaust valve
There seem to be a few different ones out there.
What fits the 193 heads?

There's different versions out there. Lightweight or sodium filled for better heat dissipation etc. I've seen them break like that. I like to take a few measurements off the one I'm trying to replace because they are not always the exact same diameter and with replacements you can get into oversized stems and heads. I've bought Melling brand stock sized single replacements a few times and haven't had an issue. I don't know how availability is over there but usually an on the shelf part here.

 

[1990Z71Swede]

Availability for wear and tear items are not too bad but pricing can be absolutely crazy sometimes.

And because of that I source most of my parts directly from the US, either from Rock Auto or Amazon.

In this case I was hoping to find something used in good condition or better yet, NOS parts from our local version of Ebay. But for that it would really help to know what applications, if any, that used the same style exhaust valves as the 193 heads.

My plan for these heads is to give them a proper performance valve job, probaby give the valves a nice back cut too. And then give them a basic cleanup in the bowl and seat area. The valvesprings will be replaced with watever works with a Comp 08-300-8 cam. I also need to make sure that there is room for the .450-.480 lift

I'm hoping to persuade a local guy to do the valve job. The rest I can cope with myself.

 

[tayto]

TBI heads benefit from pocket porting (like most sbc heads). I wouldn't waste my time with much else aside from "detailing" the runners (remove imperfections). law of diminishing returns. my rebuild turned out well for what it is, but i would go aftermarket heads if I were to do it again (and probably will). i think you are not in north america so I get it. the TBI heads make for a nice daily driver and economy potential is there.

EDIT: I would definitely do a cam, wouldn't go bigger than a RV cam, even that might be a too bit big for stock bottom end.

 

[1990Z71Swede]

Yes, I'm not going to go crazy with the porting. Just some cleanup and blending of the valve job and casting near the seats.

I havent taken the valves out yet but I think they all have just a single seat cut so there is quite a bit to gain there and if the inlet valves are anything like the exhaust a back cut will gain a little flow too.

 

[Erik the Awful]

I'm currently going through an L98 marine motor and I found that the exhaust valves in some "heavy duty" applications have .372" exhaust valve stems instead of the normal .341" stems. Check 'em. Spares are available for the larger valves, but for 3x the normal price.

I've ported a set of 193 heads, but I still haven't fired that engine up. Do a cleanup port. If you're really good, you can open up the combustion chamber around the valves. I'm not that good. You can also clean up the swirl ramps in the pockets, but do not remove them.

 

[Schurkey]

1. Valve stems are not cast iron. Typically, chrome-plated steel, welded to the valve head which is a different kind of steel.

2. Kinda guessing the valve stem popped because it was still under spring pressure. Any reasonable crack would be immediately opened-up by the force of the spring.

3. Yes, measure valve length and stem diameter, and valve head diameter. I could send you some used TBI valves, refaced/back cut (or not, your choice) but shipping to Sweden would be an issue.

4. I've been warned away from back-cutting exhaust valves, based on the idea that it promotes reversion. I still back-cut intake valves, though.

5. If you have any performance aspirations, or intend higher-rpm/stiffer valve spring usage, I'd opt for one-piece valves rather than the two-piece, welded OEM valves.

6. I keep hearing that some OEM heads have "one-angle" valve jobs, but I have some trouble believing this. I have no idea how they'd get proper seat width without a top and bottom cut on the seat at least. One angle on the valve face (plus the margin, of course) I could believe.

 

[1990Z71Swede]

#1 I admit, the title was a little bit of a clickbait, but they sure seem very brittle. I get that they need to be surface hardened, but to me it seems like they have gone a little bit overboard here and hardened the stem all the way through.

#3 If all else fails I might just take you up on that.

#4 I think that is correct, not back cutting the ex valves and only touching up downstream of valve seat. From what I've read the 193 heads seem to be quite good on the ex side compared to the inlet side anyways so no need to overdo it here.

#5 That would be prefered of course, but maybe overly cautious? Good point none the less and I will measure the Rate of the stock springs and then decide if comp 983-16 springs are stiff enough to wreck the stock valves.

#6 I will take a pic of of a seat when the valves are out, You've probably seen them before, but for those that have not, like myself it might be of some value.

 

[tayto]

#1 I admit, the title was a little bit of a clickbait, but they sure seem very brittle. I get that they need to be surface hardened, but to me it seems like they have gotten a little bit overboard here and hardened the stem all the way through.

#3 If all else fails I might just take you up on that.

#4 I think that is correct, not back cutting the ex valves and only touching up downstream of valve seat. From what I've read the 193 heads seem to be quite good on the ex side compared to the inlet side anyways so no need to overdo it here.

#5 That would be prefered of course, but maybe overly cautious? Good point none the less and I will measure the Rate of the stock springs and then decide if comp 983-16 springs are stiff enough to wreck the stock valves.

#6 I will take a pic of of a seat when the valves are out, You've probably seen them before, but for those that have not, like myself it might be of some value.

yes this is why TBI heads like "straight pattern" cams

 

[1990Z71Swede]

Ahhh, fork. this is really bad.
But @Schurkey was right.
It is NOT a single cut valve jobb.
There is a Nice but shallow blend cut in the Combustion chamber, then the 45 degre seat cut, so far so god.... THEN, there is a deeeeep 90-ish degree cut creating a sharp step, before an even deeeeeper throat cut into a throat that is about 1.6" in diameter...