I picked up a head from the yard this past weekend and noticed a extra component on it that mine doesn't have. Could someone enlighten me as to what it is and what purpose it serves?

Here's a pick of the junkyard head with the extra springy thing next to the valve spring.


Here's the one I currently have:

Is that another valve? or some sort of decompression valve?

It appears to be a jet valve, but I've never heard of a 6G72 with those. What vehicle did it come from?

Whatever it came from, I don't think you want it on your truck.

Frank

Interesting, looks to be an early Sigma head. I would suggest reworking your own heads or get a different head from a yard.

i saw those on a montero at the junkyard and wondered the same thing?

It came off a 1990 Montero. Wonder if one of the previous owners pulled heads from a different vehicle at some point. I won't be able to rework my current head. The cam seized into the top bracket that held it in. Notice the 2nd "cradle" back. Looks like I'll be returning the head I pulled and looking for another one. Bummer!

Your head can be reworked. You can line bore the cam saddle and use a main/rod type bearing in the saddle.

Line bore, eh! That sounds better than pulling another head. I'll have to look into it.

Whatever you do, I wouldn't recommend replacing just one head unless you know what the other side measures on thickness - or unless you want to spend an absolute minimum. You can measure it on the engine at the outer flats near the exhaust ports, but it ain't easy to do and is much better done off the engine and clean. If you have to replace one head, it's better to pull a good uncut pair - then while you're at it, you have a good excuse to rework the entire top end - that is, if you're so inclined.

What does the cam journal look like where it seized? You may need to replace the cam.

It's interesting that the head was on a 1990 Montero. I don't know that I've seen an original head from a 1990, but that was the year they discontinued the EGR system. It may be coincidental that the EGR and MCA jet head systems serve a similar purpose, so I wonder if some of the '90 models had jet valves as standard equipment..... never heard that they did, but I can look for an interchange on the heads tomorrow. I would think if that was standard in 1990, I would have run across a reference to it by now, so I doubt it was a Montero OE head.

I guess it could also be an early Chrysler 3.0L head. Do the rockers have roller tips, or a flat slipper as a cam follower?

Frank

From the looks of it, the previous owner removed the lash adjuster so the jet valve wouldn't open, unless he popped them off for the picture?