328 exhaust rear analyzing pipes

Those tubes are just an easy way to hook up an exhaust gas analyzer to each cylinder (the other end of each tube is hooked into the exhaust manifold near the exhaust port of each cylinder) -- they are supposed to be closed/blocked during normal operation.

But what's blocking that 4th one? Is the threaded portion of the old plug still present/stuck -- i.e., is just the "head" of the old plug broken off rather than the entire plug missing? That would be my guess (or maybe "filled" with an epoxy) -- either way, might be more difficult to fix than just getting and installing a new plug .

 

i have checked my engine and the long hexagon part under the missing nut is actually welded to the bar so unfortunately that hexagon part will not screw off.

the problem to either remove the epoxy or drill and use an "easyout" to remove the broken thread is that shreds of either the epoxy or drilled shavings will drop down into the pipe below.

you think it might be the broken thread.
the thread looks like it might be quite a small diameter maybe
about 4 or 5 mm.
there is a tool called an "easyout" which is used to remove broken threads.
suggest buy a new plug see how long and what diameter the thread is on that then drill a suitable diameter hole to suit the "easyout" only drilling a little depth at a time and then removing the swarf.
despite your best efforts you will probably have some small swarf drop down into the tube.
whether this is a problem maybe steve can comment.

when trying the "easyout" put a small spanner onto the long hexagon part to stop that from turning.

or just leave it as is since it appears to have been like that for some time?

good luck tony

 

You can just leave it...but if you wish it to be "perfect", then you would want to drill it in the center, then use a reverse thread "extractor" to remove the stub. You would need to be very careful, as those analyzer tubes are not terribly strong, and could easily be bent or damaged if too much pressure is applied with the drill. I would be inclinded to leave well enough alone.

If you do go for the fix, make sure you get all three parts as listed. The all important locking tab too. The tab is to prevent it from coming loose, without having to risk overtightening and damaging the tubes.

 

Functionally, you really don't have to do anything since it's still sealed (and it's only the very rare problem where a mechanic needs to get down to the individual cylinder level on a K-Jet system), but if I'm correct that those tube ends are near cylinder #4, I'd want to get it fixed too. 2 types of repair might work depending on whether:

1) the threaded portion is seized (i.e., the head broke off during attempted removal), or

2) the threaded portion is free (i.e., the head broke off during tightening)

For #1, it's probably a case of drilling a small hole (~1/8") thru the remaining threaded portion, enlarging the hole to the thread minor diameter, and then cleaning up the remaining material in the female fitting with a tap of the same thread size as the plug. (Try to be careful with the chips, but it not that risky if a few chips fall in -- you could even fire the engine up before you put the new plug in to try to "blow out" the line.)

For #2, you'd still drill a small hole in the remaining threaded portion, but then use an "easy-out" as the guys suggested.

(I won't suggest that you cut off the new plug and epoxy the head onto you fitting as is -- although I wouldn't bet that that has never happened )