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Classic XK Forum

Core (freeze) plugs in XK 3.4 engine

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razimm Rudy Zimmermann
Orange, CT, USA   USA
What is the best way to install the core (freeze) plugs in a 3.4 ltr XK engine. A couple of years ago I removed the rubber expansion plugs that were in the block when I bought the car and replaced them with the proper metal discs. I just placed them in the hole and hit the center with a ball peen hammer. This seemed to be good until one let go this past fall while on a road trip. I was able to use JB Weld to put that one back in place so I could continue the trip and get home. Now I plan to pull the engine and replace them all again but would like to know the proper or beat way to install them so I don't have to do this again. Any help is appreciated.

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MKJag Pat Ruster
East Tawas, MI, USA   USA
This happened to me on the way to a car show, not fun. My good fortune was that it was the center on under the carbs. I was upset because a machine shop had installed them when I had the block cleaned and honed. I had always done them myself prior to that. What you need to do is to install them with a little sealer on the outside edge to create a good bond and seal when you peen them in place. This way you should not have any further difficulty. Remember, there is little pressure on them with the exception of heat expansion.

Pat Ruster

jdrubin David Rubin
Rochester, NY, USA   USA
Upon completion of installation, the plugs MUST BE FLAT! Hitting them in the middle to seat them leaves them distorted and prone to falling out.

To do the job right, it is necessary to hit the plug all over. Initially, the plug is curved. Every part of that curve must be flattened. Light blows are required so no one spot is given a reverse curve. An air operated rivet gun might work, as these have controllable force from the hammer blows.

I use two hammers to do the job, because I don't trust my aim. I put one hammer on the plug, and hit it with another. In this way, I manage to hit the plug exactly where intended, each time.

When you are done, verify the plug is flat. If not, remove it and try again. These are available from good auto parts stores and are pretty cheap, so a screw-up is no big deal.

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razimm Rudy Zimmermann
Orange, CT, USA   USA
David, Thanks for your information. I did replace the freeze plugs last year and I used your same 2 hammer method. I did not know to check to see if they were flat but I did find that SNG Barrett sells a kit for this engine that includes a bar with an inward bend to go across each plug to keep it in. I guess I am not the first person to have one fail. This bar does require drilling and tapping 2 small holes for each plug but I thought it was worth it while the engine was out. I don't expect to have to do this again. So far I have put on 1500 miles with no problems. Thanks again for your comments.

bollux David Hadley
Brisbane, qld, Australia   AUS
Rudy, just another take on these damn plugs. Having seen a few fail, especially stainless, I fit a smaller inverted plug, similar to the XJ type in the inner hole {with sealer}, which I ream out. Much better contact area. Then place the original type over the top for appearance. They never fail, and you don't want the one at the rear of the block giving up! May be overkill but I have seen plugs come out on the first drive that have been fitted by "pros". Some say they have never had a problem but looking at old blocks, I don't think that's true.
Regards,
David Hadley

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MKJag Pat Ruster
East Tawas, MI, USA   USA
It is a pain in the a--. When my center block plug fell out on my way to a show I wasn't sure what happened until I got it back to my garage and looked. Had to take the entire intake side apart to replace the pug. The plug was .50 the Evans coolant was a bunch.

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