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TR4/4A Aluminum plug in TR3-4A cylinder head?

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TR4nut

TR4nut

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I will slowly be refurbishing a TR4a head I picked up - visual inspection shows that it could use a good bath to get rid of all the grunge in the coolant areas.

On these heads there is an aluminum plug embedded in the top of the head. Other than not understanding what it is for - is it something to protect? (i.e. avoid a caustic bath or something that may damage it?). Moss lists it as a not too expensive part, but is it a machine shop nightmare to replace?

Thanks,
Randy
 
Randy, you have to avoid the caustic bath like the plague, because of both the plug you speak of and also the PUSHROD TUBES are made of aluminum!!!!!
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Some pushrod tubes are steel, some are aluminum but I agree - beware of chemicals if you have you head hot dipped. A lot of modern heads are aluminum so it shouldn't be hard to find a safe place to have yours cleaned.
 
Thanks, I hadn't thought of those pushrod tubes. That would be a real mess.

Randy
 
The original plug was cast into place, so I'm not sure what Moss is selling as a replacement. Many racers are suspicious of the cast plug (it can corrode from below and start leaking coolant into the oil), so they tap the hole for a threaded plug.

And I agree about the pushrod tubes. They can be replaced, but the replacements frequently leak. If you do, be sure to put Loctite sealing compound on them.

BTW, I believe the hole's original purpose was as a riser when casting the head. Now of course it's just a hole that has to be plugged up, similar to the one on the back of the head (and the "freeze plugs" in a non-wet-liner cylinder block).
 
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