In the top of the TR3-4 head is an aluminum plug which partly
dissolves when the head it put into a caustic tank. To replace it, I
have been tapping out the hole and replacing with a pipe thread plug,
which is foolproof, but the tapping sis not pleasant. Recently Moss
made available an aluminum plg with the proper threads to match the
hole. I just used one and it leaks, so thank goodness formy test
stand, where I found this problem. I'm going to tap it out and use a
pipe plug again, but I wondered if anybody else has had experience with this.
By the way, I recently had a Spitfire head sawed up to determine wall
thicknesses of ports. When I got the pieces back, I was astonished to
see the amount of crud in the water passages, all but blocking water
to several of the critical areas. this supports the notion that
having the castings cleaned in a caustic tank is a really good idea,
despite the inconveniences it causes in plugging up the passages that
were previously plugged with aluminum.