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January 11, 2014

Front Sealing Block

[Click the pictures for a larger view]

The TR6 engine has a so-called "front sealing block" at the front of the engine block that closes the perimeter of the crank case and completes the sealing surfaces for the oil pan and the front plate.  It is a simple item, but is wrought with issues, mostly having to do with oil leaks.  First, the joints between the ends of the sealing block and the crankcase skirts presents an interesting sealing problem.  Because of the end clearance necessary to allow insertion of the sealing block,  the end seals must be of a resilient material that can be compressed on installation and can maintain sealing pressure for long periods of time.  Triumph's quaint solution to this is to use little pieces of wood that are forced into slots in the ends of the sealing block after it is in place.  Though this seems at first to be a primitive throwback solution, I'm not so sure it isn't a brilliant approach.   Some kinds of wood under compression are known to be very good fluid seals in applications like barrels or casks.  Gland seals of cork or other soft woods are still common.

Beyond the sealing issues, the sealing block is made of a non ferrous metal--some have said aluminum, but it feels more like some version of Zamac to me.  The common belief is that the threaded holes for the front plate and oil pan fasteners are prone to stripping.  The holes are tapped with a fine thread (5/16-24), and aren't very deep, so this could be true, especially with a little over-enthusiastic torquing.  

The threads on my sealing block were fine, but not wanting to tempt fate, and trusting all the anecdotal evidence, I decided to take measures to protect against stripping.  There  are a few sellers that offer a replacement "upgrade" sealing block made of steel to mitigate the stripping potential, but I considered these to be expensive over-kill.  There are other ways to provide strong thereads in soft materials, so I decided to improve my original block.  Besides, the outer edge of the sealing block is exposed to the elements, and a bare steel block would start rusting immediately.

I noticed that with gaskets installed, my sealing block stood a little proud of the crank case skirt.  As I was skimming the surface down, I found that the block also had about a 0.015" dip in the middle.  While this really isn't a serious problem, I was glad to find that when I got the block cut down to be flush with the skirt, the dip was gone.

The easiest way to  provide strong threads in a soft material is to use a thread insert.  These are "EZ LOK" brand inserts, but there are others.  The process is simple:  drill an oversized hole (Letter X in this case), tap the hole to the OD thread of the insert (7/16-14), and screw in the insert.  The inserts have a thread locking compound on the OD threads that activates when the insert is installed.

I had planned to use the inserts on all of the threaded holes, but it looked like a couple of the holes on the front side of the block were a little close to the edge for my comfort.  In the case of these holes, I used Helicoil type inserts, which need a smaller hole.

With the threads taken care of, I started looking at hte wood sealing blocks.  The originals were oil soaked and compressed, so it was hard to tell anything about them.  I had ordered a new one (it was an oversight--I meant to order two), but it didn't seem to bear much resemblance to the originals.  It was way too big, and had a large taper on one side.  Rather than trying to sort it out with the supplier, it seemed easier to just make my own.  I know a little something about woodworking, and the new block appeared to be a hardwood, possibly walnut or butternut (judging from color and grain, but it's really hard to make a good determination from such a small piece).  I had some walnut around, but finally opted to use white oak.  White oak has a closed cell structure that makes it essentially liquid tight.  I cut a strip of the right width and thickness, and I'll cut the seals from it when I install the sealing block.

Finally, a word about the paper gaskets.  In the same lapse of sanity as for the wood block, I only ordered one of them.  I opted to just make the other one from 0.031" gasket material, using the old originals as a pattern.  When I did that, I saw that my home made gasket was actually a better fit than the store bought one, so I made a second one.  My ordering goof ended up saving me a little money.  My hand-crafted gaskets in the middle, 40-year old used original on the right, new store-bought on the left:

The sealing block looks like it will be a good fit in the block, and I have a pretty high confidence in the threaded holes.  This was accomplished for about half of what some are asking for the steel reproduction block.

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