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February 13, 2014

Cylinder head.

Been working on the head for the past month or so, and finally finished it.

The TR6 cylinder head is a 60-pound brick of cast iron.  It's pretty ordinary in every way, providing two vertical valves for each cylinder, and a separate port for each valve.  A conventional rocker shaft holds the twelve rocker arms.  Mine was appropriately greasy, dirty, and rusty.  Here it is after the rocker gear had been removed.

First, I stripped out the valves ans associated parts so I could inspect and measure them.  Valve stems were right at or slightly outside the spec range, so this meant new valves.  Some valve springs were slightly out of spec for length too, so I ordered a set of springs.

I don't have a good way to accurately measure the valve guide bores, but judging from the fit of a couple of the valves that were just in spec, they seemed loose.  Besides, they are a relatively low cost item, so it seemed prudent to have new guides, too.  Here is my home made press pushing out the guides with a little shop made tool.

Now the bare head needed to be cleaned up.  Rather than take it to the shop for a stay in the hot tank, I decided to tank it myself.  I made a wooden box, lined it with plastic, and put the head in it.  

I poured in a  gallon or two of phosphoric acid cut 50/50 with water.  Commercial hot tanks typically use a caustic solution like lye, which is pretty effective on grease and oil, but not so much on rust or scale.  Phosphoric, on the other hand, is really effective on rust and scale, but less so on grease or oil.  Since my main concerns were with scale in the water jacket, and the exterior of the head was mainly rusty, I took the head to a coin-op car wash to remove what grease and oil there was, then gave it a soak in my acid tank.  This is what it looked like after a few minutes, a couple of hours, and the next day.

The tank did a good job, and there wasn't all that much left to do by hand--mainly just some carbon in the combustion chambers.

There really isn't too much that needs to be done to the TR6 head, but there are a few tweaks that can improve flow in the ports a little.  Anything that interferes with smooth air flow, like changes of size, shape or direction, or protrusions into the flow presents opportunities to enhance performance.  For example, the channels for the ports are formed by sand cores in the mold, and the throats for the valves are machined to meet them.  There is usually some mismatch at the intersection of the machined throat below the valve seat and the rough port channel.  I tried to remove that step in each port, or at least smooth it out.

One other thing that is commonly done to the TR6 head is to slightly straighten the inside curve of the intake port where it changes direction below the valve seat.  Removing metal has to be done in a controlled way, since too much enthusiasm in cutting could result in breaking into the water jacket.  It's reported that about 2 mm can safely be carved away from the curve, but being pretty nervous about it, I settled for a safer 1.5 mm.  One common method for controlling the depth is to use a little shop made depth gage to guide in cutting a groove to the right depth, then using the groove as a guide in cutting the rest of the metal away.  I used a carbide bur for gross metal removal, and then little cylindrical or conical abrasive "cartridges" for final smoothing.  Reportedly, the intake port shouldn't be "polished", as some texture on the walls of the port may help promote turbulence to aid fuel dispersion.

The exhaust ports were basically just cleaned up, matched to the manifold, and profiled so that the same rounded retangle shape is maintained all the way into the throat below the valve seat.  The profile tool helps with this.  Also, each exhaust port has a protuberance around the valve guide that sticks into the flow path.  I ground those away.  The second pic below also shows the one minor mod to the combustion chamber itself.  The four sharp "eyebrows" were smoothed to elimiate the edge.

So here is the ported head...

...but there was one more thing to take care of.  Notice the gaping hole in the roof of the #5 exhaust port.  That is the Exhaust Gas Recirculation (EGR) port.  I won't be using EGR, so I wanted to not only plug the EGR port, but to restore the smooth profile to the exhaust port.

The EGR port on the top of the head is threaded 3/4-16, so I started with a big 3/4-16 allen set screw.  Since the EGR port isn't threaded all the way into the exhaust channel, I cut the set screw to length and turned the bottom end down to fit the untapped part of the hole and extend slightly into the exhaust port.

I then ground the bottom end of the plug so it matched the port profile.  To keep the plug from turning, I set it in place with red Loctite.  I forgot to take a pic of the topside of the plug, but it will show up in a later picture.


At this point I sent the head out to have 0.130" shaved off.  This should take the compression ratio up to around 9.4:1.  Here is the shaved head:

Next up was to insert the new valve guides.  The stock guides were steel, and using bronze guides is a popular substitution.  I didn't see any particular advantage to bronze guides, so I stayed with the steel units.  The second pic shows the shop made drift to help push the guides in, plus the collar that limits the process to the proper stick out of 0.62" above the top surface of the head.

The new guides were just a little tight on the new valves, so ran a 5/16 reamer through them.  So little metal had to be removed that I could easily do it my hand.

Then it was back to the shop to have the valve seats cut.  Should have done this in the same trip with the shaving.  Not sure what I was thinking.  Nice 3-angle seats:

Next up was to lap the valves to their seats.  The valves get a nice matte ring showing that they mate perfectly with the middle angle on the seats.

At this point, I painted the head.  Would have been easier earlier.

Now the springs and associated hardware:

Some odds and ends:  Core plugs and the oil gallery plug.  I usually anneal copper gaskets, even if they are new.

Prepare the block to receive the head:

It's a milestone!  Now need to sort out the rocker gear.

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