Hi Mr. Greg,
I'm building a '70 T120, and asked the same questions.
Here is the long version of the reply that I have saved into a build folder.
It's all the info you will need on this topic.
I made this change as well......from what I recall on a thread I had here last year, John H. recommended placing the thackery washers on the outside of the assembly (next to the rocker box wall). AIUI, when Triumph made the change from the drilled arms to the machined ones, this assembly order was changed but the drawings were not updated.
All the pressure increase available will not overcome the fact that on 1969 and later 650 rocker shafts there is no way for the oil to be distributed to the push rod or valve tip! Then in 1973, when they finally cut a spiral the length of the shaft did the oil have a path out of the center of the rocker, but the wrong placement of the spring washer insured that the valve tips continued to get little, if any lubrication.
So,how have you got the shims and thackeray washers installed?
Drilled rocker arms have the thackeray up against the arm,and the thrust washer against the rocker box casting.
Undrilled rocker arms should have the thrust washer against the arm,and the thackeray against the rocker box.
This is often done wrong,and was for many years.It affects lubrication of the rockers,valve-tips etc.
Here is the short version: Mr. Healey
"So if you want more oil to flow through the rockers, either lengthen the oil galley on the rocker shaft or get a set of T140 rocker shafts (or cut a groove in you old shaft) and reverse the thrust washer and thackery. If you choose to use your old rocker arms you will have to grind a chamfer in the end faces of the rocker and cut a small path to direct the oil toward the valve and push rod.
There, I think this reads better...
And here is the thread... http://www.britbike.com/forums/ubbthreads.php?ubb=showflat&Number=455760&page=1
In order for the tapered spindle to seat properly with this change, you need to replace the 3/8" (70-1330) thrust washers with the 1/2" (70-1575).
Oil Return ByPass:
It might be interesting to note that the stock little Triumph plunger pump will deliver by-pass pressure at far less than 2 thousand rpm. Especially when the motor is cold.
As a matter of course when installing a fresh motor, and rollers are not available, we remove the spark plugs, put the bike in high gear, and turn the motor over by hand using the rear wheel. We do this with a pressure guage attached to the oil galley in the front of the motor. It takes a couple minutes of turning, but it is easy to get the pressure guage up to 70 pounds. This insures full oil pressure to the rod bearings at start-up. To make the job easier we pre-fill all of the oil lines as we offer them to the bike.
It is common practice in the auto engine rebuild business to pressure pre-lube the motor before start-up. This ensures the cam and rod bearings have oil pressure before the motor turns over. The practice of starting the motor and waiting for oil presure to build almost guarantees some rod bearing damage even before you start using the motor.
The oil pressure by-pass holes in a typical Triumph, there are two, will more than handle the volume produced by a stock Triumph pump. The by-pass oil is diverted through two small holes. One into the timing gear cavity and the other into the crankcase it self. I have not know, or heard, of these holes becoming blocked in a Triumph motor.
When you fit a high volume pump, like the Morgo rotary, you HAVE TO increase the size of the by-pass holes to handle the inceased volume or risk inverting the oil seal on the end of the crankshaft. For all, but the very brave who will try to open up the hole leading to the crankcase without taking the motor apart, it means total engine dismantling.
The catch for the performance minded is: you are now introducing more oil into the crankcase and there is volumes written about oil and flywheels. To avoid this, you will see that a lot of Triumphs at the track with an additional oil line running from underneath the oil by-pass valve back to the oil tank. The two by-pass holes are welded up, a .015" hole drilled through the weld into the timing cover to spray lubricate the timing gears, and the oil diverted back to the oil tank.
Diverting the oil away from the crankcase is not a new idea in the Triumph world! If you look at many of the very early twin crankcases you will see a boss in the crankcase casting just below the by-pass valve. To convert a modern Triumph crankcase a boss would have to be welded on.
You can also modify the body of the by-pass valve. Grind a groove in the body so that when the by-pass valve is fully open it exposes the groove. This runs the oil by the side of the valve into the cavity that holds the spring. The oil by-pass body acorn cover can be modified to hold an oil line giving the by-passed oil a path back to the oil tank.
Jack Wilson, Big D Cycle, claimed that on the dyno they would consistantly see an additional 1 hp when the oil was diverted away from the crankcase directly back to the oil tank. Who knows, you would probably see more if the bike was fitted with a rotary pump.
Lots of good info there...