Vintage Motorcycle Eccentrics

It was a relief to get the cam timing done. While I had the cylinders setting on the cases with tappets in place I thought maybe a good time to blue a tappet to see how it matched the cam surface. Well that didn't go well. One side of the tappet wasn't touching the cam. I checked my grinding fixture and sure enough, the 3/4" bore is out of parallel with the surface of the fixture by .002". So now it's back to getting the fixture perfect and regrinding the tappets. I should be more careful.

Darn- at least you caught it now.
Parts from Germany are actually shipped now. I will not be buying anything from that outfit again unless nobody else in the world has it.

I thought you may like this old Benelli dual engine

Now that's cool. I'll add that to the list of doubles I have started.

With the cam settings figured out it's time to clay the pistons for clearance. Also to see how close the valves are to each other. This will be different in each motor since both crankcases have been decked to get the surface parallel to the main bearings. Consequently motor #1 is .023" taller than motor #2. I can correct this with either a .023" base plate or different thickness of the head gaskets.
Another situation has cropped up due to decking the crankcases, the tapped blocks are rubbing the cams. Not a big issue, just have to grind a small amount off.

After checking the movement of the tappet block again in motor #2, I was wrong about the cam interfering with it. Actually it's the tappet bottoming out in the tappet block. Turning the motor until the cam is at peak opening, there is no movement left in the tappet. This will require a spacer under the cylinder. I will use some 24ga. aluminum for this. I had thoughts of modifying the tappet block but decided it best to leave them stock.

I've been busy gathering parts for a go kart build for two grandsons who will be visiting soon. Since they can only stay a week I'm trying to get it to an assembly stage so we can finish it and use it before they go home. They are just 9 & 10 but like building thing with Grandpa.

I found crack on one of the Triumph heads today and not where I expected. I will be Dye Pen testing both heads before assembly as they are known for cracking between the valve seat and head bolt holes. Originally these seats were cast in place making it near impossible to repair the crack, but my heads have oversize valves and seats so may have been repaired before. That's it for now.

Well, in the process of setting up the head for welding, I dropped it and broke a piece out of a fin. Too small to put back in place so just built it back up with welding rod. Can't tell now it was ever broken. I should be more careful. Next will be lapping the valves, setting the spring pressure and stem lengths. The intake valves on motor 2 are pretty thin at the seat area and may need replaced.

Not perfect but passes the test this time.

The 4 threaded bolt holes that secure the rocker boxes to the head were marginal so rather than stripped threads later I decided to helicoil both heads now. This was a common problem on these machines and even worse when running hi-lift cams and stronger valve springs.

Bigger is not always better, so when porting the intakes on a Triumph this can happen. Some castings were thin at the head bolt holes and the fix was to use a steel case bolt dowel to fit the hole. On a street bike a crack or leak here would draw oil into the intake causing the engine to smoke. This repair job looks ok so I'm not going to change it.

Mags are off to Joe Hunt Magnetos for complete rebuild. Hopefully that's the last big ticket item on this project.
I was tempted to use them as they were but had been warned that a weak or stray spark with nitro could be bad news. It would be nice to give them the rare earth treatment but that's $$$$ extra for a couple of motors that will get fired up on rare occasions.