Not exactly like the production line in Japan but I’m assembling three sandcast engines at the same time. With everything that’s going on with COVID-19 I have more free time than usual so what better than to do bike work. Overall it will take less time than doing them one at a time and it’s kind of fun especially when you get this far.

I just discovered (or maybe rediscovered) that #97 has a 19mm hex on the front turn signal stems (later are 17mm). Steven asked me about them and it jogged my memory. I had kinda remembered that there was something different about the stems on 97. The problem is that I was missing one of them so back then I decided to use the 17mm version.

I'm looking at the one I have and I could probably make one from scratch with too much difficulty. The biggest problem would be matching the knurling. It also would not be too much trouble to make them out of newer stems. Just an easy lathe job of turning off the nut and then copper brazing a bigger nut on. A minor problem is the nut is a little thicker but could be machined off. After chrome plating you would not be able to tell the difference.

I couldn't find a reference to this on the site. So do we have any idea how rare this distinction is? What VIN was it used up to? So is this a sought after part?

Here's the listing.
https://www.mecum.com/lots/LV0119-348551/1969-honda-cb750-sandcast/
Anyone know anything about this one? It lists the VIN and engine number being the same.  Too bad there isn't more pics and closeups of the numbers.

I acquired sandcast engine E1490 several years ago with the intension of repairing damaged cases and getting another sandcast engine back together. Unfortunately, there are six areas that need to be addressed. If it wasn’t for the fact that they’re fairly early, legitimate cases I wouldn’t waste my time. Here’s the number.


And the casting dates.


What happened was the outside bearing on the final driven shaft failed (probably under load) causing the final driven gear to crash into the rear of the crankcase. I understand this wasn’t as common as the chain break problem but it must have happened often enough for Honda to change this bearing on the K2’s.

This caused the crankcase to crack and the bore for the inside final drive shaft bearing to get damaged. Here you can see where the gear hit the inside of the case and the damaged bearing bore.


Here is the crack on the outside.


A closer look.


Fortunately it does not have any chain break damage.


Apparently then, after it was damaged, it must have sat around for a while. Long enough for the oil filter housing mating surface to get corroded. I’ve seen that before on E100.


And a close up.


Then someone finally decided to try to repair it. They should have had someone who knew what they were doing. The stud on the front of the engine between cylinder #3 and the cam chain tunnel is broken off.


Also the stud hole is broke out on the front of the engine on the corner by the #4 cylinder.


Finally it appears that the “mechanic” used a sandpaper disk grinder to remove the cylinder base gasket.


So I have some ideas but I have some questions too.

Should the crack be welded on the inside, outside or both? It would be nice to try to match the surface enough so the repair isn’t very noticeable.

I think the bearing hole can be cleaned out with a boring tool on the mill.

I need to clean up the oil filter housing surface to see how bad the pitting is but I can put that on the mill like I did for E100.

It would just be nice to find an easier way.

The broken stud can be removed by EDM or drilling. The other hole I think will take some welding then re-drilling and tapping and counter boring. Does anyone have the dimensions for the location of the studs? I think someone here made billet cylinders; they would have to have the dimensions.

The sanding damage has me concerned. I need to check how flat it is. It’s much worse than the picture shows. How much material could I skin off the surface without causing a problem? How about smearing some JB Weld on it to fill in the gouges then machining it flat?

Like I said, I think it’s worth the effort and if any of you have any good ideas for some of these repairs I would certainly appreciate hearing them.

As the subject line says I am trying to find the thread diameter and pitch for spoke threads. I measure 3.5mm diameter but I'm struggling with the pitch. I'd like to run a tap through the nipples before I get them plated.
Mark

Anyone have a good method for restoring the color to the RH control knob.  I need to save this rare pointerless knob.  It seems like there should be some kind of polish.  I was even thinking of using a semi-gloss black paint.

Somehow I missed the rear brake arm when I did my chrome plating.  Now I’m not sure which brake arm is the original.  Can anyone tell me what the characteristics of the early brake arm are?

Here are the 4 that I have.  They’re in the same location left to right in all pictures.  The left most one has a slight curve in it and also notice the differences in the left side of the clamp area.


Here the curve is more apparent in the left one.  The other three are straight.  The left two have raised numbers on them.


Quite a bit of variation in this view on the clamp ends.


Some subtle differences here in the size of the radius where the round end blends back to the straight arm.

My carb bowls came out shinier than I think they should be.  Does anyone know of a way (like a chemical dip or wipe) that would turn polished aluminum to a dull grey finish?