750 Katana Resurrection

[Big Block]

Previous owner let the front sprocket get loose and chewed up the splines I figure. It's a good thing I pulled it down too, the clutch hub was worn and cracked. Everything else was like new though. Really enjoying this thread, very nice workmanship.

[KiwiAlfa156]

Looks good. I was there a few weeks ago installing a new output shaft.

Yeah, it is looking good, Crank journals look pristine and lightest of wear marks on the shell bearings. Gear teeth show next to no wear, selector forks ditto. Looks like the cases have never been split. Given the ham-fisted work on the top-end, I needed to have a look to quell any doubts and I'm really pleased at the condition of the bottom-end and gearbox. I'll check all the bearings, give everything a clean and paint the cases, and start the reassembly. What was the issue with your output shaft BB?

[Big Block]

Looks good. I was there a few weeks ago installing a new output shaft.

[KiwiAlfa156]

Cases split. The rotor/fly wheel wasn't coming off with heat and some pretty heavy slams with a slide hammer. As there's no oil seal or anything to replace, I'll just leave it in place.

So clean, measure, paint and reassemble.

[KiwiAlfa156]

Got a spare 17" Eneki rear for the 750. It's marked "MT" which as far as I know is 'motorcycle tubeless' Of course being early 80s and not being specifically marked as tubeless it has the right rim profile but won't take a tubeless valve stem.



Counterbored a face for the valve stem seal. And used the metal valve stem face with some grinding paste to remove the cutter chatter marks.

[KiwiAlfa156]

Ugh: These days someone has always been there before you.

Ain't that the truth

[Big Block]

Ugh: These days someone has always been there before you.

[KiwiAlfa156]

Exhaust ports cleaned up. A couple of the inlet valves are badly cupped on the sealing face. It looks like the valves have been heavily lapped on using an electric drill. Replacements on the way. A serviceable inlet is shown for comparison.



I'm using a marker pen as a substitute for engineers blue to reveal and measure the seat contact width. The inlets appear to be over the 1.1mm limit. As do the exhausts.

[KiwiAlfa156]

Pretty much finished the inlet ports. Got some valves coming to replace some that need to be swapped out.


Tried to take minimal material out as I'd like to maintain as much port velocity as possible. Also left the throat area as undisturbed as possible apart from cutting out the casting flaws on the long side and blending a gentle radius back into the bowl. On the short side I radiused it as best as possible, removing the sharp step which is ringed in red below. Again removing minimal metal.



Cleaned up the casting core flashings in the turn of the ports and blended then into the throat area. The bottom pic above is one done, and one to be done. Surface finished in 80 grit.



Fitted new roller bearing on the clutch release shaft. Never regretted buying a hydraulic press..

[KiwiAlfa156]

Thanks Forden, that's very flattering. Just sharing the journey and posting what I think is interesting. Hopefully others, such a yourself, find it interesting too.

[Forden]

this build thread is a real education in itself, thanks for sharing your work in such detail--you say it's therapy, well, I thank you for sharing your time on the professor's couch.

I could never quantify the time I have spent fishing, either... probably best not to think about it too hard.

[KiwiAlfa156]

Did some work on the worst of the inlets


Comparison.



A mark is still visible, but it feels smooth and a dentists pick doesn't catch in it.

[KiwiAlfa156]

Had a good look at the ports and found various flaws and steps and undercuts where the inlet port joins the valve seat. Which is the most important part of the port - the throat.



Basically the turbulence created by the casting flaws at this point has is extremely detrimental to flow past the valve.


I will carefully cut back imperfection and blend this section of the port back into the bowl. What is important is to maintain the valve to throat percentage which I measured at 82% stock. The throat acts like a venturi so I don't want to disturb this area at all. Work on the port above the throat has to be carefully done but isn't as critical.



I've started on one of the less problematic ports.

[KiwiAlfa156]

More paint, primer then enamel.

[KiwiAlfa156]

Parts back from the machine shop. Barrels planed 0.15 mm (0.006") to close up squish.



Head refaced 0.07 mm (0.003").