saving a 1980 KZ750 twin

[teazer]

Much shinyness. Does that motor use hardened caps on teh valves? Ti valves need caps of some sort. Are they direct acting cams over buckets? If so the shims might be enough to cushion the impacts.

On SOHC Hondas with rocker arms, the small diameter adjusters eat the ends of Ti valves.

 

[Maritime]

Sexy. Ti valves!

 

[doc_rot]

No steel cap needed with shim buckets

 

[teazer]

Good to hear.

 

[doc_rot]

Spent some time on the lathe and mill today. Whipped up a new front axle. I repurposed a hollow katana 1100 axle and welded a custom 316 stainless nut on one end. The other side is 7075 aircraft grade aluminum. Weighs 8oz less than stock.

 

[doc_rot]

I submitted my engine info to Burns Stainless and received the following recommendations for a stepped header. This is assuming a 3" port. Its not too far from what I currently have

 

[doc_rot]

After two years of head scratching, I think this is the easiest way to adapt an oil cooler to this engine. Reclock the filter cover, and tap the cases for 1/4"npt

 

[canyoncarver]

That is a neat oil cooler idea. It does look simpler than all the oil pan mod versions I've seen. I need to pull my the oil path diagrams but it looks good from back here. I'm a big fan of oil coolers on air cooled bikes out here in the desert.

 

[irk miller]

I have zero experience with a KZ750 twin, but looking at the images it appears that filtered oil feeds the crank bearings. Without a check valve keeping your oil in the cooler components, are you going to be running startups with dry crank bearings?

 

[doc_rot]

I have zero experience with a KZ750 twin, but looking at the images it appears that filtered oil feeds the crank bearings. Without a check valve keeping your oil in the cooler components, are you going to be running startups with dry crank bearings?

An interesting question. I never really considered it because this is how all oil cooling is done on these old Kaws. Even the factory oil cooler on the GPZ takes oil straight from the filter, through the cooler, then back to the main gallery, as far as I'm aware there is no check valve. Depending on how the oil cooler is mounted it is possible to trap the oil in it. I could also mount a temp regulator to bypass the cooler on startup.

 

[canyoncarver]

Thermostatic bypass valve. I run one on my shovelhead oil cooler. It makes a huge difference. Quicker warm up times too.

 

[doc_rot]

Thermostatic bypass valve. I run one on my shovelhead oil cooler. It makes a huge difference. Quicker warm up times too.

What brand do you have? The problem I found is most thermostats open at very low temps which negates their purpose on an air cooled bike. Only a small amount of thermostats can be had with a high temp opening and most of them were spendy or massive. I did some research when i was setting up the oil cooler on my kz1000 and utlimately decided it was not worth the hassle or money. Kawasaki offered oil coolers as a factory option for the Z1/kz1000 and they were very simple setups so I cant imagine a thermostat is terribly important.

 

[canyoncarver]

Mine is an older Lockhart I got off ebay. I believe it starts to open up after 180 degrees.

I need to wash the bike.

 

[doc_rot]

Thought I'd share this observation here for interested parties. The late model connecting rods are a much more refined design, bigger and smoother radii everywhere. It may not seem like much but these details make for a significantly stronger rod.

 

[doc_rot]

I remeasured the cylinder head volume. The new titanium valves have no dish and intakes are bigger so the volume is smaller than previous. cyl 1 is 46.4cc and cyl 2 is 47cc
maintaining my desired squish (0.035") this should leave me at about 10.25 -10.35/1 static compression.

 

[doc_rot]

I downloaded the C5 ignition software and started playing around with it. its very simple to use. I decided to compare their KZ750 curve it to the stock curves and WOW what a difference! talk about turning the wick up

'76-'80 Stock ignition curve with points. idle = 5 degrees full advance 30 degrees @ 3750 RPM
'81+ stock electronic ignition. idle= 10 degrees full advance = 35 degrees @ 3750 RPM
C5 ignition curve. idle = 23 degrees full advance = 38 degrees @ 3000 RPM

 

[doc_rot]

I talked with a guy in Canada who has been racing and developing this platform. He has given me tons of good info including this tip to run the clutch from the belt drive engine. This clutch is different because it has an aluminum clutch basket, and the clutch is actuated from the right side of the bike. This not only allows a much larger countershaft sprocket by removing the clutch push rod, but also removes over a pound from the flywheel!

 

[doc_rot]

This project is pivoting. I have decided to build a track/race version with the big bore engine. I've started a build thread HERE if you are interested.

As for this bike I will be building a nice, fairly stock engine.

I had 3 spare engines lined up and I chose the best one from the bunch. Other than being stored with an exhaust valve open this may be the cleanest engine internally I have every seen. It must have had low miles because everything is barely worn, evident by the cross-hatching in the bores, and the small end of the connecting rods looks mint. Because of that I'm just going to clean it up and rebuild the top end.

I started by tearing the cylinder head down, polished all the fins back how I like them, sand blasted, re-polished the fins, and painted with Gun Kote Satin Black. After the paint is dry I wipe the fins clean with acetone before baking the paint. I then do one last polish with 320 so the fins are super bright. I find this process gives me really well defined fins and reduces the risk of damaging the paint during fin polishing significantly

I also took the time to polish the intake and exhaust runners and to blend in the valve seats. This is a common issue on these heads; the ports and valve seats are not aligned very well and leave a sharp internal edge. I'm no porting expert but I know that this is bad for flow. Other than that I mostly just removed the large casting flash present in the runners and tried not to remove much material as these ports are already too big for stock displacement. I also took the time to port match the carb boots, and polish the combustion chambers.

Now its time for a thorough cleaning in the parts washer before going out for a 3 angle valve job and getting the head decked. I will be using NOS valve springs (the big ones, cant find the small ones) along with high quality teflon valve seals.

 

[doc_rot]

before/after