KZ650 Sleeper Build (831cc engine)

This is a ongoing project bike I first rebuilt in 2012. I bought the complete bike in bits for $200 and it has been my main street bike until 2021 when I removed the engine. The frame has now been converted to run a Z1 engine.





Its a early '77 B1 frame that has been converted to use '81 GPZ550 wheels/brakes/fork/swing arm. I bought it this way, it came with a '82 CSR engine, and it had been road raced at one point (drilled/wired)

The first 650 I bought in 1984 had been rebuilt by me right after I bought it. I built that engine up with a new 831cc MTC piston kit, self ported and modified big valve head, and GSXR750R flat slide carbs bored to 33mm.



This same bike went on to be drag raced after I stopped street riding in 1992.



The engine was retired in 1996 but the chassis is still a race bike. This original 831cc engine is what is in this street bike build (cases/pistons) The pistons were originally 13:1 but were cut down to around 11:1 compression. A new barrel was built with oversized liners.



A new 650 street head was built using 35/31 SS valves sunk back and ported to flow as much as a GPZ1100. Actual measured compression with this head is 9.9:1



Cams are .400" lift WebCam #189, and carbs vary from VM26 to RS34's. In sleeper mode it probably makes around 85 HP to the wheel, more with pipe/pods.





For most of its life it was running a MAC 4 into 2 megaphone exhaust and a air box (sleeper mode) but on occasion it has had a pipe and pods.



Currently the engine is together and sitting on a cart waiting till I get another frame built for it.

This engine has been sitting in my garage for a few years now, I have been oiling the rings and cycling it on the kick start at least twice a year.

My plan is to up the compression a bit and add a oil cooler when it gets back on the road.

I rebuilt my 33mm GSXR flat slides with new OEM slides and renewed the choke plungers.

I just bought a new thinner head gasket (.040" VS .060") the old gasket was a custom Cometic. I found out the 810cc Cometic gasket is very close on the ID and only .043" thick, so going to gain some compression there. The 810 gasket was cheaper than a custom one.



I have had them make me a few custom copper drag race gaskets in the past.

I am also looking to shave the top of the barrel a bit to bump up compression there, as recorded piston to valve is good even with .400" cams.

The old style MTC pistons use the thicker style ring (NLA) In the past I have used OEM Honda rings for the CB450 twin, but those are now pricey! The repop China made rings are slightly thicker and will not fit without being lapped down.

Searched a few ring manufactures catalog's and found '72 Honda Civic 1200 EB1 rings will fit (oil ring may be too thick) Found a great deal on Perfect Circle NOS ring set out of Greece



They may have been cheaper because the kit is for a car. I found the same thing when looking for rings for my 76mm MTC pistons, used NPR rings for a Nissan!