Upgrading a KZ400 engine with 440 cylinders and oversize pistons

I'm building the engine from my 79 KZ400H and swapping it into my 74 KZ400. I rode the 79 all summer after fixing it up, then bought the 74 this fall as a winter project. 

I put about 3,000 miles on my 79 this summer. A carburetor from Murrays and electronic ignition from Charlie's Place had it running reliable and smooth. After looking into other things I could do to it I found some information about putting 440 cylinders on a 400, but not many details. The main thing I wanted to know was that yes the cylinders and pistons from a KZ440 will fit the later model 400. Bolt-on upgrade with factory parts. And the later model 400 fits the pre-78 frame, the only difference is the top engine mount. Fabricate a bracket and it's done. 

The first thing I did was buy the 440 cylinder and pistons on ebay. After figuring out a hone wasn't enough to clean up the rust I had the machine shop bore it out. New oversize piston kits from IMD were easy to find and under $100USD for the pair. A little more displacement means I can call it a 450 now so I'm thinking about new side cover badges once the swap is done. The head also got freshened up and some other things, I'll talk about that below.

Taking the engine out of the 79 was simple enough and the teardown went smoothly. Top end and cylinders, starter, clutch cover and generator cover. Everything was in really nice condition. Thought about changing rod bearings and inspecting things in the crankcase but splitting the case is deeper than I want to go. I'm doing a lot of this in my living room and have other ways I like to spend my time.

Teardown pics:

 

 

 

 

Cool. What carb are you using?

I've been running a 440 with a 2-into-1 intake with VM34 for some time now. This thing pulls hard, over 80mph, no problem. I run points though (with a high quality coil with 5 ohms on the primary resistance). People say it can't be done and it won't run well and the bike struggles over 60mph etc. but that's all nonsense.

The 440 cylinders had some corrosion that honing couldn't fix so I had the machine shop bore it out 0.5mm to 68mm. Brand new 0.5mm oversize pistons from IMD with rings and wrist pins were easy enough to find. 1.0mm os is also available shipped from Japan. This was more than I originally wanted to do but not a big surprise with old used parts. Some numbers if you're curious:
400 bore is 64mm, displacement 398cc
440 bore is 67.5mm, displacement 443cc
0.5 oversize 68mm, displacement 446cc
1mm oversize 68.5mm, displacement 449.6cc
Also I am increasing the compression ratio by milling the head and using sealant instead of a base gasket, so I cut some exhaust valve reliefs into the new pistons. From what I could find looking at pistons on ebay, most 440 pistons don't have exhaust valve reliefs. I'm bringing the pistons closer to the valves and I don't think they have a lot of clearance to begin with. The pistons that came with my 440 cylinders have nice marks on them where they met the exhaust valves and I can only guess what happened there.

 
Fresh 440 cylinder and original 400 cylinder. They use a different timing chain tensioner.

 
 
New oversize 440 pistons and the original 400 pistons.

 
Exhaust valve reliefs

 
Original 440 piston that came with my cylinders. Both pistons looked like they hit the exhaust valves.

I stripped the head down and had it milled 0.5mm (.020") and then cleaned up the ports with a dremel. I mostly cleaned up the casting and removed a little material in some areas to improve flow but didn't get carried away. Left the intake ports a little rough from the 80 grit sanding drum for fuel atomization, the exhaust ports were worked up to a fine grit sandpaper. Replaced valve seals, valve seats freshened up, and added valve spring shims (Howards Cams 96210-60).

 
Head freshly milled with clean valve seats

 
 
Intake port

 
Exhaust port

 
New valve spring shim is 1.6mm. Original is .5mm. Using these since the valves and valve seats were ground a little bit for a fresh seal and I wanted to add some spring pressure.

 
Finished cylinder head.

 

Michi wrote:

Cool. What carb are you using?

I've been running a 440 with a 2-into-1 intake with VM34 for some time now. This thing pulls hard, over 80mph, no problem. I run points though (with a high quality coil with 5 ohms on the primary resistance). People say it can't be done and it won't run well and the bike struggles over 60mph etc. but that's all nonsense.

The single carb is great. If someone says it doesn't work ask them how much time they spent tuning one. I'm using the same carb and intake from Murray's. It was great on the 400 topped out at 85 on the highway indicated by GPS. Held 80-85 on a trip through high mountain valleys at 7,000ft+. I think it'll be even better with the new build. The way it was set up on arrival was very rich on the 400 even at the leanest settings. So I changed the needle from a 6DH4 to a 6DH7 and that made a noticeable improvement. I emailed murray's and asked what jets they install for these but didn't get a real answer so I figured it out for myself. A little research and I found out the Polaris 400 and 440 use a VM34 with the 6DH7 needle and that worked great on my motorcycle go figure.

This is great, I love seeing all the detail you’re putting into it. 

Cool project. Are you using the stock cams?