Future 750-4 engine project

In 2018 I bought a used 1982 KZ750 Spectre engine to put in my KZ650. The deal also came with a complete spare head and barrel with pistons.

 

The complete engine was sitting in a unheated shed for quite a while so I ended up tearing it down for a valve job and some new rings. I also split the cases to be able to swap in a 650 transmission to convert it to chain drive. The engine did find its way back into a bike.

 

The 750 Spectre engines come equipped with GPZ type pistons (higher compression) and higher lift cams (slightly less lift/duration than GPZ but more than KZ) When I tore the engine apart I was able to confirm these differences. Since the spares were thrown into the deal I decided the head and barrel would be used on a future build.

 

The only issue with using these parts was the fact that they could only be used with the Hyvo style cam chain. This limits the use on earlier KZ 650 engines which is mostly what I own. I do have one KZ650 CSR engine from a 1982 bike that does use that style chain/crank.

I decided to use the bottom end and cases of that 1982 KZ650 CSR engine and put the spare Spectre head and barrel on it. When I measured the liners on the 750 barrel the #4 hole was close to the service limit, you can see its rusty in that picture.

I took the barrel to my boring guy who measured the liners more precisely than I could. He did find that was the only one in question, so he gave it a quick hone and found a big gouge under the rust that would need close to a 1/2 mm bore to get it to clean up. We decided I would look a 1 mm over size piston set rather than running one 1/2 mm oversize piston (cheesy fix) 

I ended up finding a set of NOS MTC 67 mm pistons = 761 cc from a member on this site about 6 years ago. Probably the deal of the century at $220

 

I ended up boring and honing that Spectre barrel so it can be used with the matching head that will be going in my upcoming DFI build.

Since I had a set of low mileage 66 mm higher compression stock pistons left over I have been on the lookout for a cheap 1980 KZ750E barrel. After 4 years of waiting I found and bought a good condition cheap barrel today. Below is a pic of the later and earlier barrels.

 

I plan to build a engine using the early 750E barrel (has slots for cam chain idler gears) with the Spectre pistons and a early 650 cylinder head (small combustion chamber)  This should make it a hot rod engine on the cheap.

I could also use that 82 KZ650 CSR head but it was skimmed by .020" a lot of years ago, but that may raise compression too high (need to measure it) I would have to modify that head to use a center cam chain idler like APE sell for the J heads. The 82 head for the 650 does not have the "bath tub" chamber reliefs like the 750 head, it also has the rounded cooling fins and it has a tach drive port.

 

So in the future one of my bikes will be running this "hybrid" small four.