Engine swap options

Hey Guys. Pretty basic question for the more experienced  builders. I'm not very familiar with Kawi bikes and am taking on a 1980 KZ750/4 build. What engines will swap directly over into this bike? I want to stay in the 750 zone and am noticing some parts bikes for sale in my area but unsure as to frame changes, etc. Thanks all.

Your bike has solid motor mounts.  The E and H model bikes use the same engine, but many of the later year bikes switched to rubber engine mounts, and those engines won't fit in your frame.

HulkSmash wrote:

Hey Guys. Pretty basic question for the more experienced  builders. I'm not very familiar with Kawi bikes and am taking on a 1980 KZ750/4 build. What engines will swap directly over into this bike? I want to stay in the 750 zone and am noticing some parts bikes for sale in my area but unsure as to frame changes, etc. Thanks all.

why do you want to change it ? what is the goal ?

I have a frame where the original engine is pretty much a boat anchor, so a swap would be the most viable option. Thanks

HulkSmash wrote:

I have a frame where the original engine is pretty much a boat anchor, so a swap would be the most viable option. Thanks

I guess it depends what you want to achieve and what your budget is, simple solution would be another 650/750 of the same era. If you are a little more adventurous search the site for a build (can't remember who) with a ZR7S motor swopped in. If you are greedy "Injected" has fitted a big bore KZ1000 in his 650 sleeper and "Bevelhead" has fitted an 1170 "J" motor in a 650. Just comes down to skill level and budget

The fastest and easiest upgrade swap would be to fit any GPZ750 engine in it if you can find one locally.

You will need to make tubular spacers to take up the extra space left from the rubber engine mount system of the later bikes. If you have a lathe this is a easy job, just takes some time. The chain line is identical and the motor mounts are the same so its a easy upgrade.

This is cheaper than building up the current engine to make the same power. There is nothing else that is pretty much a direct fit that makes more power than stock.

just throwing it out there. 1981-83 kz650-csr. slightly better fuel economy. can be upgraded to a 750. cylinder-block. pistons. cylinder head.

Injected wrote:

The fastest and easiest upgrade swap would be to fit any GPZ750 engine in it if you can find one locally.

You will need to make tubular spacers to take up the extra space left from the rubber engine mount system of the later bikes. If you have a lathe this is a easy job, just takes some time. The chain line is identical and the motor mounts are the same so its a easy upgrade.

This is cheaper than building up the current engine to make the same power. There is nothing else that is pretty much a direct fit that makes more power than stock.

Back when rebuilding my 750E, I considered modifying my frame to accommodate the rubber mounted engine mounts.  On review, the frames are different.  See below.  Do you have photos of the conversion tubular mounts?  Does the mod retain the rubber mount feature, or eliminate it?

rubbermountframe_zpsfc5d03d3 by nessism , on Flickr

P1010487_zpsf6590e2e by nessism , on Flickr

That's spooky, your painted frame has the same mounting set up as my rubber mounted "J" motor !!

My conversion to swap a '82 Spectre engine was done to a 650 frame so it might be a tiny bit different. Any rubber mounting provisions need to be removed so its like a solid mount frame.

Here are some pics without the spacers:

 

 

 

Here are some pics with 1" OD 6061 spacers:

 

 

 

The only mount without a spacer was the welded frame mount tab under the front sprocket (lower rear) I started by making sure the engine was tight against this frame tab (clamp it) then I went around and measure how long to make the spacers.

 

 

There are 7 spacers required between the frame and engine. You can make motor mount bolts out of threaded rod or source new fine threaded bolts.

 

I went for a half/half option but you could make the two pieces (green arrows) as a single solid alloy part

Thanks for the photos.  They reminded me that some engines have rubber mounts on the front, and others at both front and rear.  Maybe it's the shaft drive bikes with both?  ZR-7 seems to be front rubber mount only, but the rear mount looks different compared to the earlier frames so not sure there.