TOPIC:

Hi...I have an 81 KZ305A CSR and I'm wanting to swap the engine out for a KZ440 LTD engine that I found on eBay. I would like to know if this is doable with or without modification to the frame. Preferably without or at least with as little modification as possible. The only thing that I'm worried about is that the cam chain tensioner assembly on the 440 sticks out of the front of the engine where-as the 305 is positioned facing the rear. I'm wanting to do the swap because the 305 engine that's in the bike right now is only getting about 50 psi on both cylinders. As I understand it, they should be getting about 150-180 psi when doing a compression test.I'm not skilled enough to rebuild the engine myself and there aren't any shops around me that are willing to work on it since it's so old and parts aren't readily available for it. (e.g. Try finding a new starter for a kz305 and you'll be met with everything but what you're looking for.) If I can make the engine swap work, I'll have less working on the bike to do and more riding that I can do. It looks like the mounting points are the same between the 305 and the 440. I'm not quite sure what else would have to be swapped from the 440 system and what I can cannibalize from the 305 system either but I'm pretty sure the carbs can be used from the 305 system at least. Any help on this project would be appreciated.

Edit: I will apply as much redneck ingenuity to this thing as I have to to get it to work if it's even remotely possible. I have a CNC mill, a 3D printer, a plasma cutter, and a welder. I also don't care about how it looks since function is my main priority right now. I'll deal with the looks after.

That sounds like an interesting project.

Before you dive in, however, are you absolutely certain the compression tests were accurate? You mentioned looking for starter parts - is the starter working well enough to allow the compression tests? The valve adjustments may also be out of spec, which would affect the results. Have you tried a second compression gauge?

The rings are probably okay unless there are a lot of miles on the bike, so the issue would then be with the valves. You could pull the head off and send it to this place in CA - I haven't used them but someone here on KZR mentioned them. You can get the head rebuilt with a three-angle valve job and new seals for $189.99.

KAWASAKI KZ305 KZ400 KZ440 CYLINDER HEAD REBUILD SERVICE VALVE JOB
https://www.[ebay].com/itm/301172713155

Also consider whether you will need to convert from belt drive to chain drive (depending on the submodel from which the 440 engine was taken).

Sorry for the extremely late reply. I did another compression test after throwing some oil into the cylinders and got around 130 psi. Ended up getting the engine running for a while and then the left cylinder blew up. Started spewing white smoke and oil out of the left exhaust. Not sure if it's a burned piston or just a bad seal somewhere. Still considering swapping in the 440 engine or a 400 engine. I can get a completed and working kz400 engine for around $400-$500. Also curious as to whether or not a kz650 engine will squeeze into the kz305 frame.

Just fix the compression issue on the 305. Nothing else would be worth your while. If I really wanted an engine replacement, it would be a full-on project. Personally I'd go for one of the 454 or 500 water-cooled twins and try and make it fit. The 305s are quite rare now, I think. Much easier and cheaper to repair it than do anything else.

So I found my endoscope and checked out the left piston and it has a hole burned right through the center. 
If anyone knows of a source for good pistons, that would be appreciated. Preferably some more durable pistons if possible.

www.ebay-kleinanzeigen.de/s-anzeige/yama.../2069033446-306-2232

 

I was hoping more for a custom piston fabrication. Will the gpz pistons match up in a csr or would there need to be modifications done for them to work properly?

That's a good question, but according to Partzilla the barrels and pistons are not interchangeable.

1983 GPz305 barrels - part number 11005-1374; looks like they fit only the GPz305

1981 KZ305 barrels - part number 11005-1159; looks like they fit only the KZ305
 

KaosKontrol wrote:

I was hoping more for a custom piston fabrication. Will the gpz pistons match up in a csr or would there need to be modifications done for them to work properly?

What is your end goal ? It's a lot of hassle to get custom piston set-sets to work properly (especially if you have to outsource any machining) and on an engine of this size it's unlikely there will be any noticeable difference
PS: you also need to establish what caused the initial failure or it will happen again 

Well damn. I guess that idea is out.

I was trying to find some oversized pistons and rings one size up from the standard size (61mm) but I'm not having any luck. The standard size pistons that I've been able to find so far are usually pretty trashed by people hammering them out with a screwdriver/chisel and caveing in the dome on them. (I've already made the mistake of buying a pair of them from eBay and they're practically unusable.) As for the cause of the failure, I found an oil leak in the head gasket coming from the left side. I don't think that was the direct cause of the failure but I think it may have contributed to it at least a little. Not sure though. Seems my left carb was running lean and caused the piston to melt. Went ahead and tossed in one of the trash ebay pistons and put it back together. I'd like to do a proper rebuild but I would need a source for new pistons first and I would prefer to oversize them a little and bore the cylinders to match. Hence why I was hoping for a custom fabrication.

TL;DR - I want to do a proper rebuild of the engine by boring the cylinders and going to the next size up on the pistons and rings but can't seem to find any NOS .020 oversized pistons anywhere for my engine. Sources/solutions requested.

I've been down this road before with the KZ400/440s.
Do you have a piston you could send me?
I can take some measurements and see what I can find.


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