KZ750 noob engine disassembly - what work to do?

Hey there, friends!

I've been reading through the thread "A Newbies Adventures in Maintenanceland!" and have loved it, but now I'm starting my own, probably much simpler one, as the unemployed have additional constraints to worry about...

All of this is happening because I had a leaking head gasket on my KZ750-L3, and a shop said "if we replaced that, we might as well do xxxxx.. and it'll run you up to $2k real quick," so I thought I'd do as much of the work myself as I could. I don't want to futz with valve seals or grinding any metal down into to specified tolerances, so I'm going to outsource any of that that I have done.

I pulled the head off yesterday, which was a blast. I'm looking at the pistons and they're nasty, and the spark plugs are blackening on the threads (got carbs rejetted recently) but I don't see anything obviously awful in there. Shiny where it ought to be, gunky on the outside.

I just ordered a full gasket set from Z1 Enterprises [again, per forums here] and I'm ready to take stuff apart and put stuff back together, but I want to be smart about it - not pulling stuff off that I don't need to.

What work would y'all suggest I do to maximize the life of this machine while minimizing pains in butts? Take the head and block to a shop, get the valves done, hone the cylinders? New piston rings need to be done myself if I don't take the crank case to the shop?

My roommate took some fancy pictures of the ordeal. I'll see if I can get 'em up here.

I have never seen a 750 four full gasket set that included seals, so don't forget the extra $30-$40 for those.

I'd have a better idea of what work might need to be done if I knew the mileage of the motor

That's a good question. Instead of trying to answer it, I'll tell you the information I have: I bought it from a friendly guy who was able to answer some of my questions. It had 14k on the odometer, but the odometer was not working at that time. I hooked it back up right away. He said he didn't ride it much and that it hadn't been that way for long. The gas gauge also didn't work and eventually my whole console collapsed. I replaced it with a speedo from the internet and now it says 37k

staniel wrote:

That's a good question. Instead of trying to answer it, I'll tell you the information I have: I bought it from a friendly guy who was able to answer some of my questions. It had 14k on the odometer, but the odometer was not working at that time. I hooked it back up right away. He said he didn't ride it much and that it hadn't been that way for long. The gas gauge also didn't work and eventually my whole console collapsed. I replaced it with a speedo from the internet and now it says 37k

Probably just needs a valve job and seals. Mine didn't need boring until 75k miles. However, I wouldn't say a hone and new rings would be a bad idea if you are inclined.

I certainly am inclined!

I'm gonna try to find a car and take the head and block to my favorite motorcycle shop (Jim's Southend in Burien, WA). I'll ask them to do what seems appropriate on the valves and hone the cylinders as well. Should I pop the pistons off and have them measure them up for possible new rings as well?

..I'd really love my mileage to be better than 37 actual.

staniel wrote:

I certainly am inclined!

I'm gonna try to find a car and take the head and block to my favorite motorcycle shop (Jim's Southend in Burien, WA). I'll ask them to do what seems appropriate on the valves and hone the cylinders as well. Should I pop the pistons off and have them measure them up for possible new rings as well?

..I'd really love my mileage to be better than 37 actual.

The rings for the four cyl bikes are pricey. Too bad it's not a 750 twin, new piston/ring sets are dirt cheap like $60 each. It's really a question of how much cylinder wear you have. you can feel it by sliding your finger along the wall and check for the ridge at the top where the piston travel stops. If not much, pistons and rings are probably good.

steell wrote:

I have never seen a 750 four full gasket set that included seals, so don't forget the extra $30-$40 for those.

I have seen sets that CLAIM they come with seals but really don't... COUGH! ATHENA! COUGH!

Get some VITON seals. For a few more bucks they are way better material and last a lot longer.

So! News! I've got the block off (that was easy) and I'm staring down into the cylinder and they mostly look really smooth. Unfortunately, cylinder 3 has a strange wear spot in it. It's noticeably darker than the rest of the surface. It's not especially deep, but I can definitely feel it.




For some reason it's much easier to spot it in the picture when it's rotated to be on the top, but here it is (at about 12:05 o'clock). In the cylinder it looks much darker than it does in the picture.

Any idea what that's about? Is the piston moving strangely at the bottom of its cycle? Will new piston rings and honing solve this problem so it doesn't come back? Why is it only the one cylinder?

I'm so excited to be doing this. I'm taking the head in for inspection. I half expect them to tell me there's too much carbon on the valves, as the pistons are nasty.

bountyhunter wrote:

steell wrote:

I have never seen a 750 four full gasket set that included seals, so don't forget the extra $30-$40 for those.

I have seen sets that CLAIM they come with seals but really don't... COUGH! ATHENA! COUGH!

Get some VITON seals. For a few more bucks they are way better material and last a lot longer.

Actually I was talking about crank seals, trans output shaft seal, shifter seal, etc. Vesrah includes the valve seals, but not the others.

Hone and new rings for sure.

Dont regret not doing it 10k from now...

GL.

Do what that super smart guy in the Newbies Adventures thread did. New rings for my bike were 18 bucks a piece from Z1E and you can do the "valve job" yourself with some valve grinding paste (assuming that your engine is reasonably in good shape) and you can just clean things up the same way I did for not a lot of money at all. Enjoy the ride, it is a lot of fun when it all comes together at the end

So, bummertown.



I took the cylinders and head to the shop today. The genius mechanic for whom the shop is named said "it looks like rust" (it's not red, but he knows more than I do and it sure looks metallurgical) and "I doubt it'll hone out and we'll probably need to bore it, but we'll try first".

He laid that out for me, that the bore is $50 per cylinder and a set of new pistons runs around $500. This is well out of my price range when stacked on top of the valve work they're gonna do, so if it doesn't hone out, I'm in a tough spot.

How bad an idea is it to ride with a dent like that in your cylinder if you get new rings? Am I damning by bike forever if I do it? Have any of you ridden with obvious chunks (visible, pads of fingers can feel it, but very very shallow) in your cylinders?