Z750 Engine Rebuild - by a total amateur!

Our story starts here - 1 x Z750 Engine circa 1984ish.




Firs things first - take stiock of the exterior, which is all in good condition except for this missing exhaust stud. Not snapped just not there - the hole is empty? ?




Then onto draining the oil - the oil filter housing had a socket welded on to it - must have been rounded by a heavy handed previous owner. You can learn a lot about it's life just by things you find as you go.



Will need a new one of those...


So take sump off first (as recommended?) a fair few bolts and some heavy smacks with a rubber mallet it's off.




What am I looking for there other than all that crud in the pick up filter? What does that tell me? And what else should I be looking at now?


The points cover revealed this - look normal?




And the crank bolt pulley thing.




The machined dimples are for crankshaft balancing right - is that a lot?


At this point I should say there is what I believe to be 'compression' - if I crank the bolt clockwise with a ratchet it turns smoothly as do the cams and the starter sprocket - which is good...?


The countershaft area is a bit corroded - been left with the cover off a while I guess.





Then I took the plugs out. All are a good colour but the plugs 1 & 4 have no gap between electrodes suggesting moisture at those ends?




On to the rocker cover. Another telling story here - 3 different types of bolt used to secure it.
Not sure what I'm looking for here but if anyone sees anything suspect give us a shout. As far as I can see, the cams look okay and the timing chain / sprockets look healthy.









This amount of chain slack correct?
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Next thing is to get the cams out, all the valve gear out and measure it all up to factory spec.

Was the motor running when you got it? If not, it's possible that the P.O. just put in a set of plugs and they never were used to run the motor, in which case you have to take how they look with a grain of salt.

Yeh I'm taking no chances and assuming the worst.

The plugs had black paint on meaning the engine was blasted with black spray paint with everything still on which shows what kind of guy the OP was!

Just Musing, But if you haven't yet, roll the crank to 1-4 TDC, & look at the top of pistons thru plug holes, contact severe enough to close plugs will be apparent.if so, you might see if the 1-4 rod caps can be removed insittu, the 1st thing that come to mind in your' sittuation is that a loss of oil pressure has taken out the 2 rod bearings furthest from pump in lower end. (cam bearings USUALLY go 1st, but if you can peek, why not) luck g

all looks prety normal to me, doing a similar engine now. the slack is becuase there a slider in the cam cover, normal too but the ammount of debris on the pump screen doesnt look too good, would split the cases and have a proper look... bu that's me

It's all getting stripped down nut and bolt for super inspection for sure. Needs to be for blasting and painting (properly!).

The plugs are not 'closed' - the gap is fine but it's bridged by gunk or carbon.

I'm really interested to see what I learn about this engine as I strip it down. Primary and cam chain will be changed unless they're within 'brand new' tolerances.

Are the air injection ports (on the exhaust side, the holes next to the valve cover bolt holes) plugged already or is that just gunk in them? What country are you in? What country is the bike from? I know Canadan bikes didn't have the air injection...

I'm in London, England - home of the highway Zed rider!

The bike is a total parts build. Engine could be from anywhere but Im pretty sure it's a UK GPZ750. Air injection ports - didn't know it had anything like that.

From the first pic, it looks like they have either been blocked off or never existed. They are found on the top of the cam cover over the exhaust camshaft. It's possible the UK bike didn't have them.

kzrider.com/index.php?option=com_kunena&...ew&catid=2&id=390107

Can be blocked off using things such as these (posted originally by MFolks):
www.tpoparts.com/
www.kzzone.com/billet.html

Okay dudes, got well stuck in today and found out a lot more - not sure if it;s good or bad - you'll all have to weigh in on the pix!

First things first - the correct engine number.




This was also on the side - mean anything?




Cam Chain Tensioner off - manual type so pre-82 engine right?




Next got the cam caps off.



And Cam end.



They all look the same - they look like there's scoring in these pics but in actuality they are unmarked - good sign?
Also put the cams out the way which look fine - no scoring, marks or burns etc. Sprockets have healthy teeth.


Put the valve follower things and caps out the way all arranged in correct sequence. They will be stored in separate marked boxes with he rest of the valve assembly.




Head off - revealed this head gasket which looks almost new and in 1 piece. The areas around the pistons are metal - special type of gasket?



1 or 2 Head studs have corrosion on them - I think this engine has been standing in a damp place for a while.



That extra crud was on the outside of the head nuts and fell in - it's not the head studs disintegrating lol!


Pistons 2 & 3.



Slightly rusty No 4 Piston.


Cylinder sleeves (barrels?) are in great condition - the walls are mirror smooth with no marks or discolouration at all from the areas I can see. They measure 65.5mm with a digital vernier calliper - oversize or standard for a 750? One piston has slight rust which corresponds to the previous rusty valve shot. All carbon deposits rubbed off with little effort so weren't hard baked on.


Here's the valve side of the head. I know carbon deposits are normal but how do you know if it's beyond bad? How do I check valve clearances here? Do I need a special tool to remove each valve assembly? Are these totally effed?







And there we have it. Get the barrels off next and the pistons out for closer inspection / measuring.

I am not an expert, but that all looks just like the 5 heads I have laying around. I would clean it up with a wire brush and some kero and call it good. The only reason I would pull the valves is to replace the valve stem seals.

If you were feeling really industrious you could have the valves and seats cut and new valve guides installed, but that is most likly overkill.

Wow, talk about thorough. I've never had a 750 motor apart but I've rebuilt and been through several 650 motors before which are basically the same thing.

First, you said that you turned the engine over on the fly wheel side going clockwise. That is actually turning the engine backwards and is bad for the motor. It turns the cam chain backward can make it skip a cog (catastophic) or wear on the tensioners unnecessarily. Use the points side (ignition plate side on your motor) still turning it clockwise. Since turning it the right way on the flywheel side will back the bolt out. There are two nuts on the points side but don't turn on the small one (14mm I believe?) it will break off. Use the 17mm false nut instead.

Second, everything looks good except that the cam journals look a but worn. It's probably just the picture though. Run your finger nail across the cam on the bearing surface and see if it catches. If it's smooth then don't worry about it.

Third, the first two pics of the heads seem wet. Are they? The second two pics look fine. Alot of carbon but not a big deal.

Finally, what is stuck to the oil pump? Is it metal or rubber? I had a motor once that the PO tried to rebuild (key word, tried) and used gray RTV to seal the cases. RTV is to stiff (high viscosity) so it oozes out into the interior and then breaks off and floats off into the oil so it gets sucked into the oil screen. It looked just like that only gray. Since Threebond makes a black RTV too which is more common I'd think it might be that.

Also, good job on keeping the buckets separate. It's a rookie mistake but those buckets actually wear into the holes they sit into. And, completely disassemble the heads. You're already in there so inspect the valves and replace the valve seals. You'll kick yourself later if you don't.

Everything else looks good. Let me know if you need help I know of a coupla cheap tricks that might help.