Welcome to the next part of my Kawasaki Z650 engine refurbishment series. This is the one where it all goes wrong 😁
The objective for this session was to take the cylinder head off and see what the top end of the engine looked like. I already knew that the cylinder head was likely to need to be swapped out because one of the air intake rubber mounting lugs for #1 cylinder had broken off.
The first job was to take the cam cover off. I did this by undoing all the bolts, but keeping them in place so I know which one goes where. The bolts are a complete assortment, including one (the front right one) where the 10mm bolt had been replaced by a 13mm one, as a way to deal with a previously stripped thread. Stripping threads is a far too common occurrence n these engines. The bottom ends appear to be indestructible, but the alloy on the top ends is a little too soft for my taste.
With the cam cover off, the next job was to turn the engine to top dead centre (TDC). This is where the pistons in cylinders 1 and 4 are as high up as they go, and in 2 and 3 are as low as they go. Doing this is needed so that the cams can be refitted in the correct positions at the end of the rebuild.
It is done by using a spanner to turn the bolt at the end of the crank - at the bottom of the photo above. I forgot to take a photo, but there are markings on the timing plate showing when you are at TDC. These match markings on the cam, which should be level with the top of the cylinder head. In the photo below, the arrow with the "T" embossed into the rubber of the cam on the right (the exhaust cam), which is currently pointing nearly backwards, will be at the front and level with the cylinder head at TDC.
This is the point where I got my first clue that there was a problem. The engine didn't turn, instead I felt something inside go "ping". Not a good feeling. At this point, I strongly suspected something was seized.
The actual cams and cam chamber appeared to be in good condition. There is damage to the tacho worm drive on the exhaust cam (now at the top of the photo below), but I know that's old damage and doesn't affect the operation of the tacho drive. I've got two other sets of cams, so if either is in better condition I may swap one in, although I have a feeling the bearing surfaces on both sets aren't great.
Next up was to remove the cam chain tensioner. It lives at the back of the cylinder block and is a pretty basic manual design. As long as I don't undo the allen bolt on the right hand side of it, nothing will spring out ! You can also clearly see the broken lug on cylinder #1's air intake in this photo.
The phot below are the removed cam chain tensioner, and also the top guide wheel assembly (previously seen between the two cams, where it helps hold the chain in place). The tensioner is in perfect condition. The guide wheel has lost some of it's fused-on rubber, but is still in usable condition with no sign of loose bits waiting to fall off. It's one of the more expensive parts to replace - even a pattern one costs £76 at present, so I think this one will do for now.
In this next photo, I have removed the cam caps. The cam bearing surfaces are passable rather than great, but that is to be expected in an engine that's over 40 years old. Note that three of the four caps on the exhaust cam have had studs inserted at some point in the past, due to the bolt holes stripping their threads. This is a significant issue with this engine; the caps have to be removed by all being loosened a little at a time, re-fitted in a precise sequence (again, tightened just a little each over and over to avoid stressing them), and torqued to a precise setting. Getting it wrong inevitably means stripped threads.
The head nuts removed. The chrome on them is in terrible condition, although the threads were surprisingly good.
Here you can see I've removed both cams and using a spanner to hold the cam chain to stop it dropping into the engine. I've done that once, many years ago, and fishing it back out is not an experience I'd ever like to repeat !
Note the two bolts at the front and back of the cam tunnel; they are there so that when you reassemble the head, they locate the head to the barrels more accurately than the cylinder head nuts. Worryingly, they had worked loose; I think what I must have done last time I did a head rebuild was torque them down, then torque the cylinder head nuts, and forget to go back and re-torque the two locator bolts. Lesson learned !
The two cam chain middle guide wheels. These are trapped between the head and barrels when it's all assembled. Both are in very good condition indeed.
Aaaand... here's the problem. With the head removed, I discovered that the pistons and piston liners were in appalling condition. This is #3, which is by far the worst of them; very obviously seized, rusted and full of debris. This is very not good.
The underside of the cylinder head. Also not good. Valves in cylinders #1 and #3 would have been open while the engine was in storage, and moisture has clearly got in. As well as spiders in number 1. Numbers 2 and 4 have a bit of carbon build up but appear fine. But what has happened with number 3 clearly shows the cause of the problem, and the inlet valve has rusted open. While this head is salvagable, it would be a major project in it's own right, needing at least 3 new valves and valve guides, plus any other nasty surprises I found.
For now, I've put some engine oil into each cylinder bore. I'll let it soak for a few days, and hopefully it'll make it easier to break the seized cylinder or cylinders free.
So yeah, this isn't good at all. I had expected the head to be a mess, but finding that the pistons and barrels are this bad is very disappointing.
I'm going to have to think about where to take it from here. The idea was to do a low-cost restoration of the engine, just so I had a spare that would be ready to drop into the bike in a hurry any time it was needed. I have another spare cylinder head, pistons and barrels in storage, but they will certainly need some work before they are ready to be fitted to the engine. At the very least a good clean and honing the barrels. If they need a new set of piston rings as well, it may have to wait until I've got the funds to afford it.
Next episode I will see if I can get the pistons and barrels off to see how bad it is, and also investigate where the "ping" sound came from - I have a feeling it might be a locating pin that lives on the end of the crankshaft.