Pinned ZXR250C camshafts

First comment I'll make is that using the quite common Eutectic overlay to repair the lobes they do not get rehardened.
The Eutectic stuff work-hardens with use. If you have a cam built up and reground, it's quite possible to mark the surface with a file until it's done enough time running. The cams are cast iron and I suspect the lobe is cast quite close to finished shape
and chill hardened before being finish ground. The hard layer is very thin.

Cam lobe centers are simply a convenient way to describe how a particular cam is timed.
Broadly speaking, convention says the inlet lobe center should be a lower number than the exhaust.
If you look at online cam catalogues which quote lobe centers the A model is an outlier to convention.
Convention is accepted practise proven by time.

My own experience going back yea, these many years - I'm OLD - tells me that downdraft heads like closer lobe centers than
those with "horizontal" inlet ports. Eg - Suzuki Impulse 400 which is pretty much the last non downdraft Suzuki 400,
Likes 106/107 lobe centers. The FZR400 which is quite a steep downdraft likes 103/104 lobe centers.
In big Suzukis, the classic timing for GSX1100 race engines is 110/112 lobe centers. Late GSXR1000's like 107/107.

Put A cams in on A timing and you'll get A performance.

 

Different bore and stroke on A vs. C models. If using a higher lift exhaust cam, you must carefully check that you have sufficient piston to valve clearance, and that the inlet and exhaust valves don't collide during overlap. At minimum this means carefully turning over the engine with plugs removed and cams/tensioner installed and timed correctly and stopping if it becomes difficult to turn or won't turn. Don't force anything.

The better way to do it is to remove the cylinder head and use plasticine as a gauge and measure your clearance. I don't know if the service manual will give you piston to valve clearance measurements, that's usually something only considered on custom/built engines, so I can't speak as to how much clearance is needed.

Regarding ignition timing, adjusting it is kind of difficult unless you can program transistorised ignition units. The cheap way is to slot the mounting holes for the pickup and advance it that way, or find/produce a new ignition timing plate with advance built in. I did this on my R6, there were multiple aftermarket ones available, from -1, +2, +6 and +10 degrees of advance. The -1 degree was for California models because of their ridiculous emissions nonsense, means their model R6 had different cams to the rest of the country and the world.

Likely there is 'nothing' available for any of the 250 fours unless you search within Japan and know where to look.

 

Although there isn't any megacycle cams listed for the ZXR250 or it's bigger sibling the ZXR400 - there may be something to be learnt from comparing cams for 'similar' engines from that time as the lobe centres are comparable.

Published duration numbers between Kawasaki (ZXR250) numbers and Megacycle numbers cannot be compared it seems - which is a bugger

I don't know what lift Kawasaki is providing/calculating for their duration for the ZXR250, but it isn't 0.040" by my reckoning.
Full catalogue is here
https://www.megacyclecams.com/catalog/catalog_optimized.pdf

There's some other worthwhile notes in the catalogue with respect to measuring lift as cams with a long duration aren't measured by simply measuring the smallest -v- largest dimensions and subtracting the difference, when the cam is already effecting lift across the smallest dimension, so it must be measured with a dial indicator by rotation, not verniers or a micrometer.

There's a few conventions - duration and lift increases and the changes to lobe centres which accompany those changes and the cited changes in power characteristics, torque, mid range, top end etc.

The Yamaha FZR400/600 and YZF600 lobe centre numbers are very close to the ZXR250C and @gregt has already said 103 intake and 104 exhaust works for those engines and the FZR250.

 

That's a difference in stroke, the clearance (squish band) between the piston top (flat section) and the cylinder head (flat section) will likely be the same or very similar - and increase/decrease of 0.7mm in squish band between the models would be huge as the squish band is likely to be about 0.8mm - 1mm or thereabouts.

Consequently piston to valve clearances should be the same or very similar, differences in valve pocket depth notwithstanding.

There's likely a difference in either, or both, the compression height of the piston, less likely - the conrod length or even less likely - height of the cylinder block (an extreme outside case maybe the engine cases being different) to account for the different stroke.

I reckon if you put an A and C piston together on a gudgeon pin, there will be height differences between them

 

Valve to piston on something as small as the 250's I'd be looking for .050in.
Bear in mind a man with a mill can easily deepen the valve pockets.

Big 2 valve engines I use .080in. I have once used .040in on an EX500 racebike - but with a rider who never missed
upward changes. Next time the head was off the pockets got deepened to give .050in.

 

The cast numbers usually are not all that helpful on other bike engines I have worked on. The cast in number is just to identify the blank before it is actually ground. Sometimes it also identifies the casting machine/dies for QA purposes. Not unusual to find multiple different grinds from the same blank. There is usually some stamping elsewhere to indicate the actual grind.

 

To muddy the waters somewhat (sorry) the parts diagrams list two different part numbers for the exhaust cam for the 45hp c/d models, one the same as the a/b models and one the same as the 40hp c models

1994-1999 zxr250c
Intake 49118-1069
Exhaust 49118-1111

1991-1993 zxr250c/d
Intake 49118-1069
Exhaust 49118-1070
Exhaust 49118-1111

1989 zxr250a/b
Intake 49118-1069
Exhaust 49118-1070