A motorcycle parked in front of a tent on a pleasant green campsite

Home Repair And Restoration

Z250SL Tappets Again

Job Date 4 January 2020

By Ren Withnell

Click here for a guide on how to check the Z250SL tappets

22,900 miles. Considering that woman only rides her bike(s) at the weekend she seems to be doing some blooming miles. I recall the first/last time we did the tappets. It was a long drawn out affair that took us 2 weekends. I have ensured Sharon doesn't need the 250 for a couple of weeks and we've planned to rideout on the 125s tomorrow. I'm prepared and girded for the long hard struggle once more.

Ah, yes. Once you know how to get the rear panels off it's quite quick. Oh of course, getting the seat off is easy when you've done it before. With 5 minutes help from Sharon ("hold this, push that, slide this") taking the tank off is simple when you know which pipes and wires to remove. I'm down to the rocker cover in under an hour.

Last time I took the rocker cover out it was a nightmare, this time it just slipped out. There is just one perfect angle with a twist and turn then it comes out just fine, luck must be on my side.

Under the rocker cover we see the valve train of Sharon's Kawasaki
Hello! I wasn't expecting to see you again so soon.

The exhaust should be .15 to .24mm. Both are around the .23 mark - perfect. The inlets should be .10 to .19mm, one is .11 the other .13

Hmmm. Damn. Hmmm. Both the inlets are within tolerance but they are at the low end of the tolerance. Looking at our previous numbers it seems we had to "open" the inlets last time. This means they've closed once more. I'd be happier with them at the high end of the range rather than the low end. I reshim them and end up with them both at .19, top end but within spec.

The socket and ratchet are on the crank as Ren turns the engine to top dead centre
"it that Top Dead Centre? Just a leeeeeeeeeetle bit more...damn!

It's usually the exhausts that need reshimming because the exhaust valve seats have a far harder life than the inlet. Why? The primary reason is the inlet is cooled by the fresh charge of air and fuel. So why is Sharon's bike different? I don't know, inlet seats still "settling in"? I suspect the real reason is "Sharonness" which means everything is always odd and different for her.

Rocker cover on, camchain tensioner back in, tank on, check it runs, job done! All within 3 hours. Now she'll start mithering for an oil change, filter change, headstock bearing service and regrease, rear suspension linkage clean and regrease... and so on. I presently look after 4 motorcycles and 2 cars. Her youngest has just passed her car test so that'll be another car. I need a workshop.


If you'd like to pay for Ren to have a nice heated workshop let him know via ren@bikesandtravels.com

Reader's Comments

Upt'North said :-
Whilst I certainly am not questioning your tappet prowess Edster, in fact I'm impressed you take on such nonsense. BUT, isn't there always a but, how long do Kawasaki allow for this service item.
Do they really charge three hours at 70 or 80 quid an hour for a shimming. Gawd that would be expensive.
It's also strange that some valves seem never to need shimming whilst others are always requiring shims. Also strange with the inlet situation.
Upt'North.
17/1/2020 11:00:43 PM UTC
Ren - The Ed¹ said :-
The Kwakker service is, if I recall, 7,500 miles for the tappet check and 3,250 for a safety/levels check. Price wise I seem to remember the shop trying to charge Sharon about £210 for the first major service, but she got it for £100 as it was part of the deal she haggled when she bought the bike. You should have seen the service clerk's face when Sharon pulled out the letter stating the agreement...

It is my limited experience that suggests most tappets absolutely, definitely, totally MUST be checked often in the first flushes of life in the engine. I had issues with my CBF125 because I didn't - ahem. The CBF250 had already burned it's valve seats at 10,000 miles when I got it, presumably because the shims hadn't been done. Once settled in though they tend to wear a lot slower. The CB500X is due it's first tappet check at 16k but I'll most likely do them at 8k because, well, paranoia.

Why Sharon's inlets? Lord only know why. Valve seats not fully pressed in? Soft seats (hopefully not)? Mismatched or poor machining? I put it down to Sharon-ness, the ability to be different, obtuse, odd. Maybe it's the constant wheelies and drifting she's always doing.
18/1/2020 8:49:21 AM UTC
nab301 said :-
Re valve clearances , in general Kawasaki seem to be hard on valves ( not that I've ever owned one ) but just from reading technical queries in magazines and on online forums over the years. There's something in the back of my mind on one model about how the ramp/ profile of the cam was quite severe allowing the valve to hit the seat more harshly especially at lower revs ? It was a carbed engine and the cold start / choke was set up to keep the engine rpms high , it was apparently kinder to the valve gear...
My experience of the above in another life was a number of years in (4 wheeled ) club motor sport.... (a modified Imp if anyones interested) I chose for a a few seasons not to use a "full race cam " thinking lower rpm/ more torque would be more reliable and suited to my budget, incorrect ratios gearbox... I spent a lot of time adjusting valve clearances. In the final season with that car I threw caution to the wind fitted the "full race" cam , gained 1500rpm , ran nearer the front of the grid and never had to adjust valve clearances . (I didn't detect any loss of low down torque ). looking at the cam lobes , the full race cam had visually much smoother progression from fully open to closed ( more overlap) I can only assume that was easier on the valve seats . Aplogies for wandering off topic slightly !
Found this link ( The web wasn't around when I was racing) I went from an R21 cam to an R23 cam.
https://www.imps4ever.info/tech/camshaft.html
Nigel
18/1/2020 8:54:19 PM UTC
Ren - The Ed¹ said :-
People raced Hillman Imps?!?

I read the article and found it fascinating. I'm surprised that so much work and effort went into tuning what was essentially a basic family car back 'int day. The level of technical engineering and knowledge required to simply make a camshaft would I thought be beyond small backstreet workshop businesses. It seems I am quite wrong. To then be able to accurately set things like valve overlaps and lift heights just blows me away.

I do have a basic understanding of what the article is about but certainly not a full comprehension. I could not look at a camshaft like Sharon's and say "ooooh that's a harsh lift and/or return to the seat". I can imagine how this could be the case but I wouldn't know what to look for specifically.

We will keep an eye on Sharon's tappet gaps, I reckon they'll settle down but time will tell. As for wandering off topic, nah, this was about cams and tappets and while the article was about an Imp the principles are all quite the same. Good read cheers.
19/1/2020 9:55:57 AM UTC
Snod said :-
I did my SL's clearances at 19500 and had to change the shims in the inlets and exhausts, the inlets came with 300s but now have 290s while the exhausts came with 290s but now have a 285 and a 280. So I guess the inlets do change slightly more!

I'm having more trouble with rotten wiring and a suddenly dead battery right now, hopefully the two are not linked..
19/1/2020 12:22:03 PM UTC
Ian Soady said :-
The Imp engine was originally designed by Coventry Climax who made racing car engines, although the Imp engine itself was based on a fire pump unit. My dad had one in the 60s and I always much preferred them to the Mini but the handling could be a bit iffy with the swing axle front end. Also, the water pump was very near the top of the engine so if coolant levels weren't checked they had a tendency to run dry, overheat and blow the head gasket. An all-alloy OHC unit was pretty special at the time, but like a lot of contemporary British machinery the innovative design wasn't quite matched by the execution. Early models had a pneumatic linkage between the throttle pedal and the carb!

There were a lot of Imp engined sidecar outfits around in the late 60s / early 70s and I've seen a couple of solos.

There's a lot of knowledge about cam design out there and actually making them isn't that complex a job for a well equipped workshop. Hartwell, Piper and Kent were very well known cam suppliers - hardly back street workshops.
19/1/2020 2:19:33 PM UTC
Ren - The Ed¹ said :-
Snod - if you've got rotten wiring and a flat battery I'd say there's a fair chance the 2 are linked.

Ian - just goes to show I didn't know how much I don't know about Imps, and their racing credentials! Also aftermarket cams. I've just had a quick gander and found the Kent Cams website and they even have a camshaft for a CRF250. Mind you, is that the CRF250L street bike or the CRF250R motocross bike? The point is I didn't fully comprehend that camshafts were made by anyone other than OEM suppliers.
20/1/2020 9:03:42 AM UTC
Snod said :-
I don't think the flat battery was related to the ignition switch wire breaking away from the connector block (though maybe it is!) but it's certainly related to the lack of charging and the stator that gives low voltage/high resistance readings :( Wasn't someone on here talking about the way KXL250s chew through stators..?
20/1/2020 10:19:02 PM UTC
Ren - The Ed¹ said :-
Can't find owt on here about KLX stators...

19,000 miles? The CBF125 fried it's stator the first time at 29k, then again at 58k so at 87k it's due to fry again. Bummer. Doubt there's much second hand or aftermarket too.
21/1/2020 3:46:19 PM UTC

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