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

Home Repair And Restoration

Those Shim Thingys

Job Date 25 January 2019

By Pocket Pete

Following Ren's update on his bike's recent shim/tappet check I thought it best to do my shims as my bike had completed 15k mikes.

I had a little chat with Ren who was willing to come over and assist me. I say assist as obviously I have no idea of what to do so obviously I will be assisting him.

He's off on Mondays and Fridays so we arranged for him to come today. Rather a wet start to the day but he arrived at 10.15am on his 125 which surprised me as I've not seen him riding it recently. A nice cup of tea and we are off to the garage.

I've installed a new led roof light to brighten the place up and had the heater on to take the edge off the cold.

I have a limited number of tools but Ren has brought most of what we need. He has the side panels off In a matter of minutes and has unbolted the front fairing.  They should slide off but they're not moving at all. We don't want to force them as the plastic tags may snap off.

5 minutes later we still cannot budge them. Ren suggests a splash of WD40, I have some silicon spray. Pop! Off come the panels. That worked well. Nothing snapped.

The bright red panels of the CB500x carefully stored on the garage floor

Next it's off with the tank. Assorted pipes, breathers and cables removed. No fuel drops out which I find nice as I forgot I have a full tank. With the tank removed I can see the cramped plastic cover that needs removing, covered in cables, electronics and stuff I don't understand.

Ren's done this 3 times before and has a plan stored in his head. He removes assorted bolts, pipes, cables, in some unknown logical way. He explains how he cut the left hand part of the tray away to make life easier in future.

I'm a touch concerned seeing my bike being slowly disembowelled. But hey it's only a bit of plastic. I'm more worried when he disconnects the clutch and accelerator cables. Then it's snip snip. Cover corner cut away. Ren flips it over to the side and pins it back revealing another plastic rubber mat. Bang! Coolant pipe off and water pouring out... Rubber mat undone and slipped out. God I can't believe they made it so difficult to get at the engine.

Eventually there is a cylinder head rocker cover shining elegantly still buried under the frame. Only took one hour and 2 minutes to get here.

The CB500x is now stripped down so that we can see the rocker cover

Brew time again. Too early for bacon butties says Ren, work to do!

So on we go. He blows all the dust and crap out of the spark plug holes. Quite a bit came out. I don't know how it got in there under the rubber mats and covers. Next he's using a foot long spark plug remover tool to get at them. They appear to be clean and according to Ren "eeee, like new them".

He puts them away to use as spares in some future project. I must admit they look like new. Nothing really wrong with the combustion then. In go the Iridium plugs I got - a touch expensive but I'm told worth it.

Next it's off with the battery and off with the 4 screws holding the air filter in. I pop on the new one and the old one looks pretty dirty which I'm surprised at it's only got 10k on it as I realised my bike's not done 15k, I misread 10500 as 15k.

Next it's off with the cylinder head. It's a real struggle to get it out but Ren's done this before, a sideways twist and a lot struggling & wriggling and out it pops.

The camshaft and rockers are now exposed

There exposed are all those mysterious internals which I don't understand. I have seen a few engines and have a reasonable understanding of how an engine works but this one is mine and I'm getting a touch worried, will it ever run again? Ren points out those never before seen bits called shims sitting in little buckets. Are they really that important after all I mean they are tiny little things. I mean the rockers look much more interesting.

We are now 2 and half hours in and it's off to the kitchen for more tea, a warm up and bacon and egg butties. I've not had bread since Christmas and I must admit they were bloody lovely. I did grill the bacon rather than fry it (just in case Paula reads this) although did put butter on the bread and fry the eggs. Oops.

It's back to the garage and Ren shows me how to test the gaps. I'm quite surprised how the gaps are all slightly different. He explains the tolerances and what this means. All the gaps are within acceptable limits none are likely to damage the engine but a few are 'on the tight side'.

The shims on the rockers are being checked with feeler gauges

.27 is the best gap. +-.03 (Exhaust)
.16 is the best gap. +-.03 (Inlet)

All the exhaust and one of the inlet are all just a touch tight so Ren wants to move them all down the range a bit. I was unable to find my HotCams shim set so I'd ordered another one and as if by magic parcel force delivers straight to the garage. Perfect timing.

We now have the shims. Ren removed the old ones and replaces them with a new selected one. This involves removing a rod which hold the rockers in place. This is a simple thing to do and appears to be the only thing Honda have made easy on this bike.

He replaces all 4 exhaust shims and the 1 inlet shim. This takes all the gaps to the correct end of the range. A further test and all is well.

So it's now a rebuild or reverse of before. Much messing and head scratching later, the tank is back on. Ren turns the key, will she start?

Poop crap bollocks etc... Nothing! What can be up?

Hey good idea if we put the battery back in first.

Battery connected and she starts first press of the button. Phew... fairings back on, coolant topped up. Back to the house for a well deserved brew. 4pm. That's a full day's work, pretty tiring and we still have the oil and brakes to do. We shall save them for another day.

I reward Ren for his efforts with a small torque wrench and the set of shims, after all he actually will be able to use them. I think he's pleased as he hugs and strokes the box of tiny shiny bits of metal. I wonder if he looks at Sharon like that? He's clearly smitten with the 'Hot Cams'...

The service would have cost best part of £580 so it's a small price to pay. Plus it has the added benefit of me seeing the process which you can never do at a dealers. (Assuming they don't just take your money and not do the work).

I also expect him to use the wrench on my brakes so it's a win win for me. The mysterious shims are perhaps now not quite as mysterious. Could I do them next time without help? Of course not but I could dismantle the fairing and take the tank off maybe even the to the head. It's a good start though.

A big thanks to Ren...

Reader's Comments

Rod said :-
Looks like a job well done!
My Inazuma is much easier, taking just under two hours for a full service, but I need to do it more often than the 500 Honda. My bike is the 250F (the one with the full fairing) so over half of my time is removing and refitting the fairing.
Your point about the dealers is a fair one. In the 1970s I owned a Suzuki GT380, and being a TWO STOKE triple with three set of points it was important to check the timing and adjust/change the contact breakers. Before I took the bike in for its service I placed a thin strip in sellotape over the bottom of the points cover. When I picked up the bike after its service guess what? The sellotape was still intact so the cover had not been off.
26/1/2019 7:00:16 PM UTC
Ren - The Ed said :-
Remind me Rod - does the 'Zuma have shims or screw-n-locknut? I have not personally experienced work not being done by the shop, but, then I've only ever had 2 "paid for" services. I image that most workshops are genuine but there will always be those that are shall we say, erm, less than thorough.
26/1/2019 8:56:18 PM UTC
Ren - The Ed said :-
Oh and here are my new toys!! Cheers Pockepete.

26/1/2019 8:57:36 PM UTC
Ren - The Ed said :-
Mmmmmmmm......... shims. Mmmmmm. I'm off to stroke them one and all.

26/1/2019 8:58:57 PM UTC
Rod said :-
The Zuma is screw and locknut, and all easy to get at.
The GT380 I refered to was my first new bike. The first service was free, and this was the next service. This was the only service I have ever paid for, I have serviced and repaired all of my bikes since that day.
The bike shop I used closed years ago, and I would like to think that bike shops have improved over the years.

Pics of one of a rebuild of my winter bike which I ran for a few years.

26/1/2019 9:52:29 PM UTC
Rod said :-

26/1/2019 9:53:26 PM UTC
Ren - The Ed said :-
GS250! Last time I saw one of those would have been around 1995. My mate was throwing beer and water on it as the electrics had shorted out on the metal seat base causing a fire. I don't think that one ever got back on the road.

I can see yours had what you might call a "FULL" strip and rebuild. Is this your thing Rod, is this your hobby or was that just a one off? I don't have the patience or the eye to do a proper rebuild. I'm sure having seen some of my "effective but unsightly" works of art on here you understand what I mean.
27/1/2019 8:34:55 AM UTC
Pocketpete said :-
After this adventure i have been taking little more interest in the internal combustion engine. And looking at assorted videos on YouTube of tappets being done on assorted bikes.

Ren said his 125f was difficult but the video I watched online made it look easy... certainly easier to get at the tappets than the 500. Plus the nut adjuster seemed a little easier to do than fiddling about with shims. What are the benefits of shims ? when the locking nut system seems slightly easier as you don't require the expense of shims.
27/1/2019 3:58:47 PM UTC
Rod said :-
Yes, GS250T. I did my first full strip and rebuild at the age of 15 with the help of an experienced re-builder when we rebuilt my BSA C15. The next year we stripped and rebuilt a 350 Triumph twin. Over the years I have stripped and rebuilt four bikes, but I now live with my son, and do not have the space for a rebuild.
My rebuilds have been more of the functional and less of the cosmetic.
27/1/2019 5:34:40 PM UTC
Rod said :-
Pocketpete, As you say, the screw and locknut are the easier to deal with when servicing the bike.
The advantage of the shim over bucket method as I understand it is it eliminates the need for the rocker arms.
The rocker arms can wear as well as the valve mechanism which means a more regular service interval. The bucket over shim system is usually but not always used in higher performance engines.
You may come across other methods eg shim under bucket (as the BMW K1600GT) or hydraulic adjusting tappets which do not need adjusting, or very little adjusting.
27/1/2019 5:53:42 PM UTC
Upt'North said :-
P.P., screw and nut adjusters are used with rocker arms but maybe on other designs too. Rockers arms have to move a lot and at very high speed, i.e. rpm. Rocker arms are also heavy so the forces involved at high engine speeds are considerable, all this takes energy and is not suited to high rpm longevity. At high rpm shims are more reliable due to less moving parts and they usually stay in spec a long time. My own motorcycle engine has over 60,000 miles on it and they have never needed adjustment. Hydraulic tappets are also not normally used in high speed applications. This is by no means meant to be a complete answer because there are designs which use a combined approach to valve wear adjustment, so you may get a combination of shim and nut and screw etc.
Hope it helps.
Hope I'm right. I'm not normally.
27/1/2019 6:59:43 PM UTC
Pocketpete said :-
So if I understand, slow reving engines can perhaps use hydraulic. Smaller engines are likely to have screw and lock.

Higher performance engines shim.

Wouldn't a small cc high reving engine be better off with shims to keep the weight overhead down.

Or have I got it wrong.... ?
27/1/2019 8:09:51 PM UTC
Rod said :-
Well,,, Yes and No..
My Kawasaki GTR1000 had screw and locknut adjustment.
The other consideration is that the shim and bucket arrangement has two camshafts, an inlet cam and an exhaust cam.
A screw and locknut arrangement on a small capacity bike can use a single camshaft for inlet and exhaust.
27/1/2019 9:00:26 PM UTC
Upt'North said :-
Another adjustment type I'd never come across.

27/1/2019 11:16:56 PM UTC
Ian Soady said :-
Hi Up.

They're the same as on my 1952 Norton (and they were like that from around 1927......

28/1/2019 12:20:17 PM UTC
Ren - The Ed said :-
I suppose the adjustment being on the pushrod is no better or worse than it being on the rocker.

Sharon's Keeway is the devil's own job to do. But why? It has access holed in the rocker cover it ought to be a 10 minute task especially with only 2 valves. Well the rockers are spring loaded. Not from the valve springs but actually at the pivot point. As such the measured gap is always closed. I had to rig up a string to keep it open to check and adjust the gaps.
29/1/2019 8:47:43 AM UTC
Ren - The Ed said :-

29/1/2019 8:49:05 AM UTC
Ren - The Ed said :-
You can see the tension spring deep in the cover

29/1/2019 8:51:23 AM UTC
Upt'North said :-
Ed, what's the idea of the spring, I can only think to reduce noise or wear. Did any other versions of this engine have the same?
29/1/2019 9:45:21 AM UTC
Ren - The Ed said :-
To be frank Upt'North I have not seen this on the designs for the original Suzuki it's based on, nor on a couple of the Chinese copies' diagrams either. As you suggest the only logical purpose is to reduce noise and/or wear. I'm not at all convinced it's necessary and if it were my bike I'd remove the blasted thing.
29/1/2019 10:12:35 AM UTC
Ian Soady said :-
The screw & locknut on the keeway are a prime candidate for the time-homoured method of using the thread itself as a micrometer to set the gap. Let's say the pitch is 0.8mm(if it's a 5mm thread - best to check). It follows that a full turn of the screw is 0.8mm (.032" for those of us with imperial tendencies). So if you snug the adjuster up then back it off a full turn you'll have a clearance of 0.8mm. Half a turn would be 0.4mm and, you've guessed it, 1/4 turn (1 flat) 0.2mm. It's easy enough to estimate half a flat or even 1/4 of one.

I've no idea what the clearances are for the bike but using that method you can get them pretty close. It also avoids being fooled by wear on the adjuster / valve stem which can give wildly incorrect values.
There is in fact a proprietary tool that uses this principle - see link.
29/1/2019 4:47:29 PM UTC
Ren - The Ed said :-
I can see how that works Ian - but would it be accurate enough? Pocketpete asked a good question while doing the shims - how accurate do we need to be? Obviously Honda gives a plus or minus figure of 0.03mm but this is 1/4 of the width of a hair spliced into 20 pieces and then laser shaved. Basically it's nothing in the human scale but does it matter in the engine's scale? I'd have to suppose it does.

30/1/2019 10:18:16 AM UTC
Ian Soady said :-
How accurate? I've always worked to within a couple of thou which in modern language would be 0.05mm or so, and using the thread should easily get you this level of precision. But why not try it and see?

It's surprising how accurate the eye can be - for instance, the difference in a plug gap between .020" and .030" (.5mm - .75mm) is actually quite obvious.
30/1/2019 11:09:49 AM UTC
Rod said :-
Ian's method of using the thread is very accurate. I used it for years to save time when adjusting 16 valves on my bike.
30/1/2019 3:36:57 PM UTC
Ren - The Ed said :-
Right then gentlemen. I shall be adjusting the tappets on the CBF125 in the not too distant future. I shall try out your method and see what the feeler gauges have to say. I hope it's good because it'll make my life a lot easier. Now... I just need to find the thread pitch for the tappet screw on a CBF125. Hmmmm...
30/1/2019 4:35:02 PM UTC
Ian Soady said :-
The easiest way to check the pitch is to pop the locknut off, find a metric screw that fits it then use your thread gauge (you do have one of course) to measure the pitch on the screw. Normal pitch for M5 is 0.8mm; for M4 is 0.7mm.
31/1/2019 12:27:34 PM UTC
Upt'North said :-
Also if you've got a thread file it will give you the pitch, if you haven't got a thread file this doesn't help at all.
31/1/2019 3:23:31 PM UTC
Ren - The Ed said :-
No I don't have a set of thread gauges. Or a thread file. Maybe I'll work it out with my feelers... I might look stupid but underneath this daft exterior is a genuine idiot.
31/1/2019 5:08:23 PM UTC
Ian Soady said :-
You can get a metric thread gauge for a couple of quid, which you save the first time you avoid putting a 1mm pitch nut on a 0.8mm pitch bolt......
1/2/2019 3:04:18 PM UTC
Bob said :-
I have shim under bucket on the KLX - these I believe are the ultimate security for high revving engines. The downside is that the camshafts have to come out to alter the clearances.
My experience has been that shim top ends last longer than tappet top ends.
With a tappet the wear is always in the same place and the forces applied in the same direction, with a shim the bucket rotates in use which means the wear is more evenly distributed.
I think this plays out in the fact that tappets open up with miles, as the tappet and camshaft wear but shims close down with miles, the gradual recession of the valve into the valve seat is faster than any wear on the camshaft or bucket.
Add in the lack of reciprocating mass (fewer parts whizzing up and down) and I think that's why high performance engines use shims.

2/4/2019 10:20:32 AM UTC
Ren - The Ed said :-
As ever in the world of motorcycling (and everything else) my experience has been different. The tappets which are rocker type on the CBF125 closed up when it was new, due to recession of the valve seats. It now rarely needs adjustment as everything bedded in.

I guess the main thing to remember is to check the damn things
2/4/2019 2:49:44 PM UTC
Bob said :-
I thought the CBF has roller followers?
But yes, regular checking is the key

3/4/2019 9:00:46 AM UTC
Ren - The Ed said :-
Yes the bit of the rocker that contacts the camshaft's lobes has a roller.
3/4/2019 9:50:18 AM UTC

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