Pssst. Don't tell anyone I asked, coz I feel like should know already!!

[baldy3853]

ONLY EVER CHECK THEN WHEN THE MOTOR IS COLD!!!!! When checking let the motor cool down over at least a 24hr period and don't wipe the oil away in doing that you will get a more accurate reading

[NJona86FJ]

Cheers Arnie... I didn't think of that... valve faces wearing down...  i spose i REALLY should open my old girl up and have a look.... she s getting a bit rattly and soft.... oil consumption has gone up a bit too.... 

[Arnie]

25mm shims are used in some models of Yamaha, Honda, and Toyota vehicles.  So, if your Yamaha d(st)ealer is unhelpful, try the Honda or Toyota dealer down the road for your replacement shims.

Arnie

[Harvy]

I found this somewhere........ all use 25mm shims:

Honda
CB750, CB750C, CB750F, CB750K, CB750SC dohc (79-83)
CB900C, CB900F, CB1000C, CB1100F, CBX (all)

Triumph
Hinckly triples and fours
Speed Triple, Tiger, Daytona, Trophy, Sprint

* All watercooled three and four cyl. models*

Yamaha
SRX250T (87) SRX250TC (87), XT250L & XT250LC Dual (84)
TT350, XT350 (86-00)
XJ600 Seca II (92-98)
XVZ12 XVZ13 Venture Royale Royal Star (83-93) XVZ1200, XVZ12
VMX1200 V-Max (85-02) Vmax, VMX12
FJ1100, FJ1200 (84-93)


Harvy

[NJona86FJ]

geez wish i could "find" things like that harvey!!! i had an srx 250... never knew it was shim.....but then again didnt have it long enough to work on it!!! bastard theiving ....... and they set fire to it!!!!

[fj11.5]

if you need more incentive chech my pics for the fj head,  with very bad valves, , never ever ever checked from new, and i was at least the third owner

[Jim 92FJ]

Really? Only 4500 miles on it? Where on earth did you find such a specimen? My new '92 FJ acquisition has about 8200 miles.  I'd bet that it runs like butta...  Whether the bike needs shims or not, one thing is for certain, we have many many great miles to be had. 

Good luck!

[Windmill]

Neil said, "your shims are small metal discs of a set thickness , running under your cam lobe governing how far? your valves will open.... as they have the cam lobe running onto them they will reduce in thickness(over time)  not allowing your valves to open as far"

Actually, the shims are very hard and will wear only very, very slowly.  What changes most in these engines is the valve seat which will get pounded thinner as the valve face hammers into it with each revolution.  This eventually will take up all the free play (lash) in the setup and you'll start to burn the valve face (as has already been explained).

Arnie

Well chaps, well described by you all but..... two schools of thought here, one that seats compress/wear - closing clearance over time and other shims/cam wears - increasing clearances.

In my experience of OHC engines in general, shims were held under cam followers, hence any wear spread to contact area between cam & follower. In these cases, I was always reshimming to decrease clearances so they were increasing over time.  However these were probably poorer quality engineering so cam/follower wear may have been more significant than in an FJ engine.

Checked my clearances today and on all cams -clearances were at maximum allowable. Now I'm aware mine has not been checked for some time and previous owner advised me it was well overdue. SO, if clearances will reduce with seat wear, I'm fine? On the other hand if wear will increase them, I need to shim them down

Don't feel inclined to shim them down if seats will wear and close gaps further, my head hurts.....Don't want to stir this but would really like to know which it is, both statements could so easily be correct. Any further thoughts anyone please?  

[Pat Conlon]

Kinda like my comment on chain tightening....loose valves are happy valves (to a point) Yes,  you may lose a smige power in that the valves don't open as far (doubtful you would notice on a street bike)..however, Tight valves cause expensive problems.
Wear on the Valve shim from the rotating cam lobe is miminal due to the fact that the round shims rotate in the bucket distributing the cam lobe wear over a large surface of the shim along with being bathed in oil.

Valve seats recede as the miles roll by. Just a fact of life. Valves live in a tough environment.

If your valves are on the loose end of the specification, leave them alone, they *will* tighten up as the seat wears.

[Windmill]

Thanks Pat, ok I'll leave well alone, put them down to check again in 5,000 and see if there is any clear effect.  

If I am suffering a performance loss? it's the quickest road bike I've ever had (even in my Production racer days), so it can't be much  Just a thought though, no-one has mentioned valve stretch.......but that's another can of worms

[Steve_in_Florida]

Well, that's why the shim kit contains an *ASSORTMENT* of shims in different thicknesses, so you can insert the one appropriate to the wear you're experiencing, and still be within the prescribed factory tolerance.

Ask anyone in the Volkswagen (Air-Cooled) community: "Tight Valves become BURNED VALVES"

Too little clearance between the cam and the shim means the the valve is OPEN during the power stroke. Open valves cannot get rid of their excess heat, and become scorched and cracked on the edges. The cracks become fissures, and the fissures become canyons.

Here's a link that's worth 1,000 words:

     https://www.google.com/search?q=burned+valve&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=p3NTUe_OIpOw8ATxh4DACw&biw=1440&bih=731&sei=rHNTUaCvGJT69gTO8oCACw

Keep an eye on your valve shim requirements over time. That should answer any question you might have.

Also, you can check the stamped thickness of the old valve shim with a micrometer, and verify whether or not the shim itself is wearing.

[NJona86FJ]

   this is gold.  i suppose in overview ... I LEARNT a lot... its a case of which wears first, but please lets not do a hardness comparison test on the materials.... lol... all good info

Is it just me or when you dont play with things mechanical for a while your head goes fuzzy?.... you know brainfade an all that.... must be the blonde
lol

[ribbert]

Well chaps, well described by you all but..... two schools of thought here,
Don't want to stir this but would really like to know which it is, both statements could so easily be correct.

There aren't two schools of thought here. This is not a speculative theory in which there are two camps (like oil, tyres, octane ratings etc). Several thousand FJ owners, some for decades and 100's of 1000's of km's will tell you they tighten up with use for the reasons previously explained. Other engines and other configurations do other things.
Noel

[RichBaker]

Neil said, "your shims are small metal discs of a set thickness , running under your cam lobe governing how far? your valves will open.... as they have the cam lobe running onto them they will reduce in thickness(over time)  not allowing your valves to open as far"

Actually, the shims are very hard and will wear only very, very slowly.  What changes most in these engines is the valve seat which will get pounded thinner as the valve face hammers into it with each revolution.  This eventually will take up all the free play (lash) in the setup and you'll start to burn the valve face (as has already been explained).

Arnie

Well chaps, well described by you all but..... two schools of thought here, one that seats compress/wear - closing clearance over time and other shims/cam wears - increasing clearances.

In my experience of OHC engines in general, shims were held under cam followers, hence any wear spread to contact area between cam & follower. In these cases, I was always reshimming to decrease clearances so they were increasing over time.  However these were probably poorer quality engineering so cam/follower wear may have been more significant than in an FJ engine.

Checked my clearances today and on all cams -clearances were at maximum allowable. Now I'm aware mine has not been checked for some time and previous owner advised me it was well overdue. SO, if clearances will reduce with seat wear, I'm fine? On the other hand if wear will increase them, I need to shim them down

Don't feel inclined to shim them down if seats will wear and close gaps further, my head hurts.....Don't want to stir this but would really like to know which it is, both statements could so easily be correct. Any further thoughts anyone please?  

This is a good explanation of Valve Seat Recession, which is what causes the valve clearances to get tighter over miles....
Remember, a tappy valve is a happy valve.  

[Windmill]

Is it just me or when you dont play with things mechanical for a while your head goes fuzzy?.... you know brainfade an all that.... must be the blonde
lol

Don't worry Mate I've got it too, only it's not the blonde................it's the Gray