Adjusting tappets

[Feasty]

There's plenty of info and stories on BCF and Google searches etc, but I'm having trouble finding out more basic stuff about this.

Firstly, why do bikes need tappets adjusting? And why don't cars?

Secondly, what would happen to a bike if you never adjusted the tappets?

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Previous: Aprilia Habana Retro 50cc (beauty), Yamaha SR125 (fell apart), Honda XR125 (nippy little commuter), Honda SLR650 (Geewhizz), Yamaha Diversion 900S (Smoooooth) written off courtesy of a stupid escaped horse.
(7 year gap), BMW F650 (Relaxing ride). Aprilia Caponord ETV1000 (Big and bold). Yamaha FZS600 (got me in trouble too quick!).
Current: Yamaha TDM 900 (Comfy, light but big, power when needed). Also now a Tiger 1050, easily best of the lot!

[Itchy]

They need adjusting to annoy us, but the kickstartian answer would be that it makes the whole head of the bike smaller and lighter.


Not adjusting tappets, worst thing is that the piston hits the valves bending or cracking them, usual thing is iffy performance.
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[virus]

Cars still need 'tappets' doing, one of the Ferrari engined Lancias had a 32 valve engine, 4 hours labour to do the valve clearances on that bugger.


tappets are actually a nickname for cam followers, as they 'tap it' (it being the cam lobe hitting the followers)

Screw and locknut adjustment is by far the easiest, rotate engine to tdc on the compression stroke to close both valves, push the rocker down if there is any play, then feeler gauge in between the screw and the valve head, if its not set right then use the screw and locknut to adjust. remember to hold the screw in place when tightening the locknut otherwise it will turn and change clearances.

Shim adjustment is a pain in the arse, and if your lucky (shim over bucket) requires moving the rockers out of the way, lifting a piece of metal (shim) off the top of the valve and replacing with one that is the correct size to set the valve clearance. if your unlucky then its shim under bucket and youve got to set to TDC, remove camchain tensioner, remove cam, remove bucket, change shim then re install bucket, cam and camchain tensioner.

Screw and locknut is normally recommended to check every 1500 miles, shim generally every 3-4k

Incorrect clearances can cause many problems, if the clearance is too small or negative clearance then the valve wont seat propperly, which results in all the valve spring pressure slamming the valve head into the rocker gear, damaging the valve and gear, also if it doesnt seat you get lower compression, and valves can burn out as they use the seat to get rid of the temperature in the valve.

If the clearance is too much then the valve will open too early, can potentially hit the piston and cause expensive damage, and will also leak compression. it will also wear out the cam lobe and followers as they contact.

Cheers
John


p.s. can you tell ive been doing a lot of valve work recently?
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[Vincent]

As the valve seats wear, the valves go further up into the head leavng less gap between the rocker and valve stem. A lot of folks think that the gap gets bigger, resulting in a loud tapping noise so, unless they are making a noise, they tend to get ignored resulting n worn rocker facings or bent valve stems or push rods..

[ms51ves3]

[Blau Zedong]

Most cars that are not fucking shite have hydraulic tappets, however the general consensus is that they are not suitable for the greater engine speeds associated with bikes. Honda did give them a whirl in the CBX750 in the 80's though.
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[user]

[yen_powell]

My FJ1200 with shims on top of buckets could be checked in a few minutes once the cover was off. If you didn't bother with the Yamaha tool and used a flat bladed screwdriver instead, a shim could be removed in about 2 seconds and put back in the same time. The trick was to twist it into the notch of the bucket and the shim would pop out. You could push it back in with a thumb.

I did my old GPz750 years ago and that was a pain with having to remove both camshafts. I used tippex to mark the camchain and sprockets so the timing was okay upon reassembly.

My Africa Twin is screw and locknut (6 valves) and takes longer to check let alone adjust. It's like keyhole surgery through the small inspection covers. Having said that I have found they hardly ever need doing anyway and over the years I've gone from 8,000 mile checks to about every 24,000. Even then it's usually only one of the six that needs a slight adjustment. One of the benefits of a low power output I suppose.
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[Blue_SV650S]

[virus]

[sickpup]

[virus]

[Shreddie]

I may be a massichist but I quite enjoy doing valve clearances/balancing the carbs. I used to do it every 3k on my GPz and GT... I was almost a little disappointed when I found that the VFR I'm getting only needs it every 16k.

[Howling TerrorOutOfOffice]

Stoopid little Honda locknuts.
https://i104.photobucket.com/albums/m174/howlingterror_2006/IMG_0246001.jpg


Pat
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[Vincent]

[Blue_SV650S]