Re: Valve Clearances

[dan & ann curcio <curcio@xxxxxxxxxx>]

Eric,
Thanks for the info.  Still waiting for my shop manual so the comments helped me
understand.
Dan

Eric Sheley wrote:

> Dan, here are some responses to your questions from another source more
> qualified to answer them.
>
> Hope this helps
>
> - Eric
>
>  >At 10:18 AM 07/08/1999 -0500, dan curcio wrote:
>
>  >I think I need a little education on valve clearance problems on cycles.
>
> Our bikes have the shim on top of the bucket. The bucket diameter is 28mm
> and the shim is 25mm, The cam lobe wipes the shim off centre. This causes
> the shim to spin in the bucket. All the one's I have seen have had no wear on
> the shims at all and the gap will tend to close up rather than open
>
>  >From my experiences with DOHC car engines worn valve shims rarely cause
>  >significant valve damage.  Usually the worst problem I have seen is
>  >significant noise with reduced performance due to incorrect valve timing
>  >because the valves are closing too early and staying closed too long.
>  >Usually, the only damage to the valve is a mushroomed tip from the excessive
>  >pounding due to the large clearance and this takes quite a bit of time to
> happen
>
> The closure of the gap tends to improve performance up to the point where
> the valve is held open. The reason for improved performance is longer duration
> and lift. Our bikes run very tight clearance .010-.015 mm on the inlet
> and .015-.020 on the exhaust.
>
> Yes, bigger clearance will show up as more noise well before it does any
> damage.
>
>  >Burnt valves usually are caused by valve clearances that are too
>  >tight and the valve is not allowed to close fully into its seat causing
>  >leaking combustion gases to burn the valve/seat.
>
> Yes, The bike will also start to become rough at idle.
>
>  >A worn shim should cause
>  >the valve clearance to increase instead of decrease, right?  If this is
>  >correct the burnt valves on the T509 and Daytonas were probably caused by
>  >valve tip, head, or seat wear causing tight clearances and the shims were
>  >not the culprits.  Please help me understand
>
> Yes, the gap will get bigger if the shim is worn, The early bikes tended to
> tighten up the clearance and cause the valves to burn. I checked mine at
> 14,000
> KM and some of the exhaust valves had .004mm. This is only a couple of thou
> and
> would have been partly open when the motor heated up.
>
>  *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
>  The ST Mailing list is sponsored by the Unofficial ST Website
>    http://www.TriumphNet.com/st for ST and Mailing List info




 *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
 The ST Mailing list is sponsored by the Unofficial ST Website
   http://www.TriumphNet.com/st for ST and Mailing List info

=-=-=-= Next Message =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=