Re: Valve Clearances

[Eric Sheley <eric@xxxxxxxxxx>]

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

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