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Re: Valve Clearances
- Subject: Re: Valve Clearances
- From: dan & ann curcio <curcio@xxxxxxxxxx>
- Date: Fri, 09 Jul 1999 11:06:33 -0500
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.
>
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