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May 30th, 2004, 10:34 AM   #1
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strange noise

i raced for 2.5 hours saturday and 4 hours today, a report of sorts will appear when i get my energy levels back up!

in the meantime i need some help, the bike is making a strange noise!

it only happens at high revs and especially in higher gears.

what i've done lately
camchain tensioner extended
slotted camwheel
4 new valves and seats kissed
FC tailpipe
gone back to manual decomp

as you rev past half way the bike sounds like the tailpipe has come away from the middle section. it sounds like you've pinched yer nose and made an engine noise.

the pipe isn't that loud but this noise is!

it's in every gear but it sounds as if it starts lower in the revs as you change up. it loses power immediately!

i'm going to go through everything but it would be nice if we could cut corners here folks!

thanks for any help

Taffy
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May 30th, 2004, 10:47 AM   #2
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Hi Taffy,
What you are describing is indicative of valve bounce.

May I suggest:
Using a suitable tachometer test and see if the problem takes place near the same engine rpm regardless of gear selection and / or throttle position.

Hope this helps.

Best regards,
Dale
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May 30th, 2004, 02:36 PM   #3
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dale

i told you that i'd gone to a slotted camwheel. i'm concerned how the bike consistantly ran really well yet did this. it was on my mind but because i found the centre to tail were bolted almost apart i found myself blaming the exhaust springs at high revs.

mmmmmmmmmmm!

it's only just started though-never had this before.

head off and see soon.

Taffy
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May 30th, 2004, 05:55 PM   #4
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Sounds like a bad valve job to me. Check your seats make sure you check every measuremnt and to see if it may be out of round.
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May 31st, 2004, 09:54 AM   #5
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Dale

i have the head off and all i've noted is that the valve springs are good, the extended camchain tensioner is working a treat, the slotted camwheel isn't moving, the manual decomp looks unmarked and adjusted nicely.

there is a small leak between the centre and tailpipe. i feel the camshaft may be 1 tooth out however but that's my fault. there are no marks on the piston or valves. the cam follower bearings have finally given up the ghost! when i checked them before the weekend they seemed solid and in good nick!

Q; why do i have valve bounce this time when i've never had it happen before?

regards

Taffy
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May 31st, 2004, 10:00 AM   #6
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Hi Taffy,
Simply cutting the seats during a routine valve job can reduce the valve spring seat pressure enough to allow high rpm valve float and / or bounce.

What is your current installed valve spring height?

In addition you say the followers have failed. Please keep in mind that loose tappet adjustment as a result of worn followers will induce valve bounce as the closing ramp of the cam is now being bypassed.

Best Regards,
Dale
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June 1st, 2004, 01:28 AM   #7
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Dale

just called my dealer and described the running noise. he said:

"that will definately be your cam timing, you've got the cam one tooth out, that's all you have to do. i'm 100% certain."

then i told him that i'd found the cam timing out one tooth!

a pair of rockers, each with pin and follower bearing will cost £93 + VAT and i put in my own screw and locknut. rocker spindle should be OK.

Taffy
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June 1st, 2004, 06:43 AM   #8
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Good deal Taffy.
Please keep us posted.
Best Regards,
Dale
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June 5th, 2004, 01:08 PM   #9
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ok

fitted new rockers and adjusted tappets. set valve timing again and went for a run on the roads (read thrashed it!). no noise.

Taffy
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