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Discussion Starter · #1 ·
Hi all ive recently bought a 98 sc33 and have noticed a persistent rattle from the top end under acceleration between 2.5/3k rpm and it stops the second it hits 4k
This is on anymore than 1/4 throttle in all gears and is not changing with engine temp.
When i mean acceleration its not hard on the stop but even filtering traffic or gentle back lane work just as you open the throttle past 1/4 its starts. I can ride around it but even pulling away in first and bringing it up to 30mph etc its there.more than 4k its gone!!
Power delivery is fine no flat spots or hesitation and pulls well all the way to redline.
im a car mechanic by trade and to me it sound like a worn cam chain or piston slap but am wondering if anyone else has/had the same or similar before I start digging around under the fairing.
Im planning on pulling it apart over the winter anyway to refresh the old girl but a second opinion would be nice.
Also milage is unknown as this is not its original engine. Im told the original fell fowl to a broken chain making its self comfortable in the casing
Any advice would be appreciated.
 

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sounds like cam chain or tensioner or both. if your having a rebuild over the winter i would change both, cam chains need changing every 40,000 miles with normal riding, lower with more abuse, a mate of mine fitted a new one and with in 10,000 miles he snapped it! but he rode full throtle or nothing!
 

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Discussion Starter · #3 ·
Thanks for that , il get a chain/guides and tensioner on order then.
Im hoping its nothing more sinister, I would expect piston slap or little ends to be effected by temp change where this remains constant.
 

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If it was cam chain it'd be more noticeable on deceleration, not acceleration.
 

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Thanks for that , il get a chain/guides and tensioner on order then.
Im hoping its nothing more sinister, I would expect piston slap or little ends to be effected by temp change where this remains constant.[/QUOTe

do your valves clearence at the same time, these engines pick up rattles here there and everywhere, my bro 97 has a tap at higher rpm because of worn valve buckets but thats nothing to worry about, my chain is due and starting to rattle so i have to do it, mines just hitting 41,000 miles
 

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Hi all ive recently bought a 98 sc33 and have noticed a persistent rattle from the top end under acceleration between 2.5/3k rpm and it stops the second it hits 4k
This is on anymore than 1/4 throttle in all gears and is not changing with engine temp.
When i mean acceleration its not hard on the stop but even filtering traffic or gentle back lane work just as you open the throttle past 1/4 its starts. I can ride around it but even pulling away in first and bringing it up to 30mph etc its there.more than 4k its gone!!
Power delivery is fine no flat spots or hesitation and pulls well all the way to redline.
im a car mechanic by trade and to me it sound like a worn cam chain or piston slap but am wondering if anyone else has/had the same or similar before I start digging around under the fairing.
Im planning on pulling it apart over the winter anyway to refresh the old girl but a second opinion would be nice.
Also milage is unknown as this is not its original engine. Im told the original fell fowl to a broken chain making its self comfortable in the casing
Any advice would be appreciated.

Sounds like detonation to me, don't use hard throttle below 4000RPM.
 

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Reported Post by kev.basley

Hi bladeracer its not hard throttle literally 1/4 turn is all that is needed to do it. In first gear getting up to speed before gear change. I would understand it being detonation if I was holding it the stop but im not. Just tickling her along. Even if your cruising along in fourth say 60mph and just tickle the throttle it will do it untill the rpm hits 4k then it stops.
Il be droping the lump out shortly anyway and il get a borescope down the plug holes and look for any pitting in piston crown in case it is detonation. But seems to run too well across the rev range to be bad fueling or timing

bladeracer
[/quote]Sounds like detonation to me, don't use hard throttle below 4000RPM.[/quote]
 

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Discussion Starter · #9 ·
update on the rattle, i have the engin on the bench now and it seems bladeracer you might be right with the detonaion theory.
The chain is tight and tensioner seems to be holding good tension and guides look ok.
Having taken the plugs out it looks like its running a little lean.
Its got a micron full stainless exhaust and the carbs have 122 jets across all carbs. I thought they ran different sizes in the inner two cylinders. ?
Bladeracer do you or anyone know or can suggest a jet size. And do you think this maybe a cause for detonation. ?
I will be using a boroscope tomorrow but from what I can see through the plug holes there maybe some pitting in the crowns of the pistons backing up the detonation theory.
Any more advice is greatly appreciated
 

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Discussion Starter · #10 ·
Todays update definatly detonation. Thanks bladeracer for the heads up. Hopefully the pic will attach of the boroscope image of no 4 piston
 

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Boroscope image
Hello I think I have the same problem with my 96 blade 45 k miles a tingling noise at about 3 to 4 k checked timing did the valve shims new chain ect looks clean inside ,now to my point it has a kn filter Aviopak so manifold exaust would this possibly cause a weak mixture at this rev range under load and is it possible to re jet carbs
Many Thanks and happy riding
 
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