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i've got a 2002...ran it out of oil late last year so did a bunch of top end work to make the bike a 426...we bilieved that the connecting rod was alright and in spec, at least at the piston end....took the bike out last weekend and almost didn't make it back....i pushed the bike pretty good in high rpms and it pseudo-siezed...stopped and then kicked the bejeezes and got it started again...now it has a serious knock when i try to wick open the throttle fast...the sounds seems like it's coming from the top of the engine by the intake valves

the bike starts fine and idles fine but i don't know what to do, can you guys give me some advice? thanks alot

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If you think it's coming from the top end, then you should probably do a valve clearances check, at the very least. Might have had a nut come off one of the rocker adjusters. Next would be to take off the head cover and look things over.

Worst case, I wouldn't rule out the bottom rod bearings being bad.

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yeah, first thiing i did was check the valves when i got back home..they are still at the correct clearance

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i went out and played with it a bit today...it seems that the 'knock' or slap the i hear is only when i whick open the throttle real hard, like for pulling a wheelie...if i slowly roll on the throttle i don't get that slap or knock sound

the sound definitely seems to be coming from the intake side up where the carberator is

the compression ratio on this 426 piston is 11:1, could this sound actually be a ping or some kind of explosion of the air/fuel mixture making this sound...rather than some kind of mechanical metal on metal slap

any advice is appreciated..i'm running the stock carb...could the pumper solve this?

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If the knock wasn't there before you took the bike out and only happened after you siezed it, a pumper carb isn't going to fix it. The problem is somewhere else.

Was the ride last weekend the break-in ride for the 426?

Did you change the jetting in the stock carb for the 426?

Still running the stock cam with auto-decomp?

Was the timing chain checked/replaced for wear?

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If the knock wasn't there before you took the bike out and only happened after you siezed it, a pumper carb isn't going to fix it. The problem is somewhere else.

Was the ride last weekend the break-in ride for the 426?

Did you change the jetting in the stock carb for the 426?

Still running the stock cam with auto-decomp?

Was the timing chain checked/replaced for wear?

not quite a break in ride...i put in a fatter pilot and fatter main jet (65, 165) just too be safe, the plug was looking ok at this setting

i also replaced the timing chain at the time of this topend (Nov/Dec)

got the stock cam and auto-decomp still on there

but i started out the ride pretty gently...the bike was kind of making a fluttering sound in 4th or 5th gear at high rpm, kind of a buzzing sound that went away when i backed off on the throttle a bit

towards the end of the ride (75 mile) i started to push the bike to see what would happen...so i didn't back off on the throttle this time and the bike just kind of died out....it had plenty of oil in it...spent about 20 min kicking it and it started up again, this is when i noticed it making this knock sound when the throttle wicked open fast.

this went down a couple weeks ago...now the bike starts in two kicks and the idle sounds great...but i can't wick open the throttle without making this slap sound..oh, it doesn't make that sounds throughout the cycle, it just makes it when you turn the throttle real fast

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since it starts fine and has no "knocking" while idling, it could be detonation. i would tend to think if it were mechancial you would here all the time. 11:1 is a pretty high comp ratio. what grade fuel are you using? if you are using pump gas, even premium, it may not be a high enough octane rating. i would suggest buying race fuel and mixing 50/50 with pump gas to see if it helps.

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yeah, i'm using probably 91 octane in it right now...i can get 100 here is town...i'll try it, certainly quicker than tearing it down, and not knowing what to look for

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I had an 86 XL 600 that made a similar noise to what you describe during hard acceleration and it turned out to be the wrist pin out of spec. I replaced it and solved the problem. If it were detonation it would happen more when hot and would sound like pinging, is the knocking evident when cold?

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I had an 86 XL 600 that made a similar noise to what you describe during hard acceleration and it turned out to be the wrist pin out of spec. I replaced it and solved the problem. If it were detonation it would happen more when hot and would sound like pinging, is the knocking evident when cold?

i went out today just to start hoping the problem disappeared...the bike starts just great, literally two kicks from cold...so the engine is basically cold and i get that knock when i wick open the throttle fast, when i slowly roll it on don't get that sound

we measured up the piston side of the connecting rod, it was exactly the measurements in the book..so as in your experience, if the connecting pin were bad, then what was occuring on your bike was piston slap? the piston was making slight contact with the cylinder wall? did you see some marks on the cylinder wall and on piston skirt?

it sure would be nice if they had a video that included all the different sounds from different engine problems

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I'm wondering too if the auto cam chain tensioner was reset properly when the new chain was installed.

what do you mean, just make sure that little spring and pin are in the vylinder head...then make sure to set the cam with lobes down and have flywheel at TDC..then bolt on the cilnder head cover...right?

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Do you have a copy of the service manual? If so, look on page 7-22.

You want to make sure the plunger cannot be pushed in by hand. If it can be, then the plunger teeth are stripped. If it seems ok, then use screwdriver or tool shown to retract and hold the plunger retracted while re-inserting the assembly into the head and re-install the 2 bolts. Then let the plunger extend by removing the tool.

I'm thinking that if the auto tensioner is somehow messed up, it's going to allow too much slack in the cam chain and when you whack the throttle open you might be hearing the chain whack the inside of the head or the excessive slack is throwing off valve timing and you may be hearing a valve hit the piston.

Maybe a long shot, but something to consider when it's proving difficult to diagnose.

How does it sound if you do a steep hillclimb in first gear, using the engines torque to get you up, not a running start with lots of momentum. Does it rattle constantly while there's a high torque load on the engine?

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i went out today just to start hoping the problem disappeared...the bike starts just great, literally two kicks from cold...so the engine is basically cold and i get that knock when i wick open the throttle fast, when i slowly roll it on don't get that sound

we measured up the piston side of the connecting rod, it was exactly the measurements in the book..so as in your experience, if the connecting pin were bad, then what was occuring on your bike was piston slap? the piston was making slight contact with the cylinder wall? did you see some marks on the cylinder wall and on piston skirt?

it sure would be nice if they had a video that included all the different sounds from different engine problems

No damage to the cylinder was found, the wristpin was knocking inside the piston itself. I found very little piston skirt scarring but I did not run it long with this noise occouring, the rod end was fine the wristpin was not.

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