does wrist pin knock go away with throttle? | cvetitula.ru
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post #1 of 25 (permalink) Old 05-06-2014, 06:31 PM Thread Starter
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does wrist pin knock go away with throttle?

still trying to diagnose this tapping/knocking sound in my 300. new top end, new cam chain, new tensioner, new cam chain guides, new clutches, new plug, new oil, new filter...

today i took the rocker covers off to check the valve clearance for the 12th time in a few days. hooked the gas tank up, and started the motor up with the covers off. getting excellent oil flow, and the rockers and cam are silent. actually, they have a high-speed fan sound to them, pretty neat...
all bolts are torqued down. muffler baffle is fine. no loose parts rattling anywhere.

anyway, the noise is not there when the motor is first started. it comes on about a minute afterwards, as an intermittent tapping noise. when the throttle is blipped, it goes away completely. if i idle it up some and hold the throttle constant, it comes back. when i decelerate it is really loud. when i put it in gear and move, it goes completely away, but if i slow down, it sounds loud and faster than the engine rpms, if that makes any sense?

while the motor is under load, quiet as a goose.

my question is, what does this leave as the culprit? when i had the motor down, i checked the lower crank rod bearing, and am 100% positive it is not that, but can't remember checking the small rod end to wrist pin clearance. does that sound like the issue? does it go away with throttle and/or load in the motor?

also, i need to say, it had this noise before the rebuild, and was still doing it the first time i cranked it after rebuilding the top end.

i also need to add, the cam chain i used i thought was DID, but i found the box it came in, and it is not a DID chain. could it have been bad when i just bought it new? the tensioner will not go all the way back into the hole with it extended, lacks about an inch or so.

i really would like to enjoy this bike, but so far i have spent lots of money and still can't enjoy riding it for fear of it blowing up...

if the rod turns out to be the issue, i am not sure i want to sink another 500 dollars and the time in it to fix it. i am about as spent out on this thing as i am going to get.

when i let it idle, it begins tapping, then goes away for a second, then comes back.
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post #2 of 25 (permalink) Old 05-06-2014, 07:20 PM
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I had a bad piston pin on my Yamaha and there is NO doubt when it gets really bad. The knocking is present almost always and very loud. Perhaps your pin is not as worn as mine was because your symptoms seem similar. Mine actually ran great but the knocking was obnoxious as hell. I tore it down and put in a new piston and pin and it is running like a top now without a single knock. was a $100 fix for mine. Friends told me first it was probably the rod bearing, but when I tore it apart, that bearing was nice and tight with no outward play. I could wiggle my piston back and forth and the pin actually had a worn spot in the center from the rod.

Greg
League City, Texas
1994 Fourtrax 300 4X4
2006 Yamaha Grizzly 660 Special Edition
1991 Yamaha Big Bear 350
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post #3 of 25 (permalink) Old 05-06-2014, 07:25 PM Thread Starter
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Quote:
Originally Posted by Greg1994 View Post
I had a bad piston pin on my Yamaha and there is NO doubt when it gets really bad. The knocking is present almost always and very loud. Perhaps your pin is not as worn as mine was because your symptoms seem similar. Mine actually ran great but the knocking was obnoxious as hell. I tore it down and put in a new piston and pin and it is running like a top now without a single knock. was a $100 fix for mine. Friends told me first it was probably the rod bearing, but when I tore it apart, that bearing was nice and tight with no outward play. I could wiggle my piston back and forth and the pin actually had a worn spot in the center from the rod.
already has a new piston and wrist pin. rod bearing on crank has zero play.
does not do it all the time. only when idling or letting off of idle, NOT under load or revving.
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post #4 of 25 (permalink) Old 05-06-2014, 07:40 PM
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Did it make this noise before you did all of the work to it?
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post #5 of 25 (permalink) Old 05-06-2014, 08:02 PM
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and your working on a what ??..lol. trx300 ?.

'89 trx350D foreman 4x4...'85 vf700c magna, '03 trx450fm foreman 4x4, 2015 Yamaha waverunner fx cruiser ho, '08 vt750c2 shadow spirit
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post #6 of 25 (permalink) Old 05-06-2014, 08:33 PM Thread Starter
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yep, made the same noise before i tore it down and rebuilt top end.
and shade, it's my trx300fw.
just went out and eliminated cam chain as a suspect- we put the manual tensioner back in and tightened it to spec so it was tensioning the cam chain quite a bit, and still the same noise.

so far we have eliminated:
cam chain
valves
big rod end bearing
rockers
muffler
compression release lever
clutch noises
loose/missing bolts
valve clearance
camshaft

what else is there, besides the small rod end?
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post #7 of 25 (permalink) Old 05-06-2014, 08:34 PM Thread Starter
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here's another video i took today:

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post #8 of 25 (permalink) Old 05-06-2014, 08:41 PM Thread Starter
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and it sounded like it does do it when revving in neutral. but when you take off, in gear, no noise.
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post #9 of 25 (permalink) Old 05-06-2014, 10:34 PM Thread Starter
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I am thinking more and more about just taking the motor all the way down and replacing the crank and rod.
Everyone says it's a big job to split the cases I am wondering how long it should really take going be the manual and first time from start to finish?
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post #10 of 25 (permalink) Old 05-06-2014, 10:53 PM
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If it goes away under load,that leads me to believe it may be in the clutch or tranny????
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