Transmission knock?

[Blaner]

I know there are thousands of posts about the classic blaster knocking noises and im pretty familiar with them. From the posts ive seen mine seems alittle different.

check out http://www.blasterforum.com/engine-13/floppy-kick-starter-odd-knock-34106/ for the story when it first came about, after this post, i installed a new kicker spring but the knocking was still there, i then proceed to eat my rings as they rotated in the bore on the next outing, check out http://www.blasterforum.com/engine-13/wiseco-ring-rotation-35302/ for that story, so i waited for 2months for my new wiseco kit to get through customs, it finally came and i had the cylinder bored 0.07mm cylinder/piston clearance. chamfered ports nicely and everything is perfect, leak test is 100% as well. so finally got it running today but the knock is still there. after my first heat cycle, i stood the bike up, removed the exhaust and checked out the rings and measure squish with a piece of solder down the plug hoe, everything was in order.

i dont believe its a crank bearing as its intermittant, random and only really audible on decelaration, while the motor is reving up, its not there. i cant hear anything abnormal while listening to the motor in several places with a big screwdriver, all bearings sound good.

So could this be a knock in the transmission shafts as the load is removed and the motor decelarates? all the tranny bearings have been changed not so long ago, all genuine yamaha bearings right round, running yamalube 2stroke transmission oil. im wondering if its connected to the kicker spring issue.

OR...am i stupid and is this normal?

 

[slickerthanyou]

Sounds to me like a timing issue , but i do here a knocking.

 

[Blaner]

Forgot to mention that i turned the timing back to stock during the rebuild, i had it at +4. if it was detonating why would it do it under decelaration/closed throttle?

 

[Blaner]

video2

 

[Surfrjag]

i had an issue with that when i had my oko carb. i wasnt sure why but my guess is that during low throttle its lean but you hardly use that area for acceleration. as soon as i would let off the throttle i would hear it pinging its butt off. i started going larger on my pilot and it helped but later found that sicivic had better luck with a larger needle in that perticular carb. i dont hear much of a knock in it. is it more audible in person?

 

[Blaner]

ok, well at the moment im still running the stock 26mm Mikuni. just got the OKO. its pretty rich at idle, maybe a little too rich. it is a little more audible in person, enough to catch my attention as odd

 

[Surfrjag]

i posted before the 2nd vidio... i can hear it a little better now. did you ever split the cases? the last motor i tore down the counterweight bearings were bad enoughh that the counterweight was rubbing on the cases next to the crank case. just a thought...

 

[Blaner]

had cases apart last year july. bearings were still good, i did however notice a couple teeth on some of the transmission gear clusters looked like they had minced something in the passed, there engaging surfaces were damaged on about 4 teeth in succesion but no sign of debris, i think it was from the previous owner. im wondering if the shafts have a bit of end play, or perhaps the clutch boss? it would explain the noise when decelerating as the power is released.

 

[toytech]

check the rubber bumpers in the balance shaft gear, my buddy's just went bad and it knocked on decel

 

[Blaner]

check the rubber bumpers in the balance shaft gear, my buddy's just went bad and it knocked on decel

what rubber bumpers are you talking about here?

 

[toytech]

what rubber bumpers are you talking about here?

if you look at the balance shaft gear you will see it is a 2 peice gear with rubber bumpers in it to take the shock force of the shaft, like the springs in a car clutch,hope this helps

maybe I should call them rubber cushions?

 

[Blaner]

Mmm, ok, i found this Balance Shafts - Loose Gears Hurt Ears and it is what you are talking about, it could very well be lash at that point. does anyone else care to chime in?

 

[Blaner]

check the rubber bumpers in the balance shaft gear, my buddy's just went bad and it knocked on decel

can you tell me if the knock on your mates was the same as mine in the vids? a random, dull knock, more pronounced on decel?

i will have a look at the gear tomorrow as last year i noticed it seemed a bit floppy, even when tightened but wasnt sure if it was normal or not.

 

[toytech]

can you tell me if the knock on your mates was the same as mine in the vids? a random, dull knock, more pronounced on decel?

i will have a look at the gear tomorrow as last year i noticed it seemed a bit floppy, even when tightened but wasnt sure if it was normal or not.

it was pronounced on decel, but it made noise all the time wile idleing, but not as much.

 

[Blaner]

sounds like my problem. i dont think it possible to change the rubbers tho is it? i think the gear comes a unit?

 

[toytech]

sounds like my problem. i dont think it possible to change the rubbers tho is it? i think the gear comes a unit?

yes the gear is a unit, check yours before you buy a new one first, there shouldn't be any play in the two halves

 

[Blaner]

do you mean circumferential play or lateral? mine has no lash between the gears but wobbles laterally on the shaft a bit. i have also found the clutch basket has play..slap between the crank gear and the big basket gear, i see it ate a piece of the kicker spring, posted a vid in http://www.blasterforum.com/engine-13/clutch-basket-play-37298/#post460481.

 

[jong93]

trany cluster is cheep on ebay

 

[Blaner]

solved, was the left wrist pin clip, went missing, pin was knocking on cylinder wall which is now scored...