engine knock help needed

[chadwindom]

i have a blaster that we just rebored it and a new wisesco piston and its has a bad knocking sound wondering what it could be

 

[sicivicdude]

piston slap, circlip out of groove allowing wrist pin out of the side of the piston, bad main bearing, bad crank bearings, damaged primary gear, broken clutch basket, bent crankshaft allowing the flywheel to hit the stator.

 

[blasterdemon7]

It could be a bad bore. The piston to wall clearance could be to large. How did you do the break in?

 

[chadwindom]

we did 3 10min idles then road it easy still havent gotten on it hard

 

[blasterdemon7]

Who installed it? Was the gaps in the rings lined up with the pins? Did you do a leak down test?

 

[chadwindom]

we did it (me my dad and brother) we line the rings up (would the piston even fit in the cylinder) but we didnt do a leak down

 

[bsanders_06]

i had the same question yesterday..some people said it was normal for a blaster to sound like that and some say it isnt...still not sure but a guy posted a link to a video of another fellas blaster making the same noise and then some on here said it was normal and mine sounds just like he did..sounds like a knocking sound coming from somewhere on the topend

 

[sicivicdude]

Yamaha blaster engines are normally a little noisy even when everything is in spec. My engine makes some ugly noises and I've pulled the top end off three times and split the cases once and it STILL makes some nasty noises. Nothing has changed that.

If the sound is EXTRA bad or you suspect that there's a problem with your engine (low compression or hanging revs) you should certainly look into your engine. There are about as many sources of noise on a blaster engine as there are parts inside that engine.... you'll need to go through them one at a time to eliminate potential causes

 

[chadwindom]

ok this knock is not constant but when it does it was at mid rpms knock very much at idle

 

[Awk08]

was the old piston shattered sending shrapnel into the bottom end ???

 

[chadwindom]

a chunk of the ring broke of and chewed up the piston but only the top half of it and we found the piece in the pipe so we dont think any went down there

 

[Awk08]

was the rod bearing play checked ??? up/down and side to side measured

 

[Blaaster]

Why in your opinion did the ring break?

Are you pre mixing fuel, or is the injection still hooked up?

Have you done any mods, if so did you change the jetting?

Have you re tightened the head and jug bolts?

What is the compression reading?

 

[Blaner]

Check this out...

http://www.blasterforum.com/engine-13/transmission-knock-37163/#post461246

follow the other links in this thread and watch the vids.

Turned out both circlips were in the same hole

 

[chadwindom]

there was no up and down play but some side to side but we didnt measure it
not sure why the ring broke but we think it was to lean so we put a bigger jet in after the rebuild
we are mixing and yes we rejetted it after mods
do not no the compression but by the kick start it seems to have very good compression

 

[Blaner]

do a comp test and a leak test ASAP. they are your 1ST troubleshooting tools. if you dont do them and get the result you could chase your tail for ages.

the conrod side play (runout) is normal but it needs to be within spec given in the manual.

 

[chadwindom]

ok we will do that dont have the tools to do a leak down test. what would i need for that?

 

[Blaner]

DIY: http://www.blasterforum.com/do-yourself-20/build-use-leakdown-tester-10663/

Or contact Slickerthanyou, a member on here. he makes leak testers very nicely.

 

[chadwindom]

ok thanks alot we hopefully will be able to do that soon

 

[Blaner]

can you give more details about the knock? consistent? irregular? deceleration only? acceleration only? dull sounding? sharp sounding? heavy sounding? light sounding?

maybe when you have it running again take a vid and youtube it, post the link here. But please perform said tests first before starting it again