is it blown???
- Thread starter 91yamahablaster
- Start date
also there was a high amount of black stuff in cylinder and on top of head it was really wet and it was in all the ports
It doesn't look blown from those pictures, just coked all the pieces....
Coking is what happens when the oil and gasoline aren't burning efficiently and they leave deposits. Some deposits are normal and if that engine has been together for a handful of years, that's about right. If it's not been together very long at all, that's abnormal.
Why was the engine torn down?
Coking is what happens when the oil and gasoline aren't burning efficiently and they leave deposits. Some deposits are normal and if that engine has been together for a handful of years, that's about right. If it's not been together very long at all, that's abnormal.
Why was the engine torn down?
because i was riding it and had a known airleak.(i know im a dumbass) and then i heard some loud knocking and it died and wouldnt start back up so i figured blown motor?
from those pictures, it's not "blown" in the normal context. Knocking with an airleak is usually a sign of a lean condition causing predetonation. That piston looks like it's been getting excessive blow-by while under a rich condition....
well as far as i can tell it is i cant feel any scrathes or anything there is some lines that run up the cylinder but when i use my magnifiing glass its just on the surface. only thing with the cylinder is the ports looked caked with black gunk:-/
you should just start fresh, and buy a new piston and send the cylinder to ken for a fresh bore...
Just looks to me like it was extremely rich. or as SI says not being burnt correctly. Possibly due to poor ignition function, many causes, source coil bad, plug wire or boot bad, ignition coil bad. I have had no luck with stock ignition coils, went through 4 of them in one riding season. I will not use a stock coil ever again, On the other side of that alot of guys have had no issues! I'd start with the simple stuff-
if ya have a 03+ try this-
http://www.blasterforum.com/engine-13/ignition-troubleshooting-03-a-46160/
if ya have a 88-02 do these checks-
http://www.blasterforum.com/engine-13/ignition-troubleshooting-88-02-a-46159/
If all checks good, try another ingition coil and plug boot.
if ya have a 03+ try this-
http://www.blasterforum.com/engine-13/ignition-troubleshooting-03-a-46160/
if ya have a 88-02 do these checks-
http://www.blasterforum.com/engine-13/ignition-troubleshooting-88-02-a-46159/
If all checks good, try another ingition coil and plug boot.
Might need to measure the piston to cylinder clearance, I didn't notice the blowby... But defitely seems to be a clearance issue, rig gap, pistion to cylinder.
only jetting i did was with the air screw. and sorry if this is a dumb question but how do i measure those clearences?
Blow by isn't about the mixture ratio (lean or rich). Gas pressurized rings (the two the blaster has) are steel/iron/chrome/inconel (whatever they're made out of!) and are specially shaped rings that fit inside a groove of the piston. They're designed to slide down the cylinder while keeping the expanding gas pressure (the fire) above the piston. Fire below the pistons sort of negates the engine's purpose!
They begin their life with a certain amount of spring tension to retain their pressure against the cylinder wall. That pressure is quite light and NOT what makes them seal. They're designed to slide against the cylinder wall leaving a small gap behind them. They then seal to the piston below themselves and the pressure from the explosion itself pushes them out and down to seal better. This relies on the spring tension to begin with and a smooth cylinder wall and good condition piston to retain that pressure.
As they age, they're worn away on the outside and overheating events reduce their spring pressure.
When they don't seal well, the fire can rush down beside the piston burning the charge below the piston. This is normal on an old engine that's been together for a long time and requires what's called a "freshen up" to get the spring tension back.
They begin their life with a certain amount of spring tension to retain their pressure against the cylinder wall. That pressure is quite light and NOT what makes them seal. They're designed to slide against the cylinder wall leaving a small gap behind them. They then seal to the piston below themselves and the pressure from the explosion itself pushes them out and down to seal better. This relies on the spring tension to begin with and a smooth cylinder wall and good condition piston to retain that pressure.
As they age, they're worn away on the outside and overheating events reduce their spring pressure.
When they don't seal well, the fire can rush down beside the piston burning the charge below the piston. This is normal on an old engine that's been together for a long time and requires what's called a "freshen up" to get the spring tension back.
On a side note:
Ken O'Connor isn't the only person who can bore a cylinder.... in fact if you have a decent machine shop locally they can often do a comparable job without the shipping costs. Don't get me wrong, he does a good job but including shipping both ways, you end up paying nearly double for a bore job!
My local machine shop charges $45 for a bore and has it back in 2-3 days. I recommend finding a local machine shop in your area and mailing a cylinder out only if you cannot find a decent machine shop locally.
Ken O'Connor isn't the only person who can bore a cylinder.... in fact if you have a decent machine shop locally they can often do a comparable job without the shipping costs. Don't get me wrong, he does a good job but including shipping both ways, you end up paying nearly double for a bore job!
My local machine shop charges $45 for a bore and has it back in 2-3 days. I recommend finding a local machine shop in your area and mailing a cylinder out only if you cannot find a decent machine shop locally.
It is in the manual here>>> http://www.blasterforum.com/general-support-17/downloadable-yamaha-blaster-manual-17325/
Hard for me to explain!
OH god! Not this age old issue again!
At least he chamfers the ports!! I just had to!
lol well when i had to get my cylinder bored for my other blaster my local yamaha dealer charges 90 to bore and cross hatch a cylinder! it was actualy 88.75 but close enough
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