To me (mechanic by trade) that almost looks like detonation marks. Was the piston crown burnt down to the top ring area or worse on the same side? Just wonder if you are looking at a lean, too much advance, needs higher octane fuel problem.
Hardcore Biker
To me (mechanic by trade) that almost looks like detonation marks. Was the piston crown burnt down to the top ring area or worse on the same side? Just wonder if you are looking at a lean, too much advance, needs higher octane fuel problem.
If you are what you eat, then I'm fast, cheap and easy
I have a gas axe and a welder! What do you mean "it won't fit"?
Hardcore Biker
Yep, a good look at the photos of both the piston and liner scream "detonation".
Could be as a result of low quality fuel, too much compression or timing advance or an air leak leaning out the mixture.
If you are what you eat, then I'm fast, cheap and easy
I have a gas axe and a welder! What do you mean "it won't fit"?
Forum whore
Gudgeon pin damage seen when a circlip has been left out or come right out.
For what its worth, my guess is that a tang has broken off a circlip possibly by hammering from the pin due to a bent rod.
See page 10 http://www.mlcmotorfactors.co.uk/Tro...s/PistonTT.pdf
The damage is caused by the tang rattling around like a jack hammer at the ends of the stroke. The damage is both sides as the tang can rattle its way back and forth through the hollow little end pin. And the damage is wider than the gudgeon because the piston is relieved on the sides. Debris rattling around like this typically leave the piston pin hole looking melted.
Links to PDF's on Piston Damage.
http://www.boosttown.com/engine/piston_damage.pdf
http://www.ms-motor-service.es/ximag..._leseprobe.pdf
Forum whore
I have seen similar damage from this (really crap aluminum casting with big blow holes, exasperated by not using Torque plates when boring and honing........did the Engineer use Torque plates?), they are essential when lining a Cylinder in my experience, HOWEVER, The uniformness of both gouges makes me wary of saying blowholes is the problem in your case (as has been suggested by the poster above, removing the liner will give you your answer)Originally Posted by Grumph
Infact, the fact that the gouges are even on both sides makes me suspect something is amiss with the machining of the liner (bringing back the question of if Torque plates where used or not).... It really makes me think that the bore is just not round...... As the damage is not only concentrated at 2 heights (looks like TDC and BDC) in the cylinder, but also opposite and more or less equal to each other.... If it where piston related, I would expect too see similar damage the entire length of the stroke, not just 2 points in the bore, suggesting the bore is the problem, not the piston.
I suggest you simply Mic the bore, with the Cylinder on the bench (at 3 points on the bore, from top to bottom), then, fit each cylinder to the case, make some spacers (washers will do in a pinch), the length of which are equal to the cylinder head hight, torque the cylinder down, and re mic the bore.
The difference between the two readings will reveal alot. (if the difference between
the two readings is significant, or, the Torqued down readings actually give you a "more oval reading" (with the ovality being towards the area of the damage) then you could assume the damage was caused by not boring with torque plates, or something along those lines, where as if the readings are OK, remove the liner as has been suggested, and inspect for blow holes at the points of damage, if all is well there, then logically there is a piston fault.
A correctly machined liner will be "more round" when it is torqued down, and slightly "hour glass shaped" when not torqued down.
I think you will find that a bent rod will only create excessive wear on one side of the bore, and make one hell of a racket, the first time you started it (as well as being VERY hard to turn by hand.)
The fact that the wear is NOT on the thrust faces makes me more certain there is a maching fault.
Forum whore
Don't think so ..............
The clue to this failure is in the shear symmetry of the damage, both sides of the cylinder and finishing at the ends of the piston pin travel.
Jelly there is a lot of mis-information on the net, if you want reliable information, search out authoritative tec articles like this one http://www.mlcmotorfactors.co.uk/Tro...s/PistonTT.pdf Page 10 for pictures of a piston like yours.
Or this one http://www.boosttown.com/engine/piston_damage.pdf Page 55 for pictures of similar piston damage caused by debris trapped around the pin and page 84 for symptoms of a bent rod.
Rods are easily bent when a gudgeon pin is tapped out instead of using a pin puller when taking an old piston off. Follow the links for an explanation of how a bent rod, miss aligned little end bush or excessive side clearance on the rod or crank can lead to this sort of piston/cylinder failure buy shuttling the pin against the circlip until a piece of the clip breaks off or the clip is driven completely out.
Please post what you eventually find to be the underlying reason for this problem.
Forum whore
After a good long read of the initial job sheet this cylinder/liner unit is one that's already done quite a bit of service.
the rear piston had failed before and the liner was cracked so the dude who rebuilt the motor had put the front back one pot.
My point is that the barrell has already been proven in service, it's not a new liner/sleeve as well as a new piston.
I heated it up today and dropped the sleeve out so will order some more bits tonight...
Thanks for all the insight into it folks, the more the merrier
Forum whore
I totally agree, also be wary of School kids mascarading as experts, providing nothing but links to other sites.
Hardcore Biker
I am not sure he is the one masquerading as an expert.
Bucketracer at least knew what he was looking at and where to go to illustrate his point.
Low personal B.M.E.P.
That last is an interesting comment....remember please that those of us who have been building motors for, in my case, 41 years....don't necessarily have the computer skills you young whippersnappers do.
On the other hand we just may have seen things before....
Hardcore Biker
We know he is talented because he keeps telling us ............
And seems to know his way around the key board well enough to post supporting links for his opinions; if there were any ..........
In his last post, Jellywrestler pointed out, that "the barrell has already been proven in service, it's not a new liner/sleeve", the failure happened since a new piston was fitted.
Bucket racer suggests why the failure happened and points to places where you can evaluate his opinion for yourself, you can't ask for more than that.
Forum whore
But I do build high performance two stroke engines in Europe, and have managed to feed myself off it for the last 5 years, before that, I was a motorcycle mechanic, and raced at a national championship level in 125's and 250GP..... All of tis before Kiwibiker even existed.
I am suitably qualified to question the accuracy of websites on this subject matter.
Forum whore
Are you sure about that.
As it seems your emphatic diagnosis of cylinder/liner distortion was a bit off the mark......
In the riders seat
How many 250GP races did you do at National level?
"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough power."
Forum whore
How many 250GP races did you do at National level?
you trying to say he is lying AGAIN ?
well not lying so much as stretching the truth as far as posible
I've raced against 125gp's
and done 5 national gp's myself
"Instructions are just the manufacturers opinion on how to install it" Tim Taylor of "Tool Time"
“Saying what we think gives us a wider conversational range than saying what we know.” - Cullen Hightower
In the riders seat
Not saying anything of the sort, but you only have to race a bike once in a National round to make that claimyou trying to say he is lying AGAIN ?
"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough power."
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
Bookmarks