Top end build FAIL help

[EncyclopediaRonnie]

Top end build FAIL help now with pics pg2

hey guys so built my 1993 kx 125 top end, la sleeve pro x piston moose racing gasket kit. did a dry comp test cam,e up 125ish then ran it in and rode it maybe 5 hrs max comp tested again and was around 100 so pulled motor down to find the psiton had been picking up on the bore, ive now discovered i didnt tell my machinest to chamfer the ports :bang:

1) would not chamfering the ports be the cause of this,

2)should i give it a light hone measure up put a new piston ring etc and go nuts, or go a 0.020 oversize. IF i go oversize do i use standard head gasket still. pretty sure i would but cant hurt asking

3) there is a nos piston i can buy it has no rings or pin, circlips, ive got the ring can i run the pin and cir clips that are 5 hrs max old from my prox piston thats rooted? no damage has ocured to the pin.

4) ive got all the tools to chamfer the ports which makes it worse so, when chamfering its onli a slight say 1 mm 45 degree chamfer around the ports. corect? im asuming it needs to be done around the entire port or just the upper and lower edges not so much the sides?

cheers for the help guys.

 

[whenfoxforks-ruled]

1) not likely, no. It causes the ring to snag. 2) If you are capable of a light hone, it will save removal of aluminum flashing another way. Use normal sized gaskets. 3) never reuse, gaskets, rings or cir clips. The wrist pin is re-useable, if it is still with in specs? 4) 1mm around all the ports in the bore. Check the piston to bore clearance, at the skirt, and set the NEW ring end gap accordingly.

 

[EncyclopediaRonnie]

okay sweet light hone deffinetly do-able, sweet on gaskets ive definetly got new rings im not that dumb ahahaha cir clips being like 5 bucks will be replaced. pin is still sweet so im liking where this is going.

can you please elaborate on this please. (check the piston to bore clearance, at the skirt, and set the NEW ring end gap accordingly.)

also what you rekon could have caused this welll lets sayyy learning curve ahahah?

do you think an over bore would be beter or if cylinder is measuring up okay dont bother?

cheers hagen

 

[EncyclopediaRonnie]

the onli other thing i dont understand is why compresion was so low?

 

[whenfoxforks-ruled]

The clearance from the skirt(widest part of the piston) to the cylinder, should be .002". The ring gap should be no more than .024". If a ring hangs, it will have bad compression.

 

[EncyclopediaRonnie]

The clearance from the skirt(widest part of the piston) to the cylinder, should be .002". The ring gap should be no more than .024". If a ring hangs, it will have bad compression.

just checked with a good set of feeler gauges, on the old piston not scored etc i have around .0015 to .002" clearence at the skirt and my ring gap is around .024 to .025" . on the piston that did score my skirts somewhere around .0010 to .0015" and the ring gap is the same.


WITH A BRAND NEW std piston ring clearence at end gap is .020 - .021"


ive measured both psitons the new one that scored and the old 1
and both are within.01-.05mm with each other.

and are 53.96mm at the top and 54.6mm at the skirt.

 

[whenfoxforks-ruled]

The math all looks right. Do you know if the head or cylinder has been modified?

 

[EncyclopediaRonnie]

no other mods motor was dead stock untill i put a sleeve in. i should note that the new scored piston measures up like this around the skirt after ive cleaned it up with emory paper.


so what do i do now std piston and hope?? oversize pistons dont just pick up for no reason

 

[whenfoxforks-ruled]

The bore is clean and chamfered, no flashing/pick up left from the old piston? If there is a bridge in the middle of the exhaust, it needs to be relieved to a total around.0035"~.004". Are you following a manual for assemble? Rings in place, piston direction? If the ring spins, pushes the pin in, it will cause a sudden loss of power and compression, on a rebuild. And its REALLY easy to do.

 

[EncyclopediaRonnie]

no flashing left theres a light score mark but looks more like welll blow by burn still but thats it but ill get that of easy as, ring was in place and was corect when i pulled it out piston is in the right way, bore isnt chamfered yet but it will be dont you worry bout that. the exaust bridge is where it picked up. and oposite it when you say releived you mean honed slightly more just along the bridge? due to expansion? if so how the bloudy hell is that done

 

[EncyclopediaRonnie]

What Piston To buy

okay so after alotta pain ive decided im buying a new piston and trying again with my kx,

i wanan know who uses what who dsnt like what ive basically got the choice of

nos kawasaki.

vertex.

pro x

and wiseco

pretty much in that order of price to exept for the nos kawa item it can be at the top or bottom of the list depending lol

 

[whenfoxforks-ruled]

You can not relieve just the bridge with a hone. A straight porting tool is iffy. An angle tool is better! Even carefully by hand, and sand paper. Pistons, seem to be priced by what you get, crap on the top, the best on the bottom. You did not mention German pistons?

 

[EncyclopediaRonnie]

german???? have not found any then lol.

so basically i just whip out the emory and kero again lol and take a lil material off the bridge so its a tiny bit thinner

 

[whenfoxforks-ruled]

Not thinner? More clearance, or it will get hot and seize again.

 

[EncyclopediaRonnie]

yeah well sorta thinner lol i know what you mean but. so is it just the bridge and hoiw does that go with the ring sealing i trust you to be right, i dunno seems odd but aye

 

[whenfoxforks-ruled]

The bridge is thin, about 1/4"? When the engine comes up to operating temperature, the bridge moves first, and more than the cylinder wall.

 

[EncyclopediaRonnie]

so how much extra clearence we talking here and should it roll in smooth from the rest of the cylinder or be like a step

 

[whenfoxforks-ruled]

Your ring rides through there, no step. See post #9?

 

[EncyclopediaRonnie]

okay sweet. never again am i sleeveing now i know why ppl say dont do it lol.


im going to hone do the bridge and ports then whack up a few pics if it seems okay im buying a new piston and slaping it back together.

rekon the way it failed was a mix of things. picking up due to clearence around bridge and crappy comp from the ring being munched by the un chamfered ports

 

[EncyclopediaRonnie]

bridge relievd bore honed lightly ports chamfered. rekon shell be sweet to go clearences checked again and still good.

ive aslo read about ading a 3rd oil hole in the piston and enlarging the existing to slightly any thoughts?

 

[EncyclopediaRonnie]

The math all looks right. Do you know if the head or cylinder has been modified?

ohhhh just putting it out there now it has ahahah :laugh:

 

[holeshot]

Your best bet is to take it to a reputable machinist that knows what he is doing. This can be tough if you live in a small town (I lived in a small town of about 25,000 before, so I understand that situation). Any knowlegable shop will chamfer the ports properly on a 2 stroke cylinder.

If the ring was catching on the ports, then you certainly need a new ring. I've chamfered the ports on a '72 125 Husky (after porting the heck out of it) very similar to what you have in the pic (45 degrees), but I thought maybe the ideal angle should have been much steeper. My '03 KX 125 seems to have much steeper chamfering than 45 degrees. I'll let the real experts comment on this, though.

It's been noted here on DRN that the exhaust bridge on the KX 125 can cause problems if not relieved properly (referring to a big bore here)


The '93 didn't have a plated bore? Nevermind, I just noticed that you are sleeving - generally not recommended because of inaccuracies in the sleeving and different heat transfer characteristics.

 

[EncyclopediaRonnie]

yeah definetly understand why not to sleeve now lol. none the less im pretty happy with the ports and ive got around .004-.005"relief over the exaust bridge

 

[whenfoxforks-ruled]

When I hone, maybe 2~3 passes, maybe 10 revolutions per pass? If you used a drill, and it rotated too fast, or too many times? Check it with a bore gauge, or you will see next time, if it has an odd wear pattern. I sure hope you did not remove any metal from the transfers, intake or exhaust? Thats another story.

 

[EncyclopediaRonnie]

When I hone, maybe 2~3 passes, maybe 10 revolutions per pass? If you used a drill, and it rotated too fast, or too many times? Check it with a bore gauge, or you will see next time, if it has an odd wear pattern. I sure hope you did not remove any metal from the transfers, intake or exhaust? Thats another story.

onli chamfered ports they are as they were when they came too me. otherwise bore looks okay?