2-stroke engine problem

**gijoe1313** · 29th November 2007, 15:00

yowsa, at least you are getting onto it and sorting the donk out!

**Motu** · 29th November 2007, 16:47

Looks like detonation in the squish band.

**Richard Mc F** · 29th November 2007, 17:45

my money is on it being a big end

**k14** · 29th November 2007, 17:52

Originally Posted by Motu

Looks like detonation in the squish band.

Yeah possibly. We need some clearer photos to tell.

What fuel and oil were you running? The sparkplug is still in tact? That could have fallen out and hit the head.

I suggest pulling the barrel (you have to do it regardless to change the piston) and see what lies there. Are there any scores on the barrel?

Looks like something has got in there and pounded the head to pieces. Possibly something in the bottom end fallen out and then gotten into the combustion chamber.

**speedpro** · 29th November 2007, 18:18

My money is on a collapsed big end bearing cage and a whole pile of those bits have made it into the chamber and got friendly with the piston and the squish area.

**kevfromcoro** · 29th November 2007, 18:26

Wrong plugs.....done that once......put a hole straight through the piston
Dont think your bottom end has anything to do with it...

**Marls** · 29th November 2007, 19:46

Originally Posted by Conquiztador

Bummer...if there is no hole in the other one I owe Luka a beer...

A wild guess: Stretched conrod/damaged big end and piston hitting the head??

well, i'd be getn prepared to give him that beer, lol cause i am pritty sure this piston is the one that is causin the problem.
I guess ill start takin the engine out the bike tomoro, and start documenting the internal damage.
this is a cool hobby

**Marls** · 29th November 2007, 20:07

Originally Posted by k14

Yeah possibly. We need some clearer photos to tell.

What fuel and oil were you running? The sparkplug is still in tact? That could have fallen out and hit the head.

I suggest pulling the barrel (you have to do it regardless to change the piston) and see what lies there. Are there any scores on the barrel?

Looks like something has got in there and pounded the head to pieces. Possibly something in the bottom end fallen out and then gotten into the combustion chamber.

Ok, running 95ron Caltex fuel from wellsford.... Hmmmm dodgy, although i did run out of gas comin into wellsford, maybe there was some dirt at the bottom of th tank that could have goten into the combustion chamber.
I run Motul motor oil.... some off road brand....

picture .... is this stuff good, cause after the previous owner and the plugs, i am not to sure if i should use any of the stuff he has givn me.

I ran my finger on the inside of the barrel and it feels as tho there is a slight crease or score on the wall...

but realy small and 2 of em...
the plugs are fine, but i gues thats from the recessed postion in the chamber, it must have definately hit the top of the cyclinder, cause if u look at the damage to piston face its around the outter area, matching the cyclinder ceiling shape.

Tomorw i start the large task of taking the engine out, hopefully i do it well.
anyone Know a rough order of things to disconnect before i take the engine off its mounts and lowwer it out...
experience is key.... how do i stop the fuel from runnin out etc

any special tools i need? best i get it now... or some1 could borrow me those, that would b awesome, otherwise i got connections

**Number 5** · 29th November 2007, 20:32

Sorry to hear the sad news that its more than a holed piston, does sound as though the big end bearing failed and allowed the piston to hit the cylinder head.
This could have been caused by using differing types of two stoke oil, note it is type not make, it may have been running on a mineral oil, and sometimes the two don't mix the type you changed to may have been synthetic.
It is not really a problem on 4 strokes as they bathed in neat oil, but in 2 strokes as the big ends are lubricated by the fuel, and the oil mixed in that fuel (be it by injection or pre-mix) the oil film is washed off the bearing allowing overheating and failure.
It used to be recommended that when changing types of oil in 2 strokes that the crankcase is swilled with neat petrol, then swilled with the oil you are to use.
Sorry but this info is useless to you now.
But to replace the bigend bearing is not a job you can do at home, as the crank webs will have to split, new bearing fitted, and then then crank assembled, trued and balanced.

**tri boy** · 29th November 2007, 20:50

If you havn't split crancases/crankshafts before, or been trained in this work, may I suggest simply removing the engine as is, and allowing someone more skilled to tackle it.
One thing mechanics hate, is a box of bits passed onto them.

The strip down and inspection process allows them to ascertain the reason of the failure which will help you understand the cause.
In the long run it will be cheaper, and less stress. Too many people have thrown $$$$ into parts etc, only to make mistakes on assy that trash those parts in quick time/kms.MHO

**Richard Mc F** · 30th November 2007, 11:06

Where is the bike..........I may be able to help

**Marls** · 30th November 2007, 14:34

Originally Posted by Richard Mc F

Where is the bike..........I may be able to help

Help would be appreciated, followed by a case of beers

The bike is sitting at home, on the North Shore, i have been pricing all the parts to rebuild the engine, looking at 1500, thats 1 new crank and 2*top end rebuild kits, plus one cyclinder... (this is off ebay), any other places to price up parts would be helpful...

**Number 5** · 30th November 2007, 16:26

Shouldn't need a new crank, strip it and take it to an engine reconditioner to fit the new big end bearings (need a press to re-assemble the crank), as to the barrel there are anumber of options, 1) rebore to oversize pistons, wiseco do bigbore kits for most bikes, 2) if the barrell is beyond rebore have it resleeved if it has a cast iron liner, if it is a chromed bore this can be repaired also, look in the services section of kiwirider.
other than repairing your engine you could get a used one from a wreck, Bucket n Bits down here in Wellington may have one, google the name as he has a website showing what he has in stock.