Do I need new piston/rings

[Bjbarsted]

I have a 150 that I have been slowly trying to get into working order
I have fixed heaps of stuff on the thing and had it running every time till some thing ells broke.
The issue now is smoke a lots of it
When I start it it will run fine for a few seconds then the smoke slowly starts to build and only gets worst.
At the start the throttle is perfectly responsive and idles perfect but as the smoke starts the throttle response will stumble and slowly bog down till it even effects it at idle
And it's a bluish smoke
There is small amounts of oil on the spark plug
So my guess is either I need new piston and rings or the valves aren't sealing or some thing of the like but just wondering what's the best way to check each one for problems
Or do I just start with throwing new piston and rings in and then if that doesn't work then it should be a valves issue

 

[Bjbarsted]

One other thing not related to this but is still an issue I bought an exhaust of eBay and where the join is It does not seal at all what would be the best way to seal it up
I was thinking of using some silicone to seal it up but not sure if it would hold?
Is there any other methods people use?

 

[my67xr]

Have you checked for thing's like over filled with oil, blocked breather tube on rear upper of engine
leaking valve stem seal's etc
What about the carby, the float level isn't too high is it and it start's to flood?
If it was worn valve stem seal's then it would smoke a lot on decell, may smoke a bit on start up too.
Have you felt the breather vent tube to see how much pressure it's pumping out the crankcase ?
This would be a good sign of worn ring's and or piston
You need to remove the cylinder head from the engine and check thing's out
Take the cylinder off and remove the ring's from the piston, slip the ring's down the top of the bore about 12mm and measure the end gap's
Check for piston rocking in the bore

Normally the exhaust's are just a clamp seal, or a slip fit design.
You can buy some expanding exhaust sealer from Autobarn, Repco etc it's called Maniseal made by CRC, you don't need much to create a good seal
That work's well, normally sell's for around $5 or $6 a tube

 

[Bjbarsted]

Have you checked for thing's like over filled with oil, blocked breather tube on rear upper of engine
leaking valve stem seal's etc

OIL is sitting halfway up the window I'm assuming this is the right amount?
Will check the breather hose
What's the best way to check the valve stem seals?

What about the carby, the float level isn't too high is it and it start's to flood?

I have spent a fair amount of time getting the float right I came out of the box set to high and was flooding the engine but I have gotten it to a good point now

If it was worn valve stem seal's then it would smoke a lot on decell, may smoke a bit on start up too.

Have you felt the breather vent tube to see how much pressure it's pumping out the crankcase ?
This would be a good sign of worn ring's and or piston
Will check this one as well

You need to remove the cylinder head from the engine and check thing's out
Take the cylinder off and remove the ring's from the piston, slip the ring's down the top of the bore about 12mm and measure the end gap's
What gap should I be looking for?
Check for piston rocking in the bore
I'm guessing there should be minimal movement?

Normally the exhaust's are just a clamp seal, or a slip fit design.
It's a slip design but came with no clamp seal and the slip on bit has a good 2mm or more clearance the whole way around.

You can buy some expanding exhaust sealer from Autobarn, Repco etc it's called Maniseal made by CRC, you don't need much to create a good seal
That work's well, normally sell's for around $5 or $6 a tube
I might keep an eye out for this stuff

Thanks for your help again

 

[Bjbarsted]

Ok i just checked the breather hose is pumping out as much air as the exhaust.
Im guessing this means new piston/rings?

Here is a picture of the piston in the barrel.

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Whilst i have the bike apart how do i check the valve seals?

 

[my67xr]

The ring's need to come off the piston then be slid in through the top of the bore about 10mm
Make sure they are sitting square to the top of the bore, get some feeler gauge's and measure the gap's
Does the piston rock in the bore up near the top with the ring's removed

Take note of which way up the ring's were fitted, and which ring goes where

Have you looked into the port's of the head to see if the valve stem's are oily or built up with carbon especially on the exhaust side ?
Just replace the valve stem seal's is the easiest, that way you know they are good to go, they're cheap
pit bike valve stem seals | eBay

To remove the valve stem seal's, the spring's need to be compressed so you can remove the 2x collet's from the retainer's
Lift the retainer's off the spring's and you should be able to carefully take the stem seal's off the valve stem's
Use some pointy pliers with the end's wrapped in electrical tape or similar to stop the serrated prong's of the plier's from damaging the valve stem's

 

[Bjbarsted]

So the top ring was around 1.5mm gap didnt have a feeler Guage big enough to get it exact.
Next one down was .6mm gap
The top of the lower 3 rings is .9mm
The middle one wavey sorta one doesnt touch the sides of the bore so i cant check it
And the lowest ring is 1mm roughly but im assuming the lower rings dont matter for the seal since it looks like oil flows through there

The gap between the piston and the bore is .24mm

The intake port is clean.
The exhaust port has oil in it but i wasnt sure if that was just oil not burnt and pushed out or a leaking seal

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Also i bought new valve seals
Will i need a valve spring clamp or is there an easy way to compress the springs?

 

[my67xr]

I use a pair of pointy plier's to fit mine, the spring's don't have much tension.
I'll post up a 'how to' pic for you when i get a chance

When you measure the ring end gap's, use 2 feeler gauges together
Piston to cylinder clearance should be 0.010mm-0.040mm (0.0004"-0.0016")
Ring gap's should be; Top 0.05mm - 0.15mm, (0.002" - 0.006")
Second 0.05mm - 0.20mm, (0.002" - 0.008")
Oil (bottom) 0.3mm - 0.9mm, (0.01"-0.04")

If you are replacing the piston and ring's, just give the bore a scuff up with some green scotchbrite to give the ring's a good chance to bed in properly

 

[Bjbarsted]

Ok so i guess i will just get new piston and rings
The piston in there measures just under 56mm so im assuming i should be going with a 56mm piston with a 15mm pin
I tried to measure the hole that the pin goes in but it was reading around 14.8mm to 14.9mm but im assuming i jusst didnt have the right position when measuring to get the exact 15mm

 

[my67xr]

So it's definately a Lifan 150? 56.5 mm piston with a 15mm pin ?
56 5mm 150cc Piston Rings Kit for Dirt Pit Bike Lifan 1P56FMJ Engine Part | eBay

What is the engine model number?
Is it Lifan 150 1P1P56FMJ, YX 150 1P56FMJ-5 , or Shineray 150 157FMJ
lIFAN 150

YX150

Shineray 150

 

[Bjbarsted]

It is the engine In the top picture

 

[my67xr]

Ok too easy, so $15 ex china with a 3-4 week wait, or $23ono from aus
56 5mm Lifan Piston Rings Cylinder Head KIT 150cc ATV Quad Dirt Bike PIT Trail | eBay

 

[Bjbarsted]

Thanks I wasn't sure if it was the 56.5mm or 56mm piston
Hopefully after the seals and new piston it will be good to go for a while lol

 

[Bjbarsted]

Thanks heaps for your help mate all back together with alot more compression no leaks any more.
Now I just gotta tune it. It idles well but in first it dies through half throttle and picks up at wot. When I get to third it runs fine but I didn't drop revs so it may have just been high enough to not die off a little

 

[my67xr]

What carby is on it ?

 

[Bjbarsted]

26mm oko flatslide I think

 

[my67xr]

Is this carb that you've been playing with already ?
I'd go a #38 pilot and a #102 or #105 main jet in it with the 150, my 150 Lifan loved it

 

[Bjbarsted]

Yeh it is. Currently i think i have a 38 and 100 in it

 

[my67xr]

You could try moving the clip on the needle down to the bottom notch.
If that help's then you need a bigger main jet

 

[Bjbarsted]

I will go up in the jet first since its the easiest to get to. The clip is currently on the second notch from the bottom. If that doesn't clear in up completely then I will see how moving the clip affects it