rg150 piston...

**georgie** · 13th January 2008, 15:37

Hi all,
So, I've had my rg150 for a few months now, and after reading all that I could about them on here I decided that checking the power valves was a good thing to do (one is totally toasted, but payday is still a a week away

). While i had the thing in pieces i decided to check the piston as well... so, question time..
Pic1... Is this bad? (or should i say, how bad is this?)
pic2... whats this wibbly bit that was under the ring?
pic3... does this pin bit look ok?

also, are the rings meant to be able to move around the piston? if they are, what are the pins in the ring grooves on the piston meant to do?

Lots of questions sorry! But I am a recent convert to 2 wheeled transportation, so all help muchly appreciated

**georgie** · 13th January 2008, 16:24

Also.... the manual that I downloaded shows a picture of the piston being de-carboned by the crown being scraped. This the best way to do it? Oh and, I know what the wibbly bit in pic 2 is now ( read the manual properly georgie!!)

**quallman1234** · 13th January 2008, 16:37

Pistion Doesn't look too bad. If the second picture is the rings then that looks shocking.

When you put it back in dont forget to buy new circlips! (Never use circlips twice) Only like 20c each.

**georgie** · 13th January 2008, 16:45

haha, nope, pic 2 is something that was under the lower ring. Looking at the manual, I think it is an expander ring? maybe? Will be sure to get new circ clips before it all goes back together.

**xwhatsit** · 13th January 2008, 19:41

Is the piston supposed to be so scuffed up like that? Did it seize? It looks nasty, but I have no idea about these things.

**Ixion** · 13th January 2008, 19:44

Seen worse. Much worse. Fair bit of blow by, but. Y' might want to think about a new set of rings.

**xwhatsit** · 13th January 2008, 19:48

Blow-by? Is that scuffing caused by combustion gas?

**Nasty** · 13th January 2008, 19:51

to quote AJTurbo .... "its pharked"

**georgie** · 13th January 2008, 20:15

Originally Posted by xerxesdaphat

Is the piston supposed to be so scuffed up like that? Did it seize? It looks nasty, but I have no idea about these things.

Freaked me out a bit when i pulled it out too. he hasnt seized since i got him, but I'd guess he has in the past

Originally Posted by Ixion

Seen worse. Much worse. Fair bit of blow by, but. Y' might want to think about a new set of rings.

That makes me feel MUCH better

Originally Posted by Nasty

to quote AJTurbo .... "its pharked"

This makes me feel Much worse!!

Ah well, at least I'm learning a lot as i go. I am definitely getting addicted to my busted up little 2 stroke

**quallman1234** · 13th January 2008, 21:48

Get a set of rings def.

Pistion should be fine as long as your not fanging it too much.

Like ixion said i too have seen way worse what have been quote "fine to run".

I reckon she'll be alright unless your racing then i would get a new pistion kit.

**georgie** · 13th January 2008, 21:58

Wicked. New set of rings it shall be

... And definitely no racing for me.. yet.. hehe

One other thing, how can I tell if the bearing at the other end of the conrod is OK? what sort of tolerance should there be for side to side movement?

Thanks for the replies, you guys rock

I will have to figure out how to do that bling thing

**Ixion** · 13th January 2008, 22:01

Big end bearing it's called (cos it's the big end of the conrod - unimaginative lot engineers), a bit of pure side to side is usually OK, a millimetre or two - some very high tuned engines are fussy but an RG150 should be OK for a mm or so. But absolutely NO up and down movement at all. Ideally no rock from side to side at the little end either, but a lot of engines allow some tolerance for this

**dangerous** · 13th January 2008, 22:18

Originally Posted by georgie

Pic1... Is this bad? (or should i say, how bad is this?)
pic2... whats this wibbly bit that was under the ring?
pic3... does this pin bit look ok?

4) also, are the rings meant to be able to move around the piston? if they are, what are the pins in the ring grooves on the piston meant to do?

1) yes, dont care what the others say but thats a defnit sieze could be a cold sieze common as is that same mark on all 4 corners of the piston (4 point sieze) replace it Check the bore for corosponding damage.

2) that belongs behind the ring, it helps keep the ring out against the bore wall replace it (comes with ring kit)

3) replace it it will come with a piston kit as will the rings, circlips should also be in a kit depending on brand.

4) The rings should not rotate the wee pin should stop this, but to test you will need to compress the ring. If the rigng rotates on the piston it can and will get cought up in a port riping the top of the piston off.

**koba** · 17th January 2008, 11:50

Originally Posted by dangerous

1) yes, dont care what the others say but thats a defnit sieze could be a cold sieze common as is that same mark on all 4 corners of the piston (4 point sieze) replace it Check the bore for corosponding damage.

2) that belongs behind the ring, it helps keep the ring out against the bore wall replace it (comes with ring kit)

3) replace it it will come with a piston kit as will the rings, circlips should also be in a kit depending on brand.

4) The rings should not rotate the wee pin should stop this, but to test you will need to compress the ring. If the rigng rotates on the piston it can and will get cought up in a port riping the top of the piston off.

I second that.
A piston kit aint cheap but its gunna be a shit if you have to pull the whole thing apart again in a week!
A bike with everything running nicley is happy and rewarding, it really is worth doing that piston!

Also check the bore, if you have the right manual it will tell you how to.

**FruitLooPs** · 18th January 2008, 00:11

Thirded, mine was rooted with a piston that wasn't as bad as that, although I had a tiny wee bit of a squashed ring land. After the piston was taken off a thorough looking over found a hairline crack in the inside of the skirt too, too much of a chance to take IMO. If the power valves were stuffed you shouldn't go halfway, fix it up good. Then again it might be dandy..

If you ask Oyster for his opinion I'm sure he could show you 3 or 4 more RG pistons that look nearly the same and tell you just whats happened and if you should replace or not. Methinks replace though.

Check bore etc, that first pic fullsize looks like it has some gouging on the side of the piston, might just be carbon though.

Piston kit and rings are reasonably inexpensive when you consider it could grenade/collapse and screw the bore and spit crap into the crank etc.

Use good synth oil etc, usual 2 stroke advice.

*edit*
I'm in a good mood so I grabbed my old piston and took pics of all the bits so you can see and compare. Also note the vertical scuffing bright marks, that was in my case from a shot powervalve grinding away. No idea what that random hex bit was, its not on my piston assembly (well not how it was returned anyhow) - you should have piston, pin circlips, rings, roller bearing and wrist pin so far as I can tell.