Piston Rings

[retrofly]

hi
I see the word piston floating around the forum alot and well my bikes knackered its 2 an a half years old and ive never changed the piston rings. What are they and what do they do and if they go what do they do to your bike and how much am i gunna have to fork out.

[feef]

The piston rings (both og them) provide the piston with a (for all intents and purposes) gas tight seal, so that your bike has some compression.

Without the rings, the piston would still go up and down when you turn it over, but with no pressure there, it won't go...

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[Dylan]

How much do piston rings cost to replace??? Do you use bits of card to slip them over the piston?? I take it u have to drain the water to take the head off.
Thanks
Dylan

[Kickstart]

Hi

Babyblade gave a great answer. Only thing to add is that to check the condition of the rings you have to pull the top end off the engine, at which point you have already had to pay 95% of the labour to change them

For the NSR125RK (assume the later ones are the same) the max clearances of the rings are:-

Clearance between piston ring and piston ring groove = 0.12mm max

Ring end gap = 0.5mm max

The first you measure with the rings on the piston, compressed tightly in place and then measure the gaps between the rings and the groove it sits in.

The second you measure by taking the ring off the piston, putting it into the barrel squarely (use the piston without rings to push the ring up and make sure it is square) and then use a feeler gauge to check the distance between each end of each ring.

Worn rings means less compression and less power. Too tight rings (possible if you install the wrong ones) gives less power and will probably result in piston or ring failure.

If the first measurement is out you probably need to replace the piston and rings, if just the second then you can probably get away with just the rings.

All the best

Keith

[retrofly]

Hi
hmmm sounds like what happens, the bike is a bit erratic at the mo. Sometime then engine will tick over but if i rev the engine the engine just dies, its in a motrcycle garage now and there still scratching there heads, but they havent taken the engine apart yet

Thanx all of ya
Luke
____________________
"The food was not undelicious"
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[Kickstart]

Hi

To be honest it could be anything on that description. Worn piston / rings would likely get slowly worse rather than suddenly appear as a problem (snapped ring would cause a sudden problem).

On the Aprilia I replace the rings every 6000km (probably excessive), but I would not really trust them beyond 10000 miles on almost any 2 stroke.

Years ago on my MBX I did a top end rebuild (one of the first of many) and finished as it got dark. The bike would just about start and idle, but touch the thottle and it would die. We spent ages trying to get it to run. Turned out the reed block was still on the workbench. Fitted those and it ran fine! Had identical symptoms on a Gilera CX125 about 4 years later, but that turned out to be an ignition problem.

All the best

Keith

[Guest]

Hi
Well thats exactly what happened, it gradualy started to happen once i was strande for 30 mins before i got it started againg. I spoke to the garage yesterday and they said they had go it started and the bloke rode it for about 10 miles he said it did cut out on him once but they havn't moved onto the engine yet, they sould be doing that today actually so i should find out by this afternoon ill let you know whats goin on.

Cheers Keith

Luke

[retrofly]

Thats me (anonymous) i forgot to log in thanx again Keith

Luke
____________________
"The food was not undelicious"
-Homer Simpson (Exceptional beast : Underachiving Human)
www.geocities.com/retrofly