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65 top end when to replace rings

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Hi my daughter has a rm65 (kx65) had a top end rebuild 40 hours ago. This is her first bike and has been kept ringing when she forgets to change up she just holds it on. I was given a set of replacement rings and would like a few ideas about when to replace them.

Always run 32:1 castor927 and 98pump gas

Cheers

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My little girl did on 65 and still does the same thing on the 85. But those are tough little bikes. I suggest buying a compression tester and going by that. If not sure on the procedure, post up and we'll explain it.

 

But the 65 should be between 170-185 on a stock bike. If it's below 130, time to change. But only re-ring once. If using a cast piston like OEM, Vertex, Pro-x. I'd replace piston as well. When using a Wiseco forged, you won't be as apt for fatigue in the piston and can change rings.

The flipside to that is if changing rings at 20 or 30 hrs, the cast deals will be ok.

But I've seen 65's with a hard 80+ hrs on them. Little motors not as brutal.

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I agree with Sappers, change the rings now and get a new piston for the next build.  I prefer cast pistons because my boy does not understand to take it easy on the engine until it warms up.  Cast pistons reduce the chances of a cold seizure, where a forged piston may expand faster than the cylinder during warm up.

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Cheers for the input fellas. Found a good looking home made compression tester , thanks to the search tab, will get parts and build today.

I have the rings on the shelf ready to go but don't have a gasket set. When I rebuilt the bike gaskets were put on dry. Should I have a new gasket kit on hand also?

Sapper my understanding of compression test . Remove carby and reed block, remove expansion chamber, block exhaust hole and intake hole(where reeds go) remove plug place tester unit in plug hole. Kick over while reeding gauge

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My little brother has a kx65 and it's done 133h and the only thing are Have done is change gearbox oil, clean everything new tiers and chain and sprockets.

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Hammond...NOOOOOO. You're thinking of a leakdown tester. A compression tester threads into the spark plug hole. They are obtainable at any auto parts store for about $30 US. Not sure in AUS. But you just simply remove fuel tank & plug, thread tester in snugly, Hold WOT and kick over 3-6 times to reach max pressure.

 

A leak down tester is used more for finding a bad crank seal or leak within the crankcase.

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Hammond...NOOOOOO. You're thinking of a leakdown tester. A compression tester threads into the spark plug hole. They are obtainable at any auto parts store for about $30 US. Not sure in AUS. But you just simply remove fuel tank & plug, thread tester in snugly, Hold WOT and kick over 3-6 times to reach max pressure.

A leak down tester is used more for finding a bad crank seal or leak within the crankcase.

Cheers sappers :) went down to local auto store got compression tester $34 aus . Tested 3 times came up as 142, 138 and 144.

I am going to re ring it , can the gaskets be reused?

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No need to remove head at all. Just the cylinder. If the base gasket doesn't rip at all, you'll be fine. If it does rip, replace it. It only takes a few thousandths to change things.

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I remember as a kid (mid 80s) a friend had a kx80 and we all rode together hard all day for two years. It was our sport and transportation as we lived a godd distance apart. Run what oil he had and would just get the mix close when we pulled up to the pump. Not a problem one with rings or anything. Just made different back then I guess. Was thinking about doing a rering job on on my sons kx65. Sounds like oem piston from what I've read too. Warm up time for him is like 20 seconds. Information here is always great.

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