SR125 likely needs new piston/rings. How?!

[schooleydoo]

I have been riding my 97' SR125 for a couple of years now, happy pootling to work and back on nice days.

It was a cheap (£300), no history buy, and has always been a little temperamental. When I bought it I noticed the following:

Chain way too loose
Carb sticky
Slight oil leak on the bottom end join
Drinks oil

New chain and rebuilt carb sorted the main issues, and the oil problems were never a big enough deal to look at. I had hoped that I would pass my test before it became a real problem.

However, in the last couple of weeks it has now taken to stuttering in the mid range, and the bunny hopping/power loss isn't fun on the A roads into work. My Mod 1 test is in a couple of months, and if it starts playing up there, I will have no chance.

I don't know how to fix it though, and I don't really want to spend much on it, considering its age and mileage (25k). I am hoping someone here will know what is needed, and is happy to give some advice on how to DIY.

Symptoms... I can fill the oil level to the indicator (maybe 250ml) and ride it, the next day it will have dropped so low, I cannot see any oil through the glass. As above, it leaks a little out of the sump seal, but its not 250ml worth. Also the stuttering, loss of power.

I am thinking either the piston rings are shot, or the piston itself?
If so, is this something a newbie can do, or is it uneconomical to even try? I will also probably replace the gaskets on the whole engine at the same time....

[Damon]

It could be the valve clearances need doing. Do you have a compression tester?

[schooleydoo]

No, but I can drop by a friendly local garage on the way home. What should I be seeing?

[fiery tupp]

Is it smoking , if so what colour?
where is oil leak , clutch cover /flywheel cover /crank case ?
Have you checked plug condition / tried new plug / cleaned air filter ? Stripping the top end on these is not advisable for someone with no experience & is not an easy fix , if you get the timing one or two teeth out ta ta valves . Plus its not that cheap £30 gasket set £25 timing chain (waste of time not doing this with 25k on clock it will be well worn) £30 piston & rings ect so try everything else first .......R
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If you can't fix it with a hammer , use your head .

[Frost]

Remember that oil goes in the top and bottom of engine when running, when cold it all drains down to the bottom. A sign of rings being gone is a loss of compression and a great deal of oil burning.

Actual procedure for doing the rings is pretty easy, but if the rings are gone the cylinder might be too, thats a bit more of a pain as it may require and oversized piston and rings.

I would not have expected the rings to have gone only if the engine has over about 40,000 miles on it.

[schooleydoo]

Sorry for the lack of updates, I wanted to give it a proper test.

Right, there is no blue smoke, which is a very valid point. If its not burning oil though, where the hell is it all going

Plug looks okay, if a little carbonny for its period of use. That's mixture related right?

Oil leak is crank case, I believe.

Could it be temperature related? The day I posted this, it was very hot outside, and I did not warm the bike up properly. Today it is cold out and I did let it warm up... never felt better. I know the intake temp will be lower and engines like that, but honestly it was like a different bike.

[stonesie]

Maybe the oil leak is worse when the oil pressure builds up at higher revs? you wouldn't see it then.

A carbon fouled plug is most likely a rich mix, engines produce the most power with a slightly rich mix but your description sounds like it could stand a bit less fuel, more power on a cooler and more humid day = much higher air density balancing out the excess of fuel.


Next time she's due an oil change fix that leak and see what that does to the consumption

Edit, This chart is quite useful

https://www.v6z24.com/mods/howto/images/plugs/plugs19.jpg

[fiery tupp]

If its BP oil it could be leaking into the sea .
Now is it blowing out of crankcase breather pipe ?
Did you check & clean the air filter if this is thick with oil it will run rich & plug will be black & sooty ? This bike takes just under 1 ltr of oil I used to put 1ltr in with new oil filter & it never needed topping up i just changing about 1,500 - 2,000 miles.
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If you can't fix it with a hammer , use your head .

[temeluchus]

i'd say check your air filter first, then check the carb over-the float height can meander.

Then check the ignition is properly functioning. Pay attention to the coil/lead/cap.

After that youll need to start looking at the motor. Oil can get past knackered rings and/or a worn bore or get in via a shagged valve guide. If a LOT of oil is getting in it may not even smoke, the oil will stay in a liquid state. Some of that may get splashed on the plug casuing fouling and carboning up. The only real way to tell is to take the top end apart. Its a shame the SR is OHC as if it was pushrod it would be easy to take the head off for a look.
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