Posts
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Joined
10/10/2016
Location
GB
hi new here usually post on mxtrax as im in the UK but site seems to have a problem with pop ups
quite new to motocross don't race just been to practice tracks and doing a bit of woods riding type stuff to get used to the bike
so my problem is ive just had a new piston put in my 08 suzuki rm 125 by my local garage has approximately 3 hours on it break in just pretty much warmed it up on the stand then rode gentle for a bit then rode normal im not super fast or anything
so my problem is it looks like it has blow by on the sides only not sure if this is normal
in the pictures you it brown in the corners
any help on this would be appreciated thanks in advance sorry for such a long message
quite new to motocross don't race just been to practice tracks and doing a bit of woods riding type stuff to get used to the bike
so my problem is ive just had a new piston put in my 08 suzuki rm 125 by my local garage has approximately 3 hours on it break in just pretty much warmed it up on the stand then rode gentle for a bit then rode normal im not super fast or anything
so my problem is it looks like it has blow by on the sides only not sure if this is normal
in the pictures you it brown in the corners
any help on this would be appreciated thanks in advance sorry for such a long message
I can only assume the mechanic did check the cylinder and made sure the ring end gap was correct.
Paw Paw
I assume so to there quite a reputable family run business
I will keep an eye on it then and if it gets any worse ill will give them a call if you think its not too bad
there seems be a slight scratch on as well any idea what might have caused that ?
Thanks darren
Paw Paw
I just didn't think of that as I just assumed it was all good after he had changed the piston I will post up if i find out if its that that caused it
cheers for the help
The Shop
but from what ive read is it would possibly be caused by the bike running hot or possibly lean
this bike has also had cylinder ported vhm head and an aftermarket cdi I was told it will run fine on the premium pump fuel now beginning to wonder if this is the cause
and before anyone says yes it is wasted on someone of my talent but I like it and I only bought it cus it was cheap and it ha a full engine rebuild when I bought it the bike is like a new every nut bolt and bearing new
Thanks Darren
The edges of the piston show slight signs of detonation, not a good thing. This is normally caused by the squish not being correct or the fuel octane being too low. Make sure you run 93 octane of better in your fuel mix.
The second thing I see is the black on the underside of the piston. This is normally an indication of a crank seal leaking on the clutch side.
Also keep in mind that if the previous piston was damaged due to dirt, then the crank, bearings and seals may also have some excess wear.
Paw Paw
How many hours on the piston amd ring? Single ring I change every 10 hours and a piston every 20. Looks to be some blow by and I'd bet that ring isn't circular anymore. I noticed if I did more than 10hrs on a ring it would become square edged on the exhaust port bridge near the powervalves. 125's require pretty steady maintenance in the top end department if ridden even slightly hard.
Id deff see if dirt is getting in there. Also maybe jet richer and lean it out safely one change at a time. Or less oil and more fuel. IE try 36:1 instead of 32:1 it will run richer. Pick the oil ratio you want to run and jet from there.
Lots of good suggestions. Check squish and set it to a "safe" starting point.
jetting is fairly close to stock it was running lean on the pilot before I put 37.5 in it had a 35 and I think 370 or 380 main and 42 pilot is normally stock I will I bump them up a bit before I ride next prob 40 pilot 380 main then
I did wonder when the 1 st piston went if it was an air leak I asked them to check but if they did I don't know
on the dirt side of things I change my filter every ride recently had my carb sonic cleaned but will check and clean it I will also clean the tank out thoroughly any other suggestions where else dirt could be coming from
the squish is something I have been seeing a lot when reading about this sort of piston damage any idea what it should be set at to run premium pump fuel on a suzuki rm 125 or would I need an engine tuner for that
thanks for all the help im going to speak to the mechanic later and see what he says about the piston
Maybe things have gotten better with Rock Oil but back then it was too much of a coincidence and I have never touched the stuff again
thanks
and if I start using 30 / 1 would I have any jetting issues
Question please.
How is it known that a bad crank seal discolors the piston underside?
Does the premix oil not discolor underside of the piston the same?
I have never taken notice.
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