125-200cc I seized her again...

[Harley]

So I seized my bike for the second time on Wednesday past - cylinder is totally gone this time so I've another on the way but I'm looking for some advice/input on this most recent seizure from you more experienced folk so maybe I can pickup a thing or two!

First of all shoutout to juicypips, he has been an amazing on here to date for any questions I have asked so I'm super thankful for this community!

First time I seized was due to running lean (a rookie mistake after changing exhaust system) but this time there was a few changes... This time I was running a Lectron 36 and a Wossner piston.

I had dialed in the Lectron over the space of a week or two and I am pretty confident I was at a good setting airing on the rich side. In the days and weeks before I seized her the bike was running great with no problems. Its a supermoto and so I push it pretty hard, pretty often and it had always handled this in the past with no problems. On the day I seized it I was actually going reasonably easy and up to proper temp so it was totally unexpected.

Chatting to juicypips via PM he reckons the Wossner pistons have a pretty tight clearance and the fact that his 250 and 360 have both seized with Wossner's is more than a coincidence.

I've ran Mitaka's up until this point with no problems and it was only after reading that Wossner's were much better that I thought I'd give it a go.

Anyway, after messing around trying to get the damn Wossner off my conrod I took some pictures of the piston in the hope that maybe there are some signs of what went wrong or if my mixture may need some changes...

In this photo you can see the damage to the edges of the piston - any ideas on that? Is this burn pattern on the top good/bad or a sign of rich/lean?

Next up is these burn marks underneath, I've read this is an indication of overheating. Would this be from the event of the seizure or does this show an ongoing heat problem?

Some more pics of the piston...

 

[johnnyboy]

Detonated itself to death ! Must of sounded like a bag of marbles before it finally screamed enough.
What size base gasket was fitted ? What fuel ? Could be you were just to lean on the PJ.

 

[silverstreakNZ]

u really went to town on that thing .

 

[Harley]

Didn't notice any strange sounds

I use the thicker gasket of the two in the rebuild kits and 95 octane fuel...

Being lean on the PJ is a possibility.

I had this stutter type feeling/sound just before I got on the pipe that seemed to go away more each time I went leaner on the PJ - maybe I went too lean..

 

[johnnyboy]

I think the stutter type / feeling sound as you decribe it was the detonation, Hard to describe but sounds a little like tapping a pair of hammers together only faster than you could actually do it.
What type of metering rod has your lectron been fitted with as I can tell you that it has to be at least a ms3 with our fuels
I even grind the ms3 slightly richer than as delivered at around the 1/2 to 3/4 mark but use a real short pj tube so the pj only works when flat out , This setup works well on the 125 - 144 - and 165 really well with our fuel, The ms3 will do the job but my setup works better here in the UK but may not work in other countrys with different fuel types so dont advise people getting there griders out

 

[Harley]

Beginning to think that myself. Just now I checked my PJ and its at 1.5 turns out with my rod at almost 51mm. Starting ad Idle was fine I can only guess that PJ setting might be too lean though - any thoughts?

Running a 3-2M rod.

Anyone know the Motosportz factory setup for a 125? Was running great out of the box but float issues sent my settings out of whack and this is where I ended up after messing around. Seemed all good and felt right but I hear the rod is roughly 49.5mm from factory?

 

[JRod4928]

Need a 144 kit? Lol

 

[juicypips]

Detonation sounds like a piston hitting the cylinder at a certian rev if you hear it worse and roll on The throttle it clears up thats the point the ignition curve changes.... That piston looks like lack of oil mine were bad but not that bad.
Is your sm premix or pump? If its pump check the amount of cc it displaces by adding oil to the fuel in tank and disconnect the oil tube then running it for a minute at 2000 rpm i think then measure the oil dispensed. Should all be in the manual.

If its premix then thats another story
P.s. The top of piston crown suggests extreme lean condition /detonation will hole a piston in no time, can you strobe the engine to check timing? What was she like before lectron?, new or second hand?

 

[KXcam22]

Also if I recall correctly the piston seizures are on the corners of the piston which is cause by tight clearances - hot piston getting too large for cylinder. That is often the spot for cold seizures to happen. Definitely quite a bit of detonation erosion on the piston edges. Might need to run a tighter squish clearance at the edge of the piston. Cam.

 

[juicypips]

Ahh i wondered that, same on my pistons but 250 was worse had to part the bike out... I believe the recomended clearance to be too tight for uk set up that and the phenomonal cooling capacity of huskys leads to seize, just my findings so far.
Again a lectron
Good oil warmed up and 17hours on piston cold seize i know my fault but after 9 mins warm up she should be ready to rock.

 

[Harley]

Pretty sure my squish was at 0.9mm or there about ill be checking on that when I rebuild now. What do you guys normally go for thick or thin gasket? I heard around 1mm squish is about right for a 125... I ran 40:1 on this im thinking I might need to for more oil and run richer all round. Bike has the pump but obviously not in use now with the Lectron.

 

[wallybean]

.9 mm is a bit tight for your fuel and 125 rpms. The charge velocity through the gap is adversely affected by the tight clearance and builds excessive pressures at the margins of the piston....the detonation you are seeing. While more oil certainly won't hurt, remember you are slightly leaning out the mixture when you up the oil percentage so adjust appropriately. I would definitely opt for a richer rod like the MS3 and use your PJ for WOT only. JMO

 

[justintendo]

richen the powerjet until it fourstrokes on top end..then lean it until it just goes away. you cant afford to have a lean spot on a highway operated 2 stroke

 

[Harley]

richen the powerjet until it fourstrokes on top end..then lean it until it just goes away. you cant afford to have a lean spot on a highway operated 2 stroke

Sounds like a plan to me, thanks for that!

Ahh i wondered that, same on my pistons but 250 was worse had to part the bike out... I believe the recomended clearance to be too tight for uk set up that and the phenomonal cooling capacity of huskys leads to seize, just my findings so far.
Again a lectron
Good oil warmed up and 17hours on piston cold seize i know my fault but after 9 mins warm up she should be ready to rock.

Know what you mean there, my husky stays almost too cool and takes forever to warm up!
Unrelated, but im wondering do you use the Mitaka gasket kits by any chance? Ive been trying to get some info on exactly what size the thick and thin base gaskets are... I assume the thick one is the one to use in my case though?

 

[justintendo]

that is pretty much how i do all my jetting, on any circuit. then you know its rich enough.
my 360 took 2 base gaskets to get correct squish as per shop manual. some like to push squish to the limit, but i prefer to leave it at book spec and not worry.
does the newer husky motor have a procedure like this?

 

[juicypips]

Know what you mean there, my husky stays almost too cool and takes forever to warm up!
Unrelated, but im wondering do you use the Mitaka gasket kits by any chance? Ive been trying to get some info on exactly what size the thick and thin base gaskets are... I assume the thick one is the one to use in my case though?

Not used mitaka gaskets, i actually cut my own out of gasket paper can be found cheaply on fleabay, i do squish clearance with no gasket in and use plasterscene to measure it, do this gentally ad you dont want to risk mashing your piston with your head.
When you have found the current squish select correct thickness gasket paper an a cup o tea strat cutting.
Much easyer to trace the old one than start new.
Ive got my 360 set to 65 thou and was informed that i could go down to 45 to get the best from it.

 

[Motosportz]

Wow.

Just now I checked my PJ and its at 1.5 turns out with my rod at almost 51mm.

That to me seems pretty rich. Does not sound like a carb issue but pull the bowl off and make sure there is no crud in the carb bowl making it go lean. I assume crank seals and rear block is all sealed well? It does look like a detonation (to small squish), and or cold seize (corner seize) and man thats a good one. Looks like the piston clearance might be way to tight. Piston clearance, ring gap and compression should all be measured when rebuilding so you know what you are starting with is within tolerances.

 

[gazmcfaza]

I have almost the same bike and agree, juicy is the man for motorcycle matters. I'm a newbie but I think that piston is running too lean a set up, it needs to be a darker brown than that so too much air and not enough fuel n oil. I'd check the oil pump first, as mine went and seized everything up, or switch to premix and dissconect pump to be safe unless you got 70 quid for one new. I've got a mitaka piston kit and gaskets in mine, running brilliantly after ten hours still, cast piston btw. Wossner and a few others are generally forged pistons when created, means when they first start up in the cylinder they take longer to heat up, so if you pull away too quick the heat of piston won't match the cylinders heat and you get a ''cold seizure'' [ i think thats what happens anyway], that's why id go for cast instead as they can run a closer tolerance to the size of the cylinder, forged pistons need a larger clearance, cast tend to be cheaper to make. When forged break though they dont tend to shatter as much as cast pistons do, they are much stronger, thats why people use them

 

[johnnyboy]

Just popped this out of a mates Husky, Told him to run the .8 base gasket as his bike is fitted with one of my old top ends, Did he listen? NOPE he fits the thinnest item, Got real lucky as it never seized and has done no damage what so ever so he was very lucky,
Bike is set up pretty rich on top and runs 32.1. He said it was making a weird sound lol
Off to the spares box for a quick rebuild

 

[juicypips]

Just popped this out of a mates Husky, Told him to run the .8 base gasket as his bike is fitted with one of my old top ends, Did he listen? NOPE he fits the thinnest item, Got real lucky as it never seized and has done no damage what so ever so he was very lucky,
Bike is set up pretty rich on top and runs 32.1. He said it was making a weird sound lol
Off to the spares box for a quick rebuild
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Man thats beggers belief! So did you manage to work out how little squish he had or just crazy lean? I would be rocking back an forth if i found that in my engine.