Two stroke piston showdown.

[2T Institute]

I don't think you have 0.251mm clearence , you have 0.0251mm that is a big difference. Running ULP that CR piston will last until the first WOT run.Japanese cylinder cannot handle clearences less than 0.05/6mm There is no misprint, stock sizes for a 54mm bore are 53.94/5 a 96 piston is for a bore measuring 54.01mm

[Jeram]

Thats only 1 thou!

[TotalNZ]

Not allowing a proper warm up isn't good either. If not allowed to warm up properly the piston will come up to temp faster than the cylinder and if not allowed to equalize could potentially cause a cold seizure (four corner seizure).

Oh i definitely allow a proper warm up, but i do it without letting the motor idle on a fresh top end. Little blips on the throttle till everythings up to temp.

[Jeram]

Not allowing a proper warm up isn't good either. If not allowed to warm up properly the piston will come up to temp faster than the cylinder and if not allowed to equalize could potentially cause a cold seizure (four corner seizure).

Oh i definitely allow a proper warm up, but i do it without letting the motor idle on a fresh top end. Little blips on the throttle till everythings up to temp.

oh you've definitely gota blip the throttle, if not for the good of the motor do it so you can feel like that lucky bastard in the GP pit lane whos job it is to do exactly that

[dbf498]

Not allowing a proper warm up isn't good either. If not allowed to warm up properly the piston will come up to temp faster than the cylinder and if not allowed to equalize could potentially cause a cold seizure (four corner seizure).

Oh i definitely allow a proper warm up, but i do it without letting the motor idle on a fresh top end. Little blips on the throttle till everythings up to temp.

I never insinuated or stated you never warmed up your engine but I'm sure other riders haven't and suffered the consequences. To set the record straight, you asked what was worse; I gave you my opinion of what I thought was worse never laying blame on anyone.  If it was thought my comment was directed at any one it was not and purely unintentional. As far as the break in process is concerned, unless factual credible evidence can be provided to contradict how I do my break in's I'll continue on with how I do them. If any evidence contradicts those methods I'll consider changing, so, let's agree to disagree and drop this subject. After all, we are all two stroke enthusiasts here, not professional engine builders, helping one another the best we know how using the knowledge we have; if I have this wrong by all means correct me.

 

[Stusmoke]

I don't think you have 0.251mm clearence , you have 0.0251mm that is a big difference. Running ULP that CR piston will last until the first WOT run.Japanese cylinder cannot handle clearences less than 0.05/6mm There is no misprint, stock sizes for a 54mm bore are 53.94/5 a 96 piston is for a bore measuring 54.01mm

First of all: my bad it was actually .232. Secondly I know what I saw. If it was .0251 that would give me ultra high compression, the bike would start and I wouldn't need to replace the top end. My manual says an A size cylinder is: 53.976 mm. The B size cylinder is: 53.968

According to the manual the A size piston is: 53.933 and the B size is: 53.925

Above that it says the machine has a bore and stroke of 54.0 x 54.5 So I don't know what they were smoking

[dbf498]

I remember you mentioned in a previous post that the cylinder had a sleeve installed. I'd be willing to bet that if that is the case that could be why the bore diameter is slightly off (under). By the way, how did you set up your bore gage and what was the baseline measurement you used? I'm not doubting your measurements but just curious. Pics would be nice too.

[2T Institute]

First of all: my bad it was actually .232. Secondly I know what I saw. If it was .0251 that would give me ultra high compression, the bike would start and I wouldn't need to replace the top end. My manual says an A size cylinder is: 53.976 mm. The B size cylinder is: 53.968

According to the manual the A size piston is: 53.933 and the B size is: 53.925

Above that it says the machine has a bore and stroke of 54.0 x 54.5 So I don't know what they were smoking

Piston to bore clearence isn't what governs comp ratio, that is bore/stroke and head volume.
Would be the first time ever a B size piston is listed smaller than A. The CR will run with 0.06mm clearence, that is a simple fact.
I'm also interested how you measured down to 1/1000th of a mm ?

[Stusmoke]

First of all: my bad it was actually .232. Secondly I know what I saw. If it was .0251 that would give me ultra high compression, the bike would start and I wouldn't need to replace the top end. My manual says an A size cylinder is: 53.976 mm. The B size cylinder is: 53.968

According to the manual the A size piston is: 53.933 and the B size is: 53.925

Above that it says the machine has a bore and stroke of 54.0 x 54.5 So I don't know what they were smoking

Piston to bore clearence isn't what governs comp ratio, that is bore/stroke and head volume.
Would be the first time ever a B size piston is listed smaller than A. The CR will run with 0.06mm clearence, that is a simple fact.
I'm also interested how you measured down to 1/1000th of a mm ?

My ultra sharp ninja eyesite Nah I'm just kidding. the feeler gauge said it was .232 on it and I just quoted directly out of the book for the piston and cylinder sizes.  I can only measure up to a 100th of a millimetre with my tools. I know that piston to bore clearance isn't everything thats now what I mean't, but it sure does help

[2T Institute]

Ah ha, your looking at the imperial measurement which will be 2.32 thou(sands of an inch) which in metric is 0.05mm. What was that about Ninja eyesight 

[_X_]

elvis would revvvv that sucka!

[_X_]

like this!

[Stusmoke]

Ah ha, your looking at the imperial measurement which will be 2.32 thou(sands of an inch) which in metric is 0.05mm. What was that about Ninja eyesight 

Nope, I promise its .232 mils. I really do wish it was so but its a .232 mm gauge. This would also account for hte piston slap I was hearing when it was running. But I Promise the feeler gauge says .232 mm. Also, the idiot didn't have coolant in it when we were bouncing the sucker off its rev limiter, so I've checked the cylinder for warp too but luckily its fine. I've got the whole intake system off now and when it move that piston through its compression stroke, it sounds like you just took the drain bolt out of an air compressor.

[2T Institute]

I doubt very much you would get a 0.2mm feeler the bend between piston and bore.

[arnego2]

not that difficult to put a 0.1 mm gauge between piston and bore.