Glad I found this site. I just got a 1981 DT125H with a stock piston P/N 2A6-11631-00-96. My bike has 90PSI compression and I am looking for the next oversize piston but so far, I have had no luck finding one. I have several bikes and have been riding since 1965.
Thanks Dan

 from near Salisbury, UK.

I wonder if the 2A6 parts superseded to 2N4? If so, CMSNL have oversize kits.

Search results for 2n4-116 - page 1

 

I'd say you're correct Alan...  US online parts books are bad for that model.  

Piston should not be too hard to find. 

Thanks I will try and find out.
 

Welcome from NZ.
Tell me more about te BSA part of your name if i'm taking the correct inference from it..
I had BSA's back in the "60's.
Also worked in the local Yamaha shop through most of my working life. Cheers.
ps, apart from feeling compression by hand on the kickstart--does it feel positive or falls through with little resistance--how does it idle. Is a good idle like not going to fade off--or does it struggle to hold a possitive idle.
Set of rings is always a good idea then you know what's in there.
"81 125 Might've still had points ignition although nothing to do with compression.

  Bsadan

If the bike was running good and not rattling it might be fine...  compression gauges are not a great way to "diagnose" the smaller engines unless you have experience with that exact gauge on that engine....  many automotive gauges read way low on a 125 or smaller engine.

Greetings from Tennessee  

BSADan look forward to seeing some pix as I have the '78 E model

80 on model pistons were 3J1 not 2A6/ 2N4.  Dunno what the difference is though.  I have it in mind that the crown shape is different, but cannot remember why I think that.

I know that when looking for a new oem piston, 3j1 was common and I avoided them like the plague.
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Edit.  Barrel part number is same on both.  Head part number is different.  Betting changes to combustion chamber shape.

81 has 1bhp more power than 79 and 2ft lb more torque.

Doh. 2A6 is 125. I have 175 engraved on my brain. What can i say.... I am a sorry assed fool...

I see 125 and it automatically turns into 175 in my brain. It took a pic of the tabasco fiasco cylinder head to think.... Hang on a minute.... 2A6 on a 125?  Yup.  My bad.

Walks away with head hanging in shame.....