My nsr 125 piston and barrel, please opinions!

[david451]

Hi, i stripped out my nsr barrel for first time, i bought the bike used and it has 42k km, didnt know what maintenance it had so i wanted to see the barrel and piston myself. The barrel is a "D" while the piston has a "B" and 53.970 numbers on the top.

So, here are some questions, is this an original honda piston? shoudnt it have a "D" piston at least? is it risky to have a "B" in a "D" barrel?

Neither the piston or barrel have breakages or scratches,the rings are not glued either, since i dont know what else to look im asking for some experts opinions, how does this look to you guys?

[Fin]

Cylinder looks fine, you could probably get away with new rings.

Not sure on the exact sizes but you should be able to find the piston sizes in the manual, I'd say it's okay to fit a smaller one than you're supposed to but any bigger and you're likely to fuck up the barrel.

Get someone with a micrometer to check the bore.

[Paulf]

Looking at the piston are you get pick up the shining bit vertical that goes to the top. May be coincident with a port but it is rubbing something.
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Past bikes simsom mofa 1s, suzuki hustler 250 (£35 in 1973), suzuki ts125k, mz150, yamaha yb 100, honda pc50, honda vision 50, all 2 stroke - then cars - honda pcx 125 (sold) own honda fes 125 and Mrs 125 spares or repairs. Started 1972 all accidents walked away no insurAnce claims

[david451]

I read on the net that brown and black parts are cause rings are loosing compresion

So i guess ill change rings as minimum but maybe i change piston aswell? should i get a 53.970 for a D barrel? vertex namura meteor? or if i just change rings, all rings 54mm will fit that piston? thx!

[alains]

everything look fine except that the piston was too big
when the barrel is marked D you should fit a D
see your pict where i put a red circle , this is the weak part on the NSR barrel
buy a D piston at DSS ref : 13104 KY4 901 (£46 inc VAT)
or if you find it in UK a Woêssner forged piston ref : 8019DC (size 53.96)
remember polish the squish of the head and only top piston as a miror . this will avoid the coke to stick on
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the worst day fishing is better than the best day working

[david451]

I guess that the shinny part on the piston is from the part you marked on the picture. I barely had to polish anything cause the carbon stocked was minimal,with a bit of petrol it all came out easily, guess thats a good signal on oil and mixture?

About the letter when i opened the cylinder and saw a “B” i was a bit confused, it seems to be an aftermarket piston and aftermarket letters somehow dont correspond with original honda sizes? Isnt it weird? This is when a noob like me goes and pick a “D” letter on an aftermarket piston, get a completelly wrong size and fuck up the engine...

About piston choice there is a wossner set on ebay for about 100e, is it advised to change small end bearing aswell right? Whats the milleage scheduled for small end? Same as piston?

[alains]

about the letter see the pict (it's not the castained letter but the hammered one ....E)
dont polish the exhaust port , just clean coke
the valves and shaft must be cleaned but not polish
about the piston ref begin at 13101 for a A until 13105 for a E
price are the same except the E which is outrageous (£113)
obviously you need : base cylinder seal,head gasket,small end bearing,piston pin,2 clips,oil seal (all marked with a red point)
remember the nut from the valves shaft is a left-hand thread so undo clockwise !
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the worst day fishing is better than the best day working

[david451]

Thx for the clarification alain, my barrel is without doubt a "D".

I cleaned the ports with a bit of petrol, they didnt have much dirty on them so it wasnt hard.

Since i wont make much kilometers in summer i will put the new piston after it, i think i will take my chances with after market pistons, a wossner a vertex or a pro-x all seems to have very good reputation, that bill u show on the picture is very scary

About the size, i asume that the correct way to do it is making a cylinder bore measurement, can it be done with a caliper? anyway, i cant go wrong getting a 53.96 or a 53.97 (which is actually mounted) if the cilynder isnt in bad condition, right?

As always thx for your support guys,much appreciated.

[alains]

never go for after market pistons when your barrel is coated (for Honda it's called mikasil) . why do you think Honda give you the piston assorted with the barrel ? only to respect the clearance
after market pistons are 54.00 , your barrel require 53.96 !
see the pistons-barrel chart
about woësssner you may visit their site and see price and models
https://www.woessner-kolben.de/en/home.html
they sold piston kits see the joined file
also do not polish exhaust port and side piston
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the worst day fishing is better than the best day working

[david451]

Found a shop that sells a vertex piston kit for 85eur, they have the 53.96, i think that the piston already mounted in my bike could be a vertex cause letter "B" on vertex correspond to 53.96.

Wossner is supposed to be better quality but there is an endless fight on the net about forged vs cast that isnt solved, lot of ppl vote for cast and some other for forged, since OEM honda piston is cast i think its guaranted that cast will work properly and its slighly cheaper too

Thx for advices about polishing hehe, i though about using sand paper on side piston thank god i always look the net before fucking anything up

[alains]

good boy
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the worst day fishing is better than the best day working