125 gaskets

[noobi]

Hey there noobi, I'm no reco expert so the following simply my view. It's common practice to combine 2 base gaskets to get your squish the right dimension and the small .05mm difference shouldn't be any prob unless your compression already maxed up with wrong gasket from start. Remember higher compression is more load on engine = shorter engine life. Don't assume gasket in there is correct, you really need to measure to be sure - it's easy enough to do. Measure before taking cylinder off, but if it's already off, completely clean off old gasket, put cylinder back on without gasket, nip it up and measure difference piston height/cylinder height with a vernier or feeler guages and a straight edge. When measuring make sure piston exactly at TDC, mine doesn't sit quite at TDC due to generator magnet effect, this can be hard to spot if not careful. Be extra tidy when cleaning off old gasket. I use masking tape on top of rags stuffed into case. You don't want gasket fragments getting into your bearings etc.

If your bore is looking a bit tired, get it accurately measured top to bottom and get the correct (maybe oversize) piston for correct clearance (which will be somewhere around 0.05mm). I'd be pretty certain you'll have a Nicasil bore. Not 100% sure your description Re brown marking in port but with cylinder off and cleaned up you'll see nicasil coating does continue into ports a bit (otherwise it would chip/flake at port edges. Nicasil coating looks darker, almost like a varnish. Resist any urge to 'clean up' any raggedy looking port/cylinder edges, you could very easily bugger the coating there). Also, need to be acutely aware that although the coating is extremely hard, it's only as thin as a coat of varnish so don't get me started on honing Nicasil.

the multiple gasket thing i thought wouldn't really matter unless it had metal rings or something in the gasket for the water gallery holes? but i doubt that water would get in anyway as the crankcase pressure would be higher than the water gallery pressure?

i measured the gasket with an electronic vernier while its on the bike, i don't know how much it gets squashed by the cylinder but the measure didn't come anywhere close to 0.3mm or 0.15mm so i assume its the stock 0.5mm one

is putting the head back on a problem with the two o rings system, i was told that there not the right size and you need the freeze them to get them to the right size to go on properly?

the only other piston available is 2mm oversize not 0.2, 2 whole mm, how useless is that

yea dad is very certain that if you even take a nikasil bore near a hone that it will go right through as the coating is only about 0.05 mm thick
may just clean it up with some scotchbrites?

the coating doesn't look shiny when i look through the exhaust port, been told it should look chromey?

thanks for your help

[flyingcr250]

the multiple gasket thing i thought wouldn't really matter unless it had metal rings or something in the gasket for the water gallery holes? but i doubt that water would get in anyway as the crankcase pressure would be higher than the water gallery pressure?

i measured the gasket with an electronic vernier while its on the bike, i don't know how much it gets squashed by the cylinder but the measure didn't come anywhere close to 0.3mm or 0.15mm so i assume its the stock 0.5mm one

is putting the head back on a problem with the two o rings system, i was told that there not the right size and you need the freeze them to get them to the right size to go on properly?

the only other piston available is 2mm oversize not 0.2, 2 whole mm, how useless is that

yea dad is very certain that if you even take a nikasil bore near a hone that it will go right through as the coating is only about 0.05 mm thick
may just clean it up with some scotchbrites?

the coating doesn't look shiny when i look through the exhaust port, been told it should look chromey?

thanks for your help

oh man i hope i dont have this many problems when i do my piston. i got boyds in hamilton to run the part number off my cylinder and it came back "unknown part number"

[Rupe]

the multiple gasket thing i thought wouldn't really matter unless it had metal rings or something in the gasket for the water gallery holes? but i doubt that water would get in anyway as the crankcase pressure would be higher than the water gallery pressure?

i measured the gasket with an electronic vernier while its on the bike, i don't know how much it gets squashed by the cylinder but the measure didn't come anywhere close to 0.3mm or 0.15mm so i assume its the stock 0.5mm one

is putting the head back on a problem with the two o rings system, i was told that there not the right size and you need the freeze them to get them to the right size to go on properly?

the only other piston available is 2mm oversize not 0.2, 2 whole mm, how useless is that

yea dad is very certain that if you even take a nikasil bore near a hone that it will go right through as the coating is only about 0.05 mm thick
may just clean it up with some scotchbrites?

the coating doesn't look shiny when i look through the exhaust port, been told it should look chromey?

thanks for your help

Didn't have any problem with the rubber ring things on the head, the new ones fitted fine.

When I checked on go fasters website there was about 4 different sizes, for how much use the bike had done. Emailed them for a price shipped to nz, and they just gave me a price for a wiseco and said better to just use that. So ordered a wiesco for mine over here and it was one size fits all, ran great with it.

[noobi]

Didn't have any problem with the rubber ring things on the head, the new ones fitted fine.

When I checked on go fasters website there was about 4 different sizes, for how much use the bike had done. Emailed them for a price shipped to nz, and they just gave me a price for a wiseco and said better to just use that. So ordered a wiesco for mine over here and it was one size fits all, ran great with it.

ok good thing about the rings then

yea i look there for parts, but with the shitty exchange atm, it would be cheaper to get the piston, ring, clip, pin that barty can get
sent them an email now asking about pistons


steve, yea hope its not much of a drama ae, our local honda shop seems to be able to get all the ktm bits we need, they have parts manuals for most of the models in their workshop, we were in there today cuz the rear wheel bearing on dads ktm collapsed yesterday ops:

[camchain]

The thickness of your base gasket is what determines your compression ratio, that's what I meant by squish (not amount gasket compresses). There'll be a correct dimension for it, this varies depending on bike/model. Eg, My 200 is 0.0 which means top of piston is flush with top of cylinder shoulder. But pre 2003 200 engine correct dimension was 0.5mm (I think).
There are slight variations with any mass produced parts, hence different gasket thicknesses available. KTM has gaskets in .25mm increments, two gaskets combined to get correct dimension is fine, you shouldn't get any leaks from this. Use a torque wrench.

As rupe mentioned, you shouldn't have any probs with the head O rings fitting neatly.

That 2mm oversize piston sounds like it might be for a 150cc kit (?) - for another bike. Find another dealer. Oversize pistons (for nicasil bores) come in tiny 0.001mm increments.

The Nicasil coating thickness varies a bit but from what I can gather it's usually around 0.1mm Nicasil is super tough but wear tolerances are v small, eg KTM = 0.025mm so be extremely wary about any honing. I used a scotchbrite pad and some CRC to break down glaze but be careful as it's still an abrasive. Nicasil isn't shiny like chrome, it's darker than the aluminium underneath. When cylinder off, if you look closely you'll see the difference where coating stops just inside ports.

BTW, make sure you put the wrist pin 'C' clips in with opening facing down or up. If clip opening at horizontal position, piston speed can force the clip open and pop them off = lunched engine.

[cheese]

BTW, make sure you put the wrist pin 'C' clips in with opening facing down or up. If clip opening at horizontal position, piston speed can force the clip open and pop them off = lunched engine.

Wow that's something I didn't know. I think I put mine facing down anyway just cause it fitted easier like that.

[barty5]

BTW, make sure you put the wrist pin 'C' clips in with opening facing down or up. If clip opening at horizontal position, piston speed can force the clip open and pop them off = lunched engine.

Wouldnt the force hace to cause the clip to close up as they are spring loaded they are made too big for the hole they fit through then they sit in a groove. Sounds more like clips that havnt been put in propely to start with or reusing the old ones.

[camchain]

I'd say you'd be dead right about probs with clips being bent, re-used etc Barty, they can be a bit tricky to get in cleanly. Can't remember where I read about clip position thing but I've come across it more than once. Possibly more a theoretical thing but it can't hurt. If clip is horizontal, force tends to want to open clip (like squeezing it in a vice), but vertically it can't go anywhere. I understand it's less of a concern if using stale gas. lol.
(Stale gas good for milder power delivery which is better for those of us with crook backs Cheese.)

[cheese]

LOL hey I ran the stale fuel through and then it went mint as. Front wheel wouldn't stay down!!

Anyway, the CRs are so powerful that they need a bit of taming down to bring them the the level of the other bikes out there.

[camchain]

Ha ha. Glad you got out for a decent ride cheese. Doesn't take long to loose the bike fitness if not riding regularly. Stale body.

[LittleJohn]

Just get a real bike Noobi!!!!!! Something that is unpredictable, kick ass powerbands and hard to control, just like riding should be...

[noobi]

Just get a real bike Noobi!!!!!! Something that is unpredictable, kick ass powerbands and hard to control, just like riding should be...

whatarya tryna say mate?

[LittleJohn]

whatarya tryna say mate?

get a real 2-stroke not your girly gas gas with it's plush suspension and steering...

[noobi]

get a real 2-stroke not your girly gas gas with it's plush suspension and steering...

its ok, you can secretly like gasgas, theres one the same as mine on tm, you can join the "bikes that have nice suspension, steering, brakes and power club and have sidestands" too if you like

[LittleJohn]

its ok, you can secretly like gasgas, theres one the same as mine on tm, you can join the "bikes that have nice suspension, steering, brakes and power club and have sidestands" too if you like

What a shame I'm so broke and cannot afford it.

Wait a minute I could raid my kids money boxes, I'm sure they have a few dollars that will get me one.