Seized top end

[vinnieh]

Hey everyone, I'm new on these forums and I don't even know if my bike counts as a motorbike! Anyway, I have a little Honda Nifty-Fifty (NQ50). I know very little about the insides of motorbikes, but since I am short of money I have no choice but to fix this thing myself!

The problem is, I seized it by losing the little fan that blows air up onto the top end. I pulled it to bits and the bore is a bit scratched and I'm not too sure about the piston itself as I have never seen a seized engine before. Pics here:

Cylinder pic 1
Cylinder pic 2
Piston
Picture of the scooter if you want to see what I have.

I am pretty sure I need to get those scratches honed out. Problem is, I don't have the faintest clue where to go to get this done? I'm in Hamilton, does anybody know a place there that can do this for me? I don't know how much it will cost me either.

One more thing, if those scratches are honed out, do I need to get an oversized piston or bigger rings or something? Not quite sure how that works.

Anyway, thanks in advance for any help.

Cheers!

Vinnie

[xwhatsit]

Yeah, you're onto it, you'll need to get an oversized piston. Normally they go up in 0.25mm increments. One would assume you're on the original standard size piston. So you need to hunt down an oversized (+0.25mm probably) piston and rings.

Then take the cylinder and the oversized piston to an engine reconditioner and ask them to bore it out to suit the piston. I dunno if two-strokes need special knowledge, but I'm sure most car engine reconditioners could do it for you? Give some of them a call and eventually somebody will lead you to the right place.

Good luck! I'm in the same boat w.r.t. being unable to afford mechanics -- so DIY it is!

[Racey Rider]

Its only a NQ50, No need to spend a lot of money on it.
I would just clean up the barrell with 800 grit wet and dry sandpaper, it will be down on power slightly-but will still run o.k.

[CookMySock]

Full marks for having a go, and not leaving it a corner to rot, ike most nifty fiftys are.

Steve

[Taz]

Try the wreckers for a good second hand barrel and piston first to keep gosts down. Could also try Econohonda for new parts.

[Titanium]

Big scratches there ... 800 grit not going to do it!

As has been said, get an oversize piston and ring set, drop it off at an engine reconditioners.

BAse gasket and make sure you have no air leaks when you put it back to gether!

Easy peasy.

[YellowDog]

Its only a NQ50, No need to spend a lot of money on it.
I would just clean up the barrell with 800 grit wet and dry sandpaper, it will be down on power slightly-but will still run o.k.

That's good advice. Brasso also seems to do a pretty good job once you have broken down the scratches with sandpaper.

[vinnieh]

Hey everyone, thanks for the replies.

I think I will see how much it costs to get the bore honed out otherwise I will take to it with sandpaper. scootling.co.nz is selling a 0.5mm oversize piston kit for $95 so I might get one of those, or is 0.5mm too large an increment? Should I try and find a 0.25mm?

Also do I need to get a new gasket that goes between the cylinder and the bottom part of the engine, or can I use the old one?

Cheers,

Vinnie

[xwhatsit]

scootling.co.nz is selling a 0.5mm oversize piston kit for $95 so I might get one of those, or is 0.5mm too large an increment? Should I try and find a 0.25mm?

You can go for a 0.5mm oversize, doesn't really matter -- the only thing is, a cylinder only has limited oversizes. I.e. you can only bore it out so far before you have to throw it in the bin. So if you're in the habit of seizing it and you want to keep it for 30 years, then you would want to go for the 0.25mm if you can. But 0.5mm would be fine.

You'll want a new base gasket for sure. I think it's particularly important on two-strokes, right? Air-leaks?

[racefactory]

This is interesting- keep us posted mate. Good on you for fixing it.

Where do you get over sized pistons from? Who makes them? Can you get them for pretty much any bike?

[CookMySock]

I reckon take the bore into your local rebuilder and give them a long face and a sad story, and see if they will machine it for free... Or get your sister to take it in..

Steve

[Wannabiker]

and check there is 2 stroke oil in the oil tank!

[vinnieh]

I am waiting to hear back from econohonda as to how much their 0.25mm oversized pistons cost. Then depending on who is cheaper I'll take in to get bored!

trademe900, I'm pretty sure you can get oversized pistons for just about any engine provided it's not too obscure. I think a lot of pistons are interchangeable as well... am I right?

Thanks for all the help everyone!!!

[xwhatsit]

Where do you get over sized pistons from? Who makes them? Can you get them for pretty much any bike?

Original manufacturer normally makes them, like any other part -- they have their own part number. You just have to specify which oversize you want. If you want something `a little bit better', you can go for somebody like Wiseco, who make aftermarket pistons (bigger, higher compression ratios, different skirts, whatever you like). Often cheaper than OEM too.

I am waiting to hear back from econohonda as to how much their 0.25mm oversized pistons cost. Then depending on who is cheaper I'll take in to get bored!

trademe900, I'm pretty sure you can get oversized pistons for just about any engine provided it's not too obscure. I think a lot of pistons are interchangeable as well... am I right?

Thanks for all the help everyone!!!

Econohonda is damned good. Just ring them, don't email -- if you ring, you normally get Malcolm who practically knows half the part numbers off the top of his head. The various guys who answer the emails take ages and aren't quite so knowledgeable.

Pistons aren't usually too interchangeable, even on my RS engine, which is the same as the XL250, XR250 etc., you'll get different compression ratios from slightly different piston crowns etc. If you've got a 4-stroke you have to worry about valve clearance too.

That said, I'm hoping to jam an XT350 piston into a CB250RS engine eventually.

[Sellout]

These engines are nearly bulletproof. One of the wrecks in my garage has sat in a farmers shed for 10 years, covered in shit and starting to rust... New spark plug, cleaned the airfilter and tuned the carb and she's flyin (as much as an NQ50 can..) Let me know how the reboring/ oversizing works out in terms of power, I can see I may have to have a play with some of the bits I've got lying about...

I also have a couple of boxes of spare parts, and some plastics, so if there is something specific you want/ need, let me know! I'll be up your way in mid-September at the boat show!