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) (http://images.google.co.nz/images?hl=en&q=NQ50&um=1&ie=UTF-8&sa=N&tab=wi). 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 (http://i197.photobucket.com/albums/aa67/impavidus87/1.jpg)
Cylinder pic 2 (http://i197.photobucket.com/albums/aa67/impavidus87/4.jpg)
Piston (http://i197.photobucket.com/albums/aa67/impavidus87/3.jpg)
Picture of the scooter if you want to see what I have. (http://i197.photobucket.com/albums/aa67/impavidus87/2.jpg)

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!!! :D

[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!!! :D
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!

[vinnieh]

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!

You don't have a spare cylinder and piston do you? Haha my plastics are in terrible condition but I just bought another NQ50 off trademe... which comes minus the top end! Just my luck. Anyway that will come in handy for spare parts.

As far as plastics go, what plastics do you have, what colour are they? As far as I can tell, the NQ50s seem to have problems with the plastics breaking where they are bolted to the frame. In saying that, I guess any bike that is 24 years old would have that problem.

My mum knows this guy called Barry Free, some people here might have heard of him as he's pretty active in the motorbike scenes. I'm hoping he has some contacts that can get me a cheap rebore :D I'll update here when I find out how it goes.

[Sellout]

Yeah, all NQ50 plastics go at the bolt hole... Darryl at Jap Motorcycle Dismantlers in Chch has said he has some good nick plastics.

I have some blue and some red dash parts, 3 foot panels (2 blue one red) and a rightside (non-keyside) engine cover spare. The other full set is for the 2nd NQ I'm building for a younger brother!

I do have 3 cylinders and I'm pretty sure there are at least 2 pistons. I'll get some photos up of them as soon as I dig them out. I thought you were gonna rebore and go for performance?? I don't think any of my parts have come from seized engines, so cylinders should be good!

[vinnieh]

Yeah, all NQ50 plastics go at the bolt hole... Darryl at Jap Motorcycle Dismantlers in Chch has said he has some good nick plastics.

I have some blue and some red dash parts, 3 foot panels (2 blue one red) and a rightside (non-keyside) engine cover spare. The other full set is for the 2nd NQ I'm building for a younger brother!

I do have 3 cylinders and I'm pretty sure there are at least 2 pistons. I'll get some photos up of them as soon as I dig them out. I thought you were gonna rebore and go for performance?? I don't think any of my parts have come from seized engines, so cylinders should be good!

Well I would like to have a scooter with a bit more power but since I am poor haha I guess I will have to settle for cheapest option! How much would you want for a cylinder and piston?

My mum reckons reboring a cylinder will cost me about $250 which is wayy too much for me... considering I paid $500 for just the scooter. I have asked around and there are a few people who are going to make some enquiries about reboring for me so I will wait and see what happens with that.

But in the meantime I think I'd be interested in buying a spare cylinder and piston anyway, just in case I seize it again in the future!

[mud boy]

welll i had to post on this cos ive seized a bike well more that one...3 in on year:whistle:
wasnt the best thing and my piston where fucked like realy bad fucked lol:weep: but shit happens

[Sellout]

Yay! Managed to get one entire NQ50m operational tonight!! Full plastics (not matching but there!) and a bit of a horry job on the "ignition barrel" (think a piece of plyboard with two switches on it...) :clap:

Ummm... still gotta find those cylinders & pistons, bear with me & I'll get piccies up in the next day or two. I don't know what kinda state they're in, definitely need a clean up and maybe a polish, but what do you expect from 20 year old parts?? As to price, some plonkers on Tardme are tryin to flog parts at huge prices... A couple of beers will do for me! :apint: :cool: Figure that I've got the parts, don't really need 'em, you need the parts...

That's what KB is all about innit it?!

[vinnieh]

Hey sellout,

Do you still have any nifty fifty cylinders or pistons that you don't need?

Cheers Vinnie

[Racey Rider]

Further to my thought on just sanding it down,

I had this happen to one of my KR150's once, with scratches just like that in the barrel. Despite it being a coated barrel, I was able to use a drill sanding bit (like pic below), to take out the worst of the scratches. being careful not to sand in one spot and miss-shape the cylinder. Then a bit of 800 grit to finish off.
There was still a small remnant of the scratches when I felt I had done enough, But a new piston kit went in. I allowed plenty of time for run-in, as it sounded like the rings were going to take a while to wear to the new and 'in-proved' bore. But that bike ran well and gave no problems because of the 'Home made' remedy.

Sometimes for a small, not highly tuned motor, a re-bore is not absolutely necessary.

[Sellout]

OK. So I'm a lazy bastard. Got it.

Hey Vinnie, I have finally gone through the 8 boxes of parts I have in the garage & shed (not all NQ50, not even all motorbike!) and have found 2 cylinders & three pistons. Only one of the pistons match a cylinder, and they are both heavily gouged as the one in your original post pic was.

Sorry mate!! I was sure I still had a good one in there, but alas, none to be found. Now that I have found the gouged one, I remember that I was going to try to rebore it myself... Too many projects, not enough time!! I'll keep my eye out for you though!

Best of luck with the engine!