Not related to NC7x0 but 2-stroke engine generally.

[Guest highcast]

I got a donation as 1985 Yamaha YZ80 junior motocross bike. 

It has sat outdoors without shelter for over 10 years.

The frame seems to be in good order.

The only missing parts is the chain leg shield and the throttle handle and all of the wires from front brake and from the clutch.

Tyres are "shot". 

The engine (piston) is stuck but it's not seized by heat. 

I think it's the piston rings - I've not yet opened the engine. 

 

What are the preferred ways to unseize the piston? Some told me to let a bit of a diesel to the cylinder and let it sit. 

Is that a correct way? 

 

Obviously I will, at the end, need at least a new piston kit. Lets see how it goes. 

This will be a really slow restoration project. 

[Tex 36,816]

Interesting project! What a shame that the little bike was neglected in that way.

Yes, I would agree that the piston rings have rusted to/stuck in the bore. Remove the spark plug, pour a little 'releasing agent' in and leave to stand for a while. I have never tried using diesel, but it will probably work very well. Good luck. Let us know how you get on..

[rjp996 1,091]

As Tex says  +1 -  I would take a look in the bore to see if moisture has got in and rusted it up.

Sounds like a fun project :-)

 

[Guest machinman]

I remember riding a YZ 80 and a KX80 as a child, phenomonal amont of power.

Nothing like the wallop of a 2 stroke power band.

[commuter 262]

A word of warning about pouring diesel or any other releasant down the spark plug hole of a two stroke..... its a two stroke ....it has ports in the bore....so you can fill up the crank case, the carb, the exhaust, depending on where the piston is seized. Take the head off and the carb and the exhaust and squirt the stuff where it is needed. Not sure about the 80 engine, does it have reed valves? If so take them off as well . You then have access to lubricate other parts you wouldnt reach through the spark plug hole.

[Andy m 23,472]

Coca Cola down the plug hole is the roadside bodge. If it works you kick it out via the plug hole and go home to see if you need barrel off. 

 

Andy

[outrunner 4,457]

A 2 stroke engine that has sat that long will probably need a full strip down anyway as the crank seals will likely need renewed. Pulling the head off would be a good start to see how bad it is.

[kayz1 2,928]

as outrunner above if you stick stuff down the bore it could knacker the seals anyway ( derv comes to mind on this one )

I think i may have an old Yammy throttle tube gripy thingy in the shed will look tomorrow. Is it a premix or auto mix oiler?

As i also think i have a premix carb that came off a little yammy dirt bike..50 or 80!!!

[Wedgepilot 727]

I've had success previously with a little bit of coca cola.

[larryblag 14,236]

20 hours ago, machinman said:

I remember riding a YZ 80 and a KX80 as a child, phenomonal amont of power.

Nothing like the wallop of a 2 stroke power band.

And the smell, oh the smell. For me there's no other "fragrance" quite so nostalgic. That and the smell of a certain type of floor polish that has the opposite effect and strikes the same fear in me now as it did on my actual first day at school. 

[Rocker66 34,374]

4 hours ago, larryblag said:

And the smell, oh the smell. For me there's no other "fragrance" quite so nostalgic. That and the smell of a certain type of floor polish that has the opposite effect and strikes the same fear in me now as it did on my actual first day at school. 

I prefer the smell of burning Castro’s R

[SteveThackery 3,090]

I'm interested in old stationary engines, and many of these are recovered and found to be seized.  Almost all can be got moving by using penetrating oil, WD40, Duck Oil or other such liquids.  In a two-stroke the trick is to pour in only a small amount.  It can take several days - even a week or two - before the engine will turn over.

 

The point about the fluid running into the crankcase on a two-stroke is well made, but it's still important to unseize the piston if you can, because it's harder to dismantle when it's seized.

[Guest highcast]

On 23.11.2017 at 10:50, SteveThackery said:

I'm interested in old stationary engines, and many of these are recovered and found to be seized.  Almost all can be got moving by using penetrating oil, WD40, Duck Oil or other such liquids.  In a two-stroke the trick is to pour in only a small amount.  It can take several days - even a week or two - before the engine will turn over.

 

The point about the fluid running into the crankcase on a two-stroke is well made, but it's still important to unseize the piston if you can, because it's harder to dismantle when it's seized.

 

That's exactly what I meant. I'm not about to flood the engine with full bore of Diesel etc. 

Just a small amount to get the rings moisted and let it sit there. 

It's still untouched, "real life" hit me by family matters and I think I'm to spray WD40 over the piston through the spark plug hole and then I'll check it during Spring when the weather gets warmer. 

 

My concern is that it's liquid cooled engine. Hoping rhere's not too much of corrosion at the coolant channels. 

During the summer 2018, I will disassemble the bike and the engine as needed. 

 

Thank you all for the comments so far. 

[larryblag 14,236]

On 23/11/2017 at 08:50, SteveThackery said:

I'm interested in old stationary engines, and many of these are recovered and found to be seized.  Almost all can be got moving by using penetrating oil, WD40, Duck Oil or other such liquids.  In a two-stroke the trick is to pour in only a small amount.  It can take several days - even a week or two - before the engine will turn over.

 

The point about the fluid running into the crankcase on a two-stroke is well made, but it's still important to unseize the piston if you can, because it's harder to dismantle when it's seized.

I'd love an old Lister or similar. Why? Just to sit and watch it working. There's something so satisfying about such things 

[Guest DelBoy]

On 11/22/2017 at 17:17, Rocker66 said:

I prefer the smell of burning Castro’s R

Many moons ago when I was a lad living with my parents. I had a GT750 Suzuki which I parked on the front garden.

One day my mum asked what that smell was when I started the bike, I explained that is was the smell of the oil used in 2 strokes (Castrol R).

 

I offered to push the bike out of the garden and up the road a bit before starting it.

 

She said "no need" as she said she was just curious and in fact liked the smell...

 

Should have taken her to Brands for the day 

Edited December 2, 2017 by DelBoy

[Guest DelBoy]

18 hours ago, highcast said:

 

That's exactly what I meant. I'm not about to flood the engine with full bore of Diesel etc. 

Just a small amount to get the rings moisted and let it sit there. 

It's still untouched, "real life" hit me by family matters and I think I'm to spray WD40 over the piston through the spark plug hole and then I'll check it during Spring when the weather gets warmer. 

 

My concern is that it's liquid cooled engine. Hoping rhere's not too much of corrosion at the coolant channels. 

During the summer 2018, I will disassemble the bike and the engine as needed. 

 

Thank you all for the comments so far. 

Sounds like a plan, but you may be better off with a different product to WD40, something that does not evaporate so quickly (Penetrating oil etc) and keep applying it.

Also what you come to remove the piston it may be a good idea to heat the barrels up a bit to ease removal.

 

I would not be too concerned about corrosion in the coolant channels as you could blast that out.

 

Anyway, sounds like a fun project 

[Urhavinalaf 66]

On 22/11/2017 at 17:17, Rocker66 said:

I prefer the smell of burning Castro’s R

 

First ‘two-wheels’ at 17 was a Lambretta Li 150, I loved the smell of ‘R’ that much I paid the extra for that smell never realising I didn’t have the sort of engine tech or plug to require it.

 

Several roadside ‘conk-outs’ later before I realised it was furring the plug ....

 

Still miss the smell... and the pop-pop two stroke..... but not enough to go back!! 

[Spindizzy 7,109]

Waaaay back in the day when I rode small 2 strokes as did my mates, quite often we get fouled plugs. I used to put  a bit of redex in mine and never suffered a fouled plug again. I did the same when I used to do ground work in all out 2 stroke equipment. 

 

Of all the snake oils and nonsense its the only product I can say did away with carbon fouling, so maybe a little in the spark plug hole will dissolve some of the old crud. Diesel also helps unstick a piston. Once its running anything you put in will be ejected in a spectacular puff os smoke for a while and the oil mix will take care of the rest. I cant see it damaging bearings unless you fill it, literally to the level of the crank seals.

[Rocker66 34,374]

I’m  a bit surprised at people using Castro’s R in 2 strokes as I would have have thought proper 2Stroke oil would be more suitable. As it is a vegetable based oil rather than mineral I never used it in any of my 4Strokes but many years ago would a small drop to the petrol just for the smell😀

[Trev 18,566]

I'm fortunate to have a couple of 2 strokes in my garage at the moment, both MOT'd, insured and on the road, one a little quicker than the other 

[Rev Ken 6,327]

My first bike - 1937 Francis Barnett 250 Cruiser, was of course a two stroke but had a separate oil supply regulated by a small hand wheel sticking out of the lower fairing (yes it was enclosed!) just a small adjustment one way or another could result in a seizure or clouds of smoke resulting in an oiled plug. Finesse was required! 

 

If I advanced the ignition too far when trying to start it, occasionally it would back fire and run backwards. It once happened outside a garage and the mechanic was suitably impressed as I reversed in!

[SteveThackery 3,090]

3 hours ago, Rocker66 said:

I’m  a bit surprised at people using Castro’s R in 2 strokes as I would have have thought proper 2Stroke oil would be more suitable. As it is a vegetable based oil rather than mineral I never used it in any of my 4Strokes but many years ago would a small drop to the petrol just for the smell😀

 

Agreed.  Castrol R is exactly the wrong kind of oil to put into a 2-stroke, because it produces rock-hard carbon deposits in the combustion chamber.  Castrol R was a 4-stroke oil.

 

Yes, kids sometimes put it into their 2-stroke bikes, but that's for the smell (which we all agree is divine).  But they shouldn't - it's not the right oil.

 

It was popular with 4-stroke racing bike owners because it has an exceptional lubricity (and film strength, I think) compared with any of the mineral oils available at the time (and now, probably).  Vintage engines run to the ragged edge rely a lot on boundary lubrication, and high lubricity oils like Castrol R helped engines survive to the end of the race.

 

In common with all vegetable oils, Castrol R oxidises at a hell of a rate (compared with mineral oils) so it needs frequent changes.  Really, it's only appropriate for the race track, with vintage bikes.

Edited December 2, 2017 by SteveThackery

[Guest highcast]

Uh oh guys,

 

Now this happened. 

I showed the bike to a guy, who basically said "how much?" and almost carried the thing to his van after throwoing the cash at me 

Well, someone elses project from now on. He told he's going to use the body and the rims, and to replace all other from the "china racer" that had a body fail but the engine is still fine. 

It's going to be a small-wheel 200cc 4stroke thingie..! 

 

I got a decent amount of euros of it. I'm happy. 

[Tex 36,816]

Good result I’d say.