40 minus siezed piston/bore - ideas

[Even Chance]

Ive just been given an old 40 Minus, but it was siezed. I have soaked it in WD40 for the last week, and it began to free off, but will only move a wee bit before it comes to a hard stop again, both ways. The piston is positioned with the exhaust port open, and the piston moves about 7mm into the exhaust port before coming solid again. Whats the next best thing to try before I have to take the head off?? Any ideas? The rest of the engine looks serviceable, so dont want to consign it to the parts bin quite yet!

[bychance]

I have exactly the same symptoms with a recently aquired 40 Featherweight. My piston is about half way up, only moves about a quarter of an inch and the flywheel moves about an inch. It comes to a hard stop both ways. The driveshaft is stuck fast I suspect in mine. I took the gearbox cap off and besides a whole lot of gritty mud, the pinion gear does not have any play in it at all. I took the prop shaft out and I'm trying to get the lower gearbox off to see if the impellor area is full of crap. The centre screw that holds the gearbox on won't budge. Any more force and I will shear the slot out of the screw.

[Oyster 49]

It looks like you are doing the right things. I personally would take the head off, to see what the bore was like. I would also undo the block attaching bolts to see if the block can be pulled off, by pulling and turning the block at the same time. Take your time let the WD40 soak in.

[charlesp]

Very first thing I do in these circumstances is to separate the power head from the drive shaft. That way you can quickly confirm which end is stuck. Where there is a bit of rotation of the flywheel it often turns out to be a siezed pinion.

[Even Chance]

First thing I did was to split the two ends to see if it was box or piston that was stuck. May just take the engine itself to bits carefully and see what it is like. Any tips of engine stripping? Can I use the same gaskets ok??

[bychance]

I took the powerhead off tonight; once off, the flywheel moves normally.

As has been suggested, the gearbox pinion shaft is probably seized in the bearing.

The centre gearbox screw is still stuck fast, I'm trying to be carefull not to rip the slot out of the screw.

[Keith.P]

Its going to be awkward to remove, heat may not help, if push comes to shove, you may have to be drill out the head and remove the stud after, at least you can work on it better once its apart and get some heat directly to it, the gearbox front cover screws are the one's that I find are troublesome.
More than once I have found that an engine is not seized, its just a dry gearbox.

[charlesp]

That screw head gives more trouble than any other. I tend to use an impact driver with the right bit and a hort 1/2" extension to properly clear the casting. With the skeg held in a vice (soft jaws) and heat in the area where the threads are (gearbox casing) it generally surrenders quite quickly.

[Charles uk]

That is almost exactly what I do Charles & then replace them with stainless cap heads if it's one to use.


Is that 2 or 3 times we've agreed today?

[charlesp]

3 I think including the phone conversation.

It must be the alcohol ban at my end. Only another two days to go...

[bychance]

After much lubricating, flushing and penetrating, the driveshaft moved! Very slowly at first, but after a few minutes rotation, it became as frictionless as expected, you can turn it by finger.

I will give up trying to remove the centre gearbox screw; it still has some slot left so as long as it pumps water I'll be happy.

Time to clean it up......

[bychance]

Started to clean it, I even tried a fresh spark plug and got a healthy spark after re-gapping the points. All looks very clean under the magneto cover.

I hope this repair lasts!

A carby clean and painting next........

[Stelios_Rjk]

Hi,

I have the same problem. Piston inside the bore is not moving. Totally stuck. This SJP as far as I can understand had submerged and left with water inside the bore. So now I disassemble the powerhead and I have the bore with the piston soaking in a mixture mainly of gas and other oils/grease diluted. I have this mixture in order to soak in parts that I want to clean. Do you think it is suitable to be used as penetrant or should I go buy some diesel?


This forty minus of this topic must shine at this time, right?

[bychance]

My 40 Featherweight scrubbed up a bit:

[Stelios_Rjk]

Nice way to close the additional holes!

I managed to take the piston out of the bore! Hooray!! Now I have a crankcase, crank assembly and bore that work!

What I did. Heat (a lot), one day soaking in the petrol, various lubricants, hitting with a hammer but always there was a piece of wood between the hammer and the piston.
At the final stage a place a round piece of wood in the big end and hit it. At that time the piston start moving. I risk damaging the piston and the con rod but I didn't care a lot as I already have one broken screw in the con rod. The funny thing is that by the time the piston came out with some lubricant and a little play the rings start moving free.
The bore were cleaned with lubricant and wire wool.

After some heating etc I manage to take out the broken screw. I haven't tried the crank assembly that was originally stuck in that cylinder. With a spare crank assembly, a magneto and the original crankcase I made the power head. Add some oil in and turned it. It was a little bit stiff. I mount a carb and a DIY tank and tried to start it. After some pulls it started!! I didn't let it run for more than 3 minutes as I don't have a copper gasket and the one I made (correct thickness) doesn't allow thermal exchange. So the power head run for around 15minutes in total.

After that no stiffness! Now when you turn the flywheel it feels pretty normal and free.

Some pictures..