ffkiwi

[QUOTE=beatsal;12726397]Thanks. Just to clarify:
Enlarge the prop hole by drilling with a bit one size up till it eventually fits?

YES. The important thing is to keep the hole square in both axes while drilling, you do not want to introduce any out of squareness

A toothbrush may not fit inside the cylinder for cleaning.

I never implied it would-you use it for general scrubbing off dirt, grime etc from various surfaces-and you will be able to get it inside the crankcase via the backplate opening. You might recall that I have not suggested that you completely strip the engine-the purpose was the exercise is to get it unseized and in a state where it will run, not strip and clean every part...

Is the a connection between piston and contra-piston?

There is no physical connection between the piston and contra piston. The contra piston is a tightly fitting plug the closes the top of the cylinder and has a small range of vertical movement within the upper cylinder region. It does not move up and down of its own accord while the engine is operating. It may be moved by the operator turning the compression screw during the starting and adjusting for smooth running process. The inside face-that is the one that faces or is 'contra' to the piston forms the combustion chamber-it may be flat, have a concave shallow cone profile or a shallow concave bowl shape depending on the brand of engine-in your case the Hunter has a flat contrapiston face. There is very little clearance between the contra piston face and the piston crown at running settings-a matter of perhaps 0.010 inches or 0.25mm-certainly less clearance than you would find in a glowplug engine of similar size. This is why the risk of hydraulic lock is always present if you flood the engine-and you will need to recognise it when/if it occurs, lest you damage the engine.

ChrisM
'ffkiwi'

beatsal

Forgot to ask ref your comment below. From the point of view of just freeing the engine and getting it to start, which is the best size prop from below?

"A 10x4 is a perfect match for peak revs-or if you had CL in mind a 9x6.....in the unlikely event you felt compelled to fly it in vintage team race-then an 8x8 might be appropriate. For vintage R/C perhaps a 10x5-but if you want to chug around gently it will have no trouble hanging on to an 11x4, 11x5 or even larger diameter for something like a lightly loaded slow flying vintage model. Its a big heavy motor, and produces just over 1/4 HP. "

ffkiwi

Given your lack of experience, I'd go for something like an 11x5-it will have more flywheel effect and make starting easier. A 10x4 turns (it will vary from brand to brand of prop) about 10,000rpm on the bench-so in the air it will unwind to bang on the power peak of around 11,000,,,,,but that's academic at this stage-you still have to acquire the starting and handling skills-and that will be a little easier on a larger prop.

ChrisM
'ffkiwi'

beatsal

Mine is the gtreen one first from right

beatsal

Put it into an oven at 250F FOR 25 MINS. Took it out put a prop and it moves thru BDC OK but not TDC - seems to hit a stop at TDC, refuses to budge. Removed the compr. screw and tried - no difference. When trying TDC, it gives a slight pop sound as it leaves TDC suggesting a good fit and compression there!

beatsal

Still stuck, touching the contra on the way up. Not sure how the contra moves within the cyl head if at all?

ffkiwi

Back off the compression screw a full turn, now try and turn the engine over. Hopefully it will move back upwards. the contra functions a bit like the plunger seal in a syringe-it is not free moving of its own accord-it does not reciprocate when the engine is running. Its position in the cylinder is determined solely by the extent to which the compression screw is screwed in-the end of the screw stops it moving any further upwards-if you unscrew the screw a bit-the contra can move up inside the cylinder until its upwards movement is halted by the screw. If turn screw the compression screw in, the contra is forced lower in the cylinder. That's it-its surely not a difficult concept to grasp is it? If you screw the compression screw down-you can go too far and push the contra far enough DOWN inside the cylinder that the ascending piston will hit it as it rises towards the top of its stroke-and then it is impossible to turn the engine over TDC.

Moving the contra back up the cylinder can be achieved either by using compression to do the job-which is what happens in normal usage, or-in the case of a tight unit, by removing the cylinder setting it on a fiirm surface upside down and tapping the contra piston towards the top of the cylinder using a piece of down or a brass or alloy drift. In your case try the heating trick first-prop off, put it back in the oven again, with the compression screw backed off at least one full turn, let the engine get hot, , take it out, prop back on and see if you can turn it over top dead centre. Hopefull the contra will now move up in the bore till its movement is halted by the end of the compression screw. If the heating process does not achieve this, then you have no option but to take the cylinder off-by undoing the four screws at its base-and then proceed as I've suggested above. I hope I don't need to tell you to remove the compression screw before attempting to knock the contra piston up the bore? And only do one or two taps to move it. Then put everything back together and see if you can turn it over now. If you do have to go down the cylinder removal route, take the opportunity to clear out any gummed up oil from the underside of the contra piston with a cotton bud or tissue wad.

from your description it sounds as though ignorant fingers have played with the compression screw and wound it down so the contra is currently too far down inside the cylinder.

ChrisM
'ffkiwi'

beatsal

Removed the 4 screws and the cylinder. Seems bit rusted. Tried tapping piston (with a Al tube) with cyl upside down. No luck. Seems stuck solid.

ffkiwi

Well now that you have the cylinder off, I'd give it a thorough clean. Rusting seems odd-unless its a marine one and has been dunked....old castor residue looks a lot like rust to the uninitiated. checking on two of my display Hunters, that I know with absolute certainty are at their last running settings-the contra piston edges-that is the top of the portion in contact with the inner cylinder walls-are flush with the top of the cylinder.-so if the contra piston is further down inside the cylinder bore in your example you will need to knock it back to this approximate position. Try heat as before=just the cylinder-and then place upside down on a hard surface-a wooden cutting board or the anvil portion of a vice-and do the tapping with a hammer. I'd use something solid-like round bar, rather than tubing to drift with the hammer....and a reasonably close fit in the cylinder-say 15mm diameter...at a pinch even a piece of wooden dowel 3 or 4 inches long.

If no joy using this approach then it looks like an extended soak with a penetrating oil will be required..... See the sketch below-the contra piston cross section is shown in red-in the running position it occupies in the two examples of my own that I checked. If you can get yours to this position then you should be in the correct ball park for successful running..

ChrisM

beatsal

Here is a pic after heating to 250F. Not flush?

beatsal

What is a good pentrating liquid? Used nail polish remover.

beatsal

Hoping for reply.

ffkiwi

You were advised more than 6 weeks ago not to use nail polish remover-it is basically just acetone-which isn't a good solvent. What were you trying to achieve by posting a blurred out-of-focus photograph of the engine' cylinder head? It tells us nothing-and you're not going to achieve anything towards solving the problem until you remove the head and work on shifting the contra piston location.

ffkiwi

beatsal

Sorry about the pic. I will now try using marvel oil which hopefully can free it. Actulally, I also tried paint thinner, no luck. Now, I will remove the 6 screws on the top of cylinnder head and give it another try.

ffkiwi

Marvel oil has a good reputation as a penetrating oil-I'd be inclined to take the cylinder off the engine, remove the head and stand the cylinder upside down with some marvel oil inside-and leave it for a bit-a day or so. Then-after draining the oil out again-repeat the 'tap the contra piston with a drift' process with the cylinder upside down on a hard surface....a steel block or something similar-or the flat portion of an engineers vice, if you have one big enough. A wooden surface will probably have too much give, and absorb the hammer blows rather than the force transferring to the contra piston. Again use a solid piece of rod-ideally brass, or at a pinch alloy to deliver the blows from a hammer-imagine you're using a nail punch to push the head of a nail below the surface of a piece of wooden joinery, prior to filling the hole with putty-except in this case the 'punch' is a suitable length of metal rod that's a loose fit inside the cylinder-and you;re trying to push the contra piston further 'down' from it's existing position-which since the cylinder is upside down, will be 'up' when you have it all back together. Refer to my hand sketch above-the central top of the cylinder projects about 1/16" higher than the wider flange with the screw holes in it-so when upside down, the cylinder is resting on this central raised projection-so if you can get the contra piston to be flush with this raised rim (the top edges of the contra flush with the cylinder top rim, when viewed from the top outside of the cylinder, you should be very close to the running setting. As soon as you remove the head you be able to see how far down inside the cylinder the contra is currently located-(see my sketch again-the contra is drawn in red)-I'd be surprised if it was much more than about 1/16" down from the top, as the Hunter compression screw isn't that long, and even if screwed down as far as it can physically go, it cannot have forced the contra down any further than the extent of the screw travel-which of course is still way further than the engine can be turned over, as there comes a point where the piston will hit the contra as the former approaches top dead centre.

ChrisM
'ffkiwi'

beatsal

Got the prop to turn over now - will now remove the cylinder top to get at the contra.

1QwkSport2.5r

I’ve always had great success using acetone to free up a stuck engine run on castor laden fuel. Much better than using methanol or mixed glow fuel. I usually heat the engine up a little first to get the carb and crank moving a little bit, then add solvent and keep moving things. After 5-10 minutes, dump it out, rinse, and add oil. I use ATF mixed 10:1 with Seafoam - works a great for keeping carbon deposits at bay when used as after-run/storage oil.

Also; the very best penetrating oil I’ve used is a mixture of Acetone and ATF mixed 50/50. I keep it stored in a metal can with a tightly fitted cap to keep the acetone in - much like model diesel fuel.

just my 2¢.

beatsal

Removed cyl head per pic

beatsal

The pic of my ED 3.46 shows internal cylinder threads - what is the purpose?

beatsal

Any comment on the pic I sent?

1967brutus

Don't know what you are looking for with the comments.
I see a fairly dirty engine, the condition of which I cannot assess from here, but I see that the prop is on backwards AND broken.... Do you want to know anything specific?

beatsal

Basically, looking for comments on the position of the contra-piston i.e. is it all the way up?

1967brutus

Ah, OK, cannot tell you that, due unfamiliarity with that specific engine, would expect Chris (fkiwi) to chime in sooner or later.

Dieseltinus

The thread is from the contrapiston and is used to manufacture the contrapiston.

peterburford

Thank you. Chris really has been very polite and patient.