The New Help and Assistance Topic

[brickyParticipant @bricky]

Building an engine with a verticle cylinder with two opposed pistons.The cylinder head is octagonal with valves ,spark plug and compresion adjuster at opposing positions around the cylinder head.The depth from outside of the cylinder head to inside of the cylinder is 25mm,what i need is to know the distance from the bottom of the plug to the inside of the cylinder to give a good ignition please.

Frank

[JasonBModerator @jasonb]

It can vary quite a lot from engine to engine, some I have made have the tip of the plug right inside the combustion chamber others the plug is in a completely different casting and 40mm or so from the chamber.

 

Can you not use the image in part 1 to give you an idea of where it should be

[HopperParticipant @hopper]

Generally speaking, it is a good idea to have the sparkplug located so the cool intake charge passes over it and cools it off. If you put it next to the exhaust valve, it will get overheated by the exhaust gasses flowing over it.

Found that out on old sidevalve motorbike engines with the sparkplug in one of the screw-in valve access plugs above the valve head. Get the access plugs mixed up and put the spark plug above the exhaust valve instead of inlet, the sparkplug will have a short but heated life.

[brickyParticipant @bricky]

Jason,I will take your advice and having worked out a scale to fit the drawing ,I get 6mm but to ensure the top of the plug clears the bore I have increased it to 7.5mm .

Hopper,I find what you say interesting,the inlet is opposite, would you think this is correct.

Thank you both for your assitance.

Frank

[JasonBModerator @jasonb]

Position is probably irrelevent on a model engine like this you are not going to be using high revs for any length of time as a bike or car engine would

[bricky]

On bricky Said:

 

Hopper,I find what you say interesting,the inlet is opposite, would you think this is correct.

Thank you both for your assitance.

Frank

Knowing nothing about what engine you are building, I could not really say. If you are working to an established design, best stick with that.

That said, if the valve opposite is the intake then I suppose the incoming charge will be directed generally at the sparkplug, albeit perhaps somewhat masked by the valve head itself.

As Jason says, probably not critical on a model running short demonstration runs under no load. Bit different from a vintage motorbike engine lugging up mountain roads dragging a couple of hundredweight of bike and rider along.

[JAParticipant @ja]

Directing the incoming charge at the spark plug definately makes starting easier.

JA

[Howard LewisParticipant @howardlewis46836]

If possible, recess the spark plug as little as possible. It will be accessible to the cool incoming charge, and will require less advance to ignite the charge. (Shortens the path for the flame front to heat and ignite the full body of the charge) Obviously, you cannot have the plug body or its points from fouling the piston

Howard

[jeff220Participant @jeff220]

Hello, this is my first time of asking for help here, so please bear with me.

I have a Wabeco 1210 mill. For virtually all its time I have kept it fitted with the MT2 collet chuck that I bought at the same time as the mill (many years ago). I decided to remove the MT2 collet holder (chuck) and fit an MT2 drill chuck for a job I have coming up soon. The issue is that I cannot remove the collet chuck. Wabeco hold the MT2 collet chuck in place with a special Wabeco draw bar. The bar has a RH thread on both ends, one end screws into the MT2 taper end. The other end of the draw bar with larger diameter and finer thread screws into the top of the quill. According to Wabeco instructions they say just turn the draw bar in an anticlockwise direction by inserting the special hex key (quite long) into the hex socket on the top of the draw bar and push with some force to loosen the MT2 socket which can then be undone by hand. Needless to say I cannot undo the draw bar. I have applied so much force I am starting to bend the hex wrench. Does anyone know if it would be possible to turn the spanner flats on the MT2 collet holder. my view is it would not be possible as the MT2 is not moving at all. Anyone ever had this issue, cause I cannot see a way out at the moment. Cheers.

[Robert Atkinson 2Participant @robertatkinson2]

If the drawbar won’t loosen you certainly won’t be able to turn the Morse Taper fitting.
You could try running penerating oil down the drawbar.
Other options are to heat the MT chuck. Ideally use a hot air gun (paint stripper) rather than a flame. It will take time to heat through. Next you could use a proper long hex impact key with a impact driver. Even the hammer type would do but lower the head so the chuck rests on a metal block on the table. This will increase the force on the screw and protect the bearings.

Robert.

[Robert Atkinson 2Participant @robertatkinson2]

Follow up on the above.
As there are two different pitch threads on the drawbar if it was tighned when warm it will tighten excessively when cold. So penetraing oil down the tube the long hex key goes into is the first port of call. For heating the quill would warm and lengthen before the draw bar making it tighter. So you would have to let mild heating, say 50 60 degrees with the quill extended soak through so the drawbar gets warm then cool the quickly cool the quill tube with ice packs or similar to shrink it while trying to unscrew the drawbar.

The design is very prone to locking up through over tightning. You can’t turn the mosrs taper until the joint is broken. The taper is designed to lock in place so you can’t unscrew it from that end.

Robert.

[Peter TuckerParticipant @petertucker86088]

Hi Jeff,

I would make (or buy) some split wedges to fit between the collet chuck and spindle nose to help break the grip of the morse taper and allow you to undo the draw bar.

Hope this helps.

Peter.

[Robert Atkinson 2Participant @robertatkinson2]

I don’t think wedges will do anygood against an M10 drawbar.
Penetrating oil both ends first. Measure the depth that the key needs to be to reach the hex head of the drawbar. Then buy a long 8mm 1/2″ drive hex driver like this:
https://www.lasertools.co.uk/Product/8584/Extra-Long-Impact-Hex-Bit-1-2-inch-drive-8mm
and put a breaker bar on it.

Robert.

[Charles LamontParticipant @charleslamont71117]

Jeff220

A stuck taper can usually be broken free by a combination of a large steady axial load and small impacts.

I suggest you try something like this. Put the axial load on with the drawbar good and tight and get a large mug of tea. Now start tapping the side of the chuck body, as near to the taper as possible, with a brass or copper hammer. Not hard enough to cause any damage, of course. Or use a soft drift, but it won’t be as effective. You may need to be tapping away for an hour, but it should eventually come out. There is probably a bit of technique to it – I think it wants a sharp rap rather than a dead blow. The theory is that given the steady end load, each vibration is enough to allow contact points (asperities) to move at a microscopic level.

I would definitely advise against getting too heavy with the drawbar. You are putting it in compression and could make it buckle. Also, I am not sure about penetrating oil. If trying to use this tapping method, would penetrating oil act to damp the impact?

 

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