Webster build questions

[chucketn]

I'm working on my build of the Webster IC, my first ic engine.
A couple of questions came up. Plans call for a NGK CM-6 plug. These seem to be rare enough they go for large sums on E-Bay. Autozone and other auto stores will order them, but don't usually have them in stock. Anyone use a different, more commonly available plug?
I am going to use the weedeater ignition system I found in a build on the web. The builder seems to have disappeared and hasn't answered my other question. What is the taper spec of a weedeater flywheel? I can't get the crank out of the donor weed eater to use or copy the taper. Do all/most weed eaters use the same flywheel casting/taper? I have 2 more dead machines I can strip.

Chuck

[Jasonb]

CM-6 are very common, if you can't find one in the hundreads on e-bay try S/S who have them for $5

http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2050601.m570.l1313.TR0.TRC0.H0.Xcm-6+ngk.TRS0&_nkw=cm-6+ngk&_sacat=0

http://cncengines.com/orderpage.html

[Brian Rupnow]

The CM6 plugs have an M10 x 1 pitch metric thread. 10 mm =.394". I have one right here in my hand and the distance from the face of the shoulder to the tip of the electrode is 0.430". If you can find a plug with a 3/8" thread and a similar nose projection, it might save you the cost of a special tap.--Brian

[chucketn]

"Too late, Ethel...", I mean Brian. I already ordered and received the tap. Auto-Zone said they could get them. They're only $2.99 US, so I guess I'll order a couple.
My buddy Todd looked at the weedeater block and crank and gave me a few hints as to how to get it out. I now have the crank out of the block and with close guestimation it looks like 15 deg from center line for the weed eater flywheel taper.
I'm going to strip a couple more junk weed eaters just to see what they look like.
Thanks for the replies.

Chuck

[Brian Rupnow]

Chuck--I'm glad to see that you are ready to step into "model i.c. engine world". I hope your build goes smoothly, your valves seal tightly, and that you have a runner with little difficulty. You have picked a great engine to start on. And--if you want to have a runner without a lot of headaches, for gosh sakes use gaskets everywhere.--especially between those 3 pieces of intake manifold/valve bodies.---Brian

[RayW]

Hi Chuck from the UK. I totally agree with Brian. Speaking from personal experience, the Webster is an ideal first engine to build. As Brian says, getting the valves to seal well is essential, and gaskets between mating surfaces ensure no loss of compression there.
I originally made the carburettor as per the plans and the engine ran OK with that, but I then substituted a model aircraft carb and the difference was quite dramatic, with a much greater rev range being possible. I have attached a couple of shots of my engine and if I can be of assistance please feel free to ask, however dumb you think the question may be!

Ray

[Brian Rupnow]

And furthermore---if you use a Viton ring, then use a about a 40:1 fuel to 2 cycle oil mix to keep the ring lubricated, and you won't need that big oiler cup on the end of the cylinder.

[chucketn]

Thanks for the input folks.

Chuck

[chucketn]

Got the cast iron cylinder profiled and today, I bored it out. I was sneaking up on the bore dia. of .873 and measuring on the lathe it was .872. Took it off the lathe and it measured .904! I have no idea what happened there! Good thing is, it measured the same on both ends of the bore.
2 more questions, what do/can I use to hone the bore, and will the 7/8 Viton 0-ring still work. I see our(US) Horrible Freight now carries an assortment of Viton O-rings.
Finish on the cylinder isn't my best, but I'm happy with it. Seems the barbell cast iron is quite porous, has tiny pits on all surfaces. Pictures to come, camera batteries are flat, as seems is always the case when I want to take pictures.

Chuck

[cfellows]

Chuck, you can try the 7/8" o-ring when you get to that point, but a 15/16" is probably a better choice.  In my experience, an o-ring that's a little bit loose on the piston works better than one which is tight.

Chuck

[Hugh Currin]

2 more questions, what do/can I use to hone the bore, and will the 7/8 Viton 0-ring still work.

Chuck

A while ago I built a Webster. Had the same question about finishing the cylinder so a thread about lapping the cylinder. Applicable to lapping any bore for finish and size, and brought out some good information. i don't know about using O-rings but I suspect you need a good finish for good life.

Thanks.

Hugh

[Jasonb]

If you can source Metric rings in the US then 18.6mm ID x 2.4mm section will work OK in your bore which is near as makes no difference 23mm

http://www.ebay.co.uk/itm/2-4mm-Section-18-6mm-Bore-VITON-Rubber-O-Rings-/131666878265?var=&hash=item1ea7f51f39:m:m9L7IzE-u3nXaZKBH95UhnQ

[chucketn]

Thanks folks.

Next question. I have some aluminum from a casting sprue that I'm going to use for the piston. f you used the Viton ring, and aluminum for the piston, is it to plan except only 1 ring and to the bore of the cylinder?
I completed the cylinder today, except for the oil port, and honing/lapping.

Chuck

[Brian Rupnow]

Thanks folks.

Next question. I have some aluminum from a casting sprue that I'm going to use for the piston. f you used the Viton ring, and aluminum for the piston, is it to plan except only 1 ring and to the bore of the cylinder?
I completed the cylinder today, except for the oil port, and honing/lapping.

Chuck

Turn the aluminum piston down until it is about .0005" to .0001" under the cylinder diameter. Coat piston with 600 grit lapping paste and work it into the cylinder by hand. It won't go easily. Work it in with a twisting motion until it will pass all the way through the cylinder. To do this, make up a "fake" con rod that you can hold onto the end of, put in a temporary wrist pin and then you have something to hold onto. If you are really brave, put the cylinder in the 3 jaw chuck and set your lathe for about 50 to 75 rpm. and work the piston back and forth thru the bore until it slides somewhat freely. You do not want it to be loose. Be ready to instantly let go of the temporary con rod if the piston "grabs". You don't want to get wound up in your lathe. You will be using a "nominal" 1/16" diameter viton ring, so make the ring groove .093" wide (cut-off tool width) by .058" deep. Use only one ring.

[chucketn]

Thanks, Brian. The original plans show 2 ring grooves, where the Viton O-rig version will have only one. Is placement of the one groove critical? I plan to put the one grove where the plan shows the second grove or .188" from the top of the piston.

Chuck