# Speedys inline twin



## Speedy (Sep 1, 2012)

I am building jerry james hex two. 
currently as I am building it I am noting areas that I would like to see improvements on, right after this engine breathes life I will jump right back in to build my version of this engine.

I also plan on documenting my second build on video

sorry I am not taking you all on for the ride, first engine and its sometimes a handful, dont want to complicate things with a camera in the way, expecially when I am using the bigger tools like the bridgeport and harrison lathe.

I am very happy with the progress and my ability to make these parts, took me years of watching all you before I decided to jump in. amazing myself every day!

now just to clarify, the cox cylinder assembly, piston, carburator and plug boot have been purchased 
for all your cox needs you really should check out these guys! very kind family run business.

http://coxengines.ca/


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## rhitee93 (Sep 3, 2012)

This sounds iteresting Michael.  I am not familiar with this engine, but will be looking forward to seeing your progress.


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## Speedy (Sep 8, 2012)

cranks are getting done. 
just need to drill the passages for air and the crank pins.

[ame]http://youtu.be/oiPapnPfHOs[/ame]


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## Speedy (Sep 8, 2012)

guys I have abit of trouble. 

the author of the plans calls for a 3/32 crank pin on the crank shaft but a 7/64 fits my pistons connecting rod way better. 3/32 has allot of side play.
do I go along with what he calls for or do I use the better fit 7/64 .

im wondering if he chose the 3/32 to have abit of leeway if the measurements are off the piston will still work? but that logic sounds off as the connecting rod and crank shaft would be worn in short order.


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## sssfox (Sep 8, 2012)

I have some old Cox engines and none of them have slop between the rod and crankshaft pin.


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## Speedy (Sep 8, 2012)

im thinking the same, why should excessive slop be present. 
I will see the procedure thru with the better fitting 7/64 and take it as a learning experience if something proves down the line it should have been different.


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## rhitee93 (Sep 8, 2012)

I think your plan is best Michael.  I don't see anything good coming from leaving a lot of play in the big end bearing.


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## sssfox (Sep 8, 2012)

Michael,
I miked one of my crankshafts and it came up 0.1065.  7/64 should be 0.1094.
Theoretically, the piston rod shouldn't fit on the 7/64 rod.

Steve Fox


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## thayer (Sep 8, 2012)

Mike,

Looks like you are having a lot of fun with this build. While I haven't flown any 1/2A glow in a while, I will definitely be following along on your progress.

Thayer


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## Speedy (Sep 8, 2012)

thanks for the comments guys! 

Brian, exactly what I was thinking, at this point I am happy I went with the nicer fit.

Steve, after reading that I ran downstairs to the shop to double check thinking I may have grabbed another drill.
all checks out fine, I tried all 4 connecting rods and all slide on fine, whew close one  I am going to buy some fresh 7/64 bits to make the pins hope new ones check out just the same.

Thayer, this one is slated to be put into a custom oval midget car or something similar. I am going to build the frame out of small tube and machine my own axles. I am just getting into flying and doubt I could pilot a 1/2A yet as cool as they are.

anyhow here are some pictures, all that is left to do is machine the air/fuel mixture timing ports! eeek another but last big step on the crank.

- left to do is ream out the block
- tap the backplate and block
- piston clearance on the back plate
- 6 bolt circle on the back plate
- 1/4-32 unef a2 tap for my carburetor (out of all taps why that one haha)

pictures of the crank at this point.


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## sssfox (Sep 8, 2012)

I didn't know you were using a 7/64 drill bit.  That explains the difference.
I measured one of mine and it was 0.1075.  The flutes are slightly wider than the shank.

I guess every brand is a little different.  You may want to take a piston with you when you buy the drill bits.


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## Speedy (Sep 8, 2012)

I should have mentioned. 

do you think other then being more difficult to work with should I go with anything special for the finnish on the drill bit?
cobalt? titanium? or regular HSS drill bit.

I am stumped again, but I dont think I could properly explain what is stopping me.. but I will try.
in the plans the author tells me to machine the transfer ports I need to put the crank in the fixture and measure .450 from one side of the fixture to the crank pin (this should give the timing as it angles the crank about 18deg) anyhow I varied on the material for the crank fixture he asked to use 7/8 aluminum hex I used something smaller. so will my thinner side walls skew the port timing? I am going with yes but not sure.

** edit, I assume I could just compensate for the measurement by adding the difference of the small part to the large on on the .450 .... example if I had an extra .050 I should have had on my holding fixture I just add that to the .450 and call it .500?  sound logic?


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## sssfox (Sep 8, 2012)

Speedy said:


> in the plans the author tells me to machine the transfer ports I need to put the crank in the fixture and measure .450 from one side of the fixture to the crank pin (this should give the timing as it angles the crank about 18deg) anyhow I varied on the material for the crank fixture he asked to use 7/8 aluminum hex I used something smaller. so will my thinner side walls skew the port timing? I am going with yes but not sure.



For the drill bit, on the coated ones I have, the coating doesn't go all the way up the shank, so it won't matter which type you use.  Just make sure it is from the smooth part of the shank, not the part that has the info stamped in it.  That part will wear the inside of the piston rod.

If I understand correctly, for the measurement, if it were me, I would subtract the difference in thickness from your fixture to the dimension the author said to use.  The other option would be to make a degree wheel and figure the opening based on the actual position of the crank in degrees, if he gives that information.


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## Speedy (Sep 8, 2012)

could you give me an example of that? seems I would still be in trouble doing it that way.


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## sssfox (Sep 8, 2012)

Say the author said use 7/8" and the dimension is .450.
Say you used 3/4".  The difference would be 1/2 x (7/8 - 3/4) = 1/16 or .5 x (.875-.75) = .0625.

Take the .450 and subtract the .0625 and you get .3875.
That would put the crank pin in the same location relative to the thinner fixture.  If your dimension is not 3/4" then substitute the actual dimension.
It is just half the difference between the proposed and actual fixtures.

I hope I didn't make it harder than it really is.


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## Speedy (Sep 8, 2012)

gotcha! sometimes I just need to give it a good thinking  and a coffee break.


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## gus (Sep 8, 2012)

rhitee93 said:


> I think your plan is best Michael.  I don't see anything good coming from leaving a lot of play in the big end bearing.



Hi Brian,

I agree with you.

From my 32 years industrial experience with Ingersoll-Rand T-30 Air Compressors.

Gudgeon Pins must be push fit into piston.No slops
Con-Rod big end on to crankpin.Sliding fit. No slops.

If you can feel a slop,engine or compressor will knock and soon a loud knock and crash comes in days/weeks.

I am now building a 0.46 Glow Plug engine. About to cut the piston and con rod.Now looking for 3/16 reamers to fit gudgeon pin and crank pin.May DIY
"D" reamer .

Will be using Silver Steel as per print. Silver steel is prescribed by the designer.


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## Speedy (Sep 8, 2012)

oops, well I know the feeling now. 

everything was going smooth, all the intake slots cut fine and seemed to be dead on where they were suppose be as far as I could tell.
author called for 1/8th transfer ports to move the fuel mixture to the cylinders so I had to drill a hole to connect to the transfer slots, left the measurements up to the user so I took about 45 minutes to think it over.
set up my part and went to town, everything working well then of course the drill bit as it enters the transfer slot grabs hard moving the part in the vise and bent the drill bit hard (surprised it didnt snap with all that flex) their is a boo boo on the part pushed the metal out creating a bulge at the end of the transfer slot  I hammered it back in.  in frustration I was going to just toss the part and call it a day but I decided to continue and finnish the last transfer port on the other end.

since its just a port to move air I am hoping it will still work, the hole is enlarged and oval so it might just get more fuel mixture then the other cylinder. 
going to keep it until I know the engine wont run.


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## Speedy (Sep 11, 2012)

guys I finnished all the parts, all is left to do is tap for the cylinder and carb.

could anyone tell me the difference between a plug tap and a spiral point plug tap
I need to buy a 1/4-32 unef and the seller is asking me which I need.


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## sssfox (Sep 11, 2012)

A standard plug tap has the teeth, actually the grooves between the teeth, in a straight line.  A spiral plug tap has the grooves in a spiral pattern.
For what you are doing it won't matter, get the cheapest.


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## Speedy (Sep 11, 2012)

I'm thinking long term, if I would have the use for the spiral.
The quotes on price was for plug 14.30 canadian spiral point 21.81

I to think the cheap will be fine, I'm assuming it would work on steel if I ever needed to? Since its the glow plug thread I might have a use for that down the road.


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## sssfox (Sep 11, 2012)

This may help with your decision:

http://www.gjhall.co.uk/em/uploads/docs/08b253b7d6edbf1c40f849888df04207.pdf


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## Speedy (Sep 11, 2012)

Thanks! Great read for me, I feel the cheaper one will do everything ill need.


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## gus (Sep 11, 2012)

Speedy said:


> Thanks! Great read for me, I feel the cheaper one will do everything ill need.




Hi Speedy,

Spiral Taps are expensive and tends to break when used like a straight flute tap which we normally turn forth and back.Spiral taps best used ,clamped in drill press chuck and turned all the way through by hand. Use Tapmatic Oil.
Same tapping oil has one version for all metals except Aluminium. They also have a version for Aluminium.But kerosene is fine.

1/4 x 32 tpi UNEF taps are available from aeromodel shops.Bought mine from such shop in Singapore.Cost me US$10.

My Glow Plug Engine is progressing well.


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## Speedy (Sep 11, 2012)

thanks Gus. 
with abit of shopping I probably could have found it elsewhere but for some reason its slightly harder to locate.

here are more pics I took while building.


crank done, transfer ports 18degrees l/r for timing (hope I did that right!)






crank case done





all slides in happily, have binding on the section of the crank that has the ports. maybe need to run the reamer in it again or file more out of the crank not to sure


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## gus (Sep 12, 2012)

Hi Michael,

Please keep posting fotos as you go.

Now looking out for V2 engine plans. Radial will be tough for my limited machine tool capacity.


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## Speedy (Sep 27, 2012)

much thanks and appreciation goes out to member stevehuckss396 he kindly threaded the cylinders for me. 

finished the case off by drilling and tapped for the carb.
I cut the crank pins, but evidently a mistake was made. need to go back and re measure. anyhow thats for the weekend.

the carb seems to be happier in this position, either way I need to do some trimming to make the carb open fully, disadvantage hard to tune with no finger room











just to show the other option involving more trimming then the other and slightly harder to make it servo operated. but on the other hand way easier to tune
I hate decisions.


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## Speedy (Oct 2, 2012)

it runs, needs some tweeking. 
not sure its hitting strong on the second cylinder. 

ball bearings to come.

[ame]http://youtu.be/2a3W_FjaEVk[/ame]


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## Brian Rupnow (Oct 2, 2012)

That is really neat!!! I would like to know more about it.---Brian


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## stevehuckss396 (Oct 2, 2012)

Well what's next?






Or this!







Just kidding. I'm glad everything worked out for you.


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## WiKKiDWidgets (Oct 2, 2012)

I think that Budweiser is next. Great job Speedy.


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## Speedy (Oct 2, 2012)

a celebratory drink does sound like a good idea 

thanks for all the kind comments guys, this is my first engine and I am proud of it 

Steve, I landed a tap so I am up for making more engines with these cox cylinders, its addicting.
where did you get plans for the radial? that is great idea!

I am thinking of putting ball bearings in the front and rear. 
I want to also get the engine anodized so its not done just yet.


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## stevehuckss396 (Oct 2, 2012)

Speedy said:


> where did you get plans for the radial? that is great idea!


 

It's my own design.


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## Speedy (Oct 2, 2012)

very nice. I cant imagine making my own designs just yet. sometime I hope.

I still seriously want to start your little demon, I have ways to go but its high on my list.


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## gus (Oct 3, 2012)

You are my hero. You make it look so easy.

Gus is still trying to get his FireFly started and spin.Looks like a major rework or more likely start from scratch. Make too many errors.I.C. engines are not as forgiving as steam engines with certain critical fits.


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## Speedy (Oct 5, 2012)

Brian Rupnow said:


> That is really neat!!! I would like to know more about it.---Brian



hi Brian. the author Jerry James has these plans published for free. he also has a inline 4 and working on a v4. 

the cylinders and piston/rod come from hobby motors, the old 1/2a cox .049s. they fire 180deg from each other. I think it was the perfect starter engine 

thank you Gus. 
far to kind, your engine is far more labour intensive all I did here was make a bottom end, your doing the whole deal! it will fire up


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