Squint Scale Curtiss Model K Aero I4

[RReid]

Thank you Dave, Per, and Dave! 

A build-up Crankcase, by the looks of it - are you going to solder the supports for the Crank and Camshaft in later ?

Yes, I'm doing a built-up construction to take advantage of the brass bar stock I already have on hand.

The crank bearings will be inserted into holes either bored through the upper and lower crankcases together, as shown at the far side in the image below, or through the upper and crankcase and a separate lower block, as shown on the near side. I'm leaning toward the latter option so that the lower crankcase, which is mostly just cosmetic, can be removed without disturbing the bearings and crank.

The cam bearings will be in bored holes, but the near side hole and bearing OD will be large enough so that with that bearing slid out of place there will be enough clearance to pull the camshaft out.

[Admiral_dk]

I like your idea about the Camshaft 

.... but I must admit to thinking that you need at least a middle support for the Crankshaft (+ Camshaft too) ....      - then again, I kind of always look for potential problems 

Per       

[RReid]

Well Per, you may be right about that, we'll see. The similarly sized Westbury Seal seems to use only two bearings for the crank, which is what gave me the idea to try it. I don't ever actually put much, if any, load on my engines, so I think it will be fine. The camshaft does worry me more, which is why I increased it to a 4mm shaft from than the 1/8" shaft (3.2mm) I started with. Increasing it further is possible. If I have to, I think that adding a bearing in the middle should not be a problem, even as a retrofit, and still can be arranged to allow for camshaft removal. Same for the crankshaft.

When in doubt, I do like to do the experiment for myself.

[Admiral_dk]

The similarly sized Westbury Seal seems to use only two bearings for the crank, which is what gave me the idea to try it.

As that Engine has been known to be used in model boats - I think that you are right 

Per         

[RReid]

The boring head was used to open the holes in the crankcase top to the final diameter for the cylinder liner bases to plug into, with the help of the simple aluminum bore gauge shown.

Then I began work on the cylinder liners. Made from 12L14 steel, they are first turned to the 0.9” shoulder diameter, which also serves as the bearing surface for the steady rest. Then the short section that plugs into the crankcase is turned to 0.8” and the through bore is started, but not finished. At that point the baby liners are parted off the parent bar. The first two done to this stage are shown here.






Here's all four liners done through phase 1, alongside another bore gauge turned from scrap steel. Next step is to chuck them up on the short, smaller diameter. The clean bore and the smooth and consistent larger diameter means that either the tailstock center or the already set steady rest may be used to help in getting them set up in the 4 jaw nice and true. Then the final turning and boring can be completed.

The bore and stroke for this engine will be 0.6875” x 0.8” (17.5mm x 20.3mm)

[Admiral_dk]

My first thought seeing the last picture - Woa - those cylinders are Tall 
So I went back to the first page and had a look and was reminded how stupenduesly much longer the stroke was compared to the bore back then ....

This is almost certainly from the long experince with Steam Engines, that would have been taught back then .... How times has changes since then 

No matter - I will look forward to see them (+ the rest) take shape and end up with a running Engine     

Per               

[cnr6400]

 

[Roger B]

Off to a good start   

Did you make the fixed steady or is it commercial?

The Austin Seven engine had/has a two bearing crankshaft. When they were raced the two middle pistons were machined slightly shorter to allow for the whip in the crankshaft.

[RReid]

My first thought seeing the last picture - Woa - those cylinders are Tall 
So I went back to the first page and had a look and was reminded how stupendously much longer the stroke was compared to the bore back then ....

The Smithsonian site that I downloaded the pictures from lists the bore and stroke as 4” x 5” (102mm x 127mm) for a B/S ratio of 0.8. For my engine, the stoke is slightly less relative to the bore, for a ratio of  0.86. I did this to keep the crankshaft from hitting the inside of my relatively heavy walled crankcase.

I think the engines of this time period and state-of-art were limited to a fairly low rpm range, and as well propellers work best at lower rpm. So the long stroke provides a benefit in torque and the drawbacks of higher piston speed, etc., don't come into play so much.

Thanks CNR!

Hi Roger. The fixed steady is a Taig item. Like many of their accessories, it's simple and effective enough, if a bit crude.

The Austin Seven engine had/has a two bearing crankshaft. When they were raced the two middle pistons were machined slightly shorter to allow for the whip in the crankshaft.

Well, that's a pragmatic solution!

I got tired of the hot swarf getting spit at me out the back of the chuck, so I carefully fabricated and set-up this removeable chip guard. Like a true Taig accessory; simple, effective enough, if a bit crude...

Liners are done, short of final trimming to length.

[cnr6400]

Like the chip guard. The price was right, and it will save a lot of solvent and labour for cleaning - when it's dirty just use it to start the woodstove, fireplace, forge... (or the s'more's generator campfire in the backyard) 

[Admiral_dk]

The Smithsonian site that I downloaded the pictures from lists the bore and stroke as 4” x 5” (102mm x 127mm) for a B/S ratio of 0.8. For my engine, the stoke is slightly less relative to the bore, for a ratio of  0.86. I did this to keep the crankshaft from hitting the inside of my relatively heavy walled crankcase.

And then I got my next thought (they are dropping slowly in this build of yours) ....
A lot of what would be inside the Crancase on a more modern engine is in the lower part of the cylinder here + the Pistons are probably rather tall too ....

Again I will enjoy being enlighted as you progress     

Per

[RReid]

Like the chip guard. The price was right, ...

Thanks CNR. The price was definitely right, considering it's a fancy ventilated composite material.

A lot of what would be inside the Crankcase on a more modern engine is in the lower part of the cylinder here

Thanks Per. Certainly it is not a "modern" style engine with cylinder block and crankcase combined into one casting. Always value your comments, questions, and insights!

[crueby]

That chip guard looks effective though the visibility is off, it needs a polish!   

I use one shaped just like that but made out of some plexiglass sheet that I bent into a 90, cut a notch so it fits over the end of the cross slide, held between a couple of shcs in the t track. Saves cleaning chips out of the beard...     Current one is finally getting coudy on the inside, all pitted from the chips, going to be making a new one soon (may be one of those 2 year and 10 minute jobs)

[RReid]

That chip guard looks effective though the visibility is off, it needs a polish!   

Since it was only meant to catch the chips flying out the back of the chuck during the boring operation, no visibility was needed!

Got all four cylinder sleeves turned and bored today. They will be trimmed to length in unit with the liners. Representing the water jacket of the prototype engines, I haven't decided yet if I will try to make them functional or not. I also tried scuffing each up with some 220 sand paper while turning in the lathe to kill the some of the fresh turned gloss, or to give some tooth if I decide on paint.

[RReid]

In order to facilitate getting the crankcase drilled for the cylinder/cylinder head fixing studs I made up the drill jig shown on the left below. The lower boss fits snugly into the crankcase openings, while the bore matches the cylinder gauge. Those two tools then work together to ensure the crankcase opening is lined up under the mill spindle. From that point, the drill jig served mostly as a check on my crank counting, though it did also eliminate the need for center drilling. Once drilled, I went back around to tap all those holes 2-56.




I used a similar procedure to drill through the four cylinder jackets and the first of the cylinder head blanks. The head blank was turned to OD first and given a shallow boss to register into the crankcase, so it was transferred to the mill still mounted in the 4Jaw.


I somewhat belatedly decided to treat this engine to an 0-ring for the head to cylinder seal. After drilling that first head blank I sent it back to the lathe thinking to cut the o-ring groove there, but that was chattering too much with the only suitable tool I had handy. So I went back to the mill, and this time mounted it on the rotary table so that the groove could be cut in with an end mill. This was the better plan.


So here is the current state of play. All four cylinders are complete and have their jackets, and a start has been made on the first cylinder head. Next I'll get three more head blanks to this stage. The SHCS are temporary and will be replaced by studs and nuts in due course.