Another Westbury Seal 15cc

[Zephyrin]

The partition between the combustion chambers seems very thin to me in some places, particularly around the valves.  personally, if the size of the valve allows it, I would leave some metal from one or both side to get a slightly wider bridge to ensure a tight seal between the chambers.

[doubletop]

The partition between the combustion chambers seems very thin to me in some places, particularly around the valves.  personally, if the size of the valve allows it, I would leave some metal from one or both side to get a slightly wider bridge to ensure a tight seal between the chambers.

Point taken and you will see what I have managed to achieve in the next post. Basically the width of the section between the chambers is pretty much what it is as long as it is not made less

Pete

[doubletop]

I have done some more on this. I put the head into my photo copier/scanner to get the best representative image I can. That was imported into fusion and scaled and aligned with the existing drawing of the head.  The head was located over the cylinder block to obtain the best reference for the pistons and valve locations. So in the image, the thin grey lines are the cylinder block for reference, then the image of the casting and overlaid on that the heavier black lines are the outline of the new cavity to be machined.

This then enabled the drawing for the best representation of the existing cavities could made and opening out the cylinder cavity to the diameter of the pistons with the minimum of material to be removed. There are instances where the cutter will not remove any material but those places will require a little blending with the Dremel.

So two images; the drawing outline overlaid on the casting and the 3D toolpath also overlaid on the casting (I hadn't realised this was possible but hadn't hidden the canvas when I went into the manufacturing module of Fusion.).





I will be using a ball nose cutter to ensure a nice fillet on the lower edge but before committing to anything will try this out on a piece of scrap.

Pete

[Zephyrin]

wow, this is a nicely planed study...and a interesting thread to follow, thanks to share.
I suppose that the software can provide the volume of these complex combustion chambers.

[doubletop]

wow, this is a nicely planed study...and a interesting thread to follow, thanks to share.
I suppose that the software can provide the volume of these complex combustion chambers.

I didn't think there was a way of doing that but found that you can get the properties of an object. So for the cylinder head I set the timeline in Fusion to prior to the inclusion the cavities and then after they had been included. So 2.144 CuIn (35.134cc)  before and 1.719CuIn (28.169cc) after which makes the volume of the cavities as 6.964cc or 1.741cc each. The total volume of the piston strokes is 13.826cc so volume max is 13.826+6.964= 20.79cc and a compression ratio of 2.98:1. If the pistons are allowed to extend into the cavity, as designed, the compression ratio goes up to a massive 3.18!!.    I don't have a feel for what a typical compression ratio would be for this type of engine and thought I had seen it on Vixens thread but can't find it. The full sized Ford and Austin side valve engines from the same era were 6:1

(Where 15cc comes from is anyone's guess)

I wish you hadn't asked me now

Pete

[Jasonb]

Max volume will be less if the pistons encroach into the head which will reduce the 6.964 as some of that will be included in the swept volume

[doubletop]

Max volume will be less if the pistons encroach into the head which will reduce the 6.964 as some of that will be included in the swept volume

Jason

Yes I had mentioned that. After a bit of juggling and whatif I have gone back to the correct length conrods to use the piston overrun. This should now give me a compression ratio of 3.22:1

Pete

[Art K]

When I built my Val single I used Alibre to calculate the compression ratio. Modified the head design to get 7:1. My understanding of flat heads a high compression ratio was 7:1 and that was quite a performance engine. My Upshur was around 4-4.25:1 and would in it's glory days run 7200 RPM. Run hard put away wet as they say! I would make a sweeping statement about 2 main engines not being performance engines, but either Austin or Morris made one that was quite popular in racing probably in the 30's. When they changed to a 3 main they lightened the crank and engines were self destructing trying to repeat what the heavier crank could do.
Art

[doubletop]

When I built my Val single I used Alibre to calculate the compression ratio. Modified the head design to get 7:1. My understanding of flat heads a high compression ratio was 7:1 and that was quite a performance engine. My Upshur was around 4-4.25:1 and would in it's glory days run 7200 RPM. Run hard put away wet as they say! I would make a sweeping statement about 2 main engines not being performance engines, but either Austin or Morris made one that was quite popular in racing probably in the 30's. When they changed to a 3 main they lightened the crank and engines were self destructing trying to repeat what the heavier crank could do.
Art

Art

Apologies for the tardy reply, but you will see in the next post I have been occupied in the CAD world. I read that Ford and Austin compression ratios were 6:1 but skimmed heads and thin gaskets manged to increase that a bit. The problem I have is the volume of the existing casting determines the starting point  with the compression ratio and needs to be enlarged to accommodate the piston above the block and the lift of the valves.

Pete

[doubletop]

My last post was a week ago and I was about to commit to machining the head cavities when Fusion decided to have problems. Whatever I did it would crash at every opportunity. I wasn’t prepared to proceed with the machining until I got it under control. I didn’t want to be half way through and need the CAD to make some adjustments to the tool-path. I had done a number of test pieces but each one provided opportunities for improvements.

The problem with Fusion was one I have had before, things get a bit complicated, discipline gets lost from time to time, and then you can get circular dependencies that lock things up. To get control I was trying to delete things like joints but they wouldn’t go. In the end I moved the timeline cursor to an early point in the design, suppressed components and their associated joints, progressively moving forwards in time suppressing more components and joints.  That got things under control but things still weren’t able to be deleted. That problem still remains but at least now I can enable individual components, modify and redo the CAM.

So today it was a case of get on with the head.

First was a roughing cut to enlarge the cavities and re-align them correctly. In the photo you will see the two on the left having been machined, the third is just started and the fourth is as cast.



The next step was to do a finishing cut in the cylinder space, square sided to allow the piston to full encroach. I have given it 1/64” vertical clearance
That was followed up with a 1/8” ball nosed cutter in the valve space which enabled fillets to be incorporated. The thinking being to assist inlet and exhaust flow.



As there are still machining marks in the cavities I intend to zap them in the sand blaster, that does a great job of blending the marks. I will then polish with the Dremel.



After the sand blast I may give the mating surface a slight skim with the fly cutter. That will depend on the clearance of the valves. The drawing says 0.188”. The valve head is 0.0625 and the lift 0.0781, total 0.141”. The fillets in the cavity are 0.0625” However a quick check indicated that the 0.188” clearance is very generous so I may be able to take another 0.005”- 0.010” off the head. I do have 0.016” clearance for the pistons. That may help the compression ratio

Pete

[Art K]

Pete,
Sorry, I wasn't intending to suggest you change and raise the compression ratio. An L head engine design is inherently low compression was all I meant.
Art

[uuu]

What you will get, with your extended piston crown, is a beneficial "squish" effect - as the piston approaches the head it will create turbulence and push a jet of the mixture towards the spark plug.

Wilf

[doubletop]

Pete,

Sorry, I wasn't intending to suggest you change and raise the compression ratio. An L head engine design is inherently low compression was all I meant.

Art

Art

No, I didn’t read your comment that way at all. I was just commenting that production engines seemed to be 6:1 whereas the best this design seems to be able to achieve is around 3:1. It is sort of pre-determined by the design and the cavity already in the casting

Pete,

Sorry, I wasn't intending to suggest you change and raise the compression ratio. An L head engine design is inherently low compression was all I meant.

Art

Wilf

That is the way I have gone as the piston extending into the crown also helps recover some of the cavity volume and increase the compression ratio slightly. Once I have the pistons and conrods done I can see if I can skim the face again and get a few more thou off it


Today I zapped the head in the sand blaster which removed all the machining marks. It just needs the cavities polishing. Before and after






While I was working on the head it was time to deal with the reach of the spark plugs and the difficulty in removing them with the manifold installed. I had already moved the manifold cover attachment bolts (as did Vixen) but the spark plug holes still needed relieving. It was nearly a disaster, as I was winging it without having drawn what I intended to do. However, it worked out in the end



Pete

[Roger B]

Machining the combustion chambers seems to have been quite a battle 

Looks good now   

[doubletop]

Machining the combustion chambers seems to have been quite a battle 

Looks good now   

Roger

Thanks but not really a battle.

There were a few things to take into account, Having the pistons extend in to cavity or not. Minimising the volume of the cavities, to maintain compression ratio, whilst accommodating the cast in cavities which weren't correctly located to to drawing. (They weren't that far out)

Then I was going to CNC the machining so I wanted to test the toolpaths before I committed to the casting. I did a rough pass with the 6mm end mill, then did a finishing toolpath for the piston area to get to size with square edges. Then a finishing toolpath for the valve cavities and transition to the cylinder space with a 1/8" ball ended cutter.

Fusion playing up didn't help either

After all that then be confident enough to actually do it all on the cylinder head. I made some gung-ho errors when I started that has caused me to be a bit cautious

Pete