Another Westbury Seal 15cc

[gadabout]

With the cam you can decide which rotation you want your Seal to run by how you rotate the cam jig , if you rotate it clockwise so cut cylinder ones cams then rotate to cylinder three markings and so on it will run clockwise looking from the flywheel end if you cut cylinder two cams after cylinder one by rotating the jig anti clockwise that’s the direction it will run , anti clockwise from the flywheel end, I made mine with the firing order 1342, it runs clockwise looking from the flywheel end. Think it got this right , it’s been quite a while

Mark

[Charles Lamont]

With the cam you can decide which rotation you want your Seal to run by how you rotate the cam jig , if you rotate it clockwise so cut cylinder ones cams then rotate to cylinder three markings and so on it will run clockwise looking from the flywheel end if you cut cylinder two cams after cylinder one by rotating the jig anti clockwise that’s the direction it will run , anti clockwise from the flywheel end, I made mine with the firing order 1342, it runs clockwise looking from the flywheel end. Think it got this right , it’s been quite a while

Mark

But the Seal is a désaxé design (ie the cylinder centreline is offset from the crankshaft axis). It is only intended to run clockwise looking at the flywheel end.

[petertha]

Thank you. There will be a pump belt driven from the crankshaft. I still have not done that, but I did some research on the design here: https://www.modelenginemaker.com/index.php/topic,11615.0.html

Ah yes, thanks Charles. Your centrifugal pump work was referred to me by Vixen (Mike). I've been slowly picking away at a pump design myself. Initially to bench run with small variable speed motor, but eventually sized for an engine direct drive. I plan to 3DP parts to provide me some design flexibility. I'll post my questions there where it better belongs.

[gadabout]

Yes it is a de saxe design, I have two here , one I made with the firing order 1342 and runs clockwise from the flywheel end and another by a famous model engineer that fires 1243 and runs anti clockwise, both run well!
Mark

[Jasonb]

Here is a question for the knowledgeable. The drawings and original ME article say the firing order is 1-2-4-3 but the copy of the ME article from Hemingway is marked up 1-3-4-2!!

If you read on in the article you will see Westbury corrects the firing order to 1342 but says it makes no real difference.

[doubletop]

Interesting quite a bit of conversation going on and it seems I missed the notifications but I have been work on getting things into Fusion, So far I have done all all the castings. The exercise has helped me understand better what I am dealing with. I also need to sit down and just go through the documents and various build threads and read them



The drawings are lacking a lot of information that I had to resort to a ruler on the paper copies to get some idea of the dimensions, or just wing it. (typing this I have just realised that I had the paper copies of the plans scanned yesterday and all I really need to do is take a screenshot of the part I'm struggling with and import it into Fusion as a canvas. Fusion can then tell me the dimensions.)

It appears that the pattern maker had similar problems on some of the parts as they are not exactly as drawn

Pete

[Vixen]

Here is a question for the knowledgeable. The drawings and original ME article say the firing order is 1-2-4-3 but the copy of the ME article from Hemingway is marked up 1-3-4-2!!

Hello Pete
In answer to your previous question. The cylinder firing order is totally dependent on the Crankshaft Direction of Rotation (DIR). Dear Edgar Westbury omitted to show the DIR on his drawings. This omittion has led builders a merry dance ever since. 

When a Seal engine's crankshaft rotates in a counter-clockwise direction (viewed from the front); the cam and valve events dictate the cylinder firing order  1-2-4-3.

When a Seal engine's crankshaft rotates in a clockwise direction (viewed from the front) the cylinder firing order becomes the more familiar 1-3-4-2.

Which one is correct? The Seal engine is sufficiently docile that it does not seem to matter much, the Seal can be made to run in either direction.

However, if you consider the desaxe design philosophy, which attempts to minimise the friction and side forces on the piston during the firing stroke


https://www.mxa-digital.com/motocrossaction/january_2018/MobilePagedArticle.action?articleId=1269365#articleId1269365

You can see the desaxe configuration favors the counter-clockwise  DIR and the 1-2-4-3 firing order. This is of course what Westbury wrote in his notes but others have subsequently corrected changed, again without stating the all important DIR 

Cheers

Mike

Ps. this is effectively what Charles said back in reply # 16. "It is only intended to run clockwise looking at the flywheel end."

[Jasonb]

Pete

From having redrawn several engines from other sets of castings I would suggest taking all dimensions from your castings. Even the given machined surfaces may not have sufficient material to give what is shown on the drawings let along the usually undimensioned as cast surfaces.

[doubletop]

Here is a question for the knowledgeable. The drawings and original ME article say the firing order is 1-2-4-3 but the copy of the ME article from Hemingway is marked up 1-3-4-2!!

Hello Pete
In answer to your previous question. The cylinder firing order is totally dependent on the Crankshaft Direction of Rotation (DIR). Dear Edgar Westbury omitted to show the DIR on his drawings. This omittion has led builders a merry dance ever since. 

.....

You can see the desaxe configuration favors the counter-clockwise  DIR and the 1-2-4-3 firing order. This is of course what Westbury wrote in his notes but others have subsequently corrected changed, again without stating the all important DIR 

Cheers

Mike

Ps. this is effectively what Charles said back in reply # 16. "It is only intended to run clockwise looking at the flywheel end."

Mike

I see from your thread that you had asked the same question posting the clip from the Hemingway document. From what you are saying if you do the cams as drawn then viewed from the front (timing end) it will run 1-2-4-3 anticlockwise in the desaxe manner.  Deaxe is a design feature so it seems silly to ignore it so I think I will go with 1-2-4-3

I haven't looked at this in any detail yet but on the question of the pistons sticking out of the top of the block 1/32" is that the case in practice or just a result of basic calculation of crank throw, conrod length and piston height without taking into consideration the deaxe offset?

And a further question. The edge of the flywheel bearing housing crosses the 1/2" opening for the camshaft bushes and the flange for the bush at that end is 5/8". Thinking I must have missed something I had a quick look at you posts and there is a photo of your bearing housing doing the same. I did not see your solution, did you have to relieve the bearing housing to accommodate the bush?

Pete

[doubletop]

Pete

From having redrawn several engines from other sets of castings I would suggest taking all dimensions from your castings. Even the given machined surfaces may not have sufficient material to give what is shown on the drawings let along the usually undimensioned as cast surfaces.

Jason

I think I may pass on that as being too difficult. On a rough measure up my castings do appear to have some machining allowance but drawing them could be problematic. My cylinder block casting appears to be made from two halves of two different patterns



Pete

[Jasonb]

When you have it all assembled in CAD you can take an actual measurement of how far it sticks out.

Simple maths of crank throw, conrod and piston crown make it 1/32" too long as a simple vertical calculation, the 1/8" offset only accounts for about 4 thou reduction.

[Vixen]

Hello Pete, down there in Weeelinton, where only the tar on the roads keeps the tectonic plates from moving. 

Yes, that's right, do the cams as drawn, when viewed from the front (timing end) the engine will run 1-2-4-3 anticlockwise in the desaxe manner. The correct firing order is 1-2-4-3 starting from the timing end, as detailed in the build article and on the drawing, so make sure the cams go the right way round.  No idea who was responsible for the 1-3-4-2 mark-up. 

There is so little space in the combustion chamber, I assumed the 1/32" piston stick out would hit the roof and was probably a drawing error. I made my pistons flush with the top of the cylinders at TDC.   (Jason beat me to it again)

Yes, the camshaft bush clashes with the flywheel bearing housing. I machined a small flat on the outer edge of the camshaft bush to clear. You can just see it in the top photo in reply #125.

The sooner you start working from your own drawings, rather tha Westbury's, the better. Get away from those old school inch fractions and life gets a lot easier.

Cheers   

Mike

[Charles Lamont]

I agree with Jason that it is important to measure and draw the castings (i call it surveying) in order to work out how best to find the finished parts inside them.

I mostly do that by putting measured dimensions on a sheaf of hand drawn sketches which are then used to draw what actually exists in 2D CAD.

Fitting the part to the casting will often involve compromises and sometimes adjustments to the design. You may find, for example, that a cored holes doesn't match the external surfaces well enough to allow it to fully clean up.

I have found it necessary with some parts to do initial light clean-up cuts to establish temporary datum surfaces before it possible to accurately locate other features.

IMHO, thorough 'due diligence' with the castings can save a lot of bad language in the workshop. 

[gadabout]

Mike, this is all very interesting, my Seal, firing order 1342 runs anti clockwise from the timing end. As I at the time of making the cam thought I interpreted the drawings properly I’m not sure what’s going on.
Regards
Mark

[doubletop]

Hello Pete, down there in Weeelinton, where only the tar on the roads keeps the tectonic plates from moving. 

Yes, that's right, do the cams as drawn, when viewed from the front (timing end) the engine will run 1-2-4-3 anticlockwise in the desaxe manner. The correct firing order is 1-2-4-3 starting from the timing end, as detailed in the build article and on the drawing, so make sure the cams go the right way round.  No idea who was responsible for the 1-3-4-2 mark-up. 

There is so little space in the combustion chamber, I assumed the 1/32" piston stick out would hit the roof and was probably a drawing error. I made my pistons flush with the top of the cylinders at TDC.   (Jason beat me to it again)

Yes, the camshaft bush clashes with the flywheel bearing housing. I machined a small flat on the outer edge of the camshaft bush to clear. You can just see it in the top photo in reply #125.

The sooner you start working from your own drawings, rather tha Westbury's, the better. Get away from those old school inch fractions and life gets a lot easier.

Cheers   

Mike

Thanks Mike

We don't like to think about anything tectonic really

I am staying imperial. I note from the original drawings the majority of things are in units of 1/32" which makes guess the undocumented dimensions a lot easier. You will see that in my next post. The only exception is metric vs BA nuts and bolts. I have BA taps and dies but not for 7BA so I am going to use 2.5mm cap screws where 7BA is called for. Anything smaller will probably be 8BA and up.

Pete