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Old 05-08-2011, 10:21 PM   #1
Charles Lamont
 
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Default Westbury 'Seagull'

Hello people. This is my first post in this neck of the woods. I live in the UK, West Midlands area. I have been doing model engineering for many years, but am currently tackling my first petrol engine.

It's a Westbury designed 10cc twin side-valve job, castings from Hemingway Kits 1.

You can see my progress (not very up-to-date atm, sorry) here: 2.

The latest problem I have with the design is the cam profile. As designed, the tappets are too small in diameter for
the cams, inlet in particular. As shown by plugging the dimensions into this brilliant resource 3, for a brief part of the motion, the cam is in contact with the edge of the tappet face, which seems unlikely to be good for either, or for noise (quiet is one of my criteria of success). Design dimensions are the same as the 'Seal': Base circle radius: 11/64", flank radius: 9/16", lift: 5/64" opening angle: 120°. I probably can make the tappets bigger, but ... any advice?

(1) http://www.hemingwaykits.com
(2) http://www.charleslamont.me.uk/Seagull
(3) http://modelenginenews.org/design/CamTable.php



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Old 05-08-2011, 11:29 PM   #2
stevehuckss396
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Default Re: Westbury 'Seagull'

Well you have 3 options

(1) Make a larger diameter lifter. Great if you have room.

(2) Reduce the lift of the lobe. This will change the shape of the lobe and less diameter will be needed.

(3) Make lifters with a curved surface. If the surface of the lifter that contacts the lobe has a ball end or even any kind of radius you can run a smaller diameter.

If I think of anything else I'll get back here but thats all i have right now.

Cheers



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Old 05-09-2011, 02:50 AM   #3
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Default Re: Westbury 'Seagull'

Hi Charles, very clear construction diary. How come everything looks so clean? I can tell this is going to be a very well made model by the time it is complete. Any ideas what you will use it for yet?
Also, where in the west midlands are you??

Rob.

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Old 05-30-2011, 08:27 PM   #4
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Default Re: Westbury 'Seagull'

Quote:
(1) Make a larger diameter lifter.
(2) Reduce the lift of the lobe.
(3) Make lifters with a curved surface.
Thanks. After further exploration, there is also the possibility of a larger cam angle, allowing a 'softer' cam.
I have decided I will probably increase the tappets to 9/32", which I can just get in, even with a bush.
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Old 05-30-2011, 08:39 PM   #5
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Default Re: Westbury 'Seagull'

Quote:
Originally Posted by RManley
Hi Charles, very clear construction diary.
Thanks, Rob
Quote:
How come everything looks so clean?
Does it? I clean parts before taking pics, but try to leave a bit of swarf around when showing setups.
Quote:
I can tell this is going to be a very well made model by the time it is complete. Any ideas what you will use it for yet?
Thanks again. No - no idea. I will need some kind of load to try it against, though.
Quote:
Also, where in the west midlands are you??
Shropshire
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Old 09-21-2011, 11:06 PM   #6
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Default Lapping Timing Gears

Does anyone have advice to offer on lapping the timing gears together?

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Old 09-21-2011, 11:47 PM   #7
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Default Re: Westbury 'Seagull'

In theory you can’t lap straight involute gears because they mesh with a rolling action, therefore there is no relative movement between teeth for lapping to take place.

In practice if the gears are mounted so that one can move from side to side you can sometimes improve things. With an idler setup like the seagull you would need to lap all three gears at once (moving the idler from side to side) so unless they really need it I wouldn’t bother.

Les

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Old 10-14-2014, 11:38 AM   #8
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One of many jobs remaining on the Seagull is a silencer (US Muffler). I have an idea what I want it to look like externally, but have little clue as to what to put inside it.

I am thinking of a drum 3/4" diameter and about 1-1/2" long, with a tangential or radial entry at one end and an axial exit at the other, both in 5/16" OD tube, all brass.

I want maximum noise reduction for minimum resistance, and would prefer to avoid a stuffing that will get clogged up, unless that is the only good way, even though it would probably be arranged for easy dismantling.

Ideas?

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Old 10-14-2014, 06:29 PM   #9
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In typical RC 2-stroke exhaust systems, its common to see a silencing section to the back end of tuned pipes for noise reduction & simultaneously minimize resultant back pressure. I have seen
- series of baffled chambers with offsetting entry/exit passage connector pipes or orfices
- perforated diffuser tubes like pic (kind of like a firearm principle I imagine).
- simple deflector plates in canister type mufflers (maybe a coarse version of above?)

Disregard the tuning aspect, but just mentioning the similarity of noise reduction chunk. RC fuel has oil added, so exhaust contains gunk & similarly favors an all-metal configuration vs. noise abatement stuffing as you call it.

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File Type: jpg tuned pipe muffler section.jpg (33.4 KB, 60 views)
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Old 10-14-2014, 06:32 PM   #10
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and another pic, 4S motorcycle principle



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