Author Topic: 15cc Seal and 30cc Seal Major  (Read 29959 times)

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #210 on: August 28, 2019, 05:02:14 PM »
To avoid too much bonking with Mr Silky :facepalm2: I let H rough out the crankshaft, taking 19mm off above the journal and 9.5mm down the sides.

It is looking a little closer to the shape of the Seal crankshaft  :thinking:

Jo
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Offline Roger B

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Re: 15cc Seal and 30cc Seal Major
« Reply #211 on: August 29, 2019, 07:12:06 AM »
Excellent  :praise2: That really shows the size difference between the two engines  :)
Best regards

Roger

Offline maury

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Re: 15cc Seal and 30cc Seal Major
« Reply #212 on: May 04, 2023, 08:45:39 PM »
I have just received my Seal Major kit from Hemmingway. Looks to be a fun build.

I do have a question for Jo:
Re reply 59 where you talk about the offset of the cylinder bores from the centerline of the crank. I was unsure if the design actually is like this or if there was previous work on the crankcase which was ofset. My casting has the cored out cylinder holes offset from the cored out crankshaft bearing holes. So, did you bore the cylinders on the centerline of the crank, or did you bore then offset?

Thanks,
maury
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Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #213 on: May 04, 2023, 08:59:56 PM »
The cylinder centre lines are offset from the crankshaft centre lines on both engines.: The Seal by 3.18mm and the Seal Major by 4mm. I am guessing this offset makes for a more compact engine "width-wise".

I first bored the ends of the cylinder castings for the crankshaft, then fitted a bar through the two bearing holes. Then offset the cylinder bores from the centre of that bar.

Jo
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Offline maury

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Re: 15cc Seal and 30cc Seal Major
« Reply #214 on: May 04, 2023, 09:35:23 PM »
Jo, thanks so much for the clarification. It's things like that make me fearful of making that first cut. Hemmingway sent the prints early, so I have been spending a lot of time going over every detail.

Thanks,
maury
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Offline Charles Lamont

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Re: 15cc Seal and 30cc Seal Major
« Reply #215 on: May 04, 2023, 11:28:39 PM »
The usual argument for this "désaxé" arrangement is that it reduces the con-rod angularity during the power stroke, and therefore reduces the maximum side thrust on the piston, among other things. I can see it might allow a more compact layout too. 

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #216 on: May 05, 2023, 09:52:15 AM »
 :thinking: I had to look up Désaxé. I have been learning all about designing model IC engines over the last few weeks and had not come across that one (yet).

It increases the leverage applied to the crankshaft and angle of the power stroke  :thinking:  :thinking:  Its all still a bit too technical for how much I have learnt so far about designing model engines from scratch  :-[

Jo
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Offline Jasonb

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Re: 15cc Seal and 30cc Seal Major
« Reply #217 on: May 05, 2023, 10:30:20 AM »
It's also a feature of some of the Ball Hopper Monitor engines, not sure if yours had it Maury but the smaller" VJ" does

The Stuart Victoria can also be found with the same feature but that is drawing error probably caused by copying the taller bearing pedestals from the beam engine

Offline Zephyrin

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Re: 15cc Seal and 30cc Seal Major
« Reply #218 on: May 06, 2023, 08:55:27 AM »
Quote
The usual argument for this "désaxé" arrangement is that it reduces the con-rod angularity during the power stroke, and therefore reduces the maximum side thrust on the piston, among other things. I can see it might allow a more compact layout too.

yes, but it is the opposite during the compression stroke, which in some extent cancels this gain in side thrust !
it seems too that when the crank is at its TDC, the piston is not yet there owing to the angularity of the rod.
the gain in a more compact layout seems more interesting in a model, where room is limited for the engine. 

In addition, the désaxé must be in the proper direction according to the rotation of the crankshaft !
« Last Edit: May 06, 2023, 09:05:48 AM by Zephyrin »

 

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