Engine detail question (Airfix four-stroke engine)

[robdebie]

I'm building the 1972 vintage Airfix single cilinder four-stroke engine with cutaway sections. Here's where I'm at, nearly done:

I want to glue the crankcase on the foot, but I just don't understand the detail that Airfix molded on the foot. Here's the connection between the crankcase and the foot. Is this supposed to be a clamping ring? Or is it a flange of the crankcase halves? Or is there a simulated gasket under the clamping ring? Should I fill the gap to make a smooth transition to the flange / clamping ring?

What do you think? Any help is welcome!

Rob

[Ace-Garageguy]

I believe that what you have here is an example of what happens when the tooling designer doesn't understand the function or real-world construction of the parts he's modeling.

A more correct and likely representation could be either 1) molding the "ring" to the engine crankcase casting proper (split at the crankcase seam, of course), and scribing a deep line between the "ring" and the base to represent the joint, or 2) adding short "cast on" tabs to the crankcase above the bolt locations, allowing the crankcase to be "bolted" to the base, where the ring, represented as cast into the base in that case, would only perform a positive locating function.

EDIT: To save yourself some work, you could, of course, go with the idea that there's some unnecessarily elaborate attachment method we're not seeing UNDER the base that relies partially on the visible hold-down bolts, but in reality that would be a stupid design, and awkward to assemble.

EDIT 2: Here's a one-lunger clearly showing hold-down tabs cast in unit with the crankcase.

EDIT 3: Here's one with hold-down tabs cast in unit with a base that's bolted to the crankcase from the underside, with the crankcase-to-base bolts not visible from the top...which they wouldn't be unless there were visible cast-on tabs on the crankcase and matching holes on the base.

Edited January 21, 2022 by Ace-Garageguy

[NOBLNG]

25 minutes ago, Ace-Garageguy said:

I believe that what you have here is an example of what happens when the tooling designer doesn't understand the function or real-world construction of the parts he's modeling.

I agree. Is the Airfix model supposed to represent an actual engine, or just a theoretical teaching aid? In reality it would need a sealed crankcase of some sort.?

[Ace-Garageguy]

Here's a similar ring cast in unit with a crankcase in a way that makes practical sense.

[Ace-Garageguy]

A couple more small engines with hold-down tabs cast integral with the crankcase:

   

EDIT: And another one with a hold-down ring cast as part of the crankcase:

Edited January 21, 2022 by Ace-Garageguy

[64Comet404]

9 hours ago, NOBLNG said:

I agree. Is the Airfix model supposed to represent an actual engine, or just a theoretical teaching aid? In reality it would need a sealed crankcase of some sort.?

It looks like Airfix used an old single-cylinder motorcycle engine as their design basis, then made whatever modifications were necessary for the design. To my eyes, it looks like a Norton or BSA L-head unit.

[Ace-Garageguy]

27 minutes ago, 64Comet404 said:

It looks like Airfix used an old single-cylinder motorcycle engine as their design basis, then made whatever modifications were necessary for the design. To my eyes, it looks like a Norton or BSA L-head unit.

Well, no. If you look at the built-up engine model, you'll see rocker arms.

That identifies it positively as an overhead-valve (OHV) engine, definitely not an L-head.

Edited January 22, 2022 by Ace-Garageguy
CLARITY and ACCURACY

[robdebie]

Bill, Greg, Ken: many thanks for all the responses and insights! It's clear that all of you 'see' a flange, and the photos support that idea strongly. Thanks for searching and finding the photos! The modification to a 'flange' type construction wouldn't be too much work actually, if I would do the filling with Apoxie Sculpt, without sanding. But the thing is that I made a custom paint mix from three colors, to create RAL 6011 'machine green'. And as Murphy would have liked it, I just ran out of that paint. I need to do some hard thinking..

Bill: I fully agree with your comment of 'what happens when the tooling designer doesn't understand the function or real-world construction'. In my view, this model is full of these problems..

Greg: I think the model represents a theoretical teaching aid. I never found a picture of a single cylinder engine that resembles the model.

Rob

[Skip]

I think your question was, "What should go between the lower engine block and the base?".  That is before it got sidetracked with the other details, right?

This looks like a generic 4-Stroke Horizontal Shaft engine depending on scale could be used in applications such as a rototiller, mini-bike...

Blending the engine block to the base would make it appear as one casting, so something needs to separate the engine block from the base.

In the last pic that Bill added, it looks like they have used the base as a "fuel tank".  Represented by the fuel cap.  So, if your kit doesn't have a fuel tank would be a great, logical modification to the kit.  

The base itself is not a part of the motor, just a base.  So, a gasket or other spacer such as something to represent a separation, or vibration damper, between the engine block and its base would look right.  If you do this the round stock used to represent the rubber vibration damper could also cut away down to the bolt threads in at least one of the mounts to the base.  In a lot of these applications a squared off or round washer goes between the engine and its mounting.

[Ace-Garageguy]

1 hour ago, Skip said:

I think your question was, "What should go between the lower engine block and the base?".  That is before it got sidetracked with the other details, right?

The issue I addressed initially, as requested, is the fact that there is no mounting flange on the bottom of the crankcase. What is represented is mechanical gibberish. The mounting flange, which SHOULD be represented as part of the crankcase, is instead represented as being part of the base. There is no actual provision for mounting the crankcase. Something made as represented would be impossible to assemble, particularly if the "base" is supposed to be a fuel tank, as there's no access to the bolts from the underside (assuming, of course, that there's supposed to be some imaginary elaboration we can't see that actually holds the crankcase to the base, or 'tank").

The bolts, as represented by the model as-is, appear to hold nothing down. They just go in holes.

Regarding the primary issue, a gasket or damper is totally irrelevant.

A separation between the mounting flange and the base needs to be created, and the separation between the crankcase and the flange needs to be filled.

After that correction, the bolts would appear to actually hold the crankcase to the base.

EDIT: OR, one could simply create a mounting flange for the crankcase that matches the outline and bolt-layout of the rectangular mounting ring cast into the base, bond it to the crankcase, create a fillet at the join, then install the hold-down bolts so as to appear to be actually holding something down. Put a gasket, or dampers, between the newly created crankcase flange and the mounting pad on the base if desired.

Edited January 23, 2022 by Ace-Garageguy
CLARITY

[robdebie]

On 1/23/2022 at 3:46 PM, Skip said:

I think your question was, "What should go between the lower engine block and the base?".  That is before it got sidetracked with the other details, right?

This looks like a generic 4-Stroke Horizontal Shaft engine depending on scale could be used in applications such as a rototiller, mini-bike...

Blending the engine block to the base would make it appear as one casting, so something needs to separate the engine block from the base.

In the last pic that Bill added, it looks like they have used the base as a "fuel tank".  Represented by the fuel cap.  So, if your kit doesn't have a fuel tank would be a great, logical modification to the kit.  

The base itself is not a part of the motor, just a base.  So, a gasket or other spacer such as something to represent a separation, or vibration damper, between the engine block and its base would look right.  If you do this the round stock used to represent the rubber vibration damper could also cut away down to the bolt threads in at least one of the mounts to the base.  In a lot of these applications a squared off or round washer goes between the engine and its mounting.

You could phrase my initial question like that, yes. Based on the responses so far, this is what I currently have in mind. I want to sand off half of the 'strange detail' and retain that as a simulated gasket. Next I would add a relatively thick flange to the crankcase halves. The crankcase gets lifted by 2-3 mm. Would you agree with this approach?

 

Regarding the fuel cap on the base of the other model: that fuel cap was originally the turning switch for the electric motor. I don't see the base as a fuel tank, but one could. I removed all traces of the motorization on mine, hence the difference.

Rob

 

[robdebie]

On 1/23/2022 at 4:38 PM, Ace-Garageguy said:

The issue I addressed initially, as requested, is the fact that there is no mounting flange on the bottom of the crankcase. What is represented is mechanical gibberish. The mounting flange, which SHOULD be represented as part of the crankcase, is instead represented as being part of the base. There is no actual provision for mounting the crankcase. Something made as represented would be impossible to assemble, particularly if the "base" is supposed to be a fuel tank, as there's no access to the bolts from the underside (assuming, of course, that there's supposed to be some imaginary elaboration we can't see that actually holds the crankcase to the base, or 'tank").

The bolts, as represented by the model as-is, appear to hold nothing down. They just go in holes.

100% agreement with what you write. Can you agree with the modification as sketched in the previous posting?

Rob

[Ace-Garageguy]

12 minutes ago, robdebie said:

Can you agree with the modification as sketched in the previous posting?

Yes sir. Looks good.

[Skip]

Yes, you are spot on with your modifications, the second view is what I was describing.

Rephrasing the question; I wanted to make sure I was on the same plane you were flying on! LoL!!  I thought that was your original meaning before it was taken to left field with all kinds of other examples (albeit good ones).  
 

Reminds me of college Mechanical Engineering, where we were exposed to numerous “Cut-A-Ways” of all kinds of mechanical assemblies.  They are a great learning tool to assist the “non-visual” person to understand what the assemblies loomed and how they function.  Looking forward to seeing your finished “cut-a-way engine”. 

[Ace-Garageguy]

1 hour ago, Skip said:

...I thought that was your original meaning before it was taken to left field with all kinds of other examples.  

I'm confused by the meaning here.

The "left field" examples I posted are ALL examples of a mounting flange cast integrally with a crankcase (note: other than the single shot of the completed model necessary to refute an assertion the model represented a side-valve configuration).

This was a perfectly valid way to illustrate visually different but functionally identical versions of what the OP realized he wanted to achieve to make the model appear rational.

Nothing more, nothing less.

Where's the "left field" come in?

[robdebie]

Here's what I built yesterday. I built the two flanges (one each for the crankcase halves) from polystyrene strips, feeling my way to what looked right in terms of width and thickness. I ended up with a shape slightly larger than the 'thing' that Airfix molded.  For the rounded corners I used half of a 1/72 rocket pod body. It's a dry fit, the flanges are not attached to the crankcase yet, therefore there is no fillet. The original detail under the new flanges still needs to be partially sanded away, so the flange will sit on the 'gasket'.

Please let me know what you think. Thanks again for all the input that led to this solution.

Rob

Edited January 27, 2022 by robdebie

[Bainford]

Looks good. Blend the flange into the engine case with a fillet, and it should be right on.

[Ace-Garageguy]

18 minutes ago, robdebie said:

Here's what I built yesterday. I built the two flanges (one each for the crankcase halves) from polystyrene strips, feeling my way to what looked right in terms of width and thickness. I ended up with a shape slightly larger than the 'thing' that Airfix molded.  For the rounded corners I used half of a 1/72 rocket pod body. It's a dry fit, the flanges are not attached to the crankcase yet, therefore there is no fillet. The original detail under the new flanges still needs to be partially sanded away, so the flange will sit on the 'gasket'.

Please let me know what you think. Thanks again for all the input that lead to this solution.

Everything looks right.

Very nice, and kudos for putting forth the effort to make a model correctly represent functional reality.

Edited January 27, 2022 by Ace-Garageguy

[Phirewriter]

I have one of these in my collection, I have a "thing" for visible working engine kits, both automotive and aircraft. This has been an informative, interesting thread so far. Rob, I like what you've done so far, your build really looks great and am saving the information for whenever I get around to building mine. As usual Bill's input has been most informative. Might be an interesting thread to start for visible engine kits, there's been quite a few released over the years.

Edited January 28, 2022 by Phirewriter
Need to use my words properly...

[robdebie]

Bill, Trevor, Michael: thanks for the kind words. I'm building that fillet now, using Apoxie Sculpt, about halfway now. More photos soon.

Michael: same interest here, and that resulted in this visible engine overview. I basically made it to pick the best visible engine, but I still haven't decided, and started with the relatively simple Airfix engine. I'll publish a full build report of this Airfix model on my web site, once it done (i.e. soon).

I've been thinking: could the old Renwal / Revell 'Visible V8' be built in this style too? Fully painted but with cutouts?

Rob

[Ace-Garageguy]

6 hours ago, robdebie said:

...I've been thinking: could the old Renwal / Revell 'Visible V8' be built in this style too? Fully painted but with cutouts?

I've been thinking along the same lines, as I bought a partially assembled one some time back that ended up being much more of a glooey mess than it appeared in photos.

I believe that would be a great way to proceed. The working features could be retained.

Edited January 28, 2022 by Ace-Garageguy
TYPO

[robdebie]

Maybe your partially assembled kit could serve as a testbed? I think it requires careful study / planning / testing to create a tasteful cutaway engine. I'm getting more and more enthousiastic about this idea, but the amount of work scares me..

I made the next step with my Airfix model. I created a fillet with Apoxie Sculpt, with small cut-outs on the corners for the bolt heads. Next was the paint, from a freshly mixed batch. Next is the 'gasket' on the base.

Rob

 

Edited February 9, 2022 by robdebie

[Ace-Garageguy]

Beautiful. The clearance reliefs for the bolt heads are a nice touch.

[robdebie]

Slow progess with the Airfix engine: I painted the new flange of the crankcase, and painted the 'gasket' in a cork-like color.

I'm now working on the valve train. I used three metal colors for each valve.

The last major part to paint is the carburetor. And again I could use some help, because I have no idea what the various details represent. I never worked on a real carburetor..

Thanks in advance for any suggestions!

Rob

[Ace-Garageguy]

First impression is it's a kinda sorta vintage Amal side-draft carb. Look at some online photos, and we'll go from there.

http://amalcarb.co.uk/

EDIT:

EDIT 2: The velocity stack would almost certainly be a separate part, not cast in unit with the carb body.

Edited February 18, 2022 by Ace-Garageguy