Engine mount design

[Dave Stroud]

Looking way ahead now while still waiting for wood and steel. I'm cleaning up my 1/2 cut case VW recently brought in from Michigan and it has what I would think is a very questionable mount. The engine itself has three shock mounts, one on each side of the bottom of the case and a single one at the top of the case. The steel used is is 3/8" diameter and I'm  not sure of the wall thickness. Does anyone know of one like this in service or have any experience with one ?  It is well triangulated but man....3/8" ? I could modify or replace the back plate into a four cornered shock situation. Certainly I'd use larger tubing. My engine has a rear mag and a Zenith carb underneath which have to be worked around. What is the "standard" in tubing being used by most ?  Any and all ideas appreciated.

[Steve]

Looking way ahead now while still waiting for wood and steel. I'm cleaning up my 1/2 cut case VW recently brought in from Michigan and it has what I would think is a very questionable mount. The engine itself has three shock mounts, one on each side of the bottom of the case and a single one at the top of the case. The steel used is is 3/8" diameter and I'm  not sure of the wall thickness. Does anyone know of one like this in service or have any experience with one ?  It is well triangulated but man....3/8" ? I could modify or replace the back plate into a four cornered shock situation. Certainly I'd use larger tubing. My engine has a rear mag and a Zenith carb underneath which have to be worked around. What is the "standard" in tubing being used by most ?  Any and all ideas appreciated.

I found a relevant reference in the Forum by doing a Search with this argument "cut case motor mount": http://www.eaglersnest.com/forum/index.php?topic=146.msg500#msg500

[Dave Stroud]

Thanks for that reference, Steve. I went through it earlier today. Still wondering about the triangular mount I have.

[scottiniowa]

Looking way ahead now while still waiting for wood and steel. I'm cleaning up my 1/2 cut case VW recently brought in from Michigan and it has what I would think is a very questionable mount. The engine itself has three shock mounts, one on each side of the bottom of the case and a single one at the top of the case. The steel used is is 3/8" diameter and I'm  not sure of the wall thickness. Does anyone know of one like this in service or have any experience with one ?  It is well triangulated but man....3/8" ? I could modify or replace the back plate into a four cornered shock situation. Certainly I'd use larger tubing. My engine has a rear mag and a Zenith carb underneath which have to be worked around. What is the "standard" in tubing being used by most ?  Any and all ideas appreciated.

Stroud- if you choose to modify your mount (build a new one) I am presuming you would have measurements you would like to use.  I could CAD draw this out for you very easily as long as you know "where you want what"   I would do this at no cost.

Generally when an engine on a full case is mounted the mag, extends into the cabin (between feet) Thus when using the mount, it extends between the mount, and I am guessing yours is that way presently? by going to 4 mount points on back of engine you should gain more space.  The great thing with CAD is you can measure this protrusion and make sure all is clear.  

tubing standard-  would best be said, tubing is engineered to do the job for the HP required and generally not much more.   So no real standard, as HP, Length of motor mount, and so many other things get involved.

[Dave Stroud]

No need for any CAD stuff, thanks Scott. We'd need to know where the engine will be placed in relation to the firewall for c of g reasons etc., no ? Right now I'm just figuring out if the triangular engine mount plate on the back of the engine is suitable in place of a rectangular rear mount plate. I have a CUT CASE  1/2 VW engine as noted in the second sentence of my first post. Upon further thinking late last night it appears that the triangulation idea might be ok but the sizing and thickness of the tubing will need a substantial increase. 

I'm trying to post pics of the mount for clarification of my words but I seem unable to post pics. I've clicked on Attachments and other options below, then select pics from my album but nothing shows up over here.  I'm not getting any prompt to confirm the attachment etc.  Any better instructions on posting pics would be appreciated. Maybe I don't have enough seniority yet or something.

[scottiniowa]

No need for any CAD stuff, thanks Scott. We'd need to know where the engine will be placed in relation to the firewall for c of g reasons etc., no ? Right now I'm just figuring out if the triangular engine mount plate on the back of the engine is suitable in place of a rectangular rear mount plate. I have a CUT CASE  1/2 VW engine as noted in the second sentence of my first post. Upon further thinking late last night it appears that the triangulation idea might be ok but the sizing and thickness of the tubing will need a substantial increase.

I'm trying to post pics of the mount for clarification of my words but I seem unable to post pics. I've clicked on Attachments and other options below, then select pics from my album but nothing shows up over here.  I'm not getting any prompt to confirm the attachment etc.  Any better instructions on posting pics would be appreciated. Maybe I don't have enough seniority yet or something.

Yes, you would need to know exactly where you want things to be... ;-) CAD is somewhat demanding in that respect... Most of the time that is a good thing.
As for posting photos, try using the lower left button "attachments and other options" and not up in the screen with the smiley face.    Below this you have a second box "attach:"  and in this you <choose file> grab your photo from there.

I attached a little spark plug plane as a photo for this.

[Dave Stroud]

Test for engine mount pic

[Dave Stroud]

Two more views of the existing mount....then no more. Thin tubes, eh ? They're 3/8".

[garygans]

In my opinion, the 3/8" tubing in your mount looks good enough. I think that the 3 point mount would be OK with that mount. However, if you are installing it on a Legal Eagle, you will not have that much room on the firewall for a 5 point attachment spread out like that.

If you used large enough tubing and there is enough room to add diagonals without hitting the intake tubes, I think that the 3 point mount would be worth trying. That is just my opinion though. 

Here is a picture of the mount that I made. I used 5/8" x .049 tubing and I added some gussets and other reinforcements. That size tubing might work well for your mount.

[scottiniowa]

Two more views of the existing mount....then no more. Thin tubes, eh ? They're 3/8".

Did this mount work on something else? it looks used, if so, was there problems with it?  (cracks or excessive vibration allowed)  If not, I don't think your going to get much lighter.  Webs at engine plate work wonders and it would appear you have room for them.  They really take the stress off of clusters or better said, spread the stress out.

Not sure how the fire wall attach worked? As I have never seen a mount end in a horizontal tube as you showed..That would catch my attention first.. How is this terminated at the fire wall or attached?

Glad you got the photo part working.
Scott

[Dan_]

This holds an C-85 Continental in a TaylorCraft...  A full ring of tubes against the engine case is just extra weight.

Let the case do its job holding the tubes in place.  Attachments below. 

Note attachment indicates tubing sizes recommended for engines that weigh more than twice what the 1/2 VW weighs.

[Dave Stroud]

All good info, Lads. Thanks for that. I've forgotten I kept my old Bengelis books and saw your reference to the tubing sizes you mentioned. I think that's the size  ( 3/4"  .049 ) I used on my two place Christavia. It's now owned by another but if you look up Christavia on Wikipedia, my plane is the one in the fifth picture down on the right. C-FDWS. :-)   Now back to the number crunching just for fun. I did a quick calc and found these numbers interesting. The profile of a 3/4" .049 tube is .1038 square inches....( 100%)  5/8" .049 is .0890  ( 86%) and 1/2" .049 is .0694 or 67%. A good point was made that our engines are less than 1/2 the weight and power of the Conts or Lycs. Would that imply that a well designed 1/2" .049 would be adequate in our applications ? Would a larger diameter but thinner wall tube change things up to any advantage or disadvantage in strength ? For example a 5/8" x .035 comes out at .0648 or about 62%. The percentages would directly relate to the weight of the mount with a little fudge for the size of the clusters.

[Dan_]

Spread sheet...

Attached.

[Dave Stroud]

An excellent reference, Dan. With a triangulated engine mount for instance and given that the welds are all equal and good, I thought a leg of the mount would be stronger in compression than tension. It seems that it is quite the opposite to a factor of almost 10 times. Have I got that right ? Would that be because the tube is more susceptible to buckling ( bending ) than stretching or deformation thru tension ? Anyone ? I found another good reference table. I can't seem to copy the url but a google search on  West Coast Piet Summerhill Tubing will get you there.

[Dan_]

, I thought a leg of the mount would be stronger in compression than tension. It seems that it is quite the opposite to a factor of almost 10 times...

Yes, tension is better.  Steel is usually braced (triangulated) such that the column is effectively half as long as before...  Sometimes hard or impossible on an engine mount.

 I found another good reference table. I can't seem to copy the url but a google search on West Coast Piet Summerhill Tubing will get you there.

The Piet page is a treasure trove.  http://www.westcoastpiet.com/construction.htm  I believe at some point, I may have ran across a conversion there somewhere to go from wood to steel tubing.