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Locating engine mount holes

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naumuk(at)alltel.net
Guest

Posted: Fri May 04, 2007 5:57 pm Post subject: Locating engine mount holes

All-

     I know that this question was  posted only a couple of weeks ago, but everything but the answer wound up in the  archives. 

     I just fabricated a firewall  from scratch. What's the easiest and most accurate way of locating the engine  mount holes?

     Let's make sure the answer gets  in the archives this time!

 Bill Naumuk

HDS Fuse/Corvair

Townville,  Pa

   [quote][b]

ter_turn(at)yahoo.com
Guest

Posted: Fri May 04, 2007 7:26 pm Post subject: Locating engine mount holes

Hi Bill, 

   

  I am looking at the same dilemma myself and have decided to just wait until my engine mount attach

  fittings are bolted on and then mark and drill the firewall. That way a couple of mm one way or the other won't hurt. Good luck.

   

  Terry Turnquist

  601XL-Plans

  St. Peters, MO



Bill Naumuk <naumuk(at)alltel.net> wrote:

  [quote]        All-

      I know that this question was posted only a couple of weeks ago, but everything but the answer wound up in the archives. 

      I just fabricated a firewall from scratch.        Ahhh...imagining that irresistible "new car" smell?

 Check out [url=http://us.rd.yahoo.com/evt=48245/*http://autos.yahoo.com/new_cars.html;_ylc=X3oDMTE1YW1jcXJ2BF9TAzk3MTA3MDc2BHNlYwNtYWlsdGFncwRzbGsDbmV3LWNhcnM-]new cars at Yahoo! Autos.[/url]  [quote][b]

p.mulwitz(at)worldnet.att
Guest

Posted: Fri May 04, 2007 8:39 pm Post subject: Locating engine mount holes

Perhaps I am getting this wrong, but I think the notion of where to put the engine mount on the firewall has nothing to do with the engine.  After all, I am just a kit builder and put the holes for the engine mount on the firewall according to the plans.



 It seems to me the location of the firewall mounting bolts is dictated by the longerons attached to the fittings on the other side of the firewall from the engine.  It is the longerons that dictate the location of these holes.



 Once the mounting position of the engine mount is fixed by the fuselage design, it is the problem of the engine mount designer to build a mount that fits these bolts to the engine itself.



 Just my ideas on this subject . . . .



 Paul

 XL fuselage



 



 

 At 08:20 PM 5/4/2007, you wrote:

 [quote]Hi Bill, 

  

 I am looking at the same dilemma myself and have decided to just wait until my engine mount attach

 fittings are bolted on and then mark and drill the firewall. That way a couple of mm one way or the other won't hurt. Good luck.

  

 Terry Turnquist

 601XL-Plans

 St. Peters, MO



 Bill Naumuk <naumuk(at)alltel.net> wrote:

   All-

      I know that this question was posted only a couple of weeks ago, but everything but the answer wound up in the archives. 

      I just fabricated a firewall from scratch. 

 

  [b]

planecrazydld(at)yahoo.co
Guest

Posted: Sat May 05, 2007 1:25 am Post subject: Locating engine mount holes

The fuse side mount fittings are the primary transfer points for the loads from the powerplant into the fuse. As such, as Paul points out, they control everything. When the mount is fabricated or installed, it needs to fit those locations - not those locations fit it. Keep in mind that the mount needs to fit without straining, because that is a recipe for a cracked mount somewhere down the road.



Paul Mulwitz <p.mulwitz(at)worldnet.att.net> wrote: 	  Quote: 	
		     Perhaps I am getting this wrong, but I think the notion of where to put the engine mount on the firewall has nothing to do with the engine.  After all, I am just a kit builder and put the holes for the engine mount on the firewall according to the plans.



 It seems to me the location of the firewall mounting bolts is dictated by the longerons attached to the fittings on the other side  of the firewall from the engine.  It is the longerons that dictate the location of these holes.



 Once the mounting position of the engine mount is fixed by the fuselage design, it is the problem of the engine mount designer to build a mount that fits these bolts to the engine itself..... 	




  Dave Downey

  Harleysville (SE) PA

  Zodiac 601XL/Corvair?

   Don't pick lemons.

 See all the new 2007 cars at Yahoo! Autos. [quote][b]

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 5:04 am Post subject: Locating engine mount holes

All-

     From the responses, I can see I  didn't get my point across. I found out that the print locations will work for  at least Corvair, Jab, and Rotax installations, so that's not an issue. I know  where the holes are supposed to go, getting them there is the problem. Every  firewall (Scratchbuilt, at least) is going to deviate a couple of mm's from  print. Getting the Y axis locations isn't a problem because you can use the flat  bottom as an origin. Finding the X axis center is more iffy.

     A couple of weeks ago someone  posted a method for accurately locating the holes on a firewall and  unfortunately it didn't make it into the archives. That's what I'm looking  for.

     Since I "Slept on the  problem" a possible solution is coming to me, but it would be nice if I didn't  have to reinvent the wheel.

     Thanks. 

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

p.mulwitz(at)worldnet.att
Guest

Posted: Sat May 05, 2007 6:01 am Post subject: Locating engine mount holes

Hi Bill,



 Sorry if I misunderstood your problem.  Perhaps you are trying to make the engine mount bolt holes before it is time to do so.



 It has been many months since I did this operation, so I don't really remember how it was done.  I do remember it involved fitting the steel fittings at the ends of each longeron to both the firewall and longeron at the same time.  Meanwhile, the skin has to fit both the longeron and the firewall flange.  When all this is accomplished, the steel fittings will dictate where the engine mount bolt holes go on the firewall.  



 If my memory serves correctly (something that will get you in trouble if you depend on it)  one of the critical items was the forward bend in the cabin bottom skin.  This had to fit around the corner on the firewall and the whole thing had to be held in place by the engine mount bolts to make it work.  All in all it is a nasty Chinese puzzle to solve.



 My advice to you is to wait until you have all the parts in hand and are ready to make it all happen before worrying about the engine mount bolt hole locations.



 Best regards,



 Paul

 XL fuselage



 



 

 At 05:59 AM 5/5/2007, you wrote:

 [quote]All-

     From the responses, I can see I didn't get my point across. I found out that the print locations will work for at least Corvair, Jab, and Rotax installations, so that's not an issue. I know where the holes are supposed to go, getting them there is the problem. Every firewall (Scratchbuilt, at least) is going to deviate a couple of mm's from print. Getting the Y axis locations isn't a problem because you can use the flat bottom as an origin. Finding the X axis center is more iffy.

     A couple of weeks ago someone posted a method for accurately locating the holes on a firewall and unfortunately it didn't make it into the archives. That's what I'm looking for.

     Since I "Slept on the problem" a possible solution is coming to me, but it would be nice if I didn't have to reinvent the wheel.

     Thanks. 

 Bill Naumuk

 HDS Fuse/Corvair

 Townville, Pa

 [b]

wjones(at)brazoriainet.co
Guest

Posted: Sat May 05, 2007 6:33 am Post subject: Locating engine mount holes

Hey Bill ,I went with what the plans called  for.856mm across the top of the firewall. Bottom holes 15mm from bottom of  firewall and 610mm between centers. This will leave you with 460mm between the  top and bottom holes. Of course all this is started from the center of the  firewall  .All lined up to the longeron locations for a good  fit

 Wade Jones    South Texas 

601XL plans building

Cont.  0200

 [quote]   ---

Jaybannist(at)cs.com
Guest

Posted: Sat May 05, 2007 6:44 am Post subject: Locating engine mount holes

Bill,



As I have previously posted, the recommended way to locate the holes is to drill pilot holes in the center of the forward vertical plate of the engine mount brackets.  When the brackets have been properly located on the fuselage longerons, drill the firewall through the pilot holes.  Then drill out the pilot holes for the bolts (which WW refers to as "studs").  William Wynne has said "It is acceptable to slightly flex the motor mount in order to get it to line up with the studs. After we weld them, the motor mounts are stress relieved so they will generally slide right on the studs.  There will be a slight variation on plans built aircraft for the location of the holes, and the motor mount can accommodate this up to about 3/32"."



Jay in Dallas



"Bill Naumuk" <naumuk(at)alltel.net> wrote:



 	  Quote: 	
		  All-

    From the responses, I can see I didn't get my point across. I found out that the print locations will work for at least Corvair, Jab, and Rotax installations, so that's not an issue. I know where the holes are supposed to go, getting them there is the problem. Every firewall (Scratchbuilt, at least) is going to deviate a couple of mm's from print. Getting the Y axis locations isn't a problem because you can use the flat bottom as an origin. Finding the X axis center is more iffy.

    A couple of weeks ago someone posted a method for accurately locating the holes on a firewall and unfortunately it didn't make it into the archives. That's what I'm looking for.

    Since I "Slept on the problem" a possible solution is coming to me, but it would be nice if I didn't have to reinvent the wheel.

    Thanks.

Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 6:48 am Post subject: Locating engine mount holes

Paul-

     On the HDS you don't have a  choice- all the components that are riveted to the firewall use the mount holes  as origins.

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 7:13 am Post subject: Locating engine mount holes

Jay-

    Since this is previously posted,

                            do not archive

Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

---

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 7:13 am Post subject: Locating engine mount holes

Wade-

     Agreed, the plans locations work  for different engine installations.

                                   do not archive

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 7:14 am Post subject: Locating engine mount holes

Paul-

     Since I already responded to  this re: HDS, 

                                       do not  archive

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

kensmith(at)springnet1.co
Guest

Posted: Sat May 05, 2007 7:19 am Post subject: Locating engine mount holes

You are absolutely correct in regards to the exact location of the mount attach points. Any change in the location no matter how small should always be approved from the designing engineers at Zenith. Change in location will proably require some structural change for attachment. 

 

 Ken

 

 

 

 Paul Mulwitz wrote: [quote]Perhaps I am getting this wrong, but I think the notion of where to put the engine mount on the firewall has nothing to do with the engine.  After all, I am just a kit builder and put the holes for the engine mount on the firewall according to the plans.

   

 It seems to me the location of the firewall mounting bolts is dictated by the longerons attached to the fittings on the other side of the firewall from the engine.  It is the longerons that dictate the location of these holes.

 Once the mounting position of the engine mount is fixed by the fuselage design, it is the problem of the engine mount designer to build a mount that fits these bolts to the engine itself.

 

 Just my ideas on this subject . . . .

   

 Paul

 XL fuselage

   

   

   

   

   

    	  Quote: 	
		  

	
 [b]

dredmoody(at)cox.net
Guest

Posted: Sat May 05, 2007 7:38 am Post subject: Locating engine mount holes

The longerons do indeed dictate the position of the  engine mount brackets but the engine mount and its design and dimensins dictate  the location of the holes. I drilled the pilot holes according to the directions  (drawings and photo assembly guide) then enlarged them to the correct bolt size.  Many moons later, when my FWF package arrived form Jabiru USA the mount matched  up to the bolts pretty well, so I'd have to say the instructions and fabrication  of the mount are in agreement. 

  

 It is important to (A) locate the pilot holes  accurately (of course), then (B) back drill the pilot holes to the engine mount  brackets, then (C) enlarge them to size, preferably firewall and bracket at the  same time. If you err, make sure the error places the bolt hole slightly farther  from the base of the bracket rather than closer to it. If the hole is too close  to the bottom of the bracket it clashes with the AN3 bolts which attach the  bracket to the longeron.

  

 Dred

 [quote]   ---

planecrazydld(at)yahoo.co
Guest

Posted: Sat May 05, 2007 8:31 am Post subject: Locating engine mount holes

on April 11 I posted this - maybe it is what you were remembering? While not the easiest way it is a very accurate way to determine the "average" centerline of an irregular shaped piece with supposed symmetry:



one way to achieve a near "average" centerline:

Cut out a cardboard pattern that will fit precisely inside the flanges of the firewall blank from bend radius tangent to bend radius tangent. Perhaps some odd shaped holes in the cardboard near the edges that can be traced with a sharpie for matching positioning later?

Mark or cut the existing "tooling holes" holes in the cardboard from the firewall
Then turn over the cardboard and re-trim to fit as well as possible. Trace the odd shaped hole in the cardboard on the firewall with a sharpie again to allow repositioning later.

Re-mark or cut the hole locations in the cardboard.
Find the center between each set of holes in the cardboard and drill a 1/16" pilot hole  in the cardboard there.
Replace the cardboard in the firewall and position with that set of alignment marks. Make a sharpie mark through the 1/16" holes in the cardboard.
Flip the cardboard and repeat.  

Remove the cardboard.
Find the center between each pair of pilot hole markings: there is the centerline.Note that you can do this even if there are no pilot holes to transfer from the part. The greater the distance between the 1/16" pilot holes in the cardboard, the greater the precision of this technique to find the center of a non symmetrical part.

Bill Naumuk <naumuk(at)alltel.net> wrote: 	  Quote: 	
		         All-

      From the responses, I can see I  didn't get my point across. I found out that the print locations will work for  at least Corvair, Jab, and Rotax installations, so that's not an issue. I know  where the holes are supposed to go, getting them there is the problem. Every  firewall (Scratchbuilt, at least) is going to deviate a couple of mm's from  print. Getting the Y axis locations isn't a problem because you can use the flat  bottom as an origin. Finding the X axis center is more iffy.

     A couple of weeks ago someone  posted a method for accurately locating the holes on a firewall and  unfortunately it didn't make it into the archives. That's what I'm looking  for.

	


  Dave Downey

  Harleysville (SE) PA

  Zodiac 601XL/Corvair?

  	     Looking for earth-friendly autos? 

 Browse Top Cars by "Green Rating" at Yahoo! Autos' Green Center.   [quote][b]

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 9:21 am Post subject: Locating engine mount holes

See final

                                       do not  archive

 Bill Naumuk

HDS Fuse/Corvair

Townville,  Pa

 [quote]   ---

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 9:22 am Post subject: Locating engine mount holes

See final

                                           do  not archive

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

naumuk(at)alltel.net
Guest

Posted: Sat May 05, 2007 9:22 am Post subject: Locating engine mount holes

Recently archived.

                                           do  not archive

 Bill Naumuk

HDS Fuse/Corvair

Townville, Pa

 [quote]   ---

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