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Lower engine mounts

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richvetterli(at)yahoo.com
Guest

Posted: Sat May 26, 2007 7:48 pm Post subject: Lower engine mounts

Has anybody had trouble fitting the lower engine

mounts?  When they are attached to the firewall as per

the plans, but the mounts don't seem to quite center

over the lower longerons.  It seems that the front

angle of the brackets are a little too flat and they

don't want to follow the angle of the longerons.  With

a little force, I can spread them out a little, but

that doesn't seem right on such a critical part.  Any

ideas?  

Rich Vetterli

601XL/Corvair

Check out my progress at: www.geocities.com/stixx5a

       

http://farechase.yahoo.com/

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gboothe5(at)comcast.net
Guest

Posted: Sun May 27, 2007 5:04 am Post subject: Lower engine mounts

Rich,



That might be a better question on the Corvair List, but it seems to me that

William has said that that is normal and of little concern....guess it

depends on how far off the holes were.



Gary Boothe 

Cool, CA 

601 HDSTD, WW Conversion 90% done, 

Tail done, wings done, working on c-section

--

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larry(at)macsmachine.com
Guest

Posted: Sun May 27, 2007 5:49 am Post subject: Lower engine mounts

Richard,

The conventional thing is to off set the engine angle to compensate for 

propeller torque and perhaps this is

what you're looking at.  My Subaru is pivoted 2-1/2 degrees from the 

front propeller mounting flange swinging

the rear of the engine to keep the prop centered on the completed cowl 

nose. 

If it's a case of a tensioned fit, you need to specify how much flex is 

required for the task. In some cases, where a mount

is not quite right, the part can be flexed to a correct position and 

then a torch is used to relieve the pressure at the area

of bend.  One has to be careful during this kind of operation though to 

not use too much heat and to be sure it's properly

placed.  I looked at the mount picture on your site. You might want to 

consult with WW on this design specific area.

Very nice site by the way.



Larry McFarland at www.macsmachine.com



Richard Vetterli wrote:

 	  Quote: 	
		   



 Has anybody had trouble fitting the lower engine

 mounts?  When they are attached to the firewall as per

 the plans, but the mounts don't seem to quite center

 over the lower longerons.  It seems that the front

 angle of the brackets are a little too flat and they

 don't want to follow the angle of the longerons.  With

 a little force, I can spread them out a little, but

 that doesn't seem right on such a critical part.  Any

 ideas?  

 Rich Vetterli

 601XL/Corvair

 Check out my progress at: www.geocities.com/stixx5a

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craig(at)craigandjean.com
Guest

Posted: Sun May 27, 2007 6:46 am Post subject: Lower engine mounts

Coincidentally I was drilling holes in my lower engine mounts last night. I

think the other responders have missed the mark. This has nothing to do with

what is forward of the firewall. On *one* of my mounts if you stick a washer

and nut on the mount bolt (forward of the firewall) and tighten it then the

bracket to the rear of the firewall does not align with the lower longeron.

In other words it is impossible to put the two small AN3 bolts through the

bracket and longeron in a way that respects edge distances. On the other

mount when I do this the bracket aligns with the longeron and I can center

the two AN3s laterally in the bracket and longeron.



The latest lower motor mounts come undrilled and the mount bolt is not

welded on. So I see two places where adjustment can be made. You can adjust

the position of the hole for the mount bolt side-to-side to best align the

bracket with the longeron. And you can bend the bracket a little. I agree,

bending such a critical part makes me uneasy too. I think it is worth a

query to the factory.



One question I have is that since we are dealing with an AN3 bolt through a

piece of 0.050" 4130 steel and not a rivet in a piece of thin 6061-T6

aluminum what is the minimum edge distance?



-- Craig

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larry(at)macsmachine.com
Guest

Posted: Sun May 27, 2007 7:39 am Post subject: Lower engine mounts

Craig,

The stress tolerated by an edge distance of one bolt diameter is 2 x 

.050 times the minimum actual distance from

the .375 hole to the edge of a 70K material.  Or in this case, approx 

2625 lbs using 70K as an understated base material

strength, given that it's been welded and adjusted, etc. How that is 

affected by loading depends on the engine weight and shared loads of 

other connections.  For steel, these details have to be calculated to 

minimize weight versus strength for required loads.

I don't believe there is a rule of thumb here as set out by CH and the 

Mfr community for riveted aluminum connections.



Larry McFarland



Craig Payne wrote:

 	  Quote: 	
		   One question I have is that since we are dealing with an AN3 bolt through a

 piece of 0.050" 4130 steel and not a rivet in a piece of thin 6061-T6

 aluminum what is the minimum edge distance?



 -- Craig

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