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designerX

Well Known Member
I'm experiencing a vibration that I'm perceiving is greater than when I first purchased the -4 (though I admit I'm getting more comfortable with her and can pay attention to these things now.) The vibration is slight at idle, more pronounced from 1200 ~ 1700 and almost disappears above 1800rpm. It sounds very similar to the description in this old thread:

http://www.vansairforce.com/community/showthread.php?t=3695&highlight=vibration+mount+torque

The vibration is more noticeable in flight than when ground running (which may always be the case?) The airframe and engine now have 126 hours. The plugs are clean, mag checks are good, cylinder head temps are similar. I've closely examined the motor mount looking for cracks and can see no imperfections.

I'm wondering how to check the torque on the vibration mounts... I've searched the forum and some threads say "bottom out the biscuits" and others recommend a torque setting (which I assume is challenging with the placement.) What is the correct method and/or value? Other recommendations?

Dynafocal mount to IO-320D1A and the vibration mounts have locking nuts not castellated/cottered.

[Edit: Vibration resolved! The exhaust supports were the culprit... she's now super smooth! 03 July 2012]

Thanks,
Stan
 
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Call Lord?

Stan-
I just got the spec sheet on the 9613-40 Lord mounts usually used with d1as (which I have on my -4), and I don't see a torque spec on it. However, the engineer I spoke with at Lord was very knowledgeable - why don't you give them a call and report back here with what you find out?
Eric
 
exhaust support allowing vibration?

Hello all,

I'm also interested in identifying the 'rubber' exhaust support in the picture below (product or part number.) It appears to be somewhat cooked/cracked and may be losing it's strength and elasticity therefore offering less support to the exhaust (and encouraging a vibration.)

rubber_isolator.jpg


Eric, I'm not sure whether I have the Lord mounts or Van's standard mounts. I'll post a picture later in case one of the gurus here can visually identify them.
 
Your exhaust support mounts are usually "home-made", and aren't a specific part number.
 
From your photo, it appears that you might only need to replace the rubber itself. It is probably a strip cut out of a sheet. You could use a strip out of the sidewall of an old tire, or similar.

Hopefully some experienced builders will chime in..........:)
 
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