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Engine mount wrong?

JDA_BTR

Well Known Member
The upper corners of my engine mount seem wrong. There is 1/2 ID tube where I think there should be 3/8 so the bolt wallows around. Also an AN6-24 is too short. Any ideas? I asked Vans already but quicker answers here!!!





 
It is purposely over sized.
The only hole diam. that matters structurally is the one in the flange that mates with the firewall.
 
hard to tell with the angle, but it looks like my (14A) upper left tube might be shorter than the one in your pic, but upper left and right bolts are AN6-26A on the taildragger

v6jivl.jpg
 
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Scott, is there some manuf variability in the depth of that mount tube? My right and left upper corners both need a 25 or 26. The plans are usually dead on. I for sure have the right bolt sized it on the size chart.
 
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Scott, is there some manuf variability in the depth of that mount tube? My right and left upper corners both need a 25 or 26. The plans are usually dead on. I for sure have the right bolt sized it on the size chart.

The production drawing shows that the upper two bushings should be 1.25" long (beyond the face of the flange washer), and the lower 4 bushings should be 1.0" long.

I have not heard of any other complaints about the specified bolts being too short.
 
Measured my upper mount bushings and mine measure just shy of 1.5 inches past the big washer or 1-5/8 from the firewall. That?s an extra 1/4 too long. So do I just upsize the bolt length or get another mount?
 
Final answer on this was the tube diameter is right but my tube is 1/4 too long. Up two bolt sizes and carry on I was told.
 
maybe someone welded a taildragger tube on a tri-gear mount. taildragger upper tubes are longer for some reason
 
How much of the bolt should stick through the firewall? What is the minimum amount of threads that should show on the end of the bolt after torquing down the nuts?

My upper bolts seem to too short like stated above. I have about 1 thread showing before torquing down on the bolts.

The lower bolt will have lots of exposed thread.
 
How much of the bolt should stick through the firewall? What is the minimum amount of threads that should show on the end of the bolt after torquing down the nuts?

My upper bolts seem to too short like stated above. I have about 1 thread showing before torquing down on the bolts.

The lower bolt will have lots of exposed thread.

Page 5-18:

"A common rule of thumb for evaluating whether an installed bolt is the proper length has always been that up to three thick washers are allowed (if more than three are needed the next shorter bolt should be used), and that at least one but no more than three full threads of the fastener are to be showing beyond the nut. This rule of thumb works for the AN365 nuts that have been commonly used on RVs for years.

Some of the newer RV kits use the all metal MS21042 self locking nut. The long standing rule of thumb will not work for these nuts because they are shorter in height than the AN365 nut. For these nuts, modify the rule of thumb to ?at least three, but not more than five threads showing.? This rule of thumb will still allow for meeting the 'maximum use of three washers' rule.

You may have to educate any technical councilors or airworthiness inspectors that perform inspections on your project. Some
inspectors are not familiar with these smaller sized nuts."
 
thanks E. I did just look at that exact page in the plans and determined that the bolts are definitely too short and for all i know the other bolts are too long, which I could adjust with washers. I have not put the nuts on the lower bolts, so I don't know the answer yet. The question for the upper bolts is should I get 25 or 26 and why are the 24s too short. I thought Van's Quality control was better than that. I figured that worst case the bolts would be long and extra washers used.

It took a lot of work to get all the bolts in--used ratchet wrench and push on the bolts. Only two slid in, the rest were a pain in the butt. Maybe not an issue, but the top left bolt head does not sit flush on the end of the tube. One side of the washer barely touches the edge of the tube. In other words the bolt is tilted outwards and is not straight.
 
well, I found the issue and I am not sure what to do at this point. I have an email out to Vans to see if the attachment will be safe. I can't post pictures here, but you can see what I am talking bout on my facebook page Ken's RV-14 (https://www.facebook.com/Kens-RV14-632288410496405/?ref=bookmarks)

Clearly, the top left engine mount is not flat when placed on a granite counter top while the right one is perfectly flat. This causes the head of the bolt to not line up with the end of the mount where it makes contact even after torquing down the bolt.

Not sure if this is an issue or not.

Any thoughts?
 
Thanks for posting pictures. All my pictures on this site got deleted because I used photo bucket.

Anyway, not only is it not flat on the counter top, but there is a clear gap between the mount and the firewall even after tightening.
 
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