The International Cessna 170 Association

Does it matter which direction they are installed?


I'm having a discussion with my mechanic and he says they are installed incorrectly (that is with the bolt facing the rear of the aircraft). He feels that the bolt should face the front of the aircraft.


I'm in a quandry because my 140 has the rear two bolts facing the back of the aircraft.

I was told the heads are front, therefore if the nuts come off the rear, they will not work out.
John

The bolt head should be forward and the nut on the aft side.

When I got my plane the bolts were installed with the heads forward. What that causes is the aileron cable on the right side to rub on the bolt. Whoever installed the bolts put the aileron cable and the carry through cable on the same pulley to keep the cable from rubbing. When I found two cables on the same pulley I removed the one that didn't belong and then found why the two cables were on the same pulley. Researching the parts manual figure 7 (B model) showed the bolt head to the rear. Bought new bolts for both sides and put them in head aft and problem was fixed.

Both the 170 IPC and the 100 series service manual show bolt heads aft, nuts forward. Your mechanic will discover a clearance issue with the windshield if he tries to install the front spar bolt head forward; he can get it in, but not without scuffing the glass or binding in the hole for the first 1/8-1/4" of penetration.
As stated above, there can be clearance issues with the aileron cable if the rear spar bolt is installed head forward, nut aft.

oops, I must have been looking at my book upside down?

wingnut wrote:Both the 170 IPC and the 100 series service manual show bolt heads aft, nuts forward. Your mechanic will discover a clearance issue with the windshield if he tries to install the front spar bolt head forward; he can get it in, but not without scuffing the glass or binding in the hole for the first 1/8-1/4" of penetration.
As stated above, there can be clearance issues with the aileron cable if the rear spar bolt is installed head forward, nut aft.

I found the same thing years ago...Common sense tells you to install the bolts to the rear.....clearance, and the IPC says different.....When in doubt follow the IPC......The Feds will be on your side then .....Brad

My first annual my mechanic noticed the right side bolt was inserted from the front, nut to the rear. Like previously mentioned that will cause the aileron cable to rub on the nut. So someone had constructed a little aluminum arm and riveted a small phenolic plate to that. All secured to my wing in a fashion to hold the cable away from the nut. He had me remove all that and turn the bolt around.

I took lots of pictures back when I was shopping for a 170. Looking through those pictures today I found this. Notice anything wrong?
Another one.

Brad Brady wrote:

wingnut wrote:Both the 170 IPC and the 100 series service manual show bolt heads aft, nuts forward. Your mechanic will discover a clearance issue with the windshield if he tries to install the front spar bolt head forward; he can get it in, but not without scuffing the glass or binding in the hole for the first 1/8-1/4" of penetration.
As stated above, there can be clearance issues with the aileron cable if the rear spar bolt is installed head forward, nut aft.

I found the same thing years ago...Common sense tells you to install the bolts to the rear.....clearance, and the IPC says different.....When in doubt follow the IPC......The Feds will be on your side then .....Brad

The A and B IPCs correctly demonstrate the bolt-heads AFT of the spar, with the nuts FWD.

The "view" of the "exploded" area is from inboard-towards-outboard, or viewing FROM the cabin/fuselage. This is confirmed by noticing the view presented of the fuel-gauge.
The "ragwing" C-170 IPC depicts the forward-spar bolt-head FWD. I could not find an exploded view of the rear spar attach in the 170 IPC.

Is it possible to replace these bolts without jigging, removing or supporting the wing?

Exactly how should one go about replacing them?

4-Shipp wrote:Is it possible to replace these bolts without jigging, removing or supporting the wing?

Exactly how should one go about replacing them?

It's handy to have a another person to assist in just stabilizing the wing to prevent it from shifting, assuming you will replace one bolt at a time. Since the wing spars nest into the carrythru fittings, the wing won't fall out, but it can shift a bit. You can find some old bolts, grind the threads off, then grind a slight taper (bullet) on the shank, use it to drive the old bolt out. It will prevent shifting even if you only drive it in about half way. then insert new bolt to drive out your bullet.
Index mark the eccentric bushings before removing the aft spar bolts. I like to remove eccentric on the forward side (it'll probably fall out when you drive the bolt in anyway). I do this so that after the bolt is installed with aft eccentric in position (properly indexed) you can slide the forward eccentric onto the bolt, over the threads, and slide it while rotating until it enters the fitting. This way you insure the eccentrics are not clocked slightly different which would cause a shear load on the bolt. With both eccentrics indexed, watch while you torque the bolt because they can spin. You may have to hold the eccentric with a wrench to prevent it from rotating while torquing

When I had my airplane in Del "wingnut" Lehman's shop in Mena a few months ago, he noticed my aft spar-attach used a "shear nut" PN 374-720 just exactly as the IPC calls for.
That nut was "stripped" and would not torque to the proper specification, so he replaced it with a MS21044N7 (AN365-720 equivalent) which is a full-height tension-nut.
When I pointed out to him that the IPC actually specified the "shear" (low-profile) nut, ... he re-educated me.**

It's so nice to have so many knowlegeable friends on-board here at the forums. (We have several other professional-participants who doubtless also are amused by some of my opinions.) Brad, Jim (c170b53), metalmaster, and many many others...apologies to all I failed to mention.

** Here's the email response regarding my observation from "wingnut":
"It's a misprint. The "A" model shows a tension nut as well as the early 172's and all other 100 series are tension. The shear nut, as we discovered, will not take the torque before it strips the threads. There are several misprints in the IPC's.
..., in this situation the "B" IPC clearly identifies a shear nut, a mechanic who has worked on a few of these should at least question this, especially on a wing bolt. And, although the bolts are in shear load only, because the carrythru fittings "sandwich" the wing spar, it is important to get sufficient compression (tension) to prevent any movement, and prevent eccentrics from vibration induced rotation."

gahorn wrote:We have several other professional-participants who doubtless also are amused by some of my opinions.) Brad, Jim (c170b53), metalmaster, and many many others...apologies to all I failed to mention.

It doesn't take a professional to be amused. .... .....

N9149A wrote:

gahorn wrote:We have several other professional-participants who doubtless also are amused by some of my opinions.) Brad, Jim (c170b53), metalmaster, and many many others...apologies to all I failed to mention.

It doesn't take a professional to be amused. .... .....

Touche'