The International Cessna^® 170 Association

The parts manual lists the bolt for attaching the tailwheel to the spring as AN7-10. This comes up short. The bolt that came with my new ABI 3200 replacement kit is too long! Anyone know the correct size?

Curious

Brad

How much too long? Can you add a washer or two and make it work?

The AN7-10 is probably too short because tailwheel main springs today are the thicker L-19 spring.

Can you measure the thickness of the assembly and order the right grip length?

You do need to use multiple washers. When I replaced my main spring last year, I used an AN7-20 bolt and 4 washers, one under the head and three under the nut. It's important to use enough washers under the nut so it doesn't bottom out on the grip length of the bolt when torquing it.

By the way, Fig 94 of the IPC is the one that shows the Scott tailwheel. It identifies an AN7-20A with three washers. I needed to add the fourth for the reason I mentioned above.

It's also worth mentioning to use a steel lock nut vs the nylock ones as they tend to work loose.
I also put some torque seal on them and make it part of preflight to check for rotation

The combined thickness of just two of the washers specified in the IPC exceeds 1/8". And the IPC shows use of three of them. I don't remember the details now, but I considered dropping down to an AN7-19 and It didn't work out. But adding the washer made everything work out nicely using the bolt length specified in the IPC - no bottoming out and the right amount of threads showing above the nut. However, as they say in advertisements, "your results may vary." If I remember correctly, there are a number of discussions on the forum about adding an extra washer to prevent the nut from bottoming out.

bagarre wrote:I also put some torque seal on them and make it part of preflight to check for rotation

If one doesn't have Torque Seal handy a thin stripe of paint will do. Cessna calls this Red Lining.

I have one of the L-19 tail wheel spring bolts that some of us purchased years ago. The one with the tie down ring welded on it. I have added a flat washer to be sure I have adequate threads for the nut to tighten against. I don't know what torque is correct, but after I have flown and landed a number of times, my ring has turned about 20 degrees. Just wondering if I need to put more umph (more torque) or what else needs to be done to keep that bolt from gradually turning? If it weren't for the tie down ring I doubt I would notice this occuring.

Thanks gentlemen.

I have had some interesting landings lately. About every 20 or so landings I would get the airplane to head for the weeds and it would take all my might to keep it on the runway(when I was punished by having to use pavement) My checks of the tailwheel would seem normal. I have a ABI 3200 tailwheel about 2 years old so I was not thinking it was the problem.

Of course I had to pull it apart to see! What i found was that the bottom thrust washer jumped the pin on the fork and would rotate around when the tailwheel and turn. Once it got all the way around it would catch on the pin and jam a bit causing it to stick until I could force it to move through enough brake ect.

I called Alaskan Bushwheel to see if they heard of this and they had. They used a vendor in Oregon that drilled the hole for the pin on the fork to deep. They are sendind me some aluminum to put down in the hole so the pin does not settle far enough down to allow the thrust washer to rotate.

Thought someone would want to know!

Brad

piclr60 wrote:Thanks gentlemen.

I have had some interesting landings lately. About every 20 or so landings I would get the airplane to head for the weeds and it would take all my might to keep it on the runway(when I was punished by having to use pavement) My checks of the tailwheel would seem normal. I have a ABI 3200 tailwheel about 2 years old so I was not thinking it was the problem.

Of course I had to pull it apart to see! What i found was that the bottom thrust washer jumped the pin on the fork and would rotate around when the tailwheel and turn. Once it got all the way around it would catch on the pin and jam a bit causing it to stick until I could force it to move through enough brake ect.

I called Alaskan Bushwheel to see if they heard of this and they had. They used a vendor in Oregon that drilled the hole for the pin on the fork to deep. They are sendind me some aluminum to put down in the hole so the pin does not settle far enough down to allow the thrust washer to rotate.

Thought someone would want to know!

Brad

Wow does this sound like a serious liability issue!

Sounds like an AD in the making.

bagarre wrote:...because tailwheel main springs today are the thicker L-19 spring.

...?

Not correct. The L-19 spring is a thicker spring because that airplane is a heavier airplane. While some folks have substituted the L-19 spring for the correct 170 spring, there has not been any approval basis for that, as there is no superceded PN to use the L-19 spring on a 170.

If the L-19 eyebolt (PN 062105) which is intended for the thicker L-19 mainspring is used on the 170 setup then the shank of the eyebolt will be too long and the nut will never tighten down properly unless additional washers are installed. Some technicians will attempt to install an all metal lock nut but the problem will remain until the long shank is accommodated with washers.

According to the 100 Series Service Manual (pg 1-8) a 7/16th bolt should be torqued to 560 in. lbs. (about 45-50 ft lbs.)

The AN7-10A bolt previously mentioned was intended for the early Scott 2000 series tailwheel. If you have the 3200 tailwheel (most likely) then you need to look on page 155 of your IPC to see that the specified bolt is AN7-20A. (If you substitute the 062105 bolt then remember what I posted above.)
The eyebolt can be obtained from Air Repair in Cleveland, MS.