The International Cessna^® 170 Association

I've just recently acquired a 1956 C172 taildragger conversion done with the Bolen/Avcon STC. It was done over 15 years ago and has gone through several owners since. The logbooks are original and the proper sign offs, STC, 337's are documented, but there are no supporting documents or instructions for continued airworthiness. I know the gear legs are of Bolen's own design and manufacture. The only numbers I can find stamped on the legs are 000103L and 000103R. Would those be P/N or S/N. Also, anyone have any idea about the axles used in this conversion? Their design and structure don't match any C170/C180/C185 parts that I can find. The airplane has some serious toe-out issues documented by tire wear and handling quirks. The standard Cessna shims are considerably smaller that what is installed and of course don't have the large center hole for the "spindle" to fit through.
The current shims are drilled in such a way that you cannot restack or rotate them in anyway to adjust the toe-out to 0 or in somewhat. As everyone knows the current STC holder is non-responsive at best. In reading through the Forum I think I have identified maybe 4 members that may have a similar conversion. I would be more than happy to pay any copying cost and mailing charges if you have any more documentation on the installation of this mod, parts list, rigging instructions or maintenance procedures. The left wing was 9" lower than the right and we have gotten them within 3" of each other by putting shims under the main gear attach point under the floor. The Scott 3200 tailwheel came with compression springs and the slack chains. Brakes were the only method of steering during taxi. Changed them to tension springs and no slack and the taxiing is much improved. Did this conversion come originally with compression or tension spring setup?
Thanks in advance for any suggestions or comments.
All the best, Jim

Jim you may have to make your own shims. That is often the case with tail wheel converted aircraft. There is not enough quality control in the conversion in a lot of cases so you end up with a situation where there is not a shim made that gives you the right combination of toe in and camber.
Shawn

Jim,

I have the Bolen conversion on my 172 which was done in the early 90's before I bought the plane.

My plane has tension springs and I don't know why yours is different, but I was able to adjust alignment by swapping/flipping shims.

A couple of weeks ago someone actually answered when I called Avcon. I was asking about approved skiis for the conversion, but we ended up talking quite a bit about the "Bolen gear". Bob said their are two versions of the Bolen gear legs. The earlier ones were shorter than the later ones (circa 1990, i think). The new legs are "similar to 180 gear" which he thought should bring the height to within "1 to 1 1/2 inches" of a 180. I know that wasn't your question, but thought it was interesting.

It's a good conversion and very tough. I've heard people say the PPonk gear beef up (similar in concept to the Bolen conversion) could cause more damage to the airframe if wrecked, but I was glad to have the extra structure when I folded one of my gear legs about 10 years ago. The gear leg rotated and was completely contained in the gear box. No additional damage to the airframe.

I have some of the STC drawings, but don't know if they are complete. I'll check out what I have and get back to you.

JR

N171Q wrote:... I've heard people say the PPonk gear beef up (similar in concept to the Bolen conversion) could cause more damage to the airframe if wrecked, ...JR

If someone will tell me how hard they intend to run their car into the brick wall I'll tell them whether a heavyduty bumper will help them or not.
If someone will tell me how hard they intend to ground-loop their airplane I'll tell them if it'll do them any good to have a Pponk mod.
Of course a Pponk equipped airplane will need more repairs if it's wrecked! By the time it's wrecked sufficiently to tear out the Pponk mod entirely it's going to be a major repair anyway.
But the Pponk will save from damage many mis-handled landings that otherwise would have seriously damaged a non-Pponk airplane. Pponk will cost less than many insurance deductibles on airplanes that will probably never be wrecked because they have Pponk. IMHO

George,

I think your explaination makes total sense. That's why I was so suprised to see the damage from my unfortunate experience (long story that does not include a groundloop) contained entirely to the gearbox.