The International Cessna^® 170 Association

I have the 300-d engine with 6 bolt prop/crank. I have the recomended prop bolts but find them just a little long even with one washer under the head. The ends of the bolts just touch the cowl and with vibration I worry they would chew on the cowl. Is it legal to put a second washer under the head of the bolt. That would make 2 all together. Any ideas?? Thanks G

There are many combinations that could be the problem. Wrong spinner? Incorrect backing plate? Inusufficient number of plates? Changed, modified cowl? Sagging engine mount? Incorrect mount bushings, etc. The recommended prop bolts are only applicable to a specific prop, (altered prop), engine, spinner, cowl, etc. combination.
It'd be best to simply buy shorter bolts than to install too many washers which may alter balance and friction/tension on the bolts.

simatos wrote:I have the 300-d engine with 6 bolt prop/crank. I have the recomended prop bolts but find them just a little long even with one washer under the head. The ends of the bolts just touch the cowl and with vibration I worry they would chew on the cowl. Is it legal to put a second washer under the head of the bolt. That would make 2 all together. Any ideas?? Thanks G

Simantos

FAA Manual 43-13 (CAM 18 for us Geezers) says, and I quote page 7-5 Section 3. Bolts paragraph 7-37.

“GRIP LENGTH. In general, bolt grip lengths of a fastener is the thickness of the material the fastener is designed to hold when two or more parts are being assembled. Bolts of slightly greater grip length may be used, provided washers are placed under the nut or bolt head. The maximum combined height of washers that should be used is 1/8 inch. This limits the use of washers necessary to compensate for grip, up to the next standard grip size. Over the years, some fasteners specifications have been changed. For this reason, it is recommended when making repairs to an aircraft, whose original hardware is being replaced, that you must first measure the bolt before ordering, rather than relying on the parts manual for identification. In the case of plate nuts, if proper bolt grip length is not available, add shims under the plate. All bolt installations which involve self-locking or plain nuts should have at least one thread of the bolt protruding through the nut.”

In view of the price of propeller bolts, I would find some 1/8" washers or use two standard washers. If the face of the metal propeller is marred under the head of the bolts, I would use a fender type washer first. These are old, simple airplanes we're working on,---not the "X 15". Sometimes common sense takes precedence over 43-13.
I just can't see spending about a hundred dollars to shorten the prop bolts a sixteenth of an inch.
Remember,--- it is always easier to beg forgiveness than to get permission. There is absolutely no way they can get in trouble if they say 'NO'.

I know, ----I know, George!

I'm leading our youth astray, again, So be it.

Specifications for the X-15 were first laid down in 1954, two years before the 170 ended it's production run (and more than 30 years before it's progeny's production was ended.... the first time.)

My concern isn't with the price of different bolts or how many washers are used,... but with figuring out what's possibly wrong with the rest of his installation.