The International Cessna 170 Association

If you have a 170 spinner with the back and front plate the correct length prop bolts will NOT fill the prop flange nuts when viewed from behind. They will fall about a thread or two short. Chech you bolts to see if they are the correct length according to the IPC and that is it.

Yes normally you would think and want the bolt threads to fill the nut but I've found this case to be an exception.

j3pup wrote:Seems to me I should try the AN6-41, because I have a front and back plate for my spinner. Hopefully that and maybe a washer or two will work.

Thanks,

Randy

This bolt will be long enough, but you won't get the threads to protrude beyond the crank flange if that is what you're after (the AN76-41 is actually slightly shorter but has more threads and will have 3 threads sticking past the crank flange).


I agree with you Bruce, especially since the thickness of the flange is so great, but it's hard to argue with the guy signing off your annual (well, my annual) that since the IPC calls for this bolt that it is just fine.

j3pup wrote:I won't be changing the bolts myself, but I would like to get the numbers ready for my AP friend. Where do I find the torque values for my prop?

This is from the 1962 and prior 100 series service manual which your A&P should have a copy of if he is working on your plane: That's quite a range - from 250 lb.-in to 780 lb.-in. for the same diameter bolt. (*As George points out below, the two torque values are for different diameter bolts.) I think those latter torques are too high and probably one reason that there is a lot of problems with cracking on the spinner backplates of C-172's. I would go with McCauley's instructions. McCauley's Service Bulletin 227B lists the torque as 30-25 Lb.-Ft. (360-300 lb.-in.) for 3/16" dia. bolts.

It's interesting to see what Cessna lists for prop bolts on the various models. On the C-170 it was AN6H-45 with the thin AN960-616L washers under the heads. On the A model they shortened it to AN6H-37 bolts with the same washers. On the early B models (20267-25372) the IPC shows the bolt and washer but doesn't call out a part number. On the later B models (25373 and on), now with the large spinner instead of the skull-cap, it lists the bolt as AN6-H-45 with the thicker AN 960-616 washer. Surely one of these is incorrect. An AN6H-37 bolt has a grip of 3 5/16" and the AN6H-45 bolt has a grip of 4 1/16". That's 3/4" difference between the two. For what it's worth the thickness of the 1A170 DM hub is 3 7/16". Later C-172s with the 3 piece spinner call for Cessna p/n A2513-16 bolts. $37.41 each from http://www.iwantcessnaparts.com

I understand what your saying about the argument LBPilot82 but I've never lost an argument of this type when using the parts manual I prove to my IA that I have all the correct APPROVED parts called for and they are assembled correctly.

Gary the different bolt lengths are probably because of the difference in spinners. On early 170s the skull cap which has no back or front plate, was the stock spinner though lots have been replaced by the later design bullet spinner.

Bruce,
I was editing at the same time you were responding. 3/4" difference for the spinner? I don't think so. Looking at the TCDS for the 1A170DM prop note 1 says "the installation is to be made with special alloy steel bolts which are either furnished or specified by the prop. manufacturer". It also calls for the installation to be done in accordance with McCauley drawing C-1177. So far I have not been able to locate that drawing online.

I am going to measure the bolts tonight and count how many threads are missing. The IPC shows that my serial number should have a wood prop, so who knows if I can even use the metal prop values.

n2582d wrote:...

Prop bolt torque.jpg

That's quite a range - from 250 lb.-in to 780 lb.-in. for the same diameter bolt. ...

They are NOT the same diameter bolts. The second torque mentioned is for a larger diameter bolt.

By the way,... The McCauley manual specifies their PN: A-2513-10 bolts (8 of them) and A-1638-13 washers (also 8 of them) for the 170A/DM prop.

Any idea where you find them?

j3pup wrote:Any idea where you find them?

Call your closest prop overhaul shop. (Or McCauley themselves: 937-264-2594)

gahorn wrote:

n2582d wrote:...

Prop bolt torque.jpg

That's quite a range - from 250 lb.-in to 780 lb.-in. for the same diameter bolt. ...

They are NOT the same diameter bolts. The second torque mentioned is for a larger diameter bolt.

Mea Culpa. Thanks for catching that George. That's probably why it says smaller bolts and larger bolts, huh? I'll edit my original post to correct the mistake.

Reviving an old thread here about the bolts for the 8-bolt prop. Here's a couple of screen shots from the McCauley Propeller Systems Application Guide. Note the note on the first screen shot.Hill Aircraft has these bolts here. Looks like it's cheaper to buy the bolts individually rather than as the bolt kit B4622-36. When comparing the overall length and grip to the AN bolt chart in Genuine Aircraft Hardware Co.'s catalog it appears that it matches AN6H40A bolts. $4.45/ea at Aircraft Spruce. One difference might be a single hole in the bolt head vs. three holes.