dimensions for spinner to nosebowl gap?

[John Bickham]

Another piece of the puzzle to fit for this rookie builder.



DSCF1984[1].JPG

I got Bob's O-540 installed to do some checks. My Vetterman exhaust is arriving tomorrow I think (Thanks Clint).

I installed a 1/4" plywood mockup firewall to do a couple of checks before I settle on the final dimensions of the firewall. You notice the white poster paper in the top corners. I shorted the radius about a 1/2". So making the plywood template saved a sheet of SS so far. I'd like to make sure I have enough clearance between the cowl and the exhaust. To do that I need to position the nosebowl, that I got from Bob, with the 1/4" -. 3/8" gap to the spinner backplate.

I'm installing a Vans fiberglass, 13" CS spinner on a 84" CS Hartzell. I thought this would be easy in that I incorrectly asssumed the spinner backplate would sit flush on the starter ring face. It appears that the spinner backplate is mounted to the prop and spaced out from the starter ring plate. I was wondering if there is someplace in a book or on the web that may have that spacing dimension. Or do I have to mount the prop with spinner to get it right? Thought I'd ask before I did all that work and there is a smarter, more better way.

Speaking of smarter, while assembling my landing gear struts I made the dumb mistake of adding a little extra ATF fluid while I was lubricating the O-rings and cylinder walls. The clearances are kinda tight so you have to push the piston, spring, brass cap assembly in with some force. So guess what happens when you get the assembly to slide in with your face right over the top of it with just a little too much ATF fluid in the bottom of the cylinder???? It gotta go somewhere and it comes out the piston tube like you wouldn't believe. Luckily I had my glasses on. So stupid I just laughed. Be smarter than me! That shouldn't be too hard. Skin on my face has seemed much smoother last few days .

[jaredyates]

John, is it that you don't have the prop yet?

[Bdflies]

Hi John! You might find the dimension you seek, in a book, but I wouldn't trust it. Someone might have done exactly what you're contemplating, but even then, your mileage could vary. I suggest that you assemble the spinner to the prop and mount the whole thing onto your engine. Then, you can measure the spinner standoff, from whatever point you like, to determine where the face of your nosebowl needs to be. Measure it about a dozen times and make a plywood bulkhead that mounts on the engine flange, to hold the nosebowl. Then, you'll be sure of the relationships involved.
Hey, just thought about it: my bulkhead should work for you. (might need to modify it for your spacing). You're welcome to it!

Bill

[John Bickham]

Jared,
Got the prop from Mark G a while back. Of course I'm behind schedule. It is sitting in a safe place, in its original shipping box. I was just asking if there is an alternate way to get dimension without mounting prop. Sounds like, that the only and best way. I work by myself 99% of the time. Will have to schedule some help to get prop mounted.

Bill,
Thanks for the offer. You guys ought to be getting kinda busy getting ready to head north to Kosh. I won't bother you till you get back. Got plenty to do and redo! I'll come visit you and Ron when ya'll back. be safe and represent us CA's! I'm half Broussard!

[Glenn Patterson]

If the backing plate is available then you could temporarily bolt it to the engine prop flange. I sold a Vans fiberglass prop spinner to Clint of Vetterman's where he may be able to help you with the dimension if no one else can. It is the back of the spinner that is the governing dimension if it mounts and flanges backwards. We originally bought the Vans RV spinner as it was common but we are using a Continental IO-360 so nothing is like any other BH. We were sweating getting the nosebowl on with the prop in place and were relieved that when it was wrestled on there was a 1/4" of clearance. It was a good thing as we could not go any closer to the engine w/o the nosebowl touching the fuel pump.

http://bearhawkforums.com/forum/classifieds-4sale-or-wtb/11462-vans-constant-speed-spinner-kit-cs-13

Glenn

[Battson]

I have seen homebuilts which used a book value plus a plywood template, or something similar, and ended up with a different measurement on their final prop.
It looks ugly and creates drag at best, at worst you are forced to make a whole new cowling.

You are a little way from NEEDING to make the cowling from the look of things. Maybe it would be best to find a prop to measure, or better yet, use the one you bought with a borrowed or bought spinner. That is what I did, just bought one.

[Glenn Patterson]

I agree with Jon as you are long ways off from the firewall forward engine cowl/nose assembly. The firewall back will need to be installed before contemplating building firewall forward. We had the prop & spinner to work with. It is best that your prop and spinner be on hand as well. I used my old faithful Lee Valley Tools router circle cutter to machine a plywood disc fixture that centered on the engine hub and was stepped so that the nose bowl indexed on the disc. The back spacing was built in to the plywood fixture so that the nosebowl was held exactly where it needed to be. I split the nosebowl as it would have been impossible to bolt the prop & spinner up on our Continental IO-360 engine. It is easier to bring the two halves together behind the final installation of the prop spinner combine. We had very little wiggle room as the bowl went very close to the engine to give up the backspace required to clear the spinner. The Continental uses a bed mount so no allowances were made for engine settling on the mounts. Not sure if any allowances are made for the Lycoming dynafocal mount.