Prop and motor mount suggestions sought

I bought a 22 Y/O RV-3 with a O-320 A1A. The plane has flown regularly but I can't say the same about maintenance. I am now nearing the end of the detailed condition inspection when I discovered a few things:
1) The original prop was a 62" pitch unknown prop which did fly the airplane. I also received a 68x72 Ed Sterba prop which I just had Ed rehab and placed on the plane. Ed said it should turn around 2300 RPM, however I get 2500 RPM. Note: tach accuracy is not verified but I think it is close. Any thoughts on what this prop should do on this engine? My plan is to fly it and watch the RPM so it does not over speed.

2) The spinner is very close to the cowl. In fact there are gouges where it hit. My EAA pals suggest adding 2 .109 thick washers to the engine mount to move the engine forward. The conical mount has a number of washers in place already... ranging from 0 to 2 on the different mounts. Any comments on moving it forward with more washers?

I am looking forward to flying this plane and will do so as soon as I am confident in its integrity. Thanks.

Any input?

Someone must have some ideas?

I can't really tell you what that prop will do, but in terms of shimming the engine forward, make sure that there are no other points on the engine that will get too close to the inside of the cowl if you do - particularly tricky is the alternator. Many folsk already have problems with alternator pulleys wearing grooves in the cowl. Baffles might also fit a littel funny up front.

You mention turning the prop at 2500 rpm. I am assuming you are referring to static rpm on the ground.

Some data.
-The Sensenish metal prop on my old 320/rv-4 yielded around 2200 rpm static.

-I removed the Sensenish metal prop and replaced it with a Catto and that yielded 2080 rpms static. I was able to go wide open throttle at 11,500 ft msl and turn the prop at 2730 rpm.

-Craig wants to see the static rpms at 2200-2300 rpm. The last prop on my fastback yielded 2090 rpms static. He wanted to raise the rpm so he changed things a lot. The next prop yielded 2400 rpms static. Now at 11,500 ft msl I can turn the prop 2940 rpm wide open throttle

I imagine you will be able to turn at least 2900 rpms in flight. You will need a different prop if you don't want to go pass 2700 rpms.

Break

Regarding the cowling/washers. I would take all the washers off and set the engine on the mount correctly. The mount has offset, placing an unequal amount of washers under the mount or conical mounts changes the offset (and can affect the handling qualities of the plane). Once all those washers are off, either sand the front of the cowling down or cut the back of the spinner (not the spinner bulkhead) to create the clearance you need.

Hope that helps.

There are likely many RVs out there that have washers under the mount to correct things like cowling misalignment and engine sag. I know of several that have been flying like that for years; however, the ones I know about mostly have the washers between the firewall and motor mount.
In at least one case I know of, several washers were used to align the engine to a really poorly installed cowling and others to correct for engine sag.
You do have to make sure the bolts are the correct length if you add washers.
I also have seen washers added under the Barry mounts, but I think it's easier to put them at the firewall.
I talked to Van's once about the change in thrust line and they said it wouldn't be a problem, and per my experience, they are correct.
If the fiberglass part of the spinner extends beyond the back of the rear bulkhead, you could get some extra clearance by trimming that part off. (the fiberglass, not the bulkhead.)
Good luck

My -3 has a Sterba 70x78 prop but on a 0-320D1A, 160hp engine. Airplane is a fastback too. At 7500' and WOT, I see a little over 2700 rpm and somewhere around 2300 ground run up. This is with an EI tach, plane had a Mitchell tach that was way off. I suspect your prop will over speed at WOT but should climb good. Check your tach and fly it to find out for sure.

Update to engine movement

Upper engine mounts were replaced by previous owner who did not replace the worn lower mounts. Holes in mount were noticeably oval. I added .200 to each motor mount which moved the engine forward enough but did create some issues with the cooling baffling which I rebuilt a while ago. Now it needs some fine tuning. It also put the spinner a little high relative to the cowl and I removed one washer which helped realign it.

I have not flown the plane yet because I am refinishing the upper cowl. Hope to get it up soon. Thanks to all who commented and my EAA chapter buddies who assisted.

CAVU Mark said:

2) The spinner is very close to the cowl. In fact there are gouges where it hit. My EAA pals suggest adding 2 .109 thick washers to the engine mount to move the engine forward. The conical mount has a number of washers in place already... ranging from 0 to 2 on the different mounts. Any comments on moving it forward with more washers?

Click to expand...

My recommendation would be to shim the entire engine mount forward at the firewall, and not at the engine.

But before you do that, check the condition of the vibration isolators that fit between the engine and the mount. These rubber components were out with age. When they do, the engine can droop when static on the ground. When this occurs, replacement is the appropriate correction, but sometimes people extract some more time out of them by shimming the lower bolts to push the prop hub and spinner back up where it belongs.

It is possible that your tight space between cowl and spinner is acceptable with good isolators, but the space is too tight when the engine flops around on worn out isolators.

Because the airplane is 20 -some years old, I would hazard a guess that the isolators are overdue for replacement.

Cheers,
Rick