[scsmith]

I have an angle-valve IO-360-A1A, horizontal induction on an RV-8

I fit the spinner bulkhead to the flywheel/crankshaft with 2-1/4 inch spacer tubes.

I just finished fitting/trimming the cowl. The top-front of the cowl sits about a 1/16 inch to 1/8 inch low with respect to the spinner bulkhead to account for motor-mount sag, and the cowl is centered left-right on the spinner bulkhead. I have just exactly a 1/4 inch gap between the cowl and the spinner bulkhead.

So, it seems like the cowl is in the perfect spot.

Then, I looked inside. The cowl is within less than a 1/2 inch vertical distance, and about 1/4 inch min-distance of the left front (#2) cylinder. The point on the cylinder that is very close is the threaded lug on the cylinder where the baffle mounts.

On the right side, the clearance is slightly more, but nothing to be confident about, probably 7/8" vertical and just over a 1/2" min-distance.

It looks to me like the lugs are going to hit the cowl when it wet-dog shakes, let alone with a baffle and rubber baffle seal.

And, its a bit odd to me that the right cylinder would have more clearance, since that cylinder is farther forward, you would think the cowl would come closer to it.

What did I do wrong?
I'm wondering if they sent me the wrong upper cowl? The lower cowl is labeled IO-360, but the upper just says RV-8. If there is only one, it seems too close a fit to the bigger engine.

At first I thought maybe I mounted the cowl slightly rotated, but the lower cowl dictates the rotational position as the lower corners engage on the lower corners at the firewall. Then, the cooling openings must fit bottom to top . So I couldn't have done that wrong. I measured, and if anything, the left side is slightly higher - would have given slightly more, not less, clearance to the left cylinder. So, I'm puzzled.

 

[decathlon737]

Right Thrust

Steve,
This is common with the angle valve engine, it gets tight. There's more room on the right because of the engine offset, they move the rear of the engine to the left while keeping the front as close to center line as possible to help off set p factor. Thus you have built in right thrust. My angle valve has about 1/2 inch clearance on the left side also.

 

[RatMan]

its a bit odd to me that the right cylinder would have more clearance, since that cylinder is farther forward, you would think the cowl would come closer

Steve,

If you haven't done this yet stand in front of your engine and sight down the seam created by the two case halves. The offset can be seen by comparing that line to the vertical stab. It's pretty surprizing how much offset there is. It also explains the difference in clearence around the engine.

 

[decathlon737]

Photos

Steve,
A picture is worth a thousand words. Snapped a few for ya today.

Hope this helps.

 

[scsmith]

thanks, clearance closer than pics

Hi Decathalon737,

Your pictures are some help - it is close on #2 for yours, but on mine, your baffle where the doubler edge is would touch the cowl for sure.

I'm thinking that I will put a couple of AN 970 washers between the top motor mounts and engine to buy 3/16 more clearance at the spinner, ( about an 1/8 at the cylinder) and then remove them once the motor mounts sag into final position. Not sure that the 1/8 inch will be enough, but thats all I can get.

 

[scsmith]

BTW, did you fly yet? (decathalon737?)

I saw your pictures a few days ago, waiting for paperwork.
Did you get to fly yet?
Your plane looks great. So many -8's in WWII colors, very tempting. I'm opting for NASA colors ( white w/ two colors of blue trim) but someday, a Spitfire replica is in my future - Me and R.J. Mitchell are soul-mates!. I just need a decent propeller speed reduction gear, seems to be the Achilles heal of liquid-cooled engines.

 

[szicree]

I feel your pain

I had similar troubles when mating a mighty 360 to my little -4. I was so pleased with the way the cowl went on that I didn't even think about the clearance inside until after it was drilled, trimmed and mounted. The horiz clearance wasn't really an issue, but the vertical clearance on the front left was too close.

What I did (not easy, YMMV) was to remove the lower side hinges, move the cowl further forward at the bottom, attach new hinges, then build up the edges to close the gap. This brought the front of the cowl up a bit. Unfortunately it also screwed up the spinner/cowl alignment, so I then cut and reworked the front of the cowl near the spinner, both upper and lower, to get the alignment back. It was a bit of work, but it all came out clean as can be and looks great.

Another option might be to put some washers between the upper engine mount and the firewall to tilt the motor down a bit, and then rework the front of the cowl.

I know neither of these is very appealing, but whatcha gonna do? I think the real fix might be to just attach the motor a little lower to begin with. I would be interested to hear what Van's has to say about all this.