April 11, 2004

Today I finally got clear insight into why the baffles cracked. Remember a few days ago I took a photo of blind rivet heads having popped off on the air seals? Well...that's the culprit. Here you can clearly see the "trail" of the pop rivet head. It broke off right above the oil cooler, and fell down and got wedged in between the baffle and cylinder #4. I had worked to get the fit so tight in there (I've seen some pretty gappy baffles), and that ended up being problematic. Instead of the pop rivet head slipping down through the cooling fins, it got wedged here and did its worst. The baffle was pushed away from the cylinder...and just that 1/16" or so was enough stress, combined with the vibration of the engine, to crack the .040" around the bolt. Once that cracked, the thing was allowed to flex more, and that in turn cracked the corner flange. All this because of a broken pop rivet head that found its way into a really inconvenient spot.

I don't want to place the entirety of the blame on the rivet head...I think it just exascerbated the pre-existing problem of that bolt area not being reinforced. I suspect these baffles would have cracked eventually anyway. I'm actually glad this came up now. I can beef it up now and never wonder about it again. My advice is to throw away the baffle plans. Use your judgment...whenever you've got a fastener going through anything .040" or thinner, just double the area.

So I somewhat reluctantly drilled out all the rivets and removed the oil cooler duct...which I still want to use...and disassembled this whole mess.

I decided that the simplest fix would entail adding an .063" doubler across the whole back surface, and replacing the side baffle's rear flange with an .063" angle. Here you can see I have cut, drilled, and countersunk the .063" doubler plate, and I've marked the oil cooler hole.

Didn't I just do this the other day? I rough-nibbled out the oil cooler hole.

After filing the hole edges to get 'em perfect, I drilled a rivet pattern that I would use to attach the existing .040" to the .063" doubler.

After deburring, countersinking, riveting, etc., this puppy is back together.

I wish I took photos of the .063" angle along the corner, but you can probably picture it. I just had to cut the side flange to the contour of the rocker box cover. This sucker is friggin' strong as hell now. I've added some weight, probably 6 or 7 ounces...but it was definitely a necessary evil. The baffles are back in place, and I just riveted the air seals back on. Back in business, and no subsequent problems after another 15 hours (and counting).

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Dan Checkoway ()