Rear Engine Intake Manifold
 

This is both a question, and a heads up to anyone who has a turbocharged 337 (especially those with Riley Intercoolers)

Has anyone else ever had this problem - if not, I would suggest you remove the pilot side rear cowling and inspect soon...

I was working on my plane this evening (cleaning, etc) from my recent trip to the keys, and noticed the inside of my rear cowling was covered in a fine film of what appeared to be aluminum filings (powder)... almost like an overspray from a silver paint would appear.. I knew this was not 'good' and began searching everywhere trying to locate it's source.... What I found was very dissapointing!

From the turbocharger compressor - there is a light aluminum ~3" tube which passes behind the #5 cylinder (pilot side, rear engine, right before the prop). It curves up around the rear of the engine and goes into the intercooler - then onto the throttle body, and then back down to the intake manifold on each cylinder. Where the two pipes pass each other - mine were rubbing together, (aluminum on aluminum) and they had worn the pressurized intake manifold paper thin (it appears a tiny pinhole was blowing out, causing the fine mist of aluminum particals.... When I lightly probed at it with a small screwdriver - it poked right thru!

Now, I need to either find a replacement intake for that section, or find a weld shop that can repair that piece.. It was surprising on the way home that I did not notice any drop in manifold pressure! I did not have my camera, but will take and post a picture soon.

Routing differences...
 

Pat, et al.,

Just a note that the routing of the induction tubing from the compressor is different after S/N P337-0225, i.e., it routes more near the forward part of the engine near Cyl 1 & 3... at least on ours, which is a 1977 model. Of course the other difference being the plumbing is different between the Riley intercooler and the American Aviation intercoolers.

Always a good idea to check the band clamps and interconnecting hoses for security in the plumbing department though.

Another area of chafing to be concerned about for those who have the American Aviation intercoolers, is on the front engine induction hose that connects the intercooler to the engine's metal induction tube plumbing. These short hoses are about $60 bucks a pop and a hole will easily wear through the side where it passes through the side baffling hole on the PAX side above and between Cyl 1 & 3. Using some of that grommet style grabbing anti-chafe material, you can glue it on with some Plio-Bond and provide a cushion. Cessna used this stuff beneath the floorboards where wires and hydraulic tubing pass through the keel.

SkyKing

what's most interesting, is the apparently (cheaper) thinner-walled aluminum tubing going to the intercooler did not wear through, but the much thicker (more expensive) manifold wore through!!?? Apparently the metal composition on the manifold must be softer...

Has anyone had any weld repairs done? If so, where do you suggest? It will probably be more work to remove it than it will to weld it back up...

during annuals sometimes it pays to look for chaffing and at that time all that is needed is a little silcone and maybe a swatch of cutup hosing to prevent wear.
durng annuals everything is open and easy to spot problem before they develop.
1 dollar prevention or mucho to fix