The International Cessna^® 170 Association

Howdy All. I have two questions for the group as I am about to be replacing my rear baffle seals that seem a bit too short and keep flipping backwards and allowing air to escape without going through my rear cylinders.

The two sections of baffle seals that coincide with both access hatches is bent back and riveted in place, leaving gaps for air to pass (pictures attached). Before changing what I inherited, I wanted to see if anyone had a reason why this might have been done. I have not seen baffle seals pinned back like this on other aircraft and I am wondering if it is to keep pressure off the hatches so they don’t blow open in flight. It is only pinned back by the hatches and the rest of the seal is simply riveted on the bottom edge. My plan is to just drill out the rivets pinning the seals back and getting a good seal.

The second question is concerning my choice of replacement baffle seals. I am looking at McFarland’s Baffle-Kit-1BF which is their cowl saver, reduced friction, bi-flex- 3”x108”, retainer strips, and soft rivets. Does anyone have any experience with their bi-flex and would the 3” strip work with the slight curve of the rear baffle?

Thank you in advance for your feedback. I do have a JPI 830 with probes (CHT/EGT) for all six cylinders and have been looking for ways to keep my temp for #2 below 400. The baffling is in good condition, but after checking for light leaks and realizing the rear seals keep blowing back, I think I have found my issue.

Blue Skys,

Matthew

I will take a pic of what it's supposed to look like in the morning. ? What kind of blue paint is on your cylinders, bare unpainted cylinders dissapate the heat much better than painted ones.

The seals should fold forward such that air-pressure pushes them up/aft against the cowl to effect a good seal. That installation would concern me as-well over the possibility of rivets chafeing against the sheet-metal cowl.

Eskflyer, Thank you. I will have to look back at the logs for the type of paint, as it was before my time. A previous owner had the engine painted blue at overhaul. Ironically, the hottest running cylinder (#2) is not painted as it was replaced at about 400 hrs. Most likely due to running hot. She did not have any CHT or EGT probes when I got her.

George,

An earlier post by you alerted me to the issue of my baffle seals blowing backwards, so thank you! Funny how you just take things as "normal" when that is how you find them. I had to go back and look at my photos and realized, wow - that is concerning that the rivets could be rubbing on the cowl! For some reason, my mind had them pinned back further, but they are facing the cowling. That alone reinforces the decision to drill them out and have it correctly placed. Thank you!

This is how I installed the baffle strips 500 hours ago. Not original style but they create a more positive seal than the old rub strips. They still look like when they were installed. I used the orange silicon seals but McFarlane’s new low friction seals are excellent. Definitely use that instead of silicon, much slicker. I use “prop guard” type teflon tape on the insides of the cowl where the baffle seals rub on the cowl which prevents erosion of the cowl metal and that black aluminum oxide wear material.

I never bend the seals around sharp corners but will overlap from each direction. Also, no rivets where they overlap. Partially cut and trim the seals where they will always lay flat or bend in the proper direction around curved surfaces instead of buckling. Always bend the seals toward the higher pressure area instead of away from the pressure.


Click on picture to enlarge. Not the best picture but highest res the website allows.

Richard,

Thank you for your response and great picture! What a clean looking bird! I have ordered the new seals from McFarland and hope to have it installed once I am back from vacation! All the tips are greatly welcome and should help me ensure a great install.

Thank you again,

Matthew