The Cessna 120-140 Association Forum

Remounting C150 mufflers to my C-85 engine after installing new Millennium Cyl's . Ran into an odd problem... exhaust stud height. Old set up was (2) SS exhaust gaskets, nested, bead side against head (standard Continental gaskets, P/N: 6322837, .0165" thick), then muffler flange, internal lock washer, thin plain washer and a (tall) brass nut. This left a min. 1 1/2 threads showing, depending on the stud. All good. Then I decided to use the newer style (Rapco) blow-proof gaskets (.150" thick, pre-crush), now I'm about two threads recessed (w/brass nut). Started measuring stud heights, both old & new cyl's ... total range was .761" to .788". Millennium's stud height were pretty consistent with the old cylinders. I am assuming the variation is due to when the drive torques are reached when installing studs. I'm guessing the minimum stud height is .750" (could not find the spec). So , has anyone else run into this? Or do you change to a steel nut when using the blow-proof gaskets? Any advise? Wanted to use the blow-proof gaskets due to hearing there are less leaking issues down the line (compared to Continental gaskets). Thanks
Jim S

No washers are called for, just the gasket, flange and brass nut 22022.

Hi John. What I described is how it was assembled when I removed the mufflers, could very well be incorrect. In the Cessna 150 Service manual they say to install new gasket, mount muffler, and " When installing attaching nuts, install plain washer, internal tooth washer and nut". No part numbers, or washer AN call-outs.. Eliminating the washers gains me an additional .062". The 22022 nut is .437" tall. My muffler flange thickness varies from .187" down to .167". I suspect they used .187" steel plate for the flange, welded it in place then ground to clean-up the surfaces, making sure both flanges were in the same plane. I checked the flanges on a surface plate (.003" out of flat), pretty good I think. Worse case without washers gets me to .750" (assuming the no-blow gasket crushed down to .125"). Just not sure about going without a lock washer. Is the steel outer shape of the no-blow designed to flex and act as a locking mechanism? or do brass nuts (potentially) not back off like the steel nuts? ( I know brass helps solve the corrosion issue & are longer to add back the strength) What ever insights you can provide is appreciated. Thanks,
Jim S

Not sure what to tell you. Those gaskets won't compress a noticeable amount.

O-200 cylinders use the same studs as all the other engines in the series.

Never had a problem with the brass nuts loosening up. The O-200 parts manual doesn't show any washers.

I will second that motion, the brass nuts will stay put. Kudos for switching to the no-blow gaskets the two wafer tin foil style are junk.

Thanks gentlemen ... blow-proof gaskets & nut without washers it is!

Jim S