The International Cessna^® 170 Association

Anybody know the right size hole in these? I need to make one up. A pretty knowlegable friend said drill size #60 but that's pretty darn small.

I have looked at many of these fittings and have never measured the hole but that sounds about right. They are pretty darn small. I have had to remove a couple because of a blockage. The oil never gets changed in that line to the gauge. I have never done it but I have heard of people filling the line to the gauge from the orifice with Kerosene. I have had the oil in the lines get so old that it caused gage reading issues and slow reading.

Regards,

Jim

According to George McKinney Sr of AirParts instrument shop, the line should be filled with air. According to Cessna...kerosene. I think either would be fine but Mr. McKinney is technically correct.

"...remove the line from back of the gauge and at the engine. Blow the line out (from the instrument panel to the engine if not you will have oil all over the inside of your a/c) using shop air no more than 100 psi. Then run MEK or Natpha down the line to remove any left over oil. At this point you can put the line back on the gauge and at the engine. Make shore (sic) the line is tight. This Gauge was made to work off a column of air. With the oil in the line the bellows in side the gauge can't push the oil back down the line. Oil in the line will also show low press til the engine heats the oil up (in) the line and thins it out... then it seems to work right for the rest of that flight till the next flight then it starts all over. In the winter months you will see more of this sticking. "


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Thanks Guys. I'll probably go with the #60 then. I have never "filled" the oil line to the gauge but it seems every one I remove is full of oil. Sometime if I get bored in a year or so I'll remove it and see if it's still filled with air

This is why I'm still hanging out even though I'm now a 180 owner. These forums are great. Plus I still have a years worth of dues to work off.

I am contemplating a proposal to the Board that any Member who has sold their 170 for a larger airplane be assessed higher dues.

Dave for some reason I happen to keep one of these restricter fittings next to my keyboard at the computer.

Unfortunately I don't have any number drills to measure the hole precisely but a very close measure with piece of music wire and caliper is .04 or 1/32". The wire is a loose fit but I'd feel comfortable using a 1/32 hole.

BTW the hole for the C-65 is a different size but can't remember larger or smaller at least the one I have for my Cub.

I don't think it's critical and should be the smallest hole that allows proper gauge response.

And George, guys with time and money to polish their Red/Natural planes should pay more.

I would guess that a number 60 hole would be about right. If the hole is too big, it will cause occilations in the gage.

In the Air Force in Alaska we modified all the airplanes with a bleeder valve on the face of the instrument panel connected to the oil pressure line on the back of the instrument. About every three or four days in the winter we back bled the lines with kerosene to keep them from congealing.

A #60 drill is .0400"dia.

1/32" is .03125"

Ultimately the truth comes out. We have corroborated evidence now that will make me sleep like a baby. As long as I have that correct hole size nothing can go wrong go wrong go wrong......

Higher DUES? Dang it George I thought we were done on that subject

hilltop170 wrote:A #60 drill is .0400"dia.

1/32" is .03125"

There you go. I'd favor 1/32 over .04 or #60 based on my crude measurements of my restrictor.