blast tubes

[simatos]

Where do you guys direct the blast tubes that are mounted on the back of the large rear engine baffle. In the IPC the left one seems to be pointed at the oil screen area on the bottom of the accessory pad. On the right as I have the transverse mounted started ( WHICH ACTUALLY STARTED THE ENGINE FOR THE FIRST TIME LAST WEEK--Yahoo) there doesn't seem to be a natural place to mount it and what would it cool. I have had the appropriate "what to do "conference at the airport coffee shop and giuys say cooling to vaccuum pump and the alternator are both good things to set up. any ideas Thanks G

[cessna170bdriver]

On my '55 B-model, both blast tubes are directed toward the oil screen area, specifically the oil temperature probe. Some folks maintain that this only cools the probe itself, but I fail to see how it could cool the probe without also cooling the moving stream of oil it's immersed in.

I've never paid enough attention to O-300D installations to remember if the right angle starter interferes with the blast tube or not, but I'm sure someone here will let you know.

When I added a Jasco (Skytronics) alternator in 1990, the installation instructions required a cooling duct, so I added a scat hose adapter to the big rear baffle on the right side of the engine. I'm not positive of the size, but it's the same as the hose adapter on the alternator. Knock on wood, but the alternator is still humming along happily after 15 years and 1000+ hours of service on two different engines.

Hope this helps,
Miles

[Joe Moilanen]

I've got a 0-300D also and will check next time I go to the airport. I'm almost positive that it goes to the generator.

Joe

[jlwild]

Simantos, I have a newly installed O-300D in my "55 C-170 B. The engine has the side mounted starter and a Jasco alternator. Both blast tubes are installed and directed to the oil temperature bulb/oil screen area. The tubes discharge cooling air to the same location as on the the prior installed O-300. The right side blast tube (co-pilot side) was relocated, by my mechanic, on the back of the engine baffling to avoid the starter, etc. and still direct air to the oil screen area. The mechanic took great care to make sure the blast tube was positioned correctly, i.e. air exit location, and number of inches from oil screen, etc.

The alternator, as required, also has scat tube cooling installed from the left side of the rear baffling.

Can send a digital photo of installation if you PM me your email address.

[GAHorn]

Yep, aim the blast tubes both at the oil screen area. The Cont. engine specifies the oil "inlet" temperature at 240 degrees F (with straight wt SAE 50 or 100W) oil (supercedes the old 225-F spec). That means the Inlet of the oil pump ...which is the screen. That's why the blast tubes cool the oil in the screen. (Old wives tale is that it simply fools the probe....which is incorrect. It is actually cooling the lower sump/accy case at the oil screen/pump inlet.)
Any additional cooling requirements of the generator/alternator should be provided separately.

[DuaneShockey]

Where do you guys direct the blast tubes that are mounted on the back of the large rear engine baffle. In the IPC the left one seems to be pointed at the oil screen area on the bottom of the accessory pad. On the right as I have the transverse mounted started ( WHICH ACTUALLY STARTED THE ENGINE FOR THE FIRST TIME LAST WEEK--Yahoo) there doesn't seem to be a natural place to mount it and what would it cool. I have had the appropriate "what to do "conference at the airport coffee shop and giuys say cooling to vaccuum pump and the alternator are both good things to set up. any ideas Thanks G

George, My blast tubes both aim at the temp sensing bulb area. My 3rd one is for the alternator, per the STC Duane Shockey

[GAHorn]

Yep, Duane, that's exactly as intended and as I was pointing out. The oil temp bulb resides within the oil screen. (Although some versions of the El Reno filter STC reportedly have the blast tubes re-aligned to point at the adaptor...which in fact becomes an extension of the oil -screen/temp-bulb area.)