Engine Baffling - 0 300

[N2782C]

Should there be any baffling in front of the # 5 and # 6 cylinders on a Continental C-145-2? Both of mine run about 250 degrees CHT in cruise when the other 4 are running around 330 degrees. I have new baffling on a less than 100 hour engine....bought it that way, and I can't remember seeing any aluminum in front of the cylinders 5 and 6. Looking at a Maule yesterday and it does have aluminum about half way up in front of the cylinders themselves as you look into the front of the engine (0-360).

[GAHorn]

None of the Cessna 170 models had baffles up the fronts of cyls 5/6. Later on, the C-172 incorporated such, and sometimes 170's are seen with the 172 installations that have these baffles (which are intended to help prevent so-called "shock" cooling and also improve down-flow cooling.)
According to the IPC manuals I have, the first 172's to have the front cylinders blanked was SN 36966, which, according to FAA data is a 1958 model. (This could actually be a 1959 model tho', in accordance with the FAA methods of determining such matters.)

[N2782C]

Thanks, George. I know that both the 5 and 6 cylinders are running cooler EGT's as well which would speak more to the intake manifold than anything else...in fact, they are sometimes 100-150 degrees cooler than the others. That could explain some of the low CHT's.

[N2782C]

Does anyone have these 172 baffles on their 170 and if so, do you notice any change in the CHT's of # 5 and 6 cylinders. Is it legal to put them on a C-170?

[GAHorn]

The O-300-C and D engines were installed on the 172's with those baffles, and when those installations have been transferred to 170's it's been common to keep the engine baffling as well. My O-300-C has them, but I do not have CHT on those cyls so I cannot offer any info on the matter.

(AR Dave has attempted to get Ron Massicot to give him a detailed list of the items which are not original on my airplane, and Ron didn't notice my baffles, so I was reluctant to mention it..... I didn't want to give them a "freebie".)

[hilltop170]

I have an O-300-D from a C-172.

CHTs Before front baffles, OAT 42°F;
316, 316, 298, 321, 238, 238

CHTs after front baffles, OAT 52°F;
328, 335, 335, 327, 287, 305

[N2782C]

Richard and George,

Thank you. I have always suspected that's what would happen. I'm off to find some 172/0-300 baffling for the front. Anybody got any ideas about where to find some or will I have to make it myself?

[GAHorn]

I have a concern about the change-of-effect of what type baffles you might be discarding. It might be simplest to just ADD some "L-shaped" baffles to the front of your existing. Examine other installations and don't try to place the new ones too high. You want the upper cylinder fins to "see" the incoming air. Also you want the exhaust-valve area of the N0.5 cylinder to receive direct cool air.

Be alert to the differences that can occur dependent upon CHT-probe types. The spark-plug-gasket types run significantly hotter indications than the bayonet types. This is because of where the temperature is sampled. (The spark plugs serve the purpose of transferring combustion chamber heat to the heads.... the bayonets do not. This is why some engine models have very different CHT limits. The O-300 engines max CHT being specified at 525-F is because of the mfr's original intent that spark plug gasket thermocouples would be prevalent on these engines. Replacement cylinders sometimes have provisions for bayonet types, and most engines that use that type have max CHT's specified at 400-450 F. Such differences are largely the result of CHT thermocouple type differences.)

[N2782C]

George,

Thanks for your thoughts. I have new ECI cylinders, less than 100 hrs., and they have the bayonet type thermocoouples. I also have new baffling on the engine as it was overhauled just a year ago or so. I will make up some "L" shaped aluminum pieces and probably try them out abut half way up the cylinders or possibly a shade less. None of the cylinders have hit the 400 degree mark as of yet even slow climbing the airplane in 90 degree wx....close, but not quite 400...normal in cruise is between 300-335 (2,4,1,3) and 245-260 (5,6), leaned out. The # 6 cylinder always runs about 100-150 cooler EGT than the rest of the cylinders. As I said before, that is probably just the 1940's design intake manifold. That would also explain, partially, the lower CHT on that cylinder. Normally a 50 degree difference in CHT's is fine with me but when they are over 100 degrees apart I start to wonder.

[hilltop170]

The following pictures were taken of an original installation on a C-172.

C172.cyl5.baffle.jpg.jpg

C172.cyl6.baffle.jpg.jpg

[N2782C]

Richard,

Thanks. I'll use this for a template. I'll also let you all know how this workds out. It'll be a couple of weeks at least, probably after the EAA Convention.