New to me P337 - Is this a problem?
 

Hi,

I have a '73 Riley Rocket and seem to have an issue with the Rear engine.

In cruise anywhere up to around 15k, the rear engine CHT is more or less on the top limit, thus I need to keep the fuel flow rather hi and in some conditions need to pull the MP back.

At the same MP as the front, I'm having to use an extra few lb per min to keep the rear CHT in the green, and eventually I have to reduce MP on the rear.

The front seems limited by EGT not CHT, but the rear hits high CHT far earlier.

Is this normal? And if not, where would you suggest we look first?

Baffling.

(It's a comment and an answer.)

What are you using for engine instrumentation?

If you have a recording engine monitor, now would be a great time to pull the data from both engines and analyze the situation.

Curious, what MP, RPM, & fuel flow are you running on the front, and are the cowl flaps open at all?

An example of the settings before adding fuel to rear to cool are:

RPM both 2460, MP 30 both, FF 85lbph both, Front CHT ~375, Rear 400.

Even cracking the cowl flaps is costing around 8kts, and as we are getting ready to ferry trans Pacific, 8kts makes a bigger difference than an extra few gph.

All the baffles look to be in their correct places, and a 337 experienced A&P said they are fine, but he also said that this is normal.

My reading of the forums and your responses suggest it's atypical.

Re the type of monitoring, temps are via the original gauges, and she has E.I. Graphic Engine Monitors and a Shadin FF.

Pull the data and upload it to Savvy aviation so you can check your data.

On mine, the factory analog gauge always reads near the red-line on the rear while the front is in the green, yet the JPI digital shows the temps to be very close. I can usually run my rear 1-2 GPH richer than the front and achieve similar temps.

Rear engine running hotter is a common tale among Skymasters. I've read that if you get the rear baffling right, the rear engine can actually run cooler than the front, but I've yet to see it.

I'm told our plane had a similar problem years ago and the A&P spent a significant amount of time on the baffling and plugging holes (i.e. spark plug wires, etc.) that let air bypass the cylinder cooling fins. And after he was finished the rear ran as cool or cooler than the front at cruise.

Thanks to all.

A combination of long delays getting a simple avionics upgrade finished, and a subsequently bored and grounded company pilot who is also a mechanic seems to have fixed the problem.

A few days spent aligning and plugging all baffles seems to have done the job.