Will this replacement camshaft work in my engine?

Q: I have an O-290-D2 that I am going to use in an Experimental Wag Aero 2+2 that I am building. Although the engine was flying regularly before I removed it from a Pacer and pickled it, I want to open it up to look at the cam. If the cam is pitted, a replacement will be difficult or prohibitively expensive.

My understanding is that a Lycoming 76097 cam will fit if the accessory case is modified by removing the “cup” in the mounting area and using a new tac drive from an O-320. Any idea if this will work in the O-290D2 for an experimental?

Thanks,

MARTY FEEHAN, via email

 A: Marty, I found your email interesting, even if it did cause me some concern. I’m not sure where you heard the Lycoming camshaft part number 76097 camshaft will fit in your O-290-D2 engine. It may be true that this camshaft will fit in the crankcase, but that’s about as far as I’d want to go. I’d be hard pressed to say that it would function properly and I wouldn’t be willing to go any farther. There is a huge difference between something “fitting” and “functioning” properly.

Without doing some direct comparison using the engineering drawings, I’d never suggest just jumping into something like this even though the cam will probably “fit” in the crankcase. There is much more than just fit that has to be taken into consideration here. Who knows, without doing some serious research, that the camshaft lift and duration are the same as the original O-290-D2 camshaft?

According to the information I have available, the latest camshaft for use in the O-290-D2 is Lycoming part number 76094. Is there a possibility that your information source got the two numbers confused since 76097 is quite close to 76094? Remember, just like playing horseshoes — close doesn’t count!

Here’s an example of what can happen when things like camshafts are changed on an O-290-D2 engine. Several years ago several people complained that following field overhaul their O-290-D2 was throwing oil out the breather by what seemed to be by the quart. After checking into what parts were replaced during the overhaul we discovered that the camshaft was replaced during the overhaul by a different part number. In those days the correct camshaft for the O-290-D2 engine was a different part number than the camshaft used in the other O-290 series Lycoming engines. Because the other 290 series camshafts “fit” in the O-290-D2 engine, the overhaulers thought they could just use that camshaft in the D2 series — wrong! It just so happens that the camshaft used for the the other O-290 series engines was .19 inches longer than the camshaft used in the O-290-D2 engine model. Believe it or not, that small increase in length between the different models of the O-290 was the cause of the excessive oil being thrown out the breather. Since the 290-D2 has the front breather, what was happening was the additional length of the incorrect camshaft was causing the camshaft to act like an oil slinger and was throwing the oil right out the breather. You can imagine this does not bode well for a nice clean aircraft — even though corrosion would never be a problem, but we don’t want to go there, do we!

Sadly, the only fix for this situation was a complete engine teardown and a cam replacement using the correct part number camshaft. For the owner who probably struggled financially to have the engine overhauled in the first place, this may have meant giving up the aircraft all together or going in debt even deeper to correct the situation.

Marty, now that I’ve tortured you with all of the above in hopes it may help others in your situation or those who may have excessive oil coming out the breather so they can verify they have the correct camshaft installed, I’ll tell you this: I’ve saved the best for last. If you’ll get a copy of Lycoming Service Instruction 1218A dated Oct. 1, 1982, titled: “Parts Substitution Charts for Camshaft with Integral Drive Gear — Direct Drive Series Engines” I think you’ll be able to move forward.

Let’s hope you find the camshaft in your engine to be OK and no further action is required. If cam replacement is necessary and the price of a factory camshaft is out of reach for you, you might want to check some of the reputable engine overhaul shops and see if you can locate a good “used serviceable” 76094 camshaft.

Good luck with your project. I have a feeling all will work out for you.

Paul McBride, an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: [email protected].

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