Question for Paul McBride, the General Aviation News engines expert: I have acquired a Lycoming O-290 in an experimental. The data plate has been removed. Is there anyway with a borescope to look in and see what pistons I have to know if it’s a D or a D2?
Paul’s Answer: I wish that it was that simple to determine what pistons are in your O-290 engine by using a borescope.
However, I think I can help you decide whether you have an O-290 or an O-290-D2.
I suggest that you simply remove one of the rocker box covers and determine whether your engine has solid tappets or hydraulic tappets.
The O-290-D2 uses hydraulic tappets, and the dry tappet clearance is determined by the length of the pushrod and there is no adjustment on the rocker arm.
The O-290 uses solid tappets, and the dry tappet clearance is obtained by adjusting the screw and nut on the rocker arm.
One more thing that came to mind is the fact that you said the data plate had been removed. After you’ve determined which specific engine model you have, be certain that the proper magneto timing is correct. The correct timing for the O-290 with the solid tappets is 25° BTC and the O-290-D2 is 18° BTC.
I think these simple suggestions I’ve offered should help you determine exactly which specific model of the O-290 series engine you have.
Note that there are 4 models of the O-290-D2, – D2A, -D2B, and -D2C, per the Lycoming Operators Manual Part No. 60297-9, type cert. 229.
The D2 and D2A have 7.50:1 compression and timing is 18Deg.
The D2B and D2C have 7.00:1 compression and timing is 25deg.
the Lycoming engine parts or OH manuals may show the mechanical differences.