[NSRCA-discussion] YS discussion, add pushrod o-rings to your list of things to check

[Bob Kane]

One of the things that I found on my YS160DZ right after the NATS this year was the o-rings that support/seal the fuel pump and exhaust pushrod cover were worn and leaking.  This area is under supercharging pressure (see last paragraph) and needs a good seal or a variety of issues can arise.  In my case, there was an unusual amount of oil residue inside the cowl and blowing back on the fusealge. The engine was also flat in the midrange, but the idle and high-end were good.  Prior to the NATS I did a partial rebuild and replaced the bearings, front seal, and piston ring under the assumption the front seal was bad. The problem continued. It was after the NATS that I discovered the worn o-rings. I replaced them and the leaking stopped. The midrange issue was resolved also

This past weekend another person's 170DZ started acting up.  There was also evidence of an oily leak. He did not have replacement o-rings but turned them around so the pump was sititng on a fresh surface.  This seems to have cleared the leak and the engine ran good but other parts were replaced so the source of the original problem may remain unknown.

So, my recommendation is you replace the pushrod o-rings every season on these engines. It is a quick job and you can do it without removing the engine from the plane.  I never had this issue with the pre-DZ series of engines, the added mass of the fuel pump causes them to wear out.

Last paragraph:

For those of you who study YS parts diagrams, you will notice the front crank seal was introduced on the YS120SC.  It was on this engine that YS drilled holes around the valve stem boss to utilize the area under the valve cover as an air chamber and allow them to remove the bulky aluminum box between the carb and head as on the "AC" series. This was a very efficient way of storing the pressurized air without extra parts, but made it necessary to seal every opening from the valve cover forward. So, the pushrod covers, cam cover, and crankshaft all require good seals.

 Bob Kane
getterflash at yahoo.com