Hi Dave,

The fact the piston and liner are aluminum/chrome is no surprise as it is the most used combination for piston engines, from RC to full scale aircraft piston engines, but backwards, where the piston is steel; An aluminum body is easier to manufacture and it is lighter, but I do think the grooves in the piston might be all that was needed to solve the situation you had, how many flights did you have on that pump? 600+?

I fully agree with you about the oil, I still run 23% oil and never had problems, but no Castor, castor in this pumps is a killer if you let the engine sit for a while, my engine was in a bag for over a year, and the old fuel stained the piston, now that I took the pump apart to take a picture for you is when I realized if I want to store this engines, it is better to take the pump apart completely, clean it and lube with a light oil. Personally a have been using 3 in 1 since I was a kid and started on Rc with great results. What do you think?

The 185 is identical to the 170 and it's predecessors, exact same dimensions and physical appearance, the only way to tell which is the 185 is on the pump, the reference pressure hose it is not used anymore, look at the picture I previously attached, apart from that, like with previous models it is a bolt on replacement.

Best regards

Alejandro