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Aug 09, 2019, 04:13 PM
Grumpa Tom
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Customized Merco .61 Mk. I

I did not know much about Merco engines, except that I recalled the brand name from being in the hobby all of my adult life. I did not even know that they were made in England. Until recently, that is.

I had been thinking of getting a Merco, mostly because it seemed to be a somewhat obscure brand of engine and I wanted one for my collection. How wrong I was! Thanks to the website Sceptre Flight, which has dozens of old engine reviews from the long gone print magazines, I learned just how much the Merco was revered back in the day, and what a world champion caliber competition engine it really was.

But before I had read any of those old articles, I had purchased from the RCG classifieds, a well used and castor oil coated Merco .61 Mark I. I intended to tear it down, and rebuild it.

This particular engine was frozen solid like a rock! The old, dried castor oil had welded every part to each other. It took copious amounts of heat to get anything to loosen up so that I could disassemble something as simple as the back plate. To get the cylinder out I had to machine a drift from bronze, and use a lead hammer while wearing thick leather gloves to protect my hands from the searing heat due to having to super heat the crankcase to loosen up the burnt on, dried out castor oil residue.

Once I had the engine completely disassembled, I soaked the parts in an ultrasonic cleaner with a diluted cleaner concentrate. That took care of most of the old castor oil but some of the parts needed further and more aggressive treatment, such as 24 hours in carb cleaner, and mechanically scraping it off.

Since this is a British engine, I thought that painting the crankcase British Racing Green would be appropriate. Other parts I polished. I replaced most of the worn out and rounded out Phillips head screws with stainless steel socket head screws.

This engine is constructed unusual, compared to most of the American, European, and Asian engines I have rebuilt. The crankcase is in two parts. The upper part is a machined and finned cylinder cover. Another oddity is how the connecting rod is removed and installed. The piston and piston pin must be removed first. Typically, on other engines, once you have removed the liner you can remove the piston and rod together as a unit.

So it is all cleaned, painted, and polished. Ready for a test run on my PSP engine stand.
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Aug 12, 2019, 06:19 PM
Grumpa Tom
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This engine had a clamp on muffler when I got it, but it originally had an exhaust baffle plate linked to the carb lever. So I made one today and got it installed.
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