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Nylon rope, with the ends melted to avoid fraying. Not cotton rope.
I'm going to estimate that I'm the veteran of well over 200 engine dis-assemblies using this old-timer's short cut. I learned it from a technician who did engine development at the Ford Dearborn plant for thirty years. He retired in 1996 and said techs were still using it. He learned it from his father before him, who had been using it since the 30s.
Probably half of my dis-assemblies or better are Volvo red blocks... with the rope trick. In fact I'm probably the guy that first said "rope trick" instead of rope method--all those years ago here on the BB--and got some pretty hefty ribbing for the negative implication. Over those same years I've had two people write me to say they had bad results. In one case it was determined that the user did not have the engine on compression stroke and bent a valve due to a misunderstanding of the term "top dead center". The second problem involved a crank bolt so frozen that the user put a jack handle on the breaker bar and somehow managed to bounce his full weight on the bar...before things broke.
Is it possible to get things so lopsided in the combustion chamber that something is strained? I suppose so. The beauty of the rope is that it compresses gradually, as the torque on the crank bolt gradually releases the balancer. I can certainly imagine someone running the piston up against the rope and then bouncing on the breaker bar so hard that a slightly cocked piston could be compromised or a rod bent. I think that would take an incredibly ham-fisted (or footed) jerk on the bar though.
Maybe it's time for a detailed review post of how the rope trick is done. Unlike our magical friends' display on stage, there is no smoke and mirrors sleight of hand involved in having this procedure provide reliable results.
DS
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