08-02-2014, 11:35 PM #1
XLT 1200 rebuilt, newley rebuilt won't turn over by hand!
Short version, I am in process of rebuilding the top end my XLT 1200. For the job I am using re-plated cylinders (core swap), with new PRO-X pistons and rings. Everything went together no problems, then pressure tested the casing, 7psi bleed down to 5psi over 1hr. After the test was complete, but before putting the engine back into the hull I randomly decided to rotate shaft by hand seemed like a good idea.
Unfortunately the shaft will only rotate 1.5 rotations before coming to a hard stop in both directions. Is this normal? The head was off while doing this test. I pulled every cylinder individually and had the same problem. When I removed all 3 cylinders the shaft rotated freely. I don't understand. I even tried holding the reed valves open in case there was reverse compression into the casing.
I marked the shaft to confirm the number of rotations, and the shaft stops at the same point each time. As I watch the shaft rotate each piston moves from TDC to BDC. The shaft only comes to a hard stop when Piston #1 is just past TDC, and Piston #3 is about to cover the exhaust port.
The PRO-X pistons have an anti rotation pin for the rings on the inlet port side of the piston/ cylinder. This is also the location of the ring gap. Could a ring be slipping out of the groove, and be getting caught on the ports?
The reason for the rebuild is the #3 piston decided to commit suicide. Apparently the piston should run inside the cylinder not outside.
Any information would be helpful. I don't want to install the unit till I know it is safe to run.
08-03-2014, 10:24 AM #2
- Join Date
- May 2014
If the spark plugs are in it gona hit compression , so it will stop and take a lot more force to turn try taking plugs out it will then rotate free if not you have a problem disassemble it
08-03-2014, 10:28 AM #3
- Join Date
- May 2014
If the spark plugs are in it gona hit compression , so it will stop and take a lot more force to turn try taking plugs out it will then rotate free if not you have a problem disassemble it also check powervalves be sure they are clearing
08-03-2014, 07:25 PM #4
The plugs are out, and the head is off. I watched shaft go through 1 complete rotation, and each piston goes up and down full stroke. Till it stops. I pulled all the cylinders, and found no material in the crank case. As I pulled the cylinders 1 by 1 the shaft still stopped at same points. It wasn't till all 3 cylinders were removed did the unit rotate freely. I am at a loss. If it would not complete 1 full rotation that would be different.
08-04-2014, 06:19 AM #5
- Join Date
- Aug 2006
Hand cycle the power-valves open to see if a piston is hitting one. In the first section you mentioned a top end rebuild, however the picture shows a rod thru the side of the crank case. You also stated this does it even when each cyl is removed independently, but not when all three are off?
08-04-2014, 11:19 PM #6
With power valves cycled the shaft still only rotates 1.5 rotations. Something is internally hitting a hard mechanical stop. The confusing part is as the shaft rotates I hear no scraping, and the shaft rotates through the stopping point before it always stops in the same position. So I am fully miffed about what to do, or the cause.
08-06-2014, 10:58 AM #7
Found the problem, one of the alignment pins was in the crank case of the #3 cylinder. The pin would push between the wall of the casing, and the connecting rod stopping the rotation of the shaft. As simple as it was it took forever to find. Thanks for all the suggestions above.
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