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I have a 2011 BigRed (MUV700). I've had it for a couple of years and have totally rebuilt the engine about a year ago. Apologies for the long post. I like to be as thorough as possible.
*Issue Summary*
Turn the key and the starter turns, but then locks up at full compression. Starter can't push it past the compression stroke. Mess around with it long enough and you'll strip the starter gear teeth as the starter TRIES to turn the engine over but fails.
*Build-up*
I've recently been trying to chase down a coolant leak that started (and appears to be internal; nothing leaking externally). It's also had a hard-start issue (another thread on that) where you have to give it gas and crank it for quite a while. Well, one of the last starts ended in a catastrophic failure for the starter. It backfired and then the starter would no longer engage. It would spin, but not the engine. Pulled the starter, and yep, the gear teeth on the start stripped.
So while I was waiting on a new starter, I stripped down the top-end to see if there were any signs of an internal water leak. Pulled the head cover and cylinder head to check. Having found no obvious issues there, I turned the engine over to TDC on the compression stroke, rechecked timing (which was good), replaced the gaskets, bolted it back up, and re-set the valve clearances. Afterwards I did an oil/filter change (because of the stripped gear teeth, had to make sure no metal in the oil; which there wasn't) and refilled the coolant.
*Problem Presents Itself*
I found a backup starter that I forgot I had so I bolted it in. I hooked up the compression gauge to make sure that was still good. Initially, the starter turned the engine over enough to get about 100psi. I always check compression 3 times and take the average. On the second turn, the starter turned the engine over once, but then stopped at the compression stroke. Compression test only got up to 70psi (because the engine couldn't turn over more than once). Given that the first test seemed ok and based on how it sounded, I thought I had a weak battery so I put it on the charger. Let it charge to 100% (and still hooked up) and then I tried a third time. This time the starter wouldn't crank it over past the compression stroke at all. It "locked up" at peak compression the first time around. I checked the battery and the ground and then, like the idiot I am, I kept trying. Eventually, I was too aggressive trying to get it to turn and the starter stripped its teeth.
The new starter arrived so I went back to it. I changed the oil again before bolting it up. Exact same symptoms as the above paragraph. Not wanting to chew up another new starter, I stopped there. I pulled the compression tester and turned the key. Starter quickly turns the engine over all day long as long as the plug is out. Engine is not locked up or bound up; it turns as I would expect it to through the crank access cover. Removed the valve covers and the valves operate as I expect them to. I pulled out the starter and had a helper turn the engine over while I felt inside of the starter hole. Starting gear doesn't feel damaged at all and the clutch seems to operate as it should. Both turn by hand and seem to operate as they should.
*What Could It Be?*
I am 90%+ sure that I set the valve clearances at TDC on the compression stroke. I've done that enough to know the process. When I set the valve clearances, I did err on the larger side (thinking maybe the valve clearances were too tight, thus causing the hard-start issue). Still, I don't believe the valve clearances would have anything to do with this issue, right?
The ONLY thing I can realistically think of this being is a failed decompressor on the camshaft (I've had that happen before). The lobes on the cam were still fine and I didn't touch the cam at all when I had the head off so I don't know why the decompressor would all of a sudden fail; unless it was already on its way out when we had the very first start issue previously alluded to. The cam was replaced when the engine was rebuilt last year so it's only a year old with probably under 100 hours on it.
Before I go down the route of buying another new camshaft, can anyone think of any other reason why the engine apparently has too much compression for the starter to turn it over?
*Issue Summary*
Turn the key and the starter turns, but then locks up at full compression. Starter can't push it past the compression stroke. Mess around with it long enough and you'll strip the starter gear teeth as the starter TRIES to turn the engine over but fails.
*Build-up*
I've recently been trying to chase down a coolant leak that started (and appears to be internal; nothing leaking externally). It's also had a hard-start issue (another thread on that) where you have to give it gas and crank it for quite a while. Well, one of the last starts ended in a catastrophic failure for the starter. It backfired and then the starter would no longer engage. It would spin, but not the engine. Pulled the starter, and yep, the gear teeth on the start stripped.
So while I was waiting on a new starter, I stripped down the top-end to see if there were any signs of an internal water leak. Pulled the head cover and cylinder head to check. Having found no obvious issues there, I turned the engine over to TDC on the compression stroke, rechecked timing (which was good), replaced the gaskets, bolted it back up, and re-set the valve clearances. Afterwards I did an oil/filter change (because of the stripped gear teeth, had to make sure no metal in the oil; which there wasn't) and refilled the coolant.
*Problem Presents Itself*
I found a backup starter that I forgot I had so I bolted it in. I hooked up the compression gauge to make sure that was still good. Initially, the starter turned the engine over enough to get about 100psi. I always check compression 3 times and take the average. On the second turn, the starter turned the engine over once, but then stopped at the compression stroke. Compression test only got up to 70psi (because the engine couldn't turn over more than once). Given that the first test seemed ok and based on how it sounded, I thought I had a weak battery so I put it on the charger. Let it charge to 100% (and still hooked up) and then I tried a third time. This time the starter wouldn't crank it over past the compression stroke at all. It "locked up" at peak compression the first time around. I checked the battery and the ground and then, like the idiot I am, I kept trying. Eventually, I was too aggressive trying to get it to turn and the starter stripped its teeth.
The new starter arrived so I went back to it. I changed the oil again before bolting it up. Exact same symptoms as the above paragraph. Not wanting to chew up another new starter, I stopped there. I pulled the compression tester and turned the key. Starter quickly turns the engine over all day long as long as the plug is out. Engine is not locked up or bound up; it turns as I would expect it to through the crank access cover. Removed the valve covers and the valves operate as I expect them to. I pulled out the starter and had a helper turn the engine over while I felt inside of the starter hole. Starting gear doesn't feel damaged at all and the clutch seems to operate as it should. Both turn by hand and seem to operate as they should.
*What Could It Be?*
I am 90%+ sure that I set the valve clearances at TDC on the compression stroke. I've done that enough to know the process. When I set the valve clearances, I did err on the larger side (thinking maybe the valve clearances were too tight, thus causing the hard-start issue). Still, I don't believe the valve clearances would have anything to do with this issue, right?
The ONLY thing I can realistically think of this being is a failed decompressor on the camshaft (I've had that happen before). The lobes on the cam were still fine and I didn't touch the cam at all when I had the head off so I don't know why the decompressor would all of a sudden fail; unless it was already on its way out when we had the very first start issue previously alluded to. The cam was replaced when the engine was rebuilt last year so it's only a year old with probably under 100 hours on it.
Before I go down the route of buying another new camshaft, can anyone think of any other reason why the engine apparently has too much compression for the starter to turn it over?
