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Registered
Join Date: Sep 2003
Location: Minneapolis, MN
Posts: 670
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Flywheel to camshaft bolt hole question
As I went to reinstall my flywheel last night on my early-911 6-bolt crank I noticed the last flywheel bolt didn't thread smoothly beyond the first couple of turns. I knew better to force the matter and removed the bolt versus muscling it in.
Naturally I don't want to damage the crank threads. My plan is to chase the hole with the proper tap to clean it up. Any reason why I shouldn't do this? |
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03-12-2020, 06:39 AM
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It's a 914 ...
Join Date: Jan 2008
Location: Ossining, NY
Posts: 4,715
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Get a thread chaser, which is different than a tap. You don't want to risk cuting any more than necessary.
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03-12-2020, 10:47 AM
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Registered
Join Date: May 2004
Location: Boulder, Colorado
Posts: 7,275
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Maybe try looking into the hole on the end of the crank. One of those little LED lights on the end of a flexible wire would fit in to give you good illumination. Someone may have used Loctite, or somehow some oil or something coked in there. You might be able to clean the threads with dental picks or the like. Because it is a bit hard to imagine how this one hole got its threads buggered up. Was one harder to remove? I suppose at some time the flywheel was removed, and cross threading occurred on the reinstall, but that seems kind of unlikely to me - they are fine threads, hard to imagine anyone trying to use a different threaded 12mm bolt, if one even exists with the shallow 12 point inhex head.
You can (in theory) make your own thread chaser. Take a sacrificial bolt, and cut lengthwise slots in its threads. They don't have to go the whole length of the thread, as the tip area is the most important. However, cutting slots in metric hardness 12 bolts can't be easy. Easy enough with, say, a spark plug. Maybe not with these. |
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03-15-2020, 12:06 AM
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Join Date: Jul 2000
Location: So. Calif.
Posts: 19,910
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Agree with Walt. Use a thin (e.g. 0.040”) cutoff wheel to create 2-3 kerfs along the length of your DIY thread chaser. Remove kerf burrs with a wire brush/wheel. The kerf slots will collect burrs, grit, etc. to achieve proper thread rotation. Use a light lube, penetrating or cutting fluid.
Sherwood |
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03-18-2020, 12:49 PM
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Registered
Join Date: Sep 2003
Location: Minneapolis, MN
Posts: 670
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The problem was residual loctite buildup from the last mechanic who installed the FW apparently. Careful work with a thread chaser got the job done and the new flywheel is now installed. Thanks all for the input.
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03-18-2020, 01:51 PM
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