Small crack around top motor mount bracket in head - Honda Rebel Forum
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post #1 of 4 Old 03-30-2019, 03:54 PM Thread Starter
Join Date: Dec 2012
Posts: 115
Small crack around top motor mount bracket in head

Planned to try epoxy but ended up using some hi temp Permatex RTV. Also inspection showed a fine crack on both sides of the mount. Could see a small crack on the inside of the head when I had the valve cover off, and was temped to apply something there but didnt. Its not a huge loss, but seems to be a mist that develops on the top of the motor case under the intake. Several questions here:

1 Thinking I'll try JB Weld next

2 Should I try to put any over the crack inside that valve cover?

This bike will rarely be used, so welding the head is not a top priority at this time, however, that could change. A local fellow had a small crack welded on his head while installed on the bike- any issues there?

George Penick
2004 Rebel 250
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post #2 of 4 Old 03-30-2019, 05:22 PM
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Location: Maine
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only welding will heal that wound - welding can be done on parts in place but for this part it would be better to take it off to weld inside and out

1985 Rebel 250 ... 2005 Ruckus 50
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post #3 of 4 Old 04-02-2019, 03:05 PM
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Location: Northern Virginia
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Depending on the location for "welding a part while mounted on the bike" could, I say could, put a nearby part at risk, specifically gaskets and seals.
Air-cooled engine seals have to deal with the oil around 250F up to almost 300F under most conditions.
welding creates spot heat of well over 3000F and can absolutely burn away a seal.
and the risk of any coating of oil on the inside igniting.

safer to unmount and clean the part to weld....

2009 Honda Rebel 250
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post #4 of 4 Old 04-04-2019, 04:35 PM
Join Date: Nov 2016
Location: Chandler, AZ
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I would definitely weld it. Or better yet replace the head. Aluminum has a crystalline structure, and once a crack starts, it doesn't stop (kind of like a crack in a windshield) You can weld both the outside and inside, and it will still be cracked in the middle. Vibration and heat will eventually cause the crack to come back. Heat causes the aluminum to expand, then it contracts when it cools. Every expansion/contraction cycle will make the crack worse. That's why I make such a big deal about warming up an aluminum engine as slowly as possible.

2016 Rebel, 2013 Royal Enfield B5, 2009 Genuine Stella, 2006 H-D Sportster 1200, 2006 Vespa GT200, 2001 Yamaha XT225
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