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2018/12/02 17:26:36

sneakyben

Stripped Aluminum Thread?

I had an oil leak at the valve cover gasket and was in a hurry to get it back together. I cross threaded the bolt and ran it in before I knew it. I looked up the bolt and it is called a self tapping bolt? Can I just go up a size with another self tapping bolt or do I need to buy Loctite thread maker or a helicoil? I mowed for the last time and was putting it up for winter so I have time. Just want to figure out what I'm looking at. Thanks for your help.suggestions! Ben

7 comments Leave a comment

AVB

What are you working on? Resizing may not be possible depending amount of area available. Even with helicoil there must enough area to oversize for the coil.

Either way you be going to a standard SAE or metric thread moving from self tapping.

2018/12/03 02:22:24

kshansen

A picture of the stripped hole would help get a better idea of what repair method would be best, but I would personally lean towards the Heili-coil type insert more than the Loctite Thread maker unless there is very little material around the damaged threads.

This is one reason I'm not fond of the use of self taping screws/bolts that some manufactures use to save a few pennies building things. I would be tempted to replace them with "normal" fasteners when ever they need to be removed. Even if it may mean using an actual tap to carefully clean up the threads in the hole.

2018/12/03 04:52:33

kshansen

Double post deleted

2018/12/03 04:52:46

sneakyben

I'm sorry.... I knew to add this when I started and just let it slip my mind. It is a TORO LX425 mower with a 20hp Kohler motor. It is a thru bolt. I have about 3/16" sticking out the other side.

2018/12/03 09:38:16

AVB

Okay had a little time to check couple scrape heads.

Briggs 280000, 310000, and 33000 series using 1/4-20 screw would need to be resized to 8-1.25. Drill out @.250 (1/4) then tapped. I would not recommend going to the 5/16-18 size; though, it will work just few threads per inch. (Tested)

Kohler using 6mm-1.00 would need to be resized to 7-1.00 Drill out @ .234 (15/64) then tapped. (Tested)

When tapping don't use oil or attempt to tap dry. Use rubbing alcohol as you lubricate and remove chips frequently. Otherwise the tap will stick and possibly break making a simple repair much worse. Trust me on this as I have broken several taps and ease outs over the years. Once tap is broken only carbide will cut it out. Even than the bits tend to drift into the softer metal.

You mention thread forming epoxy. I don't know if it will work or not as it has 300F temp limit and you must make the area is 100% oil free. Supposedly it will hold up to a little over 100 ft-lbs. Personally I don't have a lot confidence in epoxies when it comes structural holding power especially with the amount vibration these engines are subjected to.

2018/12/03 10:14:54

AVB

Okay that is a Courage engine. I see the screws are 6mm-1.00.

Hopefully you are deleting the cork gasket as they don't seal well and fail just any other cork gasket. If using RTV you remove all oil that that is present. Flatten any and all mounting screw holes in the cover. Apply the Permatex surface prep spray to both surfaces. Apply 1/16" bead and mount the cover finger tight then let sit overnight before torquing to specs; otherwise, the RTV will not hold.

Do not start the engine during this time or you will need repeat things. Oil prevents the RTV from setting.

2018/12/03 10:30:56

sneakyben

I did do away with the cork gasket. I did not use a prep spray though. Thanks for you advice!
Ben

2018/12/03 12:10:11

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Stripped Aluminum Thread?

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