I was replacing the spark plugs and went to put the upper intake manifold back on but haven’t been able to tighten to the torque requirement. I found a fix for the shorter bolts using a larger diameter bolt to rethread the plastic. The longer bolts are more of an issue as I can’t find anything similar in length. How can I repair these threads? Helicoil or brass inserts won’t work as the bolt size is weird. M5.74x1.81x135. Do I fill the hole with JB Weld, coat the bolt in Vaseline and then insert and let cure? Would rather not have to replace the lower intake manifold for this.
SCA55
Your 5.74mm bolt outer diameter is about .2259 inch diameter, the tap drill size for 1/4-28 is a #3 or .213 .
The 135 length is 5.314 inch. So you could use 1/4-28 socket head cap screw 5.5 inches long, available from McMaster Carr and most likely any other decent fastener supplier. May need to shorten slightly depending on if 5.5 will fit. Since the stripped diameter is likely .012 larger than the recommended tap drill size for 1/4-28 it isn't going to be full strength but it may get you by.
The other alternative is to fill the stripped holes with epoxy and redrill and tap. Tap may not be available handily for that size but you can dremel a cut flute on the bolt and it will self tap in epoxy. The drill size to tap drill on 60 degree thread for 75% engagement is generally major od minus pitch, ie m6x1 thread uses a 5mm drill or 1/4-28 = .25-1/28 = .214, #3 is closest at .213.
The 135 length is 5.314 inch. So you could use 1/4-28 socket head cap screw 5.5 inches long, available from McMaster Carr and most likely any other decent fastener supplier. May need to shorten slightly depending on if 5.5 will fit. Since the stripped diameter is likely .012 larger than the recommended tap drill size for 1/4-28 it isn't going to be full strength but it may get you by.
The other alternative is to fill the stripped holes with epoxy and redrill and tap. Tap may not be available handily for that size but you can dremel a cut flute on the bolt and it will self tap in epoxy. The drill size to tap drill on 60 degree thread for 75% engagement is generally major od minus pitch, ie m6x1 thread uses a 5mm drill or 1/4-28 = .25-1/28 = .214, #3 is closest at .213.
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