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Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: BobWitt ()
Date: April 19, 2017 04:19PM

So, the pulled 1/4 - 20 bolt holes in aluminum (pan bolt holes)... So that is a 1/4" (6.35mm) hole, right?


Drill for a M6x1 HeliCoil is 6.217 - 6.407mm before Tapping for HeliCoil...


So, can I skip drilling the 19 holes and simply tap for a M6x1 metric HeliCoil?


It would save a lot of time and reduce risk from hand drilling.


What do the experts here think??

BobWitt - South East Michigan
Member: Corsa and DACC

1966 Corsa 140 - Follow my build On CorvairForum


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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: cnicol ()
Date: April 19, 2017 04:26PM

Metric???

In my experience the 1/4-20 helicoil tap goes right into a stripped-out hole in aluminum without drilling. If you did want to chase the hole first, .2656" 17/64" 6.7mm

Craig N. Coeur d'Alene ID.
66 Black Monza 4dr, 4.2L V8 49k
61 Seamist Jade Rampside 140 PG
60 Monza coupe project
65 White 4-dr 110/AC/PG (parts)
66 Sprint Corsa convt - First car! Re-purchased 43 years later

+18 Tons of parts

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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: BobWitt ()
Date: April 19, 2017 04:35PM

Wow - thanks Craig! I was just writing an email to you to ask that you weigh in!

I value your knowledge and opinion. Will return to 1/4 - 20...

BobWitt - South East Michigan
Member: Corsa and DACC

1966 Corsa 140 - Follow my build On CorvairForum


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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: Frank DuVal ()
Date: April 19, 2017 08:02PM

I agree, 1/4-20 Helicoils tap in just fine. Grease the drill (and tap) if you are worried about chips. Gravity is in your favor, unless you turned the engine upside down!smiling bouncing smiley

Frank DuVal

Fredericksburg, VA

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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: Bob Helt ()
Date: April 19, 2017 09:15PM

Hi Bob, I like to do as good a repair as possible so I suggest that you use as much of the entire length of threaded hole as possible. Most of those pan bolt holes are 7/8" in length so why not insert two helicoils (end to end) in each hole and then use appropriate length bolts 7/8" in length?

That way it is highly unlikely they will ever pull out again.

Bob Helt

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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: texas yenko dude ()
Date: April 20, 2017 04:51AM

I like Time-Serts much better than Helicoils. I have never had one back out.

Texas YENKO Dude
YS-070
YS-199
YS-320
Southeast of Disorder


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Re: Pulled Oil Pan Bolt Threads - anyone go directly to a M6x1 HeliCoil?
Posted by: TexasAg77 ()
Date: April 20, 2017 12:17PM

Glad I saw this. One of the bolts for the right valve cover stripped out and I was pondering about the heli-coil need. As all the treads were not stripped, I put a longer bolt in for now, but want to fix the issue before it happens again. Not sure how it stripped originally as I have always been careful when tightening anything into 50 year old alum.

Really like this site just for this reason!

Ed McClintock
Cleveland TN
Choo Choo Corvairs
'61 Lakewood,,63 Vert, '83 Jeep CJ-8 Scrambler- [www.cj-8.com]

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