Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

harrylarson

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May 7, 2011
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27
Rebuilding '78 Johnson, 150 hp, cylinder head bolt hole is stripped. I've read through several threads most recommend a Helicoil. What I don't understand is if I have to retap for Helicoil why not just retap for a larger bolt and thread? I'd rather trust a machine shop to do it but I have it almost completely reassembled and it would be tough to transport it.
 

JB

Honorary Moderator Emeritus
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Mar 25, 2001
Messages
45,907
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

I had a similar problem with a Honda bike head. Drilled and tapped for a bigger (stronger) bolt. Worked very well.
 

Capt Ken

Commander
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Jul 30, 2002
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2,269
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

You may not have enough meat to drill for a larger bolt. The bolt you stripped the threads on is a 5/16. You would have to go to 3/8 and depending on which hole it is, you chance cracking into a cooling gallery. Heli coil is the easiest Method.
 

F_R

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Jul 7, 2006
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28,195
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

Do whatever you want, but I wouldn't even consider the larger bolt. Heli Coil it.
 

1946Zephyr

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Oct 21, 2008
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5,556
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

Whether you heli-coil it, or not, you will be cutting the hole out bigger. I would follow F_R's advice though and heli-coil it, because you will have steel threads to bolt into, versus aluminum.
 

boobie

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Nov 5, 2009
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20,826
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

A heli-coil is actually stronger than the orginal threads. Go with that.
 

kenmyfam

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Aug 10, 2006
Messages
14,385
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

Agree. Helicoil. Then you get to use the same size bolt (body diameter) so there should be no interference issues.
 

Faztbullet

Supreme Mariner
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Mar 2, 2008
Messages
15,589
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

Use a keensert as it the strongest and will handle full torque...
 

harrylarson

Cadet
Joined
May 7, 2011
Messages
27
Re: Stripped Cylinder Head Bolt Hole, Helicoil or Larger Bolt

Thanks all! The threads in another hole looked bad also, today I put a Helicoil in both. It was easier than I thought. Installed gaskets, heads, and torqued to 20 ft lbs as specified in manual. Awesome! Thanks again.
 
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