'59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

Gr8ham

Seaman Apprentice
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Aug 3, 2003
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39
I've been working on a '59 Lark and a while back sheared a head bolt almost level with the block.

I got a centre punch, drilled it out and ended up slightly off to one side, taking about 1/3 of the original threads with it and leaving a firmly stuck section of bolt in place. Tried prying with sharp objects and eventually managed to use a drillbit to shave off enough to let me work loose what was left of the old bolt.

However, it has left me with a hole that is rather sloppy at the top but with (what I think) are some well-gripping threads at the bottom.

Since this bolt hole is separated from the cylinders by the water chambers am I right in thinking it will not get into the temperature range where JB Weld would fail if I filled the gaps around the top of the bolt with that? Will the head gasket seat correctly and not leak?

Should I just bite the bullet and take it to my local marine shop where they can drill it out and install a helicoil for $80?

Is there another workable option? Could I drill a larger hole, insert a threaded rod and drill and retap that (something like a home-made helicoil)?

This revitalisation project is becoming a rather expensive learning experience! Still fun though.

Thanks for any thoughts.
 

HighTrim

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Jun 21, 2007
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10,486
Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

There are some incredibly strong epoxy's/fillers available, JB Weld being one of them.

I have filled the hole with a product similar to JB Weld, I cannot remember the brand off hand but will look it up, and while still wet, tapped the the JB Weld, then left to harden. Once hard, I was able to successfully torque my head bolt again, without stripping the repair.

The problem with a repair like you mentioned with the threaded rod, is if you make a mistake drilling/tapping into the rod, well then you have a big mess to deal with right? Not to say it would not work if you took your time, but there is a bigger chance of a mistake.

You can get a welder to fill the hole, and then drill/tap but you will likely be up around the $80 mark that the marina would charge you to install a heli coil.

I would personally try filling the hole with a quality epoxy, drill and tap it. Worst case scenario you are back to where you were without spending any money, best case scenario your job is done.

Just my 2 cents.
 

HighTrim

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

...another option would be to use the spare powerhead I gave you and do a full restoration! :)
 

boobie

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

I'll still stick with the heli-coils. There're stronger than the orginial thread.
 

Gr8ham

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

Sounds like a good plan!

Haha! And the only reason I thought I would try this myself is that I know I have the spare as a back up if I royally *%^ it up!

Another consideration was the serial number tag on the top of the block. If at all possible I'd like to keep the numbers matching and don't see a way to swap those... Have you ever done that?
 

HighTrim

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

They are easy to swap, just plugs.
 

Gr8ham

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

Really? How do you get them out then? Is there a straight shaft somewhere inside that they can be tapped out/tapped back in? I don't recall seeing that covered in the Service Manual!
 

HighTrim

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

Welllll, not really supposed to do it I imagine, thats why you will never see it in the service manual. Usually when serial numbers are missing/swapped you think HOT engine. I had a guy try to sell me a newer motor with all serial numbers/model number tags removed once, I discreetly called the police. I think its disgusting how someone would steal a motor that a guy/gal may have taken a while to save for to take his kids fishing/boating/general water fun. Not right.

Anyhoo, they are just a welsh plug, pry em out, tap em back in. Simple and easy. The trick is to get them in/out without it showing later.
 

Gr8ham

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

And is there a trick that will help me do that? A certain diameter gizmo that will allow me to tap them out/in without damage? Can't be as simple as getting a screwdriver down the edge... That would ruin the edge, no?
 

HighTrim

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Re: '59 Lark Head Bolt Issue - Helicoil vs. JB Weld vs ??

Sorry, meant to put a little happy face beside the "simple and easy" statement.

I find it hard to do it without damaging the plug a bit or the powerhead. I have popped them with finessing an extremely small flat head screwdrive around the exterior, almost a jewelers driver. I scratched the paint, but was painting it anyways. There were others I mangled, so you win some you lose some I guess. I simply mask them now and leave them in.
 
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