Repairing a crack in the head

[Careless]

54 minutes ago, Zed Head said:

Got any old aluminum castings?  Crack some and experiment.

I still think a Loctite compound might work easily..  I didn't look through all of their products but wouldn't be surprised if there was a "crack fixer" compound in the list.

I Googled Loctite metal crack repair and http://www.loctite.com.au/metal-filled-compound-4081.htm

i've used similar epoxies designed for this particular use, and i can honestly say that i've never had one that didn't still sweat fluid out from underneath the epoxy. i've used on both iron and aluminum trans cases (as well as magnesium), and also iron/alu cylinder heads with cracked coolant jackets, even engine blocks too. The best of them worked very well for months, and then all of a sudden would develop their own cracks, or worse- the edges would come away/raise from the substrate, and even break off into tiny chips at the ends because its smeared on very thin at those points. 

 

the only time i can say i successfully used an epoxy of that kind for what it was intended was to repair a wollowed keyway on a crankshaft that should still be operating today (i think) and prevented me from replacing the customers motor outright- it wasn't worth it.

I did actually use JB weld one time to restore metal on a gouge that someone created when doing a previous cam seal repair on my old VG30, and all I had to do was smear some on the aluminum gouge with a sliver of an old plastic/credit card, and then hit it with 600 grit paper to smooth it down to accept a new seal, but the seal is what's holding in the fluid in this instance- no sweating of fluid there.

 

Edited September 6, 2016 by Careless

[grannyknot]

Ben, the guy who did the nice custom Tig welding on the modified oil pan has agreed to come down to my place with his potable tig unit and have a go at that crack while the head is still bolted to the block.

I'm thinking this is the safest/best option, it will save me from pulling the head and things won't get much of a chance to heat up until most of the welding is done, then the inside of the crack will be sealed with something, not sure yet. I ground out a small v along the length of the crack with a steel burr cutter, also noticed the crack is getting longer.  Should I drill a small hole at the end of the crack to try and stop it?

[Patcon]

That's great he will come to you. Keep a fire extinguisher handy.

[Zed Head]

A thought that popped in to my head a day or two ago - drill and tap a hole through the cracked piece in to the meat of the head, countersink the loose end, and pull the crack closed with a small screw.

[grannyknot]

1 hour ago, Zed Head said:

A thought that popped in to my head a day or two ago - drill and tap a hole through the cracked piece in to the meat of the head, countersink the loose end, and pull the crack closed with a small screw.

I thought about that too but what about the dissimilar metals heating/expanding at different rates?

[Zed Head]

Head bolts, cam tower bolts, front cover bolts, all the same issue.  Steel bolt in aluminum substrate.  Metal stretches and compresses.  It's elastic.  The high end head bolt guys use a stretch calculation for their tightening.  So many degrees of turn equals so much force exerted, based on bolt stretch.

It's just one of many things that might work.  Probably comes down to what operations you're comfortable doing.  The welder likes welding. the chemistry guy likes adhesives, the machinist-type might like the drill and tap idea.

You could probably paint the inside of the head at the crack with glyptal and be fine.  I don't even really know what glyptal is but race engine guys coat the inside of their blocks with it.  Apparently it sticks.  http://www.glyptal.com/

[Patcon]

I believe Glyptal is a high end coating that was originally used in electrical transformers. Racers like to use it in their blocks to seal the casting so no loose grit can shed into the oil and it enhances oil drain back to the sump. At least that is the way I remember it. I researched it once for a motor rebuild but never used it...

[Namerow]

12 hours ago, grannyknot said:

Should I drill a small hole at the end of the crack to try and stop it?

That's the accepted way of stopping crack growth.  Because you're going to have the crack welded, though, doing this might be either: a. even more important (large thermal stressing), or; b. not necessary (welding solves the issue).  You won't know the correct answer until after the heat hits it.  Because of the fear that the correct answer may be 'a', a compromise solution might be to drill a hole to half depth.  Looks like a 3/16" bit would be about right. 

If your welder buddy has a lot of experience with aluminum casting repairs, he should be able to offer a better opinion.