[SEL] Cracked Head

[Jim Hardman]

Hi all...

I spent my working life in the epoxy business and agree that the 5-minute 
formulations are not the best for water resistance.  The slower setting 
varieties will perform a lot better, especially when driven to a more 
complete cure under heat.  Yes, warming the head at the time of application 
will thin the mix and promote pentration.

I used a 5-minute epoxy to make a repair inside a boat house and a year 
later it had reverted to a cheezy mass, about like chewing gum except easily 
flaked.  Slower varieties will do a lot better inside shower stalls, boat 
houses or engine water jackets.

My father-in-law repaired his broken boat throttle with our 5-minute epoxy 
and it scared the lights out of me when he'd come charging in to the dock at 
a full plane and then haul back on the throttle at the last second.  The 
good Lord was watching over him. Repairing a broken throttle arm with a 
butt-joint repair with 5-minute stuff ain't smart.

If I can offer a suggestion to anyone using epoxies, mix them twice as long 
as you think you have to.  The extra mixing time allows greater association 
between the resin and the curing agent and results in a much stronger cure. 
And avoid adding solvents to either thin the mix or extend potlife. 
Reaction rate doubles with an increase of about 18 degrees fahrenheit (10 
degs. C.) which also benefits the final cure.

Maximum temperature allowed varies with the recipe, but anything over the 
boiling point of water should be suspect.  Use silicones to repair anything 
exposed to higher temperatures.  JB Weld should do fine for a crack in an 
engine head as long as there's enough cast iron to take the stresses of 
compression and ignition.

As for surface prep, grind down into fresh metal and wash down the surfaces 
with  a fast solvent like toluene to get rid of any oil residue.  Avoid 
mineral spirits (paint thinner), it takes too long to evaporate.  Wipe up 
the solvent with a clean rag, that's the only way to reduce oil film. 
Evaporation just leaves the oil behind.

But I'll bet you already know all this.

Jim in frozen Vermont


> Eldon,
> That's a good point.  A little heat will make the epoxy suck
> into the crack.  But, if a little heat is used then its probably best
> not to use the JB Quick formula.  It sets up in about 5 minutes under
> normal (75 degree) temps.  Adding heat can make it set almost on
> contact.  I've had great luck with JB Weld and if its just a matter of
> stopping a seeping crack on the exterior of a cylinder or head, I'd
> prefer it over the other choices (welding or brazing).
>
> Tommy Turner
> Magnolia, KY