Thread: JB Weld on a crankcase question
09-07-2012, 06:48 AM #1
JB Weld on a crankcase question
Let me preface this one with "No, I'm not doing it" That being said, it is more of a curiosity than a fix request. So, I had a case with a crack in the bottom of the block about 3/4" long where a chunk of piston skirt dropped recently. Of course we paid the $150 to do it right and have it welded but i have always wondered if this thin crack could have been filled with a reasonable chance of success with JB? Of course it would have had to make it all the way through the crack till it squeezed out the other side but then I thought it could be "backed" up with a nice thick blob in the wedding pattern on the bottom of this 1200 if the outer surface was just scratched up a bit to help it hold. Anyway, I personally think JB should be peanut butter flavored, served on toast and dispensed out of a nipple because it is just that good but is it JUST THIS good? Thoughts worth 2 cents or more are appreciated.
What got me thinking about this again this morning was the thought of doing my breakdown test coming up after work and the very low pressure used in the test. What type of pressure is in the crank case during high RPMs anyway? I assume 10PSI or less if that is what we are testing with?
09-07-2012, 07:05 AM #2
It wont last , good temp fix but the oil,gas and vibration will cause it to leak sooner or later.........I have repaired a lot of blocks.pans and valve covers that were "JB welded" ...JB weld is good stuff , good in a pinch , just not permanant.....
09-07-2012, 12:37 PM #3
There are some other products out there that work great and are 2 part mixtures like JB weld. I've had good results with JB weld and still holding for now. surface prep is a must and if you want to try another good crack filler there's the stuff they coat gas tanks with. i have some when mixed is red and spilled it on the concrete and almost couldn't get it off after it set up had to use a hammer and scraper. the gas tank coating is good stuff and oil and gas resistant. `
09-07-2012, 06:52 PM #4
- Join Date
- Jan 2007
- Milwaukee, Wisconsin, United States
All adhesives fail. Given enough time and stress. It usually happens when you are least expecting it. Replace or re-weld the case.
09-07-2012, 07:47 PM #5
09-07-2012, 07:58 PM #6
my fuel baffle went bad in my seadoo and had to dismantel it and I used the Marine jb weld to put it back together, so well see how it holds, the sender works great.
09-11-2012, 05:14 AM #7
- Join Date
- Jun 2012
If prep is done correctly a good quality adhesive is as strong or stronger than metal, I have been using epoxy's for decades on intake ports on high performance race engines with no problems. Lets not forget many if not most automotive manufactures are "glue'n" body panels and other structural parts together. u-pol makes 1 of the best epoxys out there.
09-11-2012, 10:37 AM #8
If it's just a crack from being pushed out by stray metal and the reinforcement ribs are still intact epoxy would be fine. The case would need sandblasted then heated with a small propane torch to sweat the oils from the aluminum. Then cleaned with brake parts cleaner, then sweated and cleaned, until all oils are pulled from the aluminum pores. Then a good quality epoxy can be used to fill the cavities between the ribbing and be left to cure. Bolt it back together and run it, I've done it.
09-11-2012, 02:25 PM #9
I appreciate the insight from both sides. I could imagine that propping would be key if It were to be done. One thing is for sure, I would only do it on a ski that I intended for use on fresh water so I could hit shore eventually in the event of a Fail! .
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