How to properly prep for a cracked block repair!

brandonh · Aug 26, 2009

Hi All!
I have a '89 Merc 3L with about a 6" crack on the exterior of the block (cylinder walls are fine!) and I'd like to try to JB weld. I've seen a few posts stating that this is the way to go and has worked for most. What is the proper way to prep the block for this procedure and is JB weld the product to use or do you recomend another.
Thanks in advance!

HT32BSX115 · Aug 26, 2009

Re: How to properly prep for a cracked block repair!

Howdy,

Last summer I replaced a 3.0L long block for a friend here in the NW. He took the "core" block back to the rebuilder and they said they could repair the block. The 3.0L block appears to crack in a structural area near and parallel the "deck" and if you just slop some epoxy on it you may still not get a good head gasket seal.

having said all that you need to clean the block until it's squeaky clean and dry. Then sand (or grind) where the epoxy is going to go. maybe clean it with a little actone too before you apply the epoxy.

It may still leak afterward. There's no real pressure on a raw water cooling system so if it has good bonding the only thing that might dislodge the epoxy should only be heat cycling etc...

I wouldn't try it. I would replace the engine block, but as you said there are a lot of people that claim success....You don't have a lot to lose unless you like to boat on the Niagra River upstream and near the falls.....

Good luck,

Rick

jtybt · Aug 26, 2009

Re: How to properly prep for a cracked block repair!

The real question is what caused the crack. If it was from freezing, there's at least a 50/50 chance there's is also a crack that you haven't found. Get it pressure tested as well ad magnafluxed...even pressure test after the JB weld fix.

i think heating to about 450* will burnout any oil contaminants and not crack the block any further.

fabrimacator21 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

JB weld is a HACK fix.... no where near the strength of an actual weld. I've done my fair share of JB weld fixes and I'd NEVER put it on an engine block. It lasts for a while but eventually breaks down and is no where near the strength of actual weld (even if it is nickel rod). You can get a new/magnafluxed block for 150-200 bucks.... why risk JB welding it? That chit could break apart (which I've seen it do) and cause serious damage.

If you insist on staying with the cracked block then get it ARC welded.... JB weld won't last long.

Bondo · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

I have a '89 Merc 3L with about a 6" crack on the exterior of the block (cylinder walls are fine!)

Ayuh,.... Where exactly is it Cracked,..?? Down low on the portside,..??
If So,... Epoxy will work Just Fine....
If it's Cracked up high, near where the head bolts on,.... Forget it,... You need another block....
Btw,... The cylinder walls almost Never Crack,...
It's usually where I ask about, or on the Inside of the block, down low, opposite the block Drain....

JB weld is a HACK fix.... no where near the strength of an actual weld. I've done my fair share of JB weld fixes and I'd NEVER put it on an engine block.

Really,..... Just how Strong does a repair need to be to hold 15psi of water pressure,..??..??
I Strongly Disagree with you.....

a70eliminator · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Nickle stick arc weld, depending on the type of crack and it's location. I had a block that cracked right across the back of of the block (water jacket of #8) The guy that welded it up for me instructed me to pin it (drill a tiny hole at the ends of the crack) then V grove it out along the crack. The block was a rare vintage racing 406. I did what I was instructed and the weld worked perfect.

tmh · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Guys, the OP said it's a 1989 3.0L engine, which means it's a little boat 20 years old. If it were mine I'd sure want to avoid all sorts of expensive OR time consuming fixes for a boat worth $1500 max. Some of you guys can replace the block as a "simple" job, but for most it would be a HUGE job that they (we) couldn't even do themselves! I get a kick out of "just replace the block" advice - I'd no sooner try that myself than "just build a new house" if mine burnt down. Just pulling the drive and engine is FAR more than most can or will do on their own.

Follow bondo's post and you'll be fine. As he said, not much pressure AND I doubt any safety issue if it does leak again. Where the crack is does matter though, according to what I've read on this subject.

brandonh · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Thanks Guys-

bondo... the crack is towards the the top near the head bolts. Do you fear a bad head seal due to the crack or ???. The crack actually runs below the blot threads.

Bondo · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Do you fear a bad head seal due to the crack or ???. The crack actually runs below the blot threads.

Ayuh,.... Unfortunately,.... Your block is Junk.....Even Welding Ain't gonna fix That 1....
The headbolts will Never be able to provide the proper clamping force, without separating that Crack....
If it was down Low in the water jacket,... It'd be a different story,....
It must have been a very Hard,+ Quick Freeze that split it....
Sorry....

Bifflefan · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Bond-o said:
Btw,... The cylinder walls almost Never Crack,...

I have only seen one, in 27 years of woking on engines. It was not from freezing eather, it had a bad casing and when I bored it out, there it was.

Bondo · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

It was not from freezing eather,

Ayuh,... That's what I was implying,... A Cylinder is a very strong Structure,...
Structure wise anyways.... It's hard to crush by pushing In on it....

HT32BSX115 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

You can get a new/magnafluxed block for 150-200 bucks

Um....... where do I send my check? That includes shipping right?

When I replaced that 3.0L engine last year, the reman engine came from US Engines in Kent, Wa.

If you look there http://usengine.us/mercruiser.html you'll see that they get $1895 exchange. (+$500 for the core) If you have a cracked core, they say they can fix it for $300.

The one I replaced was cracked up near and parallel to the cyl head in the same manner you described.

Your block will either have to be professionally repaired or replaced.

Good luck,

Rick

Bondo · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

HT32BSX115 said:
Quote:
You can get a new/magnafluxed block for 150-200 bucks
------------------------------------------------------------------------------------------

Um....... where do I send my check? That includes shipping right?

When I replaced that 3.0L engine last year, the reman engine came from US Engines in Kent, Wa.

If you look there http://usengine.us/mercruiser.html you'll see that they get $1895 exchange. (+$500 for the core) If you have a cracked core, they say they can fix it for $300.

The one I replaced was cracked up near and parallel to the cyl head in the same manner you described.

Your block will either have to be professionally repaired or replaced.

Good luck,

Rick

Ayuh,.... Rick, you're comparing a Bare block to a Long block motor....

HT32BSX115 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Bond-o said:
Ayuh,.... Rick, you're comparing a Bare block to a Long block motor....

Absolutely Right. But I don't think you can buy a "ready-to-go" 3.0L block for $150-200.

US engines will fix a cracked 3.0L block for about $300. They gave my friend about $200 for the "core". Of course it included a presumably regrindable (is that a word?) crank, resizeable rods, and camshaft.

Would that make the repaired bare block worth $150-200 by itself? (prior to cyl and align boring etc?)

Bondo · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Ayuh,... No doubt Rick,... I guess I was just stating the Obvious,....

I get $100. for a core Block, from a local Machine Shop,.... Whether it's loaded or Bare....

Post count ya know........

fabrimacator21 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

Bond-o said:
Really,..... Just how Strong does a repair need to be to hold 15psi of water pressure,..??..??I Strongly Disagree with you.....

Not very strong at all.... however the crack will keep spreading after heat cycles.... JB weld won't stop a crack from spreading. Weld will.

Sounds like that block is junk though.

TowRoper · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

lol no it wont there is still a 50/50 chance it will keep cracking not to mention the cracks the welding can cause its the nature of cast.

fabrimacator21 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

TowRoper said:
lol no it wont there is still a 50/50 chance it will keep cracking not to mention the cracks the welding can cause its the nature of cast.

uh 50/50 seems a little off.... I've welded TONS of cracks on cast parts
for heavy equipment... haven't had a comeback yet. Done right it shouldn't crack. If it's a REALLY bad cast then it probably will but I've had real good luck with Nickel rod, preheating, and peening.

TowRoper · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

yeah......

fabrimacator21 · Aug 27, 2009

Re: How to properly prep for a cracked block repair!

TowRoper said:
yeah......

I do it for a living....

How to properly prep for a cracked block repair!

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