Hi All, I’ve just discovered a cracked mounting thread on my engine block. So only 2 of 3 are good. What should I do?


Bolt mount crack

[Edited on 13-5-20 by Chaz]

Is the crack actually in the block or is it just the paint? Clear the paint off and get a better look.

100% the block. It was stiff as I tightened and then I noticed the crack

Not ideal,but from the pic, it does look like theres plenty of meat to drill and tap the hole deeper, and use a long bolt?

I know it's not ideal but if it was me I would cut into the crack with a slitting disk, preheat it and throw some very hot welds into it. Then run a tap through it to clear anything out of the threads.

Ok great suggestions thank you

[Edited on 14-5-20 by Chaz]

I've successfully welded up a cracked cast iron Ford exhaust manifold which I think will be very similar to the block, I had to actually heat it till it was starting to glow and then weld (with a reduced current setting) and then let it cool down naturally. If you don't it seems the iron cools down too quickly compared to the the weld and all you hear is cracking and the weld just falls off. Tricky repair that but if you have access to a oxy torch and a tap to clean up the thread it might be possible. I'd also chamfer the edges of the crack quite a bit almost down to the hole, but not quite.

good luck

More great advice! Cheers muchly

I've just welded a boss onto a cracked lawnmower casting using stainless steel mig wire - a tip from the mig welding forum. Seems to have worked a treat with no pre-heating

Could you alter the mount to pick up another bolt hole what type of block is it
Jacko

I would go for drilling the hole deeper, and tapping the thread further in,


But the what do I know about tapping a new thread ??

http://www.locostbuilders.co.uk/viewthread.php?tid=216687

steve

So I know little about this kind of stuff however it would appear to me that the forces are mostly trying to force apart the existing threaded bit. So I'd be tempted to drill a hole at the end of the crack, grind a notch into the crack, weld it / grind it flush then use a cutting disc to slice a notch into the gussets and place a ring over that stub that has the same I/D as the O/D of the stub (this might need to be machined on a lathe) and then well and truly well that in place. The "ring" would need to sit 4-5mm "onto" the stub so that there is space for a good bead of weld.

Perhaps overkill but it surely wouldn't go anywhere in a hurry. Damn- you could probably just JB weld that sucker in place.

Hi BenB,

Thanks for that. What is JB weld please?

quote:

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Thanks for that. What is JB weld please?

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It's metal impregnated epoxy. Pretty steering stuff. Certainly strong enough to act as a filler between the stub and the ring I would imagine.

yeah but would you JB weld on an engine mount....?!

I suggest you repair it correctly

I wouldn't trust an engine mount that was just JB welded back in place but the sleeve I described JB welded in place would likely suffice. It looks like there's plenty of clearance so the sleeve could be pretty damn chunky- can't see the forces involved splitting it. The only issue would be those gussets- they'd need notching to make space for the sleeve. If one of those had an oil way or water way behind it slitting too deeply could be bad news.

Im in the weld it and drill and recap rather than an Epoxy metal filler.

I have had really good results with the filler but just can't bring my self to trust it fully....

I don't think he was suggesting filling it with epoxy, he was suggesting using JB as a retention adhesive for a collar to prevent further cracking. Which I think would probably work but I wouldn't choose to go that route myself.

My first stab would be to assess how much meat you have behind the threaded section and whether you can lop it off, re-drill and fit a spacer.

I am in the use JB Weld camp. Lets face it the crack must have been there since the last time the bolt was put in. It is one of 3 on either side. The forces on an engine mount (twisting force) are not that great and are shared by all of the bolts. Many engine mounts have a single bolt which takes all of the force. If it breaks it breaks - a broken engine mount is a drive home slowly job rather than a slow ride to the crem....

OK so a good weld is the best solution but with a deep crack that will be a lot of heat. To get it clean and ground back would be a long job.

An alternative might be to stitch the crack using threaded fastners although it is in an awkward place....

There is a lot of space behind the crack,

Drill out the hole 10mm further, and re tap the thread,

Insert a suitable bolt into the hole as far as it will go,

Jb weld the broken part back on and clamp it with a g clamp or similar

as the JB is going off, take the bolt out carefully,

Wait for the weld to set hard, normally about an hour

Re tap the thread carefully with the g cramp still in place

and reassemble,

Its what I would do, if in that situation

steve