'Engineering' fix required for broken casting

[mrscalex]

I have a nasty problem following my engine swap - I've been burying my head in the sand but need to sort it out now. When I was removing the gearbox bolts one of them was difficult to undo, it turned out the exposed threads were corroded and a small section of the engine casting broke off.

Now that's one of the big boy bolts that hold the engine and gearbox together and I figure it would be silly to run the car in anger without the bolt. But how the heck do I fix this?

I have the pieces that broke off but a) would I ever be able to weld/stick them back securely and b) the thread is shot anyway.

So I guess I'm into a make do and mend scenario. The basic option would seem to be to cut the remaining area away so I have a flat section to get a nut and bolt on. This would make the engine side much thinner. Would it be too thin? Can it withstand the torque from the bolt? Any forces generated in that area from the transmission. That type of long, torx head bolt must be used for a reason.

So I'd cut away the dotted area in the image below.

Can anyone think of any other options? I'm very interested to hear as I don't like the thought of cutting metal away.

 

[t-tony]

How far away from this are the next ones each side Rob? The reason I ask is I very often see cars missing a belly bolts with no ill effects whatsoever.

Tony.

 

[mrscalex]

How far away from this are the next ones each side Rob? The reason I ask is I very often see cars missing a belly bolts with no ill effects whatsoever.

Tony.

Good point Tony. Would be happy to take your view on that as someone who knows.

It's bolt number 5 in the 2 diagrams below (box turned 90 deg counter-clockwise where it rests on the floor - not my diagrams btw). So has a close neighbour. You can see the tail of bolt 4 in my own pics.

Yellow is E14, green is E12, blue is E11, and purple is 10mm hex. So unfortunately my bolt 5 is a big 'un and bolt 4 is a diddler. I wonder why the 2 are so close?

So am I worrying unnecessarily?

 

[t-tony]

I wouldn't say worrying unnecessarily mate, especially when you're a guy who likes things right, but an odd fixing missing isn't the end of the world.

Tony.

 

[Brian4]

Ally casting can be built up with weld but I guess that won't be an option as the engine would probably have to come out to do the weld and redrill the hole.

 

[Brian4]

There are some aluminium epoxy repair pastes which might be useful to fix the broken pieces you have back to the main engine casing. Clean out the hole and redrill the treads if they are damaged.

 

[Jack Ratt]

I wouldn't be worried about a missing bolt but understand your concern. As an engineering surveyor I have seen engine / motor casting with similar damage on many occasions. Sometimes there is an attempt to repair the damage but more often than not it is left "as is".
The common fixes are to build up with weld, then re drill/machine, or much simpler is to use a "molecular metal" filler such as Belzona, (not sure of the spelling). This is basically a metal putty.
We used to use it to fix steam pipes, fuel pipes etc when I worked at the steelworks many years ago.

 

[mrscalex]

There are some aluminium epoxy repair pastes which might be useful to fix the broken pieces you have back to the main engine casing. Clean out the hole and redrill the treads if they are damaged.

The likes of JB Weld are fantastic for many purposes. But I'm not sure it would withstand the amount of tensile pressure from a bolt.

 

[the Nefyn cat]

Think I'd go with cleaning it up as much as possible to a flat surface and putting a nut and bolt through it. There's plenty of other bolts holding it together, and I seem to remember a dowel or two as well.

 

[mrscalex]

What's in the back of my mind is reading one of those garage corner columns in a practical car type mag a few months ago. Where someone from a commercial garage writes the thing based on what's come in for work during the month. I remember the guy being horrified at a car coming in with a bolt missing from the bell-housing.

But this very clearly doesn't tie in with @t-tony 's experience which I'm happy to take in preference. And this was the same guy who struggled to get an engine out of a Mk 1 or 2 Escort. Then discovered by contacting a specialist that you put longer subframe bolts in and drop it 2" to get the clearance. That's a very well known trick in enthusiast circles and indeed one I used myself back in the day. But it's not rocket science for a professional mechanic to go figure.

I guess if it's still niggling me I try a repair and if it fails it doesn't matter. As long as I don't weaken the casting by cutting back the surface.

 

[gookah]

.....but an odd fixing missing isn't the end of the world.

Tony.

Are the 'even' fixings a problem?

 

[t-tony]

The even ones are ok if there's only an odd one missing, but even if there's an even one missing even that's ok if the odd one's are there. OK?

Tony.

 

[5harp3y]

Just jb weld it

 

[NZ00Z3]

Depending on how damaged the native thread is, you may have to consider fitting a helicoil.

The hard choice is going to be what to remove to fix the problem, gear box or engine?

 

[mrscalex]

Depending on how damaged the native thread is, you may have to consider fitting a helicoil.

The hard choice is going to be what to remove to fix the problem, gear box or engine?

Neither! They've both only just gone in!

 

[NZ00Z3]

Just remembered that there will be an alignment dowel on that bolt (engine side). If you go for a helicoil, you'll need to remove the dowel to do the drill and tap, then put the dowel back in. So either box or engine will need to come out.

The torque setting for the bolt is 72 Nm, so you'll need a strong fix.

 

[t-tony]

Well Rob, if it's going to cause you sleepless nights mate A relatively simple fix would be to make an "L" shaped bolt and slot it through from the gearbox side and then fit a nut and washer on the engine side. Not ideal, but better than nothing. If the bolt is normally 3" long, get one 4" long and bend 1" over at right angles, it will "lock" itself and allow you to tighten the nut. If the bolt is 12mm dia. you could use a 10mm dia. one.

Tony.

 

[mrscalex]

Well Rob, if it's going to cause you sleepless nights mate A relatively simple fix would be to make an "L" shaped bolt and slot it through from the gearbox side and then fit a nut and washer on the engine side. Not ideal, but better than nothing. If the bolt is normally 3" long, get one 4" long and bend 1" over at right angles, it will "lock" itself and allow you to tighten the nut. If the bolt is 12mm dia. you could use a 10mm dia. one.

Tony.

It's dropped down my priority list as you said you've seen it a few times and feel it will do no harm.

But yes, ideally I'd fix it somehow. I'm afraid I don't get what you're saying though or why I'd need an L shape bolt.

 

[t-tony]

I'll make a drawing tomorrow and try to explain what I mean mate.

Tony.

 

[mrscalex]

Actually I've just realised exactly what you mean. But the bolt would have to go through from the engine side as that's where the damage is we need to bend the head away from.

I really like this idea! It's a great peace of mind fix until I can engineer something more permanent. Thank you.