20 replies to this topic

[Sabre75]

Afternoon folks 

 

I've been a member for a while now and have made good use of lots of existing threads for troubleshooting various issues, but now I'm after a bit of advice ...

 

Last year my girlfriend bought herself this 90/94 1.3 SPi Mayfair/Sidewalk (I'll cover *that* in a different thread; coming soon!)

Mini_no-reg by Sabre75, on Flickr

 

Foolishly she didn't hide the keys from me, so it currently looks like this ...

Mini_no-rear-subbie by Sabre75, on Flickr

I took the subframe off to repair an irritatingly located rust-hole; you can see the repair in the empty wheelarch.

 

While the rear subbie was out I decided I'd tidy it up, give it a lick of paint etc. etc. - when I was cleaning it I noticed the rust damage on the frame, shown in the picture below:

subbie_damage-marked by Sabre75, on Flickr

 

Close ups here:

subbie-damage_ps by Sabre75, on Flickr

subbie-damage_ds by Sabre75, on Flickr

 

Now it looks like water has run down between the metal and rusted through - the piece 'underneath' the damage in the photo seems to be solid. Looking at how the subframe is constructed it seems the rust-damaged piece isn't carrying any load.

In the photo below the existing welds are show in red. I was planning to cut the damage away and re-weld the frame shown by the blue lines (welds underneath shown by dotted lines).

subbie_proposed-repair by Sabre75, on Flickr

 

To my mind the repair will be stronger than the original construction, but I was just after some advice from people with more experience to see whether it's a good idea or not.

 

Many thanks,

Tom

 

 

[Jordie]

Magnum panels make a repair piece, might be worth looking at those.

[mr cooke]

I was told by my mot guy that you can no longer repair sub frames

[mr cooke]

oh nice mini by the way

[cambiker71]

Your MOT man is wrong mr cooke, you can't weld suspension components (like lower arms on modern cars for example)
Subframe repairs are fine if welded correctly, they're classed as small chassis sections.
This was a subject brought up on my tester refresher training last year.

[Jordie]

Ideal time to put some reinforcement in for aid with jacking and stands. Seam weld the edges up etc...

[Sabre75]

Many thanks for all the replies so far, and I'm glad to know you can weld subframes otherwise I'd be knackered! (or at least down the cost of a new subbie).

 

I've now done a little angle-grinder assisted investigation and it seems my plan A was a little over complex. I'll make the most of the remaining daylight and post a few more pics/ideas later - watch this space.

[Sabre75]

Right - update as promised:

 

I cut the rust away and ended up with this ...

subbie_rust-removed-closeup by Sabre75, on Flickr

 

As you can see the metal underneath doesn't look too clever and 'frame' left by cutting the rust away is effectively doing nothing. As I'd gone this far I thought I might as well carry on so I cut & ground the rest of the frame away, and given the condition of the underlying metal I cut that out as well, which left me with this.

subbie_section-removed_inc-wreckage by Sabre75, on Flickr

 

Here's a close-up of the above. The plan is to cut a new section (shown by the solid blue line) and butt-weld it round all the edges (solid red lines). Not only should this give a strong repair it should also prevent the problem reoccuring, as it was caused by water getting between the layers and then the rust blowing through both sides. I'll also spot-weld (red triangles) it to the uprights, and seam-weld the edges (dotted red lines) where I can. And obviously I'll paint it and use seam-sealer to prevent the water getting back in.

subbie_proposed-repair-b by Sabre75, on Flickr

 

I'll probably add some strengthening and incorporate jack points into that as Jordie suggested (cheers  ), probably using some square tube section or similar, but I'll have to be careful to avoid creating more water traps. I'll do that once I've rebuilt the section though.

 

Soooooo that's all of my evenings this week accounted for; I'll keep the updates coming as work progresses though.

 

Tom

[Sabre75]

Hello again folks - not alot of progress to report due to the inconvenience of having to go to work, but I did manage to grab an hour or two to get something done this evening.

 

Due to the fact I never throw anything away I managed to dig up some knackered old desk brackets that were made of just the right gauge steel ...

scrap-metal-brackets by Sabre75, on Flickr

 

... so using the old cereal packet card template trick and bit of time with the angle grinder and fettling with a file I now have a nicely fitting repair panel 

subbie_repair-panel by Sabre75, on Flickr

 

Rather than rush it and balls everything up at this stage I thought I'd call it a night. I've got some offcuts to practice on to fine-tune the welder; using 0.6mm wire for this as the steel's only ~1-1.2mm thick and I don't want to blow holes through it 

I'll see if I can get it welded up tomorrow.

 

I've also had a think about the jack-point location. I'm thinking the best point for it will be over the vertical ribs within the frame, so once I've welded in the repair panel I'll probably weld a square tube section on in the location marked in red below, unless anyone's got any better suggestions or can see an obvious problem with this? ...

subbie_proposed-jackpoint by Sabre75, on Flickr

 

Right, that's it for tonight. My apologies if this isn't the world's most exciting thread but if I keep posting my progress it means I'm more likely to press-on and actually get it sorted!

Night folks

[Sabre75]

Evening folks - not alot of progress to report, although I did have a bit of a play to work out the settings for spot welding.

(Although technically it's not spot welding as I'm using a MIG; you drill through the top piece and then weld through onto the lower piece. I think technically that makes it plug welding).

 

Anyway the picture below shows the test piece (and some lovely lino flooring!). As you can see all the welds look fine from the top, but looking at the underneath you can see the welds on the left had zero-penetration into the lower piece and it just fell off! After a bit of experimentation I found the settings that worked (on the right, looking from underneath). You can see the discolouration on the lower piece from the welds.

 

If anyone's interested these are the settings I used on my Sealey MightyMIG 150. Power: MAX 2, Wire feed-speed: 6.

 

spot-weld_test by Sabre75, on Flickr

 

That's all for now; tragically I won't be spending all night in the garage tomorrow but I might have an update on Thursday 

[sonikk4]

That looks ok, what size holes are you drilling?? For something like that I would be drilling 1/4" holes for max strength.

[Sabre75]

Hi sonikk4; the holes are 5/16" (I think!) - I bought a stud & spot welding kit for my MIG, and it came with a pair of double-ended drills, so that's what I used ... and because the standard drill set I had to hand was sh*te 

So that'd be 0.3125mm (5/16") rather than 0.25mm (1/4") - do you think it's worth dropping down to 1/4" then?

[sonikk4]

The bigger the hole the stronger the plug weld. I normally plug weld at 1 /4" everywhere i can but no smaller than 3/16". 5/16th is big but on a subframe will be fine.

[Sabre75]

Evening folks,

 

It's been a productive-ish day in the garage. I've managed to get the welding to the underneath of the subframe sorted.

 

So here's the patch patch prepped for welding. As sonikk4 suggested I used a 6.5mm drill; it was as close to a 1/4" as I had.

(also ignore the mm measurements in my previous post; it was late and I was reading the wrong part of the conversion table!)

subbie_repair-plate-drilled by Sabre75, on Flickr

 

And here it is plug- and spot-welded into place.

subbie_repair-plate-fully-welded by Sabre75, on Flickr

 

The other leg of the subframe wasn't as bad so I cut away the overlap and plug-welded the 'upper' piece to the subframe leg.

subbie_repair2-spot-welds by Sabre75, on Flickr

 

I then butt-welded the 2 pieces back together; it's a fairly wide weld as I went over it a second time to strengthen it. You can also see the weld pentration from inside the subframe leg where I seam-welded the inner seams.

subbie_repair2-fully-welded by Sabre75, on Flickr

 

This is some of the seam welding inside the subframe leg. It's not my best work but it does the job.

subbie_outer-seam-weld by Sabre75, on Flickr

 

Unfortunately when I turned the frame over to weld the inner seams I spotted some more rust on the top. I dig a bit of digging and found this; and yes, that is a hole where I pushed a screwdriver though the metal! 

subbie_upper-damage by Sabre75, on Flickr

 

So once again I cut the rust out. Tomorrow's job; weld a new plate in here too.

subbie_upper-section-cutaway by Sabre75, on Flickr

 

The other side isn't as bad but it'll need a bit of work too.

subbie_upper-damage2 by Sabre75, on Flickr

 

I'm thinking a new frame would probably have been easier, but since I've come this far I might as well carry on!

Edited by Sabre75, 01 February 2015 - 12:31 AM.

[Shawbags]

you've done a good job of that and saved a lot of money , nice one , hope I can get to that standard of welding .