CB550F2 Cracked rear engine mount

[mtrhead]

Hi folks,
Quite embarrassed to say my 79 CB550F2 rebuild fell by the wayside since I first acquired it in a seized state and posted about it almost 10 years ago. Life, a CB350K4 restoration and other stuff got in the way but I'm determined now to get it done. Just prepping the frame and after having had the top end sorted I'm now turning my attention to a problem I hope isn't going to defeat me!
I stupidly managed to crack the left hand rear engine mount casting after an attempt to pull the engine out on my own. I now have two problems! The original engine mount bolt is completed corroded in what is left of the engine mount casting and I can't get it out. Secondly, assuming I get the bolt out I've then (presumably) got to get the broken bit of the casting welded back on.
Just picking the collective wisdom here:

1) I searched the forum but just wondering, has anyone else hit this problem?  I've pretty much mullered what is left of the bolt trying to drill it, angle grind the side of the bolt but its defeated me so far. I'm wondering if I can perhaps stick weld a nut on the remnants of the bolt but I'm wary, I have a cheap and nasty stick welder but I've never used the welder in anger and am worried about ruining the casting (further!)
2) I'm pretty sure the bottom end of the engine is good. I don't really want to go hunting for a replacement bottom casting as I suspect I'll just hit more issues with this approach. However I wonder if its actually going to be less pain in the long run. Any thoughts, what would you do?

If anyone has any recommendation for a good welder in the Bucks area that would be good. My (very local) engineering shop weren't very complimentary about welding bits back onto a Honda engine when I dragged it down there for a viewing 

[Seabeowner]

Is that the upper or lower mounting?
Not that its any use I had an awful job removing the upper bolt on me F and had to saw it off to get the engine out of the frame. Tried whacking t, soaking, heating to get the remainder out. Had to drill out one side before it shifted.

[mtrhead]

Thanks Seabeowner, its at least good to know others have struggled here before me. Its the lower mount!  Clearance is a bit restricted, have burnt out a couple of flex drives and blunted multiple hss bits already trying to drill the remains of the bolt out.

[Bryanj]

Welding old corroded alloy is not easy, you probably dont want to hear it but replacement cases is easiest way to go

[K2-K6]

On various recent "projects" I've experienced that corrosion bond of steel bolt in aluminium, oh how very secure that can be, far beyond how you could imagine it.

Various tactics, Asda maintenance spray to soak is most effective I've found. Takes time to get any discernable movement at all, ultimately using an SDS hammer drill with rotary stop to just keep rattling it. You'll likely need ear defenders too  they don't seem like they are going to move, but more and more corrosion dust slowly comes out until they eventually yield.

Without pictures it's hard to give orientation opinion, but if the "outer" flat surface is available to place on a vice or similar, then approach from broken end, possibly  ?

[TrickyMicky]

Can't help re. the stubborn bolt, but, many years ago I worked for a firm rebuilding gearboxes, and now and then we would receive a mini box (alloy), with a corner knocked off where it sits under the cylinder block. We used a product called Belzona with good results to rebuild the corner. It could be machined and drilled. We tested it once on a scrap casing with a club hammer, the casing broke beyond the repair!! Wishong you the best of luck.

[Oddjob]

You cannot replace just the bottom casings, they are machined as a pair and must be replaced as a pair. You then need to calculate and replace the crankcase shell bearings as they will most likely change due to the change in casings.

A cheap pair of casings is the way to go imo.

[Seabeowner]

I have some 550 cases. They were probably off a 550K0. About £45 or make an offer, but don't want to go to the bother of posting them. Buckinghamshire is just across the Thames from me. But then you will have the problem of shells. They are marked BBABB.

[mtrhead]

Many thanks to everyone who replied, really appreciate the feedback and various perspectives!
I'm going to have another go at it tail end of next week (away at the moment) and will update on progress or otherwise.

Just in time for Halloween, welcome to my nightmare, photo attached, complete with broken casting, side of the bolt attacked with a grinder, mullered nut and sheared off end of the bolt, all the white gunk is corrosion!

Seabea,

Really appreciate the kind offer, can I have first dibs at that price but will let you know once I've attacked it one more time? Give me till the tail end of next week and if its defeated me  I'll venture south of the river. As far as I can tell the upper/lower crankcases of a K0 will fit the frame and top end of  a CB550F2 right?

[Bryanj]

All the sohc 550 engines are the same just numbers vary, there are some parts that are worth changing whilst in bits, my email is in my profile if you want i can tell you what and where to get best prices from

[Laverda Dave]

When I found what I thought was a crack in the lower case of my 400/4 I found a guy in Banstead who is a specialist welder.
He welded the crack for me (he also did a lot of welding on the cylinder head of my Triton) He made a great job of both.
He's a one man band so he might be a bit difficult to get hold of as he works a lot on sites.
His name is Andy and the company is called Specialist Welding Services. Contact number is 07957557935.