Cold Case repairs

[sirhrmechanic]

One of the things that we get faced with from time to time is the repair of crankcases. While the ideal solution would be to weld them, at times castings are either too thin or too oil-soaked (and therefore too full of impurities) to weld. Then they have to be cold-repaired.

This week, we were faced with such a problem on a flange for a 1920 Silver Ghost crankcase which had, about 50 years ago, thrown a rod. It was repaired in one area, but the flange, which is critical to keeping the seven main bearings in alignment, had a major crack in it. The crack had been stabilized by the addition of an aluminum plate held in with 4 bolts, but this was not a good solution and flex in the crankcase had shown up in uneven wear on rear bearings. The flex, btw, comes from the fact that these crankcases are mounted rigidly to the frame. So any movement of the frame rails (and there is plenty) can translate to the engine. Not a good thing and this was corrected with later designs that incorporated rubber buffers, sliding tubes, torque reaction dampers, etc.

Because we could not weld it safely, we opted to use a cold repair using aluminum 'dogbones' made out of pieces cut off a billet. These were tapped in to place (holes were cut with a mill, the pieces were hand-filed to shape and fitted with blue and scraping) and pulled the crack up tight. Then tapered threaded pins were used to lock everything together. Then the repair is blended in with the sand casting. This took about 16 hours of work to complete, but the end repair is very hard to see and incredibly rigid.

Here are a few photos of the process.




This is the crack. About 4 inches long and along a flange/buttress on a crankcase. Evidence of old welding that is very solid. But crack formed in the middle of the weld. The blue shows repair 'stitch' pattern.



Using a mill to cut out the repair area. Used a two-flute to plunge cut the initial holes then final cut the holes with a 7/16 mill. Connected the holes with a .200" mill that opened up the connection to just under .250".



This is what the finished recess for the insert-tie looks like. Now to make the insert...



Insert is hand-filed from a piece of billet. It is slightly tapered so that as it goes into the hole it will pull the crack together. The 'insides' of the dogbone (closest to the bridge) are tightest, acting as a wedge.



This shows the insert, ready to be filed to tightly fit in its hole. You can see one tie already in place. Note how tight the joint is. A lot of careful filing and fitting.



As I can only put in 5 photos per post... we'll continue in the next reply.

Cheers,

Sirhr

[sirhrmechanic]

This tie/key is in the process of being fitted. Basically, you put blue sharpie on it... tap it in. Find the shiny spots and file. Takes about an hour per key from start to finish.



Key fitted with Red Loctite. Ultimately, this will also be pinned in place and the whole crankcase will be vacuum impregnated which will fill any slight gaps in the joints.




This shows all four keys fitted and dressed with a dyna-file (small belt sander... see below) and hand files. Now we are ready to put in aluminum taper pins to lock everything together. At this stage, those keys are in tight. They are also pulling the crack solidly together. They do not move, except with a punch and good hammer strikes. Just how we want them in place.



Here we see the holes where aluminum threaded taper plugs will be fitted. See my earlier post on heli-coil alternatives for an explanation. These are put in after the hole is tapped with a taper tap. Then the pins are threaded in and locked with red Loctite. Excess is cut/filed off.



Here we see the pins in place and the beginning of the process of 'stitching' the crack itself. We did not want to leave the crack visible. But stitch repairing it with aluminum threaded plugs we both made it invisible, but also added additional strength as the threaded plugs put the 'keys' under tension/compression, further locking things together.

More in the next installment...

[sirhrmechanic]

With the keys and pins in place, now it's time to blend in the repair and make it go away.... starting with a dyna-file which will dress the high spots. This takes off material FAST. I use it to get to just above flush and finish with a single cut flat file. Prevents divots.



Here is the Dyna-File in action removing the bulk of the raised aluminum on the keys and pins.



After working with the dyna-file and a hand file, we have a repair that is blended in at one level, but we have removed the 'sand cast' look from the casting. So though smooth and with invisible joints, the repair still sticks out like a sore thumb. We now have to restore the sand cast look to the casting. So we use our vibrator hammer:



This little air hammer has a ram that will plenish the surface at about 1000 beats a minute, depending on air pressure. It will dimple aluminum beautifully. By working it randomly over the site to be blended, a 'rough' finish can be added. After a few rounds with the hammer, it is sanded and I further imitate sand casting by using 36-grit sandpaper, placing it upside down on the casting and tapping the back with a hammer. Grinding the grit into the aluminum. It works wonderfully well.



This shows the finish after 'rough' plenishing with the hammer. This is actually too rough. It still gets some smoothing and working after this stage.



The four holes on left/right of this picture (which held the big bolts with Nylock nuts) still have to be filled and there will be some final blending to match the castings up after this, but this shows the repair area fairly well. I have better photos now and will post one next week. But the repair is solid and invisible. Now we can get to line-boring the engine.

This same technique can be used on motorcycle casings and, more importantly, in certain applications on cast iron, which cannot be welded except under certain very difficult conditions. As I mentioned at the beginning, if welding is possible, it is preferable to a cold repair under many circumstances. Not all... but many. But because of oil contamination, alloy quality, condition, etc. this kind of cold repair of a critical casting can be an option. It also doesn't take any fancy tools. Most of this can be done with a drill and files if you are patient. All our fancy power tools do not make this job better, merely a bit faster. I tell everyone the first tool to master if they are going to work on old cars or old bikes (besides the credit card) is the file. With a good set of files, almost anything can be made, repaired, etc. Factoid for cocktail parties... the file is the only self-replicating tool. With a file, you can make more files. Can't do that with any other tool.

Hope this helps someone else with a sticky problem.

Cheers,

Sirhr

[T. Cotten]

Awesome.

With humility I wish to add that "dry erase" markers occasionally work better than common ink markers, especially at the beginning of the process when interferences are widely spaced.

If the tie-bars are also to be peened, I would have suggested Seal-Lock "Fluid-Weld" for a goober, as it has been the 'staple' of the industry for the tapered pin procedure for generations.

Looking forward to your progress!

....Cotten

[MMasa]

I needs me one of them air hammers. Looks like a vintage tool. Do they still make / sell them or do I have to happen upon one? Who made it?
Thanks
Mark Masa

[sirhrmechanic]

Mark:

They may have been a 'production' item at some stage, but this one was made by a genius who taught both me and my business partner at the garage how to do machining.... and line boring of engines. Ed was a toolmaker for Smith and Wesson and, later, did car restoration in his retirement. Did I mention genius with metal?

So I don't know where you can find one, but next week, I will take some detailed pictures. If you have a lathe, you can make one. Toughest part is the piston, but as long as you can keep things within a thou... it's a piece of cake.

It's a treasured tool around our place. Along with the set of wooden 'tool bits' Ed carved me years ago to show me how to make lathe tools correctly with a chunk of HSS and a grinding wheel. Kenametal inserts have taken the place of HSS cutters ground to shape. But the patterns are treasured as a remembrance of my friend Ed.

Cheers,

Sirhr

[BoschZEV]

Hope this helps someone else with a sticky problem.

Very impressive work. How many minutes... I mean hours... no, I mean days, did that repair take?

Count me as a second person interested in the details of that mini-air hammer.

[sirhrmechanic]

Very impressive work. How many minutes... I mean hours... no, I mean days, did that repair take?

Count me as a second person interested in the details of that mini-air hammer.

About 16 hours. Not terrible... but I was cross-eyed by the end.

Cheers,

Sirhr

[BoschZEV]

You mentioned welding, and the problematic aspects of oil-filled castings. Still, how often does your shop use welding for repairs? To rephrase that question, how often do you use TIG when dealing with engine or gearbox cases that are damaged in some way. It's fine if you also want to estimate your uses of MIG and/or TIG for body work, but I'm specifically interested in the utility of TIG for repairs on motorcycle cases. That is, cases that have held oil but that also are small enough that it's reasonable to preheat them whereas it might not be for a car crankcase (also, where the walls are thin enough that you wouldn't need a 20 Megawatt TIG like it looks like the Rolls Royce would have required).

[sirhrmechanic]

Hi ZEV... first, we farm out any TiG welding. I have a welder, and I am great at making puddles of slag and ruining things. I do some light stainless work or hawging together mild steel for jigs, stands or other crude projects. I never learned to weld properly and I know my limitations. TiG welding is definitely one of them.

Second, we almost never attempt to repair crankcase or head castings via welding. It's just a recipe for disaster. The aluminum just ends up crumbling or making a mess and rarely does the repair (because of impurities and age) work. For bad aluminum heads, we buy new ones. $20,000 for a new head... but that's what they cost! You can spend hours/days trying to fix a rotted out P1, P2 or P3 cylinder head and it will still leak in the end or put an otherwise perfect engine at risk... and customers get pissed if the repairs don't work, even if you warn them in advance. So we won't do it. Crankcases are generally not available new. Well almost never available. Personally, I would not even attempt to repair something like the rod hole that was/is in the side of this crankcase had it not been repaired before and still holding well. Whoever did it in South Africa in the '60s did an amazing job. Maybe we might attempt in an emergency. And by emergency I mean a crankcase that cannot possibly be replaced. But as there is now a guy casting Ghost crankcases... I would not try and fix a rod through the crankcase 'injury' as was the case with this one years ago. Fortunately, this was a crack that was in an area that was just perfect for this kind of repair, with the biggest challenge being that it is an unsupported flange. So you could not just taper pin, or the pins would simply have spread the crack and caused more problems than they solved. But this repair was quite easy and straightforward... thus it was something worth posting for others who may have similar challenges.

BTW I know the history on this 1920 car and the rod hole in the block (in number 5) was repaired for expediency. It came out of a field in Rhodesia where it had been used as a truck. When it threw a rod, it was left to rot for years until the father of the current owner rescued it and it was restored/rebuilt in South Africa. He was a very talented hobbyist. Tens of thousands of miles later, the engine is in rebuild stage and we are trying to correct some things that the first round of repairs left lacking not because the owner was bad at the job, but because capabilities and resources have changed in 40+ years. Same with motorcycles. It's interesting to note that the rod destroyed the cam, too. And it was welded back together using a spacer piece... and ground. NEVER would we attempt such a repair today when new cams are available. But the repair on this is magnificent, the cam is in perfect working order the lobes align perfectly... and we're going to reuse it.

All that said, I had a '38 Indian case welded last year... and it was a highly successful repair. But it was at a spot where there was not much oil and the welder built up the area as opposed to welding a piece back on. Then I re-machined it. The case is pictured in this thread:

http://www.antiquemotorcycle.org/bbo...ht=#post126910

So that's probably a long way around saying that I would rather not weld cast aluminum parts that are exposed to water/oil at all. That said, there are some people out there with specialist skills who can do just about anything... and I'll probably hear from some on this thread. Which is good, because we are always open to new techniques or capabilities. New ways of de-greasing castings or getting rid of impurities... new ways of welding... whatever. For example, I mentioned cast iron welding above... generally a big no-no as you end up with cracks along the heat joints when you weld cast iron. But there are folks like Columbus Col Weld who hot weld things (put the part in a furnace, heat it, weld it and cool it to get rid of stresses)... so never say never.

It's one of the nice things about forums like this where we can compare notes and learn new techniques... and one of the reasons I post stuff like this because it starts conversations and leads to new ideas and exchanges of information. Always a great thing.

As a last thought, additive manufacturing is coming. And within a generation, we'll be printing new crankcases. Probably printing entire new engines. How cool will that be!

Cheers,

Sirhr

[BoschZEV]

Your post was very helpful indeed. I've brazed and gas welded for years but never took the time to learn how to arc weld even though I have two MIGs and a 40 kW TIG at my disposal at work. However, recently I've started thinking it's about time to learn because of my interests in motorcycle restoration, but that immediately raises the issue of the size of the welder. If only used for sheet metal plus frame tubes the welder doesn't need to be as large as would be needed for cases that are 1/4" or more thick. But, if it's essentially hopeless to deal with cases anyway, that takes a big constraint off the table. Again, thanks very much.

[c.o.]

Awesome.
....Cotten

Precisely what I was thinking!!! This is awesome! Thanks for showcasing this repair Sirhr!

[Tom Lovejoy]

Very interesting, have never seen anything like that. Thanks for sharing.

[Steve Little]

Well done Sirhr.
Thanks for taking the time to post pictures and describe the procedure on this interesting repair.
I have never seen the like of it before, and wonder at the influence for the thinking behind it
If I was to guess at its origins I would say shipbuilding, Blacksmith, or perhaps tool room influence. Maybe Ed’s ghost is still whispering in your ear.

When I googled Grey Ghost it came up with this http://www.youtube.com/watch?v=rUIsdfgfg_g
Nope. Too many cylinders. Then I figured you may be working on an old Bentley or Rolls.

Wish you hadn’t shown us the marvelous little hammer. Now there’s going to be 30 of us trolling eBay vintage tools for one.
Regards Steve

[dane]

Woodworkers use a similar technique to "stitch" cracks together and prevent further splitting. I believe they are referred to as Dutchman.