Seeking advise on engine cases repair

I have to repair damage to a 2-stroke dirt bike's cases. The damage occurred when a bolt or a threaded stud ended up in the cases (don't
ask how - I have no clue) and was pummeled around by the crank shaft. It was wedged against the case by the crank shaft in a few spots and created half a dozen small cracks around the perimeter of the case before getting sucked into the intake port, embedding itself in the piston crown, and seizing the motor.
Here are a few photos of the damage: http://iillyyaa.smugmug.com/gallery/1109070/1/51599943
I would like to repair the cases, but don't have the expertise to decide what method would be best. At my disposal I have a squarewave inverter TIG power source. I am also open to using some sort of a low-temp aluminum brazing alloy, as that would probably have the least chance of screwing up the cases. Or any other method that the group thinks would work.
Can anyone please suggest the best way to repair the cracks?
Thank you very much in advance for your help. -- Ilya
PS: I don't think it's of any importance, but the bike is a 2001 Yamaha YZ250. The cases are not a stressed member, so air- and oil-tight seal is the primary consideration.
PPS: This group has been a great resource for me, allowing me to add welding to the small arsenal of tools at my disposal, which is a great help for my motorcycle hobby. For example, this is the latest of my welding projects, which I wouldn't have been able to accomplish without learning everything I did by reading the posts here: http://iillyyaa.smugmug.com/gallery/1050193/1/48758779 (It's a rear sub-frame for my roadracing bike. It weighs 3 lbs, compared to 9 lbs that the stock weighed. So, now I can put on 6 lbs of fat over the winter and still come out even! :-) ) Thanks!
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snipped-for-privacy@gmail.com wrote:

If you feel that the case is structurally sound and you just want to seal the cracks then it may work better to thoroughly clean it with a non-oily solvent (a quick soak in acetone, perhaps), let it dry, then epoxy the cracks. Ideally you'd have some way of driving the glue into the cracks.
This would only work well if you could drive the glue into the cracks and if they did not flex in use -- otherwise welding is probably the right way to go.
--

Tim Wescott
Wescott Design Services
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If you need to ask on here about doing the repair, then it would perhaps be advisable to take it to someone who knows what they are doing, as if its not done right first time its likely to cost a lot more than paying someone to do the job for you.
k
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Ken, while I understand your argument, I cannot accept it in this case. The point is not only to do the job, but also to learn how to do it. Let's just say that in saying that "I'd like to fix this", on balance, I put more emphasis on "I" and less on the "fix it" part. If I botch the repair, I will have still learned a lesson. I can't simply forego that opportunity. :-)
Tim, I have though about epoxying. That is still an option, of course. I was thinking that I would have to either Vee-groove or dovetail each crack before filling. But I suspect that the service life would not be the same as with a weld or braze repair. Additionally, proper metal epoxies are pricey, and in my mind JB Weld and the like are more of a trail-side repair that needs to be redone once you get home.
What I'm looking for is advice from experience on whether to use TIG and filler or a propane torch and those fancy Alumalloy-type rods. Also, some guidance on how to prep the work area: clean, v-groove, chem-treat, etc.
Thanks! -- Ilya
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I would try and get a ruined case / chunk of case somewhere and experiment on that. You could find out if tig welding the crack is going to work without ruining your valuable part.
Happy groundhog day.
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herman munster wrote:

Preferably from the same model and year of bike -- the alloy they use will probably be their own, and will have a significant impact on what you need to do.
--

Tim Wescott
Wescott Design Services
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If you want to try TIG welding on bike parts, then firstly you need to know what the parts are made of (some cases are magnesium). Secondly I would advise baking the part needing repair, in an oven to remove all oil residues from the casting. Thirdly DPT the part and mark so you can see exactly where the cracks are, and then drill 3mm holes at the ends to prevent cracks spreading further. Next step is cleanup of part, ideally using blast cleaning, then veeing out so you can get a good weld. Finally you are now ready to weld and if the case is aluminuim rather than mag, something like 1.6mm 4043 filler, using a 1.6mm ceriated tungsten will work pretty well. However on a crankcase repair its very very easy for a beginner to put too much heat into the part, and either destroy it entirely or mean that its needs machining before its usable. As other poster has said it would be a very good idea to get hold of some damgaged bike cases, and attempt to repair them first. Finally I personally would forget about using any of the zinc/tin solder products for a repair like this, as any failure could result in major engine damage, and possible personal injury to yourself.
k
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Thanks for all the encouragement and advise. I will try to give it a go this weekend. I will stop by a nearby bike shop and see if they have some junk casting for me to practice on first. Hopefully, that'll let me zero in on the right technique. Will try using a copper or stainless heatsink to prevent melting too much of the base metal. I don't think I'm worried about getting complete penetration, since all I need is a decent oil seal, not strength.
If all fails and I botch the job, my next step is to learn aluminum casting and make the whole part from scratch. :-) Not really, though it would be pretty cool to try. I need to do some reading on that.
Following Rob's advise, I ordered 1lb of HTS2000. I may try it for this repair, but it sounds like a good thing to have lying around. Whenever I go on trail rides or to the race track, I always brind a small torch with me, which already came in handy a fouple of times for soldering the control cable crimps. Sounds like a few of those HTS rods would be a welcome addition to my emergency repair kit. -- Ilya
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Is the TIG you have an AC/DC set? If its DC only you are not going to find welding casings that easy. Before trying any sort of welding on a casing, make sure you can weld together 2 pieces of aluminuim sheet, that are about the same thickness as the part you want to repair. You dont have any need to use a heatsink for this sort of repair...............TIG welding does mean the amount of heat you are putting into the job is very easy to control accurately.
k
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I mentioned that it was a squarewave inverter TIG in the first post, so it is AC/DC. I can butt-weld 1/8" aluminum sheets fairly well, but I have mostly welded 6061. I am not sure what alloy they used for the engine casting, and whether it is as weldable as 6061.
I'm sure that between all the helpful replies that I have gotten so far, I'll be able to get it done. I'll try to remember to report back on how the repair went after I'm through.
Thanks! -- Ilya
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Thanks to all who helped. I ended up just TIG-welding the cracks and grinding/filing to shape.
http://iillyyaa.smugmug.com/photos/52503000-M.jpg
http://iillyyaa.smugmug.com/photos/52506534-M-1.jpg
One thing I discovered (or should I say confirmed) is that an old oil-bathed aluminum casting has a lot more impurities in it then, say, a brand-new extrusion or a freshly machined billet. And that all those impurities seem to be trying to find their way out, right though my weld puddle. Gack! -- Ilya
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snipped-for-privacy@gmail.com wrote:

The trick with oil contaminated parts, is either to bake in oven to sweat the oil out, or alternatively to do with same thing with your TIG arc. Only start welding when all the black contaminants have bubbled up to the surface, and been wire brushed away.
k
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It looks to me like the damage is in unstressed areas. If so, an epoxy repair would be much easier, safer, and adequate.
Don Young

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Crankcase of a 2t MX engine is not unstresed!
k
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Ken wrote:

Good advice, except unless you get some advice here, how do you know if the person you take it to really knows what they are doing.
I am interested in what the replies are on this. I have a Briggs and Stratton lawn mower engine with a cracked aluminum case. It was given to me so no big deal if I can't repair it, and the lawn mower shop did not think it was worth trying to repair. Damn motor runs as it is, but of course leaks oil.
Dan
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snipped-for-privacy@krl.org wrote:

This repair is very small, but still as said before, very hard to get rite first time.
Any form of welding is going to add material to the part, requiring good machining/cleaning to get a good oil seal.
I am very BAD at welding Aluminium, with both MIG, and GAS, never tried TIG, so when my Thermostat housing cracked I needed a cheap repair as it was an old car, and there were few spares around to replace it.
I went to my local BOC, and they introduced me to TECHNOWELD. I believe its a form of Alloy, which is used to Braze, rather than Weld.
You have to get the area up to the annealing temp of Aluminium, tested with soap, you then add the rod, which at this point often sits in a ball, but after using the Stainless Steel wire to cut through the oxidised layer of the Aluminium it all works fine.
Got a great fix, and very little cleaning after.
This stuff will also fix coper pipe to aluminium fuel tanks good enough for the MOD, so it is good stuff if used correctly. Costs around 25 for the basic set, and any form of reasonable heat source will do the job, it doesn't have to be Oxi/Asset, but it must do the whole area, so I'd suggest baking it on High for a few mins in the oven first.
OK not a true weld, or probably the best fix, but this is the way I'd go if it were mine, but remember cleanliness is the real answer with this stuff. Try the TECHNO web site for more info:
http://www.hindleys.com/technoweld /
Hope this helps, all the best
Vaughn
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If this is in an area of the case that is flat all the way around, I'd be tempted to use a flat piece of aluminum and drill and tap a bunch of holes around the edge of the hole to hold it on. Apply gasket maker, screw down and ignore. It's okay, you can stop cringing now...
--Glenn Lyford
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On 8 Jan 2006 16:47:48 -0800, snipped-for-privacy@gmail.com wrote:

How easy is it to get a new case ? From my limited experience with bikes, they seem to consume heads, cylinders and moving parts, but cases for popular models just accumulate. If you could get another case, should you need one, then I'd dive in with the TIG and try welding it.
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Ilya, This is one of the instance where there is a rod that you can fill in the voids rather easily with MAPP gas or a rosebud on a ox/act torch easily. I have preached this stuff in the past, I have clients using it. I use it religiously and have nothing but positive things to say about it. Others on this group have tried it as well and have had positive results as well. This even being noted on a casting such as yours, I know it works. I just fixed a cracked KX-250 that took a rock through the lower case and cracked it but good. Three weeks of hard riding and it does not leak a bit. I have attached a web-page link to the manufacturer. It's well worth you investigating and myself, and some other of the crew here can help you out if you need it. I don't know how severe the damage to the cylinder wall or piston and rod are but while you have it split, a hone and a new rod/piston if needed is the way to go. Also, I have used a GTAW torch on DC- to heat this rod up into cracks as well.... Works like a champ. It's HTS2000 rod and here is some info and the link to the vendor/manufacturer. The video clip is well worth watching to see if it meets your repair needs. This rod is NOT ONLY for Al. it and others are out there on the site for your need but the Kawasaki is held tight with the 2000. http://www.aluminumrepair.com/order.htm
Respects,
Rob Fraser
Fraser Competition Engines Chicago, IL.
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Having looked at your project. That Subframe is Aluminum right?
if you can do that you can easily close the cracks and i WISH i could weld AL that cleanly
its extremely important that you said that the frame is NOT a stressed member/ you would not want to screw with the temper or heat treat of a part
the cracks seem to be small and because all you need is a seal you could reflow them, basically melt the Al at the edge of the crack and walk the pool right up to the edge of the case it will just melt and reform. I would recommend putting some material like steel or copper though so that when you rech the edge you dont drop through or "Pour" the bead out past the edges
But I'm no certified welder either
If youre operating under the assumption that if you didnt know how to weld you replace the cover and if you mess it up youre no worse than you are going to just be abel to give it an honest effort and if you mess it up oh well youre no worse off.
IN theory if the welds work youve fixed it for a few dollars of gas and electricity and an hour or 2 of work
really nothing to lose ad a lot to gain and learn
snipped-for-privacy@gmail.com wrote:

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