Hitchcocks Forum

Has anyone any tips on a good way to split iron bullet engine cases. The engine has been stood since the 70's and was seized. After a couple of months of soaking in diesel I got the barrel off. Managed to break one fin, now expertly welded back on by a fellow club member (thanks Paul). I have finally got the timing pinion off the end of the crank and can't see anything else holding the cases together. The trouble is there's nowhere convenient to lever or tap to get them apart and I'm paranoid about doing any damage. They look well and truly bonded together, any tips from those that have done it before?

Hi Chris: I would suggest heating along the joint which might, with a bit of luck, crystalize the sealant and cause the cases to expand and spread apart slightly, then tap one side with a hide-faced hammer or heavy hammer on a block of wood. I must admit that I have never had to do this on any motorcycle myself, but am talking from experience of doing similar jobs on commercial machinery. It might also help start separation by gently tapping a sharp knife into the joint to start it off, taking care not to gouge the aluminium. Make sure there are no circlips retaining bearings which will foil all your efforts. As they say in the colonies,`best of British luck.'

Hi CHRIS, ---------------- soaking for months !!... You must have the patience of a saint ??...With regards to parting Aluminium assy's. in general, I have used the heating method before but heat the whole assy. until stinking-hot---then leave in a cold garage etc. to cool down. Repeat a couple of times-- the idea is the expansion/contraction eventually disturbs the bond between the two mating faces.... enough for more "traditional" methods to then be used..( I'll leave that bit to your imagination !!).

Nowt wrong with diesel oil for penetrating (sounds rude)but as said it`s heat treatment for breaking that seal.

hi chris ,try nice and carefully !!!i don,t have access to aluminium welding kit at the moment!!
atb paul

Hi Chris. I reckon the mainshafts have rusted onto the main bearing inner races.... By heating the crankcases in a hot oven at 200 degrees C for about half an hour will ensure that the two halves separate easily, as any tight main bearing will slip out of its alloy housing. This will not harm the cases at all. In fact you will have to re-heat in the same manner anyway to remove the remaining bearings by slapping the case down on a wood block. As your cases are saturated in diesel, I would wash the cases with petrol then have a large bowl and use very hot water and detergent to wash of the petrol and allow it to dry. If you use a large quantity boiling water there is a good chance that this heat might be sufficient for separation, but if not, allow the case to dry which will be very rapid and then do the oven baking. The hot wash will remove most of the smell, but the oven can be de-odoured by taking it up to maximum temperature for a short time and allowed to cool with the door open.

BTW, I do not think the central crankcase jointing goo is holding it all together, Every old case I have separated, the jointing goo has always become brittle and has no holding power at all...as said it will be the rusty bearings preventing separation....Oven baking will ensure the cases just fall apart with ease.

Great, thanks all for the replies, heat it is.

Just to add I would never recommend localised heating with a gas torch. Aluminium is a very good conductor of heat so as you are piling in the heat at one spot it is constantly soaking away into the surrounding areas and then being lost by convection. All you will have is a temperature gradient across the cases, so to get the wanted areas heated to say 200 degrees C you will never get there unless you raise the localised temperature of the metal you are heating way OVER the 200C level as the second you stop, the temperature drops instantly as the energy is sapped away into the rest of the case material. Not only that the temperature of a gas torch can easily reach 1300 C and more so you stand a very good chance of damaging the alloy if not melting it. Stick with oven heating. The air inside the oven will be regulated very close to the setting you choose (I recommend 200C) This will ensure the not one part of the engine will rise above the regulated temperature, and every part of it is at the SAME SAFE temperature...BTW I check the temperature of the heated cases with an Infra-Red digital thermometer, so I know they have been fully heated.

Forgot to mention that localised heating can cause distortion of the cases too as if one part is heated hotter than another part. The area of hot expanded metal will be forced to distort the cold neighbouring metal to accommodate for the greater size of the hotter area. However, on cooling the distorted neighbouring cool metal is not likely to bend back to where it was before being forced to bend so is likely to remain distorted, that is of course, if it hasn't cracked already from the strain. This stress event doesn't occur when everything is heated uniformly in an oven.