Dismantling a Seized Engine


    When I got the first 350/4, the engine was in a rather sorry state, 2 plugs were missing – so the bores were rusty.  The sump pan and oil filter housing were missing, so there was no oil to preserve anything.   As I had another part stripped engine from the autojumble parts I had bought, I used that initially, but had always intended investigating using at least the crankcases from the seized one as it has the correct early engine number.


Stage one - Assessment


    No fins broken, no bolts butchered, all tappet caps undamaged, original (but smashed) speedo showed 10000 miles and judging by the condition of other parts, this could well be correct, so this engine might be worth a closer look;  on removing the cam cover, everything was very clean, with no evidence of previous work having been carried out.  The cam lobes were lightly scored but not scrap.  The alternator stator and cover were missing but the rusty rotor was still there, which allowed me to determine that there was end float present at the crank – this at least told me that the main bearings were not seized.  Sods law dictated that the motor had stopped with only one cam sprocket bolt accessible, so how was I going to get at the other one when I couldn’t turn the cam?  



Stage two - some drastic measures


    There is precious little room to split the chain anywhere and I had a couple of spare cam sprockets from 400’s (same part number), so I hack-sawed across the chain side plates and into the sprocket and let the chain drop.  The cam could now be lifted away.  The head came off surprisingly easily, to reveal a few stuck valves and a red, white and black dried sludge in two of the bores.  I filled the bores with diesel and just left everything to soak for a few weeks, occasionally replenishing the supply of diesel. 


    Returning to the motor sometime later, guess what had happened? ---- nothing, so it was time to think about stripping the whole thing to try to get to a state where I had crankcase top, barrels, pistons and rods separated from the rest.  I will not go into a blow by blow account of how to strip a 350 or 400 four engine – there are plenty of excellent manuals for that purpose.  Have you noticed though, how they glibly say that ‘reassembly is in the reverse order of removal’.  Cobblers!!  They neglect to say that you need to be a malformed dwarf, with three bent fingers and a broken thumb to get some of the bits back again!  (No offence to anyone who might possess those particular, occasionally useful attributes)


    Dismantling the clutch really confirmed that this was indeed a low mileage motor - the whole assembly was like new.  Next to come away was the gear-change mechanism, followed by the whole points assembly and then the oil pump.  It was now time to separate the crankcases and remove the big end caps, so that the crank could be extracted from the rest.  A visual inspection cheered me up - there was no evidence of scoring or wear.  Next to be removed were the gears and shafts - again all looking in excellent condition.


    I now carried the crankcase top, barrel, pistons and rods over to the hydraulic press to try to remove the 3 stuck pistons, the whole assembly only just fitting in the space between the press sides.  I protected the mating faces with hardwood packings, so that nothing could be damaged.


Viola! but easy does it, as the barrel has to be raised gradually, with progressively thicker packing pieces under it.



Stage three - reassessment and measurement


    All big ends and little ends were free, but one cylinder bore was badly marked.  Liners are now unavailable, so I decided to make one.  I gently heated up the barrel and pressed out the liner, after turning a suitable mandrel to fit the bore.  All pistons came away without any damage and miraculously, so did the rings!  Many folks reading this might find it strange that I should contemplate using the original piston rings in this engine.  I will pose these questions:  What are we hoping to accomplish when we restore a machine of this type?  Are we intending to use it for travelling 15000 miles each year at full throttle?  Or are we merely going to potter around a bit to an an odd show or two and perhaps enjoy an occasional 200 mile round trip.  I think I know the answer in the majority of cases.  With this in mind, I carefully measured and closely inspected all of the important features.  Naturally I would not dream of re-using gaskets, 'O' rings or lock washers, but I see no reason why unworn components should be needlessly scrapped, it's all a matter of careful judgement.  We all frequently see top notch restorations, having thousands of pounds spent on them, which will never actually be completely run in again in their lives.




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