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separating navigator crankcases



I've got to the stage of trying to separate the crankcases on my navigator. (I believe) I've removed all of the bolts etc holding them together - including the hidden ones - does the separation require pullers of any description (as someone has mentioned to me) or should they separate with a small amount of heat and persuasion? It's one of the original 'de lux' models 1960 and I would think the engine hasn't been split since it left the factory 60 years ago so it's being slightly stubborn. But for obvious reasons I don't want to 'push it'


Thanks in advance for any tips / help / guidance




Over far to many years in mechanical maintenance I've split all kinds of casings, (gear boxes, motor covers, cylinder end plates, etc), many of which hadn't moved since leaving the factory. After checking that all bolts, screws, fasteners etc have been removed, (check then check then check again just to make sure), a tried and tested method is to use thin wedges lightly tapped in to the joint along its whole length. As you move along the joint you should find it starting to open up. Once it opens it will be necessary to keep the faces square to each other until the halves separate enough to clear any locating dowels. Gentle heat applied along the joint should release any sealing compound and lightly tapping with a hide (or rubber) mallet may help to loosen things up. Whatever method just be careful you don't crack the cases. Remember "softly, softly catchy monkey".



When you say the hidden ones, don't forget the one in the gearbox - of course you have the two hidden in the cylinder head sleeve holes.. I had similar issue and did not have them all out. Glad I checked before I got too keen.


What you need is a steady pressure between the case halves while you heat around the bearing housings and bump the case mouths appart using a softwood drift and mallet. I have not have had to resort to wedges but have had to fill the bruising caused by clumsy use of metal wedges.Its also likely that the bearings are too tight a fit to the shafts , so heating around the cases may allow the bearings to come out of the cases.  Shafts can be eased a bit for re-assembly.


Hi Chris,

If you get a good quality kitchen knife with a sharp blade. I bought one from Ikea about 3 ins blade. The wife wouldn't let me use her Sabatier knife.

Find a likely place like the rear of the crankcases or near sump, put the sharp edge into the joint, and tap the back of the blade with a light steel or copper hammer. Don't use force and just let the blade taper do the work. No levering. Move along as the gap develops.

Robert and John probably don't realise that the drive side roller bearing will separate without any resistance. The inner stays on the shaft and the outer stays in the crankcase.

Andrew has the right suggestion in that you may have left one of the fasteners in place. Have you removed the two cap screws deep in the timing chest alongside the gearbox wall? Hidden by the timing cover gasket. As well as the ones between the cylinder locations?

Good luck with this one.



hello guys  well soon I will be separating my set of crankcases normally I sit the left-hand side on my wooden made square bloc witch is made from four 1.1/2 thick mahogany by 6-inch across and six-inch square  so you can sit on there and the crankshaft is free and does not touch anything and then you can work ok  and normally heat  the right-hand side with a good plumbers gas blowlamp so the ball timing side bearing come out with not much trouble  but with the navigator, I suppose you do this operation from the other way round as it has a gearbox  to consider  so this leaves the gear cluster in situ   after removing the clutch and drive side gear all in one with its twin-row chain  and then the drive sprocket which has a left-hand thread  and warming the left-hand cases  so the bearing do not give that much trouble,  and my navigator engine as a mystery problem as when I bought it I was told it was a Seized engine  but after removing the primary cover and getting out a spanner and trying to turn the engine over it was free to a point  were you could only turn it over about 2/3 thirds of the way and it then stopped  would not turn any farther  then after removing the rocker covers  and checked the valves were operating they were all ok  so its not that  so next is to remove the cylinder heads and investagate even more  into this problem  and the other problem I have is finding a rear wheel rim to the right spoke pattern  as centeral wheels are convinced the rear wheel are 19 inch and 40 holes  where I count 36 holes and a 18 inch rear  wheel rim,   or sould I  tell them is a Francis Barnett rear wheel rim intead  cannot any put so light on this  , yours  Anna J  


Interesting that the 1964 parts manual shows different part numbers for the rear rim between 250 & 350 although the spokes are the same part number & qty (36).  Maybe a WM3 instead of the WM2 for 250 - or maybe lock bolt holes for the 350?


hello   rob yes that's what I found  and they same to be a bit arrogant too    like they know better then you that ownes the bike in question, your anna j

Anna, My 1964 standard Navigator rear wheel has 36 holes and is 18" dia I have a photo of the wheel before the rebuild if you need it for reference also I can let you have a copy of my drawing of the wheel offsets.

As to Central Wheels, I found them helpful and even got a bigger discount for being a member of the NOC and VMCC, quality of the rim and spokes are also good, must be down to the person you deal with.


hello, steve yes that would be really helpful contact me at  or phone me if you like too at 01430 430 831 anytime  for a chat  

Hi Bruce,

A knowledgeable friend of mine, Peter Fairbank, also very observant, notes that the Jubilee wheel rim carries the warning that this rim only suitable for up to 250cc. The Navigator rim carries no such warning. No lock bolt holes or WM3 either.

Hence the different part numbers.

I would not like to guess other differences between the rims which warrant the warning, but it explains the different part numbers for very similar 18inch, 36 spoke, chrome, WM2 rims.





Sorry to come late to the party.

Chris - did you separate your crankcase halves succesfully?

When you undo all the visible bolts and screws, there are 4 more to find. Two are in the timing case along the gearbox wall, & you need a very long Allen key to reach them - and there are 2 more between the cylinders - which are fiddly to remove.

Once they are all out, the drive side case should come off first. Make sure the conrods are at BDC. You can try to coax it with wood and a mallet, between the cylinders, back of gearbox & sump - or (if strong) try to thump the engine sharply down onto a solid bench - or lump of wood - onto the alternator end of the crankshaft. If its 60yrs worth of gasket goo, then work it gentry with the mallet approach.

Once the drive side is off - then support the timing side case as best you can (I use old shelving & car axle stands) with the crank hanging down and lots of old towelling below to catch it. You then need a sleeve to pass over the oil feed end (you must NEVER hit the oil feed end) of the crank, such that it abuts the crank under the bearing. I have sacrificed an old AF box spanner for this task.

With everything in place, a sharp rap on the sleeve over the crank should suffice to dislodge it. Again, make sure the conrods are at BDC, so they do not catch.


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