splitting the crank case
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eric650
- Posts: 5
- Joined: Mon Jan 01, 2001 12:00 am
- Location: CUMBRIA UK
splitting the crank case
Hi I think my big ends are worn my question is can I split the crank cases without removing the timing gear? Or is this just a silly question I should add this is a 1960 AJS Model 31 (650 twin)
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eric650
- Posts: 5
- Joined: Mon Jan 01, 2001 12:00 am
- Location: CUMBRIA UK
Re: splitting the crank case
I found this info on the site I wonder if I can split the cases without removing the timing gear?
Note. Any work must be done using an instruction manual, all you have here is advice. Before starting any work read instruction manuals completely !
Dismantling the engine is not difficult and no special tools are required until after the crankcases have been separated. The cylinders may have to be eased out of the crankcases by tapping very gently with a soft headed mallet.
The crankcases can be split without removing the camshaft timing gears by simply doing the splitting operation upside-down. The camshafts can then be pushed through the gears. The timing side pinion and magneto gear have to be pulled off with a screw type extractor.
The timing pinion bolt and the camshaft nuts have left hand threads.
A valve guide should be removed by pushing it out from the combustion chamber side just far enough for the circlip to be removed. The guide is then pushed through to the chamber from the top of the head. This must be done with the head uniformly heated.
The roller main bearings outer races are kept in the cases by local peening. This has to be scraped back before the race can be removed. Usually it will come out when the case, vertical face, is dropped on to a sheet of wood after being heated to about 160 deg C. If the race is obstinate, clean it thoroughly and glue a small piece of clean 1/8" steel plate across the face of the race using Araldite. Make sure you do not get any glue on the crankcase. Heat the lot again to about 160 degrees C for about half an hour. Then try to remove the race by tapping against the plate with a drift from the outside of the case.
The camshaft bushes and intermediate gear spindle can be drifted out of the hot cases. In all such operations, the case must be well supported in the direction of the drifting.
The crankshaft big end journal sizes can be decreased to 0.060 and 0.080 inch if Mini (BMC A-series engine) shells are used. The width of the shells have to be decreased by 0.030 inch and the anti-rotation slots cut in the opposite side of the conrod end cap (the wisdom of this modification can be questioned). I know of nobody who has had the journal surfaces rebuilt successfully and I doubt if it can be done (the depth to the journal surface from the rim of the flywheel is probably too great). It should be noted too that rebuilding does not restore the strength and is not a cure for sharp fillet radii, the alternative is to have a new crank machined out of steel such as EN24. At the same time, it may be worth changing the conrods to a steel pattern variety. (This option is very costly and should only be entrusted to someone who knows what he is doing).
The best way to grind the centre main is by using a grinding machine which holds the crank between dead centres, the next best is between a chuck in the mandrel stock and a dead centre in the tail stock, if the run out is very near zero. The worst - but also the easiest - is between two chucks.
Regards Eric
Note. Any work must be done using an instruction manual, all you have here is advice. Before starting any work read instruction manuals completely !
Dismantling the engine is not difficult and no special tools are required until after the crankcases have been separated. The cylinders may have to be eased out of the crankcases by tapping very gently with a soft headed mallet.
The crankcases can be split without removing the camshaft timing gears by simply doing the splitting operation upside-down. The camshafts can then be pushed through the gears. The timing side pinion and magneto gear have to be pulled off with a screw type extractor.
The timing pinion bolt and the camshaft nuts have left hand threads.
A valve guide should be removed by pushing it out from the combustion chamber side just far enough for the circlip to be removed. The guide is then pushed through to the chamber from the top of the head. This must be done with the head uniformly heated.
The roller main bearings outer races are kept in the cases by local peening. This has to be scraped back before the race can be removed. Usually it will come out when the case, vertical face, is dropped on to a sheet of wood after being heated to about 160 deg C. If the race is obstinate, clean it thoroughly and glue a small piece of clean 1/8" steel plate across the face of the race using Araldite. Make sure you do not get any glue on the crankcase. Heat the lot again to about 160 degrees C for about half an hour. Then try to remove the race by tapping against the plate with a drift from the outside of the case.
The camshaft bushes and intermediate gear spindle can be drifted out of the hot cases. In all such operations, the case must be well supported in the direction of the drifting.
The crankshaft big end journal sizes can be decreased to 0.060 and 0.080 inch if Mini (BMC A-series engine) shells are used. The width of the shells have to be decreased by 0.030 inch and the anti-rotation slots cut in the opposite side of the conrod end cap (the wisdom of this modification can be questioned). I know of nobody who has had the journal surfaces rebuilt successfully and I doubt if it can be done (the depth to the journal surface from the rim of the flywheel is probably too great). It should be noted too that rebuilding does not restore the strength and is not a cure for sharp fillet radii, the alternative is to have a new crank machined out of steel such as EN24. At the same time, it may be worth changing the conrods to a steel pattern variety. (This option is very costly and should only be entrusted to someone who knows what he is doing).
The best way to grind the centre main is by using a grinding machine which holds the crank between dead centres, the next best is between a chuck in the mandrel stock and a dead centre in the tail stock, if the run out is very near zero. The worst - but also the easiest - is between two chucks.
Regards Eric
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1608
- Member
- Posts: 2493
- Joined: Mon Oct 05, 2009 1:00 am
- Location: ESSEX UK
Re: splitting the crank case
Eric, I answered your first post in the 'HELP' section.
Re this query, I can't say I agree with all of it, especially 'pushing the cams through the gears'. Anyway, I think you had best stick to the manual to the letter or seak some competent help from somebody close to you.
Re this query, I can't say I agree with all of it, especially 'pushing the cams through the gears'. Anyway, I think you had best stick to the manual to the letter or seak some competent help from somebody close to you.