Upon assembling my NH -57 after it being in boxes since early 80*s, I met the following anomaly. There's an angular misalignment between clutch sprocket and engine sprocket. When I place a ruler against the clutch sprocket it shoots to the middle of engine sprocket teeths. After carefull measuring using the inner chaincase joint line, a ruler and feeler gauges + feeding the result in my calculator it seems that the gearbox main shaft is 0,5 degrees out of parallelity with the cranksaft. Actually the hole gearbox casing is at the said misalignment. Is this a common anomaly? After further investigation it seems that the gearbox lower pintle (dia 1/2 in) and the bore in the casing are both worn 0,2-0,3 mm. This happening at both ends causes said 0,5 degrees rotation in horizontal plane. I'm planning to bore out the casing to oversize and install eccentric bushings. Has anybody done a more straightforward rework? Regards, Vesa
Ariel altered the chain lines in 1956 to accommodate the fully enclosed rear chain guard. It is possible that your problem is due to a previous owner fitting incorrect parts. Do your engine and gearbox numbers match those given in the Draganfly catalogue for 1957? Is the spacer behind your engine sprocket the same thickness as quoted for 1957 NH?
Paul Jameson 36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), 54 4G Mk IV (project), Healey 1000/4 (project) Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser.
The inner chaincase line might not be a good datum, but if the crankshaft and the mainshaft are misaligned is the frame true in that plane? If you align the two in the way you suggest, will you have alignment in other planes? I hasten to add that I have no experience of this problem, just applying geometry from a few decades ago.
Thanks for your comments. There are no nonmatching parts as I know the history of the machine well. The spacer is .711 long as per Draganfly catalogue. So, I'm not talking about offset of the sprockets. Also, the frame is neither bent nor distorted. Maybe the first owner didn't have the gearbox bolts properly torqued, thus causing the wear of lower pintle pin and the casing bore. Anyway, the direction of the moment caused by primary and rear chains to the gearbox is same as the misalignment in my case. If I get the mainshaft parallel to the crankshaft, there shouldn't be misalignments in other places, since I'm not moving the gearbox sideways.
Vesa I had a similar problem with wear in my 1951 Triumph 6T bottom gearbox pivot. It was impossible to adjust the primary chain with the correct play as the pull of the rear drive chain twisted the gear box on the worn pivot, tightening the primary chain and twisting the clutch sprocket out of alignment.
I bushed the pivot hole and that totally solved the problem.The only equipment I had to re-drill the pivot hole with some degree of accuracy was a pillar drill. I have attached a video of how I went about it. I know the procedure is a bit rough and ready but it worked fine and the primary is now aligned correctly and the primary chain maintains the correct tension.
I did not use eccentric bushings, I centred the drill in the unworn section at the mid point of the pivot hole and used a parallel bush.
click play and then click on the YouTube text to view it on You Tube and then you can see it full screen. Cheers Alan