English French German Italian Spanish

Camshaft problems

Submitted by warren_dagnall on Tuesday, 3 July, 2012 - 01:00
Forums
Heavy Twins

Basically my 57' 99 dommie died on me the other weekend - it seems the woodruff key on my camshaft has sheared, meaning the gear will spin on the cam. one of the lobes (lh ex) has picked up a little burr on the crankcase in the follower cutout, the lobe now touches this on every revolution. another lobe (rh ex) has left signs of touching the crankcase on the lowest part of its travel.

also the cam seems to run a little out of true, although this could be something to do with the casting not being parallel to the machining?

cam endfloat is 15 and a half thou, there doesn't seem to be any up/down play.

no marks on the piston crowns or valves, all of which are straight and true.

anyone have this before or any suggestions for me please? - I'm going to have to split the cases by the looks of things, I'm guessing the woodruff key hasn't broken on its own accord - what could have caused it?

Submitted by gordon_johnston on Wednesday, 4 July, 2012 - 01:00

Permalink

It sounds as though your camshaft is bent, though it usually takes an impact by a flailing conrod to do that. Yes, a split of the crankcases in required .

Submitted by alan_dawes on Wednesday, 4 July, 2012 - 01:01

Permalink

I doubt it would run OK for long with a bent camshaft. Failed camshaft bearing? Either way Gordon is right; take it apart.

Submitted by warren_dagnall on Wednesday, 4 July, 2012 - 01:02

Permalink

well, its apart - I measured the runout on the cam before removing it - although only on the unmachined surface near the middle, right next to a lobe it was 0.4mm / 15 and a half thou. I guess this area might be a little off anyway as its not part of the finished machining although it would send it out of balance.

the bushes either end look good and there is no damage on the cam, no markings on it either to identify.

removed one of the big ends and its clear that some junk has gone through there, also some scoring on the crank - mick hemmings is taking the pinion off tomorrow so I'll ask him about that.

still not found anything that might break the woodruff key - maybe it was just worn out when it was installed?

Submitted by gordon_johnston on Wednesday, 4 July, 2012 - 01:03

Permalink

Could a valve spring be coil bound on full lift? Something may have inhibited free turning of the camshaft. Usually, a pushrod would bend rather than the camshaft shear a woodruff key. Is it a standard camshaft? I presume so. Most odd. A snug fitting key rarely breaks.

Submitted by warren_dagnall on Wednesday, 4 July, 2012 - 01:04

Permalink

Cam is interesting - as mentioned above - no markings on it whatsoever, just measured its lift and intake and exhaust are both different.

Intake - circa 0.365"

Exhaust - circa 0.322"

Can't find anything close onhttp://atlanticgreen.com/camsurvey.htm

Fitted with radiused lifters - I've just found a little chunk of steel embedded in the cam tunnel that one of the lobes touches - could have been the cause of it locking up and snapping the woodruff key - looks very recent too.

I think the pistons are non-standard too - they have domed crowns stamped I.D.2, and inside the skirt is 16606, AE and AM413? - +60 though

Submitted by steve_marshall on Wednesday, 4 July, 2012 - 01:05

Permalink

Can somebody clarify for me how Dominator cams are located longtitudinally - I have seen camshaft thrust washers and shims listed, can't remember exactly where (maybe for Commandos). The official parts list has none.

Is it just a case of the flange against one side of the T/S bush and a sprocket on a woodruff key up against the bush on the other? Losing the woodruff key wouldn't let the cam move though, unless the nut came loose.

Looks like you would need a new pinion to restore the correct interference fit.

Steve

Submitted by phil_hannam on Thursday, 5 July, 2012 - 01:00

Permalink

I once examined a 99 with a similar problem. In this case, the thread on the end of the camshaft had not been cut long enough and the nut was consequently failing to put any load on the sprocket. I have also seen a similar problem with magneto auto-advance units.

On another Dommie engine, I looked at, that had both sheared the key and bent the shaft, one of the Stellite feet from a camshaft follower had broken off and then wedged between a lobe and the cases. Check out everything in your engine that moves.

Submitted by warren_dagnall on Thursday, 5 July, 2012 - 01:06

Permalink

Thanks Phil, just had another look at the camshaft and it has a 5mm spacer on the gear end (same o/s diameter of the bit of the cam that the gear fits on) effectively covering a thread or two - looks to be home made, so this could be part of the issue. No obvious issues with the followers, but the 2 cast follower tubes on the barrel both have chips missing from the edge, this looks historical though and the piece of metal I found embedded in the crankcase, under a lobe, is certainly not a piece of cast.

crank split today and didn't find much in there except 3 bits of a rubber seal? still on its standard grind, and needs taking down to -10 due to scoring and slight wear.

Another question about the cam - its got 4 cutouts for a woodruff key - is this normal? - also the followers seem to be 5" diameter?

I'm very new to engine building, let alone norton engines, so please bear with me

Tom

 



© 2024 Norton Owners Club Website by 2Toucans