Discussion in 'Norton Commando Motorcycles (Classic)' started by concours, Jan 8, 2018.
Very good. It's 50% obscured. I'll relieve the new shell to suit. Other rod is spot on.
Kind of disconcerting that its off that much.
Maybe too tight a clearance C1 or C2 bearing fitted instead of C3? If case bores still need serious heat to release/replace outer races from cases then lucked out big time. The end of the flake damage distinctly ends at outter edge of less worn inner race rim. Hm. Cranskhaft combustion heat and loads would heat bearing from cheek outward most with coolest part deepest in case from oil flow and case heat conduction. Too tight installed clearances with rollers getting hotter at one end than the other, taking on a cone shape may account for the damage size and shape. Rare but case bores might be tad tight another checking consideration to avoid another flaky image.
Ever keep track of wrenching worrying vs relaxed riding hours?
That engine owes me nothing... 31,000 miles of spirited great riding times.
I'll be checking everything, to rule out a repeat performance.
hehe that's the spirit fix em up use em up till ya can't. Such obsolete cycles just shouldn't keep exciting us easy thrill seekers so much but sure glad they do. Ok inspired enough to go shopping again, thanx I think.
Looks obstructed from here, so be it.
It is obstructed. I think my choice of word was poor...
not a problem. you can even totally block it by swapping the top and bottom shells with NO bad effects and some do it deliberately.
If you buy Carrillo rods etc, they do not come with oil holes as standard. So many a good engine has indeed been built without these holes, with no ill effect.
If you think about it, where else can the oil go? Without the holes, more will simply exit out of the sides of the shells and result in ‘splash’. Thus essentially doing the same thing as the hols would have. Plus, the added pressure build up caused by not having holes, must be beneficial to the big end journals.
What is the actual bearing ? is it dot 2 or 3 . The factory did turn to Japanese suppliers at some point who seemed to prefer tighter clearences For instance the factory fitted sleeve gear bearings (made in Japan) were dot 2 and they failed...But there is another possible issue here, there is no positive crank location with double roller bearings so maybe there was excessive endfloat
The seriously disconcerting thing about oem rods is that the factory stopped balancing them one against the other, engineering by accountants who thought that because the rider would not feel vibration thanks to the isolastics there was no need
Engineering by accounting...sounds much like my place of employment It's Ok to sit on a paint shaker as long as the seat and bars don't move, right?
More like lack of investment in tooling and modern design. And not taking the competition seriously. Wonder how many of us are rolling on cases align-bored with a chunk of 2x4 jammed between the arbor and the upright?
the late John Hudson who worked at Bracebridge street said that the machining of the crank cases was so accurate that they were treated as being interchangable..There is actually an amazing website called workingatamc.. What astonised me was how uptodate the tooling in use at Plumstead actually was.. The engineering by accountants came later and was simply penny pinching. Do not know what year it kicked in , but if i had a Combat engine certainly I would want to ensure the rods had been balanced. 72 saw the most number of revisions to the original engine..
What are you using for ignition.
Too much advance will do that.
Not Norton, but when I replaced the timing side bush on my BSA A10 I mounted the drive side on the mill table, indicated the main bearing hole to within +/_ .0001 and then bolted the timing side case on. It was almost .008 out of alignment. Ended up fabricating a much undersized bushing and boring it to suit. These were matched number cases, unknown number of miles, but the holes were still round, just not aligned.
Might that be the effects of pre-ignition then Jim? Excessive combustion chamber pressure putting a much higher load on that one spot of crank rotation?
Boyer, 1980 mfg. date. I strobe timed it, it felt numb, Dyno dave heard me ride across his yard, "sounds retarded"...
So, I bumped it up a couple degress until it pulled and sounded good, yet no audible pinging.
The half dozen times I got shit gas sold as Premium, it would audibly protest 1/2 to 1 mile from the pump. I'd try to go easy, not ask much of it, free rev rather than lug, and dilute with (another attempt) at good fuel after 30-50 miles.
There were heavy combustion chamber deposits, so compression could have been a bit up.
That is the only reason I do not like the old analogue Boyer.
With the lazy advance curve it has you have to advance the timing quite a bit over the recommendation to get it to pull strong through the midrange.
Then you end up with 36 degrees at 5000 rpm and that is too much. Even without audible pinging the bearing load would have a spike that probably shortened it's life. Jim
Huh, too adv spark would resist crank journals rise, which would bow mid crank down so ends supported in bearings would tend to 'piviot' there and pry upward. It was sloppy point adv mech in early Combats that vastly accelerated their crank bearing fails. So real 1st cause may of been trying to nurse a failing battery too long.