Cam runout
- Thread starter jimbo
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My NOS 06-1084 real original norton factory = 0.000"
My later, bent from new, combat cam = 0.0015" runout
I had expected more, but I did try to press it straight and ended up using my new from shenstone norton combat cam that I picked up when visiting norton. Pete Kogut and I were there to interview Philip Leroux(sp) for the INOA newsletter.
My later, bent from new, combat cam = 0.0015" runout
I had expected more, but I did try to press it straight and ended up using my new from shenstone norton combat cam that I picked up when visiting norton. Pete Kogut and I were there to interview Philip Leroux(sp) for the INOA newsletter.
acadian
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I just assembled a motor with a new cam, thrust washer properly oriented and placed, and with new cam bushings in the cases (1 piece, tophat to the inside).
With the cases assembled and no cam sprocket or tach gear, and with the cam pulled up against the TS bushing, the cam lobes were perfectly aligned with the followers and the cam journal lip sat flush with the edge of the TS bushing in the timing chest.
With the cam sprocket and tach gear installed I have 0 runout.
With the cases assembled and no cam sprocket or tach gear, and with the cam pulled up against the TS bushing, the cam lobes were perfectly aligned with the followers and the cam journal lip sat flush with the edge of the TS bushing in the timing chest.
With the cam sprocket and tach gear installed I have 0 runout.
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jimbo
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Yea ,but the threaded hole to mount the rotor would be OOT also
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I've just removed the timing cover from a bike I'm trying to bring back to life. I wanted to check the cam chain tension and replace the oil pump to cover seal. The chain tension varied wildly between the correct degree of up and down movement and being quite taught. A dial gauge revealed camshaft runout of 0.010" at the timing cover seal location. I'm surprised that 10 thou has that much effect on the chain tension and I haven't yet checked for other contributory factors, but if it does turn out that the runout is the sole cause then I would imagine that 0.005"would still be having a significant detrimental effect on the chain.
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If the engine is assembled, than the tight/slack is from the cam thrust against the lifter/valve spring. This would happen four times in two crank revolutions.
FWIW if I counted correctly, it takes 38 crankshaft revolution for "a marked chain roller" to phase shift all the way around to match back up with the chain sprocket dimple again. So wear or stretch would seems to be spread out among the whole chain set of rollers.
FWIW if I counted correctly, it takes 38 crankshaft revolution for "a marked chain roller" to phase shift all the way around to match back up with the chain sprocket dimple again. So wear or stretch would seems to be spread out among the whole chain set of rollers.
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I'd love for something in the timing chest to be the main cause of the uneven chain tension, so I don't have to open up the crankcases. The chain goes slack-tight-slack with one rotation of the camshaft. The factory manual gives useful advice; to use a spanner on the camshaft nut to counter the effect of the valve springs on the cam lobes and to make sure the lower run of the chain remains taught over the tensioner, so that all of the slack is in the top run.
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pop off the rocker covers and see which (cam) valve event is happening when the slack tight event happens
concours
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It bears repeating an old story.... my $225 (early VIN) combat when first disassembled (1988) showed crescent shaped wear patterns on each journal. Sure enough factory 2S cam WAS bent. I couldn't straighten it enough to satisfy myself, so I bought a new one. That was when I learned about the defective valve spring cups that were flat instead of contoured like the head. The cam probably coil bound one of the intake springs and the cam yielded...not welded cam...
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I already have the head off, but the point of maximum run out aligns, more or less, with the right inlet cam lobe which is the one furthest from the bearings, so it would be the prime suspect. Having said that the cam and followers look to be in good shape with no signs of friction heating or scuffing. The cam turns freely, but the dial gauge shows no clearance in the bearing. I'm surprised there can be zero clearance in the bearing and 0.010" run out where the sprocket is seated, maybe when I split the cases I'll find the crescent shaped wear pattern.
Yes
It's most likely the original cam since the bike has just 20k miles on it and the license plate shows tabs from 1995.
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If you have another cam sprocket , will be nice to check , some were not so good ..........
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bearings are on both ends?
RH/LH is normally in respect to the driver sitting on the bike
timing side is RH
drive side is LH
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Yes, I'm using the same RH/LH convention as you are. When I say furthest from the bearings I mean closest to the middle of the "beam" that's supported by the bearings. Closest to the middle of the beam will create the greatest bending moment for any given force.
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If I follow you the RH intake lobe is up (actually IIRC 13 degrees toward the rear).
A bent cam will wear away the cam bushing til there is just enough clearance to not drag anymore. So that might also indicate a bent cam.
Would it be a 200000 series engine? My combat was dead at under 10,000 miles
A bent cam will wear away the cam bushing til there is just enough clearance to not drag anymore. So that might also indicate a bent cam.
Would it be a 200000 series engine? My combat was dead at under 10,000 miles
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I have the cam out of the crankcases now and I spent a lot of time figuring out how best to measure the distortion or bending. Mounting it (the cam) between centers in a lathe I'm able to measure the run out at the journals and also at the base circles of two of the cam lobes The maximum runout is 0.008" at the timing side journal, but that might be a bit misleading since the cam is located in the cases by the two journals and the cam turns freely so they must be reasonably concentric.
Trying a different approach I clamped the timing side journal in a v-block and measured the run out at the two ends of the cam (by turning and re-clamping). There's a small amount of runout at the drive side journal and a considerable amount (approx 0.010") at the timing side nose. So, everything between the two journals seems to be reasonably aligned, but the nose (the bit that protrudes into the timing chest) is bent. It's hard to imagine how enough force could be applied to the nose (since it only protrudes by about 1 1/4") without damaging other stuff.
I have another cam and, taking the same measurements, that one appears to be bent between the two journals while the nose is still in-line with the timing side journal. If I put that one into the cases it binds and does not turn freely.
So that's two cams that look perfect, but are unusable. I've got to try to straighten them, or at least the one that's bent between the journals, the other one I think I would damage in applying enough force to the short nose.
Dave, do you have any advice?
Trying a different approach I clamped the timing side journal in a v-block and measured the run out at the two ends of the cam (by turning and re-clamping). There's a small amount of runout at the drive side journal and a considerable amount (approx 0.010") at the timing side nose. So, everything between the two journals seems to be reasonably aligned, but the nose (the bit that protrudes into the timing chest) is bent. It's hard to imagine how enough force could be applied to the nose (since it only protrudes by about 1 1/4") without damaging other stuff.
I have another cam and, taking the same measurements, that one appears to be bent between the two journals while the nose is still in-line with the timing side journal. If I put that one into the cases it binds and does not turn freely.
So that's two cams that look perfect, but are unusable. I've got to try to straighten them, or at least the one that's bent between the journals, the other one I think I would damage in applying enough force to the short nose.
Dave, do you have any advice?
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Camshaft straightening went quite well, it reduced the between centers runout by half and when installed in the cases the cam turns freely and there is only 1 1/2 thou runout at the nose (this is not the original cam with 10 thou runout at the nose). I was confident that this would result in very little variation in chain tension; but no, although improved there was still significant variation. So, next I checked the chain and sprockets. I haven't figured out a way to measure chain wear accurately, but the sprocket on the idler gear did not seem to be concentric with the bore. I checked a spare sprocket/gear which looked better and the chain will now rotate several revolutions of the sprockets before, occasionally becoming tight. It seems to be that, now and again, the chain climbs out of grooves cut into the steel surface (no plastic facing) of the tensioner. A little tweak of the chain and it falls back into the groove relieving the tension. I think I'l get a new chain and a (plastic faced) tensioner and call it good .
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