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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> another cam chain epiphany /cgi-bin/YaBB.pl?num=1239408660 Message started by verslagen1 on 04/10/09 at 17:11:00 |
Title: another cam chain epiphany Post by verslagen1 on 04/10/09 at 17:11:00 797566677C7578782527140 wrote:
Tech section is for How-To's, not What-if. |
Title: Re: another cam chain epiphany Post by verslagen1 on 04/10/09 at 17:20:18 Your task young paddle-on is to find a inexpensive mod, a cost effective bearing that will fit in the alloted area. |
Title: Re: another cam chain epiphany Post by marshall13 on 04/10/09 at 18:35:47 forgive my mis-placement of my original post... was kinda wondering why it hadnt been reponded to ...lol ... the bearing wont be a problem, got a ton of local distributors, and those are some helpful hungry dudes.... only problem is i dont have one of the bikes... ive admired them since their intro mid-80s, rode big 4 cyl hondas in those days, and had a 20 year plus riding hiatus... the local (sunny south east florida) weather has raised the 2 wheel fever in my blood again, and i was considering a savage, but when i read of the grenade/adjuster dilemna, i was ready to give up on them.... then epiphany struck.... so, ill answer the assignment with a request... if one of you current savage owners can give me some pertinent measurements for the design... width and depth of the pocket in the right rear head... diameter of cam side gear... depth of pivot from parting line of head / headcover.... width of cam chain... pivot bolt diameter... clearance between cam chain and outer wall of cylinder.... ill be able to wrestle the correct bearing from the various vendors at my disposal, as well as submit for your approval a properly dimensioned plan for a manual adjusting system i dreamed up... im also considering buying a full adjuster set-up to get the "feel" of whether one can replace the hunchback with a bearing, and retain the auto-adjusting grenade.... my feeling is that the downleg is too darned flimsy, and will bend under load, but one can work around that if space allows....worst case scenario with the bearing is having to turn an oil soaked bronze bushing as the bearing surface (a bronze roller)... i figure it's safe to assume there will be no oil starvation problem.... edit: failing that, if a local (ft lauderdale, and 100 mile radius) forum member has an engine with the head opened for a cranial surgery session,and would allow a tattooed, shaved head geeper with a set of dial calipers to examine it, i'd be able to collect my own measurements.... though i can kind of guesstimate the bottom size of the chain tunnel on the head... savage greg's pics wil allow me to use the bore as a reference, and scale the size of the opening.... the other dimensions, of course, would be much harder..... |
Title: Re: another cam chain epiphany Post by verslagen1 on 04/11/09 at 08:50:10 too bad you're on the other side of the mountain. emailing you some pic's |
Title: Re: another cam chain epiphany Post by marshall13 on 04/11/09 at 22:15:37 okie dokie... as the locals are all closed, i went to that noble reference and supplier, mcmaster-carr... they stock an 8mm id x 15 od x 12 width needle bearing... 2423K21.... 13 bux... hardened and ground sleeve to press on 5 mm raw shaft (no grinding an axle)... 2423K41... 5 bux.... 18 bux is kinda borderline for "affordable" in my book, but the source IS mcmaster-carr, they dont have a rep as a discount house by any means.... ill probably be able to shave a few bucks off at the local level... the press-sleeve is a super handy item, and it allows a decent standoff from the actual 5 mm shaft... whatcha think? :-/ edit: forgive my poor social skills... thanks for the excellent pics!!! one more note on the bearing... 860 lb dynamic load, 29k rpm redline.... speed might be a little low, huh? |
Title: Re: another cam chain epiphany Post by justin_o_guy2 on 04/11/09 at 22:36:04 The number of blowups is really small. Its just made a lot of when it happens. Avoiding a problem is easy. These things arent "maintenance free" but they are generally dependable & easy to keep on the road. The cam chain adjuster doesnt just explode for no reason. It requires being ignored & allowed to go past a limit. That can be avoided without much effort & there are mods available to make it dang near impossible. |
Title: Re: another cam chain epiphany Post by verslagen1 on 04/11/09 at 23:33:12 Hey jog2, if he got an idea he's willing to put some effort into, I'm not going to discourage him. And it might be the magic bullet for this problem as we haven't completely solved the issue. We just made sure it doesn't go boom. 15mm is about the size of the shaft the cam chain sprocket goes on. the driver sprocket is about twice that. max rpm is 6500 so the bearing will be about 1300 or so. even if i'm off by a factor of 10 we're ok. What kind of lube do those needle bearing need? there won't be any except a mist. almost prefer ball bearings. The stock tensioner is pretty stiff and the arm that attaches to the adjuster is riveted on then the bearing material is over molded. The tensioner would make a good starting point. The shaft for the bear could be a shoulder bolt and the arm of the tension removed and a new arm made. then drilled and tapped for the shaft. I would think keeping the original bearing surface of the tensioner would be beneficial. And try to mount the bearing in line with that. |
Title: Re: another cam chain epiphany Post by marshall13 on 04/12/09 at 00:54:18 ok, if lower gear is 60mm, and turning at 6500 rpm, the proposed bearing is doing 26k.... well within spec.... i think we have our bearing locations at opposite ends in our visions... the most efficient method of taking up slack in a chain is extending the distance between gears, but short of stacking stainless shim stock head gaskets, that's impossible in this situation.... next comes wrapping the chain further around the larger gear on the slack slde(this is what the forward shoulder of the rear tensioner does when new, though only enough to pilot the chain down the tunnel)... it has the added benefit of decreasing the per-tooth load on the driven gear (in theory, but with as little actual slack as these chains have, it probably wont be a factor in this example)... about the least efficient method is what happens when the plastic wears, wrapping the slack side of the smaller gear... this is what the vershlagy does.... i checked how the dr650 handles slack adjustment, and it's basically the same grenade adjuster, just designed to go through the back wall of the chain tunnel in the jug...this puts the adjuster in a place where it only ratchets out 1/2 as far to do the same amount of adjustment, gives it less leverage advantage to bend the tensioner, and moves the "wrap" to a midpoint between both gears... that's why no reports of the same problem.... my idea is to use the bearing to tuck the TOP end of the chain, on the slack side, closer to the centerline of the 2 gears... either by using a modification of the original tensioner form (and retaining auto adjusting), or, if that proves too daunting a task, by using the existing pivot bolt for the tensioner( in the head, not the adjuster in the case), as a pivot point for a dog-legged lever, with the bearing at the tip..... manual adjustment done by a bolt/jamnut combo drilled and tapped through the rear wall of the head.... at this location, the bearing will be awash in the bearing splash of the center and right cam bearings, so im fairly certain an adequate supply will be available to it.... as to the mounting to the adjuster/tensioner, as the ground sleeve already requires a press step in the assembly, it would be easiest to to just make the 5mm pin an interference fit to the holes in the bracket, and press it through the 3 at once, ensuring it can never unscrew, un dove tail, etc.... i agree a ball bearing is a much more ideal form for the idea, but the available space constraints kind of demand a needle bearing..... still not happy with 18 bucks for the bearing sleeve combo, though it will be the most expensive component by far.... |
Title: Re: another cam chain epiphany Post by BurnPgh on 04/13/09 at 00:11:35 where am i? All very interesting and confusing enough to grab my attention. Visual aids maybe? |
Title: Re: another cam chain epiphany Post by verslagen1 on 04/13/09 at 08:37:53 I think the intent of the current system is to wrap the driver sprocket with as much chain as possible. Since it's greater than 180° wrap, the likelyhood of the chain disengaging is minimised. I've seen almost no wear on the leading edge of the tensioner guide and I don't think it's designed to wrap the chain around the driven sprocket. And being that this gear is twice the size of the driving gear, don't think chain wrap is important here. I was thinking of a manual adjuster when we were discussing this long ago. There is a spot on the lower rear cylinder where a fin or two could be faced off and a threaded hole created. I also looked at what it would take for the chain to be disengaged. Manually, very difficult. But this is why some chains are broken I'm sure. As when the chain climbs the sprocket enough to disengage, it's about to hit the case. |
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