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So for you that actually take your ct-70s on the logging roads, are you seeing that your bikes are getting warm enough to see the heat come off in excess? I noticed what I myself would say the engines getting very warm while riding up the mountain after about 4-5 miles of up hill. I could hear the valves more at this time. ( I turned the bikes down hill to assist in oil reaching the head ) but what I am wondering is. Am I destroying these engines prematurely or is this normal operating quirks. We were averaging 8-10 mph with short spurts of 20 mph by myself =) ( hey dad has to have a little fun )
 

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I'm in Missouri, with no hills like you're probably talking about, but I use my hardtail Z50 around the farm and on occasion it runs for extended periods at slow speeds, trying to go as slow as I can but keep the clutch fully engaged (so, more than 3500 rpm or so). We have a kennel and sometimes I exercise dogs this way, on a long lead, at dog-trotting speed, and when we have to drag cut or fallen tree branches I ride one handed and drag with the other.



On really hot days, well into the 90s, I can do this for more than an hour, rarely getting up to any kind of speed that would qualify as a cooling air breeze. You can tell it's getting hot; you can smell it, but it runs fine and has never given me trouble. I think being aware of the clutch engagement point and not being in too high a gear is important. I rode around with a "Tiny-Tach" inductive tachometer on my bike for awhile to verify the rpms it engaged at, ran out of power at, etc. It was interesting but not necessary. If that clutch is slipping, it's heating the oil unduly.



You should be getting oil to the head regardless of uphill/downhill...it's pumped up there. If you're doing serious enough grades to be causing the oil pickup to not be under the oil...you must have antigravity tires.
 

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mexicanyella said:
You should be getting oil to the head regardless of uphill/downhill...it's pumped up there. If you're doing serious enough grades to be causing the oil pickup to not be under the oil...you must have antigravity tires.


Too funny, and I was thinking the same thing....well at least the oil is pumped to the head part, not the antigravity tire thing. Kind of a dumb question, but how long has it been since your last oil change and what type are you using? I do like Mexicanyella's point about being in the right gear as well. Cruising around at 8 to 10 mph in third gear going uphill probably isn't helping if that's what you're doing. Funny to think that keeping your revs up would help, but that's making your pump spin at a higher rate as well. Plus I don't think you have done any motor work, maybe a H/V oil pump would help?
 

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Good points there, and I'll kick in some more on them too. My take on oils is not the popular opinion and is based on running a well-worn stock 50, not a hopped-up pitbike, so figure that in.



But I weigh around 250 and regularly do everything from two hours of sub-10mph riding in summer heat to extended 7,500-8,000 rpm riding in all temperatures (down to single digits sometimes in the winter, up to 100 or so in the summer)...and I use mineral (non-synthetic) car oil. I run 10W-30 in the winter and I've run both detergent 30W and 15W-40 Rotella in the summer, and as far as I know, my clutch is original from 1971. If it was ever replaced, it was before 1992, when I got the bike. Works fine; I don't have to adjust it way outside the adjusting range to get it to work and it engages fully by 3500 rpm or so. It's easy to get it to disengage enough for smooth shifts but still kick over with the starter without much if any slippage...that's what we want, right? But if I leave the 10W-30 in there and the weather gets warm early, the bike seems to run hotter and smokes more until I change to the summer-weight oil. I think I feel a more gradual engagement, especially when hot, with the thinner oil too. It still engages fully at about the same speed, but the engagement curve feels a little different to me.



I think I just made up the term "engagement curve." You can quote me on that.



I got myself a little sidetracked there, but my original point was that I think the proper weight oil and frequent enough changes is more important than whether it is "wet-clutch-approved motorcycle-specific oil" or not. At least in low-hp applications like a stock 50 or 70.



Might not hurt to pop off the clutch cover and clean out the oil centrifuge thing in the clutch hub and the pickup screen at the case bottom, just to make sure. Also, have you tried starting it with the valve adjustment caps off to verify plenty of oil is in fact getting pumped to the top end? This is a good step to take on the living room carpet, or in the kitchen. It makes the oil output really apparent.
 
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