pete roper Posted January 3, 2012 Share Posted January 3, 2012 Really interesting theory to let the outlet run looser . . . Playing with the timimg by running significantly different gaps is not a panacea for all ills. Nor is it without probems or risks. Early twins used different materials in the valvetrain and inherited soft, simple cams from the police and military heritage. Wide gaps were specified because these bikes were expected to sit for long periods idling with A copper or squaddie on board. Later machines have gone away from this and with the otherwise identical machines small clearances were specified for the USA, probably for noise reasons. These gaps are so small they can lead to the tappets 'Riding' the cam. I have to say Ihave NEVER had a prblem with the 'Euro' specs of 4 thou inlet and 6 exhaust on any squarefin, in any heat, and you don't run the risk of the tappets by-passing the ramps on the cam. I maintain that for quiet, happy, running there is little to be achieved from running clearances of 5 and 7 on roundfins and 4 and 6 on squarefins as long as you are not playing with stupid cams or pushrods of a non-original type. YOMV. Pete Link to comment Share on other sites More sharing options...
docc Posted January 5, 2012 Share Posted January 5, 2012 I maintain that for quiet, happy, running there is little to be achieved from running clearances of 5 and 7 on roundfins and 4 and 6 on squarefins as long as you are not playing with stupid cams or pushrods of a non-original type. YOMV. Pete Hi, Pete, Is that to read clearances (other than) 5/7, 4/6? Or (greater than) . . . or ? Thanks for the clarification. Link to comment Share on other sites More sharing options...
pete roper Posted January 5, 2012 Share Posted January 5, 2012 I maintain that for quiet, happy, running there is little to be achieved from running clearances of 5 and 7 on roundfins and 4 and 6 on squarefins as long as you are not playing with stupid cams or pushrods of a non-original type. YOMV. Pete Hi, Pete, Is that to read clearances (other than) 5/7, 4/6? Or (greater than) . . . or ? Thanks for the clarification. Sorry, quite right. Clearances for roundfins were basically 8 and 8. I've used 5 and 7 for years with no problems and a significant reduction in clatter. For any squarefin the 'Euro' specs of 4 and 6 seem to work fine. When are problems most likely to manifest themselves? After periods of hard running in high ambient temperatures or poking along in traffic also in high ambient temperatures. When I rode with Sean across the USA on my, now Chucks, Scurra we were hammering across the west Texas plains between 90 and 100 MPH FOR long periods. Neither of our bikes stopped running smoothly when we slowed down or stopped. LIKEWISE WHEN i was staying with on in Cannoga Park and poking around in LA traffic in 90+ degree heat did it EVER misbehave or show evidence of closing up the gaps to the point it was effecting valve seal. Admittedly that scura has a PCIII and hauls ass like no other V11 I've ever ridden, (I still have no idea why!) but I think Sean's bike is essentially stock and it had no problems either. The thing is that playing with valve gaps DOES have an appreciable effect. Try it and you'll find your idle speed will change noticeably. Whether this will actually translate into any appreciable 'Performance' increase I don't know. What I do know is the wider the gaps the greater the risk of tappet and cam damage due to the tappets by-passing the rampings and simply slamming into the opening flanks of the cam. Changing the gaps though is easy. Far easier and cheaper than other 'Performance' options. That, because of its very simplicity makes it an attractive proposition and *may* lead to people who have experimented unintentionally seeing benefits that dont really exist. At the end of the day, it's the owners choice. Personally I don't think the benefits are anything more than perception. As always these are simpl my beliefs and observations and hold no more or less veracity than anything else you'll read on the innerneck. Pete Link to comment Share on other sites More sharing options...
luhbo Posted January 5, 2012 Share Posted January 5, 2012 ... What I do know is the wider the gaps the greater the risk of tappet and cam damage due to the tappets by-passing the rampings and simply slamming into the opening flanks of the cam. ... Don't worry about the ramps, they're 'endless'. Dial in .3mm and you're still well within the ramps. Hubert Link to comment Share on other sites More sharing options...
aermacchi250 Posted January 7, 2012 Share Posted January 7, 2012 You affect the valve timing when you increase or decrease the valve clearance. The same can be said for point type ignition systems. When the clearance is decreased, the timing advances. I think as you decrease your point gap,you're ignition timing becomes later,not earlier.The wider your point gap is,the earlier it contacts your "Ramp"therefore opening sooner. Link to comment Share on other sites More sharing options...
gstallons Posted January 7, 2012 Share Posted January 7, 2012 You affect the valve timing when you increase or decrease the valve clearance. The same can be said for point type ignition systems. When the clearance is decreased, the timing advances. I think as you decrease your point gap,you're ignition timing becomes later,not earlier.The wider your point gap is,the earlier it contacts your "Ramp"therefore opening sooner. You're right.....Thanks for pointing that out ! Link to comment Share on other sites More sharing options...
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