Tim D. Posted October 29, 2018 Report Share Posted October 29, 2018 Out of interest, does the belt system on the end of the crank provide any damping? Cheers Tim Quote Link to post Share on other sites
john.r.davies Posted October 29, 2018 Author Report Share Posted October 29, 2018 Don't know! I'd ask more experienced engineers that question! But I believe that a belt that has no slip at all would need to be under so much tension that it would shorten the life of the belt and the pulley bearings. Most belt efficiency comes from operating at the slip point but not quite (like tyres), so some slip will occur, making a damping effect unpredictable. John Quote Link to post Share on other sites
Peter Cobbold Posted October 31, 2018 Report Share Posted October 31, 2018 On 10/29/2018 at 8:13 AM, Tim D. said: Out of interest, does the belt system on the end of the crank provide any damping? Cheers Tim Tim, I've read that yes it does, but cant recall where. IIRC on a 6 pot 153624 the first serious crank resonance is at 5000 rpm - John will know. With a blower there's little need to go up to those rpm. Drive the torque ! Peter Quote Link to post Share on other sites
Tom Fremont Posted October 31, 2018 Report Share Posted October 31, 2018 Any crankshaft, like any solid object, has a natural ( resonant ) frequency. When excited at this frequency the amplitude of the torsional deflection increases just like pushing someone on a swing. There are multiple speeds where resonance occurs, and one or more where it is critical in the sense that failure is possible. The main damper on these engines is the flywheel. TRIUMPH fitted rather heavy ones to the later TR6 engines, and we can safely assume this was not done to degrade acceleration - I speculate it was done to eke out another 300 rpm of redline and squeeze the last drop of HP from the emissions controlled ones especially. A notorious UK TR specialist assured me years ago " the TR6 crankshaft is notoriously reliable " and claimed it is good for 7000 rpm. I wouldn't take that to the bank, but note Kastner tested their race engines to 6000 rpm. Fitting superlight, unbreakable Carillo rods to my high compression engine with steroidal cam ( 0.502" lift ) was a revelation: never experienced such a smooth revving 6-pot TR engine before. These rods deduct ~ 4 lbs from the throws of the crank, where it matters a great deal. With forged pistons I wouldn't hesitate to run it to 6000 on a regular basis. Stock '250 flywheel and NOS damper fitted: Cheers, Tom Quote Link to post Share on other sites
ed_h Posted October 31, 2018 Report Share Posted October 31, 2018 It seems that since the belt would couple the outer ring of the damper to more mass, that it would affect function of the damper. With some slipping and the resiliency of the belt, the coupling would be imperfect, but I'd think there is still some effect. Wouldn't be an easy thinng to model. Ed Quote Link to post Share on other sites
Peter Cobbold Posted October 31, 2018 Report Share Posted October 31, 2018 2 minutes ago, ed_h said: It seems that since the belt would couple the outer ring of the damper to more mass, that it would affect function of the damper. With some slipping and the resiliency of the belt, the coupling would be imperfect, but I'd think there is still some effect. Wouldn't be an easy thinng to model. Ed Ed, All the blower pulleys I've seen are solid. It needs to transmit up to typically 10-20hp so the rubber-damped stock pulley is not used to drive the blower. I use an additional pulley that replaces the fan, not sure about the Moss kits. Peter Quote Link to post Share on other sites
ed_h Posted October 31, 2018 Report Share Posted October 31, 2018 Didn't know that, Peter, but it makes sense. I actually had non-blown systems in mind when I made my comment. Ed Quote Link to post Share on other sites
Tim D. Posted October 31, 2018 Report Share Posted October 31, 2018 Yes the blower pulleys don't have rubber inserts. I also think that they are alloy, but not 100% certain. Peter, agree regarding torque. Very selldom need to go above 4000rpm. Tim Quote Link to post Share on other sites
john.r.davies Posted October 31, 2018 Author Report Share Posted October 31, 2018 Superchargers should note. The 2L damper pullies ARE solid from the hub to the V-groove. Their damper rings are mounted on a boss on the front of that. Of course, a 2.5L crank won't have the same resonance as a 2L, thanks to the different dimensions needed for more stroke, so one may not be as useful on a supercharged 2.5L. But at least you won't rip the V-groove ring off! JOhn Quote Link to post Share on other sites
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