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R vs. Std tappets #795972 01/19/20 12:06 am
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MarksterTT Offline OP
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I can't remember so thought I'd ask, how much difference in duration is lost when going from R tappets to Std radius tappets and is there any mechanical downside to going with std. such as being a little harder on the cam lobe? Thanks, Mark

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Re: R vs. Std tappets [Re: MarksterTT] #795975 01/19/20 12:38 am
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On my dual engine 650 racer using a #330 Web Cams grind , .410 valve lift, 276 degrees duration at .050 lift, an R tappet added 4 degrees duration compared to a S tappet.I do believe it has an effect on performance aside from duration... I do not know if this would be the same with other cam profiles...


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: R vs. Std tappets [Re: Hillbilly bike] #795996 01/19/20 10:15 am
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Originally Posted by Hillbilly bike
On my dual engine 650 racer using a #330 Web Cams grind , .410 valve lift, 276 degrees duration at .050 lift, an R tappet added 4 degrees duration compared to a S tappet.I do believe it has an effect on performance aside from duration... I do not know if this would be the same with other cam profiles...

I don't have your experience with racing and fierce cams Tony, but here's how I see the cam and lifter relation:
The cam hits the large radius lifter earlier and initial lifter acceleration is faster. As the lifter climbs on the cam acceleration will gradually decrease until it's actually lower than with a standard lifter.
The net effect is a longer duration, which could mean some low end power loss due to the increased overlap, but more power overall due to the same combined with a faster lifting valve.

That's the theory anyway, but I can't bring myself to use anything than R lifters with sportier cams.

SR

Re: R vs. Std tappets [Re: MarksterTT] #796000 01/19/20 12:27 pm
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I used the R tappets on the intakes and the S on the exhausts ,same cams on both. I was trying to change the torque curve....Can't say for sure it made any noticable difference .....


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: R vs. Std tappets [Re: MarksterTT] #796056 01/20/20 2:43 am
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Thanks Hillbilly, I thought I remembered something like 4* but wasn't sure and I hadn't considered what Stein Roger mentioned about initial lift, acceleration etc., still thinking about that...thanks guys, Mark

Re: R vs. Std tappets [Re: MarksterTT] #796059 01/20/20 2:53 am
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Maybe related, maybe not... Using Triumph cams in my race bike- T140 intake and T120 exhaust, both with R lifters. The intake lifters show scuffing on their leading and trailing edges. I take from this that 750 intake cams have a steep ramp that is more compatible with the std lifters. So far the cam looks ok, going to run it for another season and then maybe look at something to compliment the new head???

Edit- If I were going to use R lifters with a 750 cam again, I'd think about radiusing the leading and trailing edges on the lifters a little

Last edited by Mike Baker; 01/20/20 2:56 am.
Re: R vs. Std tappets [Re: MarksterTT] #796067 01/20/20 11:44 am
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Mike ,my race bike also has some scuffing on the cams with less running time than yours....R lifters on Sifton 390 cams where S lifters are recomended. The Sifton probably has shorter clearance ramps and more duration between .040 lift than the Triumph T140 intake but about the same lift... I don't know if the Sifton cams were nitrided....I was using Redline oil, then switched to Valvoline VR1 full synthetic..I dress the lifters by hand in a home made jig...


79 T140D, 96 900M Ducati ....On a bike you can out run the demons..
Re: R vs. Std tappets [Re: MarksterTT] #796079 01/20/20 4:08 pm
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Weren't R lifters originally prescribed for Thruxtons, and used with Thunderbird cams which had a longer ramp in their lift profile?
Surely if you use more aggressive cam profiles you will be running the risk of the cam surface meeting the very ends of the lifter?

Re: R vs. Std tappets [Re: MarksterTT] #796082 01/20/20 4:42 pm
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I thought Thruxtons had 3" radius lifters?

The reason I asked originally was because I have some cams (Norris R, PM1060, mega 1030) that I believe I would be happier with if they weren't as big as my eyes were back in the olden days when I first ran them. That and the fact that Megacycle site says most cams with R lifter recommendation can also run STD for more lower end torque with a little less top end, however, I've always thought that if STD were recommended that you shouldn't use R's. I do know that my Norris cams recommended more valve clearance to reduce duration if looking for more torque on tight tracks.

Mike Baker, what have you done to this new head you mentioned? I have an engine build that will need some good head work and I'm currently comparing my options of different style heads.


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