Heavy lifters and valve bounce (2015)

Thus requiring removal of the tappet block to remove / re fit them?

Not so maintenance friendly!

chaztuna said:

Jim,
... I've noticed that even with the Photobucket anti blocker add on for my Firefox browser, I can not view the image in this post ...

...How do the A65 BSA lifters differ from Triumph T120 & T 140 lifters?...
Charlie

Click to expand...

The new JS2 smooth ramp completely eliminates the valve bounce problem of the PW2. See new graph below. Good for 9000+ RPM with beehive springs. This in an entirely new cam, different than the previous JS2.



The opening and closing ramps are more gradual - the jerk stress has been cut in 1/2 compared to the PW3 - now its the lowest of any available Norton cam (except the JS3 smooth ramp).

The BSA tappets have and thicker shaft and are stronger than the Triumph tappets which can break in severe racing.

If 9000 RPM means moving to a much stronger short stroke bottom end and highly modified top end and cam , you might do better by starting with a different motor. Is the major objective to go fast in a race class specifically for bikes with Commando motors ? - A Triumph motor with a different head might perform better and be cheaper in the long run - at least the inlet and exhaust cams are separate.

acotrel said:

If 9000 RPM means moving to a much stronger short stroke bottom end and highly modified top end and cam , you might do better by starting with a different motor. Is the major objective to go fast in a race class specifically for bikes with Commando motors ? - A Triumph motor with a different head might perform better and be cheaper in the long run - at least the inlet and exhaust cams are separate.

Click to expand...

Just a reminder, Alan, because you seem to keep forgetting. This is the Commando forum. We work at improving our Commandos because we're Commando folks. Clearly, if we just wanted to go fast, we'd dump the Commandos and buy new Yamahas or BMWs or whatever, and not old Triumphs (and many of us do also have modern bikes). But that's not the point. The point is having fun doing cool things with our Commandos.

Ken

Nortons eat Triumphs for breakfast.

Lurking question is where extra rpm benefit ends in Commando size type engines. I had a few years of nail polished marked 750cc for 9000 rpm joys after it was National dragged a couple years before me yet only its drive trained seemed the weak links. It idled at 600 and would spin street rear no brake in 4th by snaps at 1000 rpm and could not take WOT throttle w/o spin till over 60's in 4th. It was such a responsive neck whip-lasher it would be leaping ahead of triple 2 strokes before their engines could hit power band in lower gears - too late by then. Keep in mind my bench mark for whats possible from obsolete clunker and perspective of pioneers to match let alone beat. A 9 or even 10 grand Commando might be most exciting thing ya ever try to control.

The idea of valve float self limiting 'over rev' is very insightful to me so wonder if that could be planned for a 'soft' rev limiter w/o valve or piston clash. So how would one determine an experimental engine's redline?

hobot said:

So how would one determine an experimental engine's redline?

Click to expand...

Using valve float to self limit rpm in a Commando engine - bad idea for all the obvious reasons.

A starting point for redline is to calculate the mean piston speed at redline for a stock Commando (89mm stroke) and then apply that mean piston speed to the new stroke you are contemplating. If you are going with a shorter stroke, then you need to assess the ability of the valve train to perform reliably at the higher rpm.

Fast Eddie said:

Thus requiring removal of the tappet block to remove / re fit them?

Not so maintenance friendly!

Click to expand...

You do have a point there. I've been using the circlips because that's the way the first engine I acquired with the conversion had them, and I just never gave it any thought. I like the idea of just using rubber hose. The circlips are kind of a pita. They tend to loosen up when removed and re-installed, and I wouldn't really like to see them bouncing around inside the tunnel.

Ken

Ok I'll stick with Powerarc ign rev limiter but still up in air where to set it on my experimental. Its not piston mean speed that matters, its the acceleration jerks after TDC/BDC that does, though piston speed friction also limits useful rpm, especially long strokes. Btw I think crank flex/jump rope/candy cane twist binding on rod journals width and tipping through end bearing races may be a significant hi rpm friction factor too, besides levering cases to fracture. Not sure if 920-1004cc engines benefit with 10k rpm valve train but sure not downsides.

What I like about Norton power curves engine inertia/friction is predicable enough to snap just right amount of tire spin to step/skip into better line with predicable hook up back upright out of there - on higher throttle openings- just done smoother for hook up. Other engines/gearing tend to either under spin or over spin - which may be something to do with flywheel inertia. More than the extra ease to spin up lighter crank, if over powered to begin with, is the life saving faster slow downs in my case.

Keep in mind cryo tempering to help protect investments.

To acotrels comment I think its mainly a hormonal response to Norton sassy looks of engines that keep us devotees nose to grinding wheels.

Fascinating thread, surely valve train issues will also effect the rate at which an engine gets to its rev / power ceiling

oldmikew said:

Fascinating thread, surely valve train issues will also effect the rate at which an engine gets to its rev / power ceiling

Click to expand...

Definitely. You don’t need to be chasing high revs to see the benefit. IMHO though, you only see the real benefit when you reduce spring pressure in accordance with your lighter valve trains lowered requirements. When you better that right, it makes a noticeable differences to how and engine revs.

Trouble is, unless you’re a guru with fancy software, it’s a rather long and arduous trail and error process to really optimise.

I got it bang on with a racing Triumph motor and, as Hobot eluded to earlier, I actually used valve float as a rev limiter / gear change indicator.

All that ‘chattering’ wore out the cams in a season though!

A few years ago there was some supposedly Triumph expert who used to post here bad mouthing Nortons and Norton owners. Not to return again, I hope.

I don't go to a Triumph forum or even a Harley- Davidson forum, and bad mouth the owners and their bikes. In the case of Harley ownership, I see it as self-loathing. The owners' self-loathing, that is.

jseng1 said:

snipped The BSA tappets have and thicker shaft and are stronger than the Triumph tappets which can break in severe racing.

Click to expand...

Jim, which of your cams would you recommend for a nice 850 street engine? I really like the idea of the lighter BSA lifters, titanium retainers, etc, even for the street.
Charlie

Next pioneer phase will be new construction methods and composite alloy/ceramic materials to stand the loads of un-supported components with optimal shapes and heat toleratance. Every now/then I look for small dia roller lifters but none exist yet nor Norton space to accept either. Thank goodness even hi rpm peaky Commandos and maybe all Brit Iron make good tire stressing front lifting power very soon off idle, compared to other race only cycle engines that almost won't run below 3000's.

Another thing about good power/wt ratio is how quick redline reached in lower gears so extra rpm more allows pilot time to react w/o having to peddle/hesitate as much. Can hit higher speeds in lower gears longer through turns too.

Ms Peel Combat head had Deere 7mm valve train factory size seats and assembled by late friend Micheal Strarky/Britis Toys NC, also shimmed my lightened rockers that survived many 100 miles/40 min long all out dicing with angry moderns till WOT stuck throttle disappeared tach needle bouncing off both sides of peg stop yet Ken Canaga had it all apart to convert to 920 finding nothing damaged. Jimmy came out with rods/pistons that changed Peel's engine contruction but not BSA lifter wonder so will go w/o for a time.

hobot findins on what most limits Commandos once valves adequate is the crank jump rope which destroys cam tensioner or pulls pinion shaft/ bore/cog apart which makes ignition mis fire and valves out of time for their damage that may of been secondary to crank whiplash.

THE Wildest Weirdest thing I report for insights on over-rev event was after I fell back on sudden start I got back to throttle in couple seconds to hear see engine hesitate with tach needle held on back side of tach but just as slammed hand back on throttle engine caught second breath to slam hand off throttle from engine bounce back on isolastics before I got recovered back in another second or so to see needle turn to blur then vanish!!! Maybe as chain tensioner got turned to chewing gum the cam and ignition advanced enough to raise power band and the over big hogged out Combat ports could supply it. Started after smoke cleared to ride broken heartted with 1/3 less power for 2000 miles before decided new engine needed. I'm still flabbergasted as did not mis a beat spiking power nor after just wouldn't rev much above 5000 ignition max out.

I had hot 650 Triumphs for years when I was a kid. The only advantage they have are the separate inlet and exhaust cams. They are easier to work with when you are optimising the settings to get best performance. The one-piece cam in the Commando is a pain and there is no easy way around it.
I wouldn't use the cam profile as a rev-limiter. As it is, we never know when the valve springs have collapsed too much to continue to be safe. The head of a valve stuck in a piston can make a very big mess of the cylinder head.

Once engine components can tolerate say 9000+ rpm - the heat dump becomes an issue to sustain such power-fuel burn. Lightness of crank, pistons, rods plus slope of ign advance likely more noticed on engine rev up time more than the cam/valves, which only determine what rpm they become effective. At some point exotic exhaust valve material and heat transfer mods may be needed to sustain over redline blasts.

Having a cam with ramps that will allow 9000+ RPM does not mean that you get to revv the motor to 9000. What it means is that valve bounce is no longer an issue.

With a Commando engine, valve bounce is not an issue at 7,500 RPM unless the valve springs have collapsed. The issue is the bottom end. By the time you have changed the crank, rods, pistons and the cases, do you still have a Commando engine ? I have only ever been impressed by the torque characteristic of the 850 motor and I gear to suit it. The bike is fast enough to win in Period 4 Historics - what else is needed ? Any extra speed comes at the cost of reliability. It might make my life slightly easier, but if your bike is up with the leaders in races, better to concentrate on riding it well. There are more ways of winning races than wobbling around corners and blasting down the straights.

If you look at the history of Commando road racers, Peter Williams was competitive against Yamaha TZ750s with very few of the trick parts that are available these days. That is fast enough for anybody. If you think you can out-drag a modern bike in a side-by-side race using a Commando, you are kidding yourself. When Peter Williams won, it was about handling and getting the power down earlier in corners, also braking further into corners and keeping the speed up everywhere. If you think about it, a good guy on an RS125 Honda would make any 750 Commando look stupid on most race circuits.