80 HP at 8700RPM by Herb Becker

jseng1 · Feb 25, 2016

Had some recent communication from Herb Becker. He's put together a Commando racer for Doug M. A recent dyno run showed 80 HP at 8700RPM - thats right - 8700RPM. This is a 80.4mm short stroke.

Another Norton he's working on is going on the Salt flats (for Andy I believe). This one is a little lower budget and uses a Triumph 82 mm stroke crank. I don't know what the peak HP and RPM is but its getting 76 HP at 7000RPM while Dougs bike is getting 74 HP at 7000 RPM. He gave me some torque numbers but I don't remember all the specs exactly - but I do remember that Dougs bike had more torque. Doug's bike also has a bathtub squish head - made from an unfinished casting that was provided gratis by Full Auto.

Both bikes are using modern internal components to reduce reciprocating weight and a better 2:1 rod/stroke ratio for Doug's bike to keep things from exploding. Herb made some aluminum rods for the landspeed bike with the Triumph crank.

Another project Herb is working on is a twin Nort engine Drag bike. God only knows what he's going to do with it - one thing for sure - he'll get to church on time.

Unfortunately Herb doesn't post here. It would be great to see photos.

lcrken · Feb 25, 2016

Good to see Herb still building outlandish stuff. Are those rear wheel HP or at the crank? I'm guessing rear wheel.

Ken

chris plant · Feb 25, 2016

jseng1,any info on the pistons and rods he,s using

jseng1 · Feb 25, 2016

chris plant said:
jseng1,any info on the pistons and rods he,s using

He's using my lightweight domed pistons and longer Carrillo rods (lighter without the bronze bush - using DLC pins). He made his own aluminum rods for the landspeed racer to fit the smaller Triumph crank journal.

78mm Domed JS lightweight piston approx 215 grams bare

Longer bushless Carrillo rod

Used/raced DLC pin and bushless Carrillo rod small end

Two Full Auto heads. Bathtub squish by Herb on the left. Regular combustion chamber on right.

Rohan · Feb 25, 2016

Bathtub squish heads and domed pistons have to have a lot of compression, right ?
(and look great).

What fuel is he allowed to use ?

And how does he get so many rpms...

jseng1 said:
Two Full Auto heads. Bathtub squish by Herb on the left. Regular combustion chamber on right.

Domed JS lightweight piston

acotrel · Feb 25, 2016

If it is desirable to use an 82mm stroke Triumph crank, is the difference in the journal size more than could be safely built up with hard chrome ? I've heard of Norton cranks being used in Triumph motors, however this is the first Triumph crank in a Norton motor I've heard of. Perhaps a Triumph crank with Jim's long carillo rods and standard pistons might make the necessary shortening of the barrels easier ? Most one-piece Triumph cranks will cop 8000 RPM, it is usually the crankcases which fail first. The fastest and most reliable 650/750 Triumph I know of, is built to pull rather than rev. I rode it once many years ago and it goes like a blur.

jseng1 · Feb 26, 2016

Rohan said:
Bathtub squish heads and domed pistons have to have a lot of compression, right ?
(and look great).

What fuel is he allowed to use ?

And how does he get so many rpms...

jseng1 said:

Two Full Auto heads. Bathtub squish by Herb on the left. Regular combustion chamber on right.

Domed JS lightweight piston

Click to expand...

C.R. is 11.8 to 1 I don't know the fuel octane.

First of all – it’s a short stroke and a top end short stroke can rev to 8000. Even higher RPMs are possible because of the lowered frictional forces and reduced stress offered by reducing reciprocation weight. Traditional long skirt pistons create a lot of drag on the cylinder's and you run into a wall created by the friction. Shorter pistons with a higher pin location don’t have as much surface area so the drag is reduced and the friction wall is elevated to a higher RPM.

Short stock length rods (5.875”) have too much angle at mid stroke - creating a lot of side thrust against the cylinder. Longer rods (6.4" for long stroke and 6.57” for short stroke) have less angle at mid stroke with corresponding lower side thrust and reduced frictional losses. Also – the longer rods smooth out the jerk at the top and bottom of the stroke. All this adds up to less stress, lowered friction on the pins, rod journals and main bearings. To answer your question – these are the things that make higher RPMs (& more HP) possible (everything else being equal).

The gain in RPM has shown up on dynos and race bikes. A 1000+ gain in RPM was reported on a 1000cc motor. A long stroke 850 went to 8400 on a dyno. Now someone’s gone to 8700 with a short stroke. I’m not saying its OK to rev this high. But I don’t have control over what people do with my parts. I just keep track and make notes as I go. I’m just happy to know that stress and vibration is reduced on my street bike and that customers have reduced the risk of breaking their cranks and cases.

As for Triumph cranks – I don’t know much about them other than they have smaller weaker rod journals. But they are cheaper than a new short stroke Norton crank.

Rohan · Feb 26, 2016

Thanks Jim.
Thats all very well, but the valve gear in my 850 wouldn't rev to 8700 rpms,
even if the engine had no crank in it.
Somefink must be rather different....

WZ507 · Feb 26, 2016

Rohan said:
Thanks Jim.
Thats all very well, but the valve gear in my 850 wouldn't rev to 8700 rpms,
even if the engine had no crank in it.
Somefink must be rather different....

Regarding means for getting a valve train under control to 8700 rpm, back in the spintron discussion Comnoz showed excellent control of a relatively heavy valve train at 8500 rpm, as well as specialized valve trains under control at significantly higher speed regimes (if memory serves perhaps up to nearly 10,000 rpm?).

I was always impressed with the heavy valve train operating at 8500 rpm. Recall that the subject valve train employed a Web 86C cam, 3 mm OS steel (heavy) intake valve, stock lifters (heavy) ground with a 3”offset radius, lightened rocker arms and conical valve springs.

about-time-for-the-spintron-t21837-195.html

Incorporating a little titanium into the equation (IN valve) and some lightweight lifters to remove some mass from the system would likely allow this combination of components to operate stably at even higher speed regimes.

acotrel · Feb 26, 2016

I haven't even polished and lightened the valve gear in my 850. Surely the standard stuff should cop 6,500 RPM very reliably and I try to always keep below 7000 RPM.

jseng1 · Feb 27, 2016

Rohan and WZ507

In response to your conversation about valve gear and high RPM. Lighter valve train components are a sure way to achieve higher RPM.

The photo below shows the parts in Herb/Dougs motor before assembly. Note the Conical Beehive valve springs. They are about ½ the weight of racing dual springs.

Below is a new BSA lifter for use with special radiused cam lobes. Nearly ½ the weight of stock Norton lifters.

Jim Comstock achieved high RPM with currently available cams by re-profiling the stock lifters. This worked well because it had the effect of extended the closing ramp and brought the lifter down slowly and gently. The smooth closing of the valve prevented unwanted valve bounce. It’s the exhaust valve bounce that wants to tangle with the opening intake valve. Both valves bouncing will kill the motors performance and limit the RPM. An even better way to do it is to design the cam so it has smooth, gently closing ramps to prevent valve bounce and throw in the lightweight lifters as well. This is what I’m working on now. I’m starting with a Triumph grind which is nearly identical to the famous PW3 profile (but for lightweight lifters). Then I’m giving it a smoother ramp.

Below is the jerk graph comparing the JS2 smooth ramp improvement to the PW3

Below you can see the difference in the closing ramps

acotrel · Feb 28, 2016

The need for slow capture of the valve train as the valve closes is something of which I became aware when I was a kid. However I've plotted the lift verses crank degrees for a few racing motors and have never detected it. I think it was common with BSA singles, to use a cam with a slow back off to stop the valve snapping shut too quickly, mainly to stop dropping valves. The early GP triumph cams were known to be valve droppers. however the E3134 cams were superb. If the cam is symmetrical a lot depends on the lift rate. In my short stroked 500cc Triumph, the cams took forever to open and close and the lift was not high. It would rev easily to 11,000 RPM. I only ever clipped a valve once.

badbird · Feb 28, 2016

https://www.youtube.com/watch?v=jgkLhxxJMGY

jseng1 · Mar 3, 2016

badbird said:
https://www.youtube.com/watch?v=jgkLhxxJMGY

Thats a good video but its an early one from last year. There has been some development to get more HP such as longer manifolds etc. You can always keep developing and get more power but as Herb said "At some point you've got to quit working on it or you'll never get to the race track."

Swetune · Mar 3, 2016

jseng1 said:
Rohan said:

Bathtub squish heads and domed pistons have to have a lot of compression, right ?
(and look great).

What fuel is he allowed to use ?

And how does he get so many rpms...

jseng1 said:

Two Full Auto heads. Bathtub squish by Herb on the left. Regular combustion chamber on right.

Domed JS lightweight piston

Click to expand...

Click to expand...

C.R. is 11.8 to 1 I don't know the fuel octane.

First of all – it’s a short stroke and a top end short stroke can rev to 8000. Even higher RPMs are possible because of the lowered frictional forces and reduced stress offered by reducing reciprocation weight. Traditional long skirt pistons create a lot of drag on the cylinder's and you run into a wall created by the friction. Shorter pistons with a higher pin location don’t have as much surface area so the drag is reduced and the friction wall is elevated to a higher RPM.

Short stock length rods (5.875”) have too much angle at mid stroke - creating a lot of side thrust against the cylinder. Longer rods (6.4" for long stroke and 6.57” for short stroke) have less angle at mid stroke with corresponding lower side thrust and reduced frictional losses. Also – the longer rods smooth out the jerk at the top and bottom of the stroke. All this adds up to less stress, lowered friction on the pins, rod journals and main bearings. To answer your question – these are the things that make higher RPMs (& more HP) possible (everything else being equal).

The gain in RPM has shown up on dynos and race bikes. A 1000+ gain in RPM was reported on a 1000cc motor. A long stroke 850 went to 8400 on a dyno. Now someone’s gone to 8700 with a short stroke. I’m not saying its OK to rev this high. But I don’t have control over what people do with my parts. I just keep track and make notes as I go. I’m just happy to know that stress and vibration is reduced on my street bike and that customers have reduced the risk of breaking their cranks and cases.

As for Triumph cranks – I don’t know much about them other than they have smaller weaker rod journals. But they are cheaper than a new short stroke Norton crank.

I´ve been racing the same Triumph T140 engine since 1999 and never had a crank failure. I changed main bearings once because a piston blow up made the oil dirty and circulating to the crank. However I now about people that has had it. Things that have come apart have been pistons, broken gears and bent mainshaft because of missing a cushdrive unit which I actually for the first time has been testing. The Triumph T140 crank is good and yes has weaker ends at the journals but It doesn't seem to be a problem if pieces are built properly. And still I rev mine to max 7000. Why, because on the dyno there wasn´t more power after 6800 were it peaked. This might be because the characteristics of the engine, the carbs being 34 mm Mk2, the problems we have in Sweden with noice regulations not letting us above 98 dB which of course makes it necessary to use bigger and silencers with increased resistance to gas flow. Before noice regulations we had 72 Hp and after between 65-68, rear wheel. It seems like an interesting idea. The later crank after 70 had 30 mm inner dia on the journals and the right hand shaft is splined but you could probably quit easy use a splined front pulley and the norton clutch basket. Then use some go MAP s steel ARP long rods and flat pistons.

Dances with Shrapnel · Mar 3, 2016

Swetune said:
I´ve been racing the same Triumph T140 engine since 1999 and never had a crank failure. I changed main bearings once because a piston blow up made the oil dirty and circulating to the crank. However I now about people that has had it. Things that have come apart have been pistons, broken gears and bent mainshaft because of missing a cushdrive unit which I actually for the first time has been testing. The Triumph T140 crank is good and yes has weaker ends at the journals but It doesn't seem to be a problem if pieces are built properly. And still I rev mine to max 7000. Why, because on the dyno there wasn´t more power after 6800 were it peaked. This might be because the characteristics of the engine, the carbs being 34 mm Mk2, the problems we have in Sweden with noice regulations not letting us above 98 dB which of course makes it necessary to use bigger and silencers with increased resistance to gas flow. Before noice regulations we had 72 Hp and after between 65-68, rear wheel. It seems like an interesting idea. The later crank after 70 had 30 mm inner dia on the journals and the right hand shaft is splined but you could probably quit easy use a splined front pulley and the norton clutch basket. Then use some go MAP s steel ARP long rods and flat pistons.

According to one online reference, the stock T140 stroke is 82mm stroke whereas a stock Norton stroke is 89mm so one would expect a slightly higher redline of about 8.5% (89/82 X 7,000 = 7,600 rpm). I seem to recall tachometer markings for redline at 7,000 rpm on a T140 so maybe it was a practical limit for British big twin valve train rather than max piston speed or crank speed. Having a one piece crankshaft has benefits but usually the big gains are in material of construction. The Norton stock cranks are cast steel cheeks with cast iron flywheels; not the most durable materials if you are going to push things. It would be nice to know what the Triumph cranks were made of. I have seen only one billet one piece crank break; it was a Nourish in a Triumph twin.

I am using a spline pulley on my Nourish which powers a Norton Commando style clutch basket. If I recall correctly, the pulley was sourced through Newby.

jseng1 · Mar 3, 2016

Dances with Shrapnel said:
.... The Norton stock cranks are cast steel cheeks with cast iron flywheels; not the most durable materials if you are going to push things....

Below is what can happen to a stock cast iron flywheel at high RPM. The ugliest flywheel explosion I have ever seen – Yikes! Lucky no one was killed.

Here’s what the racer said.

“It was a stock crank with lightened flywheel... All parts of the crank was crack tested prior to assembly. The revs was below 7000 rpm when it happened and there wasn’t any indication prior to it.

The engine had con rods, pistons, cam and lifters from you and the throttle response and the way it revved up to 7500 rpm was like no other Norton I’ve had before.

The only thing that was able to salvage was the head and the carburetors (even though a piece of the flywheel cracked both float bowls).”

See a piece of flywheel to the right in the photo above. Parts of the flywheel were never found.

Wee bit of daylight in the cases above.

I used to lighten my own flywheels and I thought the smaller diameter helped reduce the likelihood of explosion. I raced the shit out of them but they never blew. It’s a crap shoot and I was lucky. The stock crank/flywheel in the testbike below has been revved to 8200+

Big Dumb lunk getting ready to thrash his poor little JSM test bike once again (28,000 miles now).

madass140 · Mar 3, 2016

YIKES!!!!!!

Rohan · Mar 3, 2016

Yikes just isn't even the word for that mess....

jseng1 said:
“It was a stock crank with lightened flywheel... All parts of the crank was crack tested prior to assembly.

It could be interesting/instructive to see/know how the flywheel was lightened ?
Reducing the dimensions significantly, in any direction, could seriously affect the strength.
Notwithstanding the cast iron material aspect to it.

Swetune · Mar 4, 2016

Rohan said:
Yikes just isn't even the word for that mess....

jseng1 said:

“It was a stock crank with lightened flywheel... All parts of the crank was crack tested prior to assembly.

Click to expand...

It could be interesting/instructive to see/know how the flywheel was lightened ?
Reducing the dimensions significantly, in any direction, could seriously affect the strength.
Notwithstanding the cast iron material aspect to it.

You shouldn´t be racing with a cast iron flywheel. It´s a potential exploding bomb between your legs. The material is brittle and when you machine it for getting it lighter it weakens it a lot. Then also the material of cast iron is not tensile and there are small cracks in the material because of the metalstructure of cole and iron. It is porous and good as liner for example as it may keep oil in the pores. I machined onedown and theres no strenght to it. Do a new flywheel/balance weight in tensile steel.