Billet versus Forged cranks

[Worx_55]

Hi All,
This is an interesting subject, because I’m currently on the lookout for a new crank for my Historic racer here in Australia.

A little bit of background, I had been running an EN40b crank from a supplier in the uk (not Minispares or swiffy) that what supposed to have been machined and so on by arrow, but it has failed by cracking through No: 4 big end following the oil hole to the radius and starting to run around the radius, at first I thought it was a hair, that’s how noticeable it was, lucky I caught it! The sad part about it was the engine its self had only done 6 race meetings! After some close inspection and chatting with NDT people, the crack had started from rough machining on the chamfer on the oil way hole (it had left machining marks running perpendicular with the oil hole) and the angle of the oil way hole was way too close to the surface of the big end journal (1.5mm - 2.7mm material thickness for the first 10mm of the hole). However with further inspection, there had to be something to start the cracking, and it was from a poorly machined 2 piece harmonic balancer that the outer ring does not line up true with the pulley, causing the outer ring to be out of centre with the pulley(one big counter weight at 8000 rpm). When discussions occurred with the supplier the old saying "This has never happen" came in to play, anyway no point bashing my head against a brick wall!

Also on top of that, we have had 3 A....s M.. Billet cranks over here self destruct, 2 straight through the centre main and one the tail came off! And the tail jobbie crank was heat treated that well the owner had no problems filing any part of it!

My question is who does good cranks and balancers that will last longer than my last disaster? I am currently exploring manufacturers in the US but what premade cranks are the better options to go for in the UK?

[olddad]

My old 1293 race motor ran to 8500 all the time race after race on 2 thou main clearance with Redline oil. The Gordon Allen billit crank with standard throws never faltered and was never ground.

Maybe a former employee is still alive?

[Spider]

Hi All,
This is an interesting subject, because I’m currently on the lookout for a new crank for my Historic racer here in Australia.

A little bit of background, I had been running an EN40b crank from a supplier in the uk (not Minispares or swiffy) that what supposed to have been machined and so on by arrow, but it has failed by cracking through No: 4 big end following the oil hole to the radius and starting to run around the radius, at first I thought it was a hair, that’s how noticeable it was, lucky I caught it! The sad part about it was the engine its self had only done 6 race meetings! After some close inspection and chatting with NDT people, the crack had started from rough machining on the chamfer on the oil way hole (it had left machining marks running perpendicular with the oil hole) and the angle of the oil way hole was way too close to the surface of the big end journal (1.5mm - 2.7mm material thickness for the first 10mm of the hole). However with further inspection, there had to be something to start the cracking, and it was from a poorly machined 2 piece harmonic balancer that the outer ring does not line up true with the pulley, causing the outer ring to be out of centre with the pulley(one big counter weight at 8000 rpm). When discussions occurred with the supplier the old saying "This has never happen" came in to play, anyway no point bashing my head against a brick wall!

Also on top of that, we have had 3 A....s M.. Billet cranks over here self destruct, 2 straight through the centre main and one the tail came off! And the tail jobbie crank was heat treated that well the owner had no problems filing any part of it!

My question is who does good cranks and balancers that will last longer than my last disaster? I am currently exploring manufacturers in the US but what premade cranks are the better options to go for in the UK?

Just to be clear, was this a) a billet crank and b) nitrided?

[sandman]

Just curious... what sort of camshafts and carb setups do you guys run that require 8500 rpms all day??

I had a chat with Swifty at Raceretro, he's currently developing a new 3 mains crank.... and it look edreal nice onpaper.
Why not give him a call.

[olddad]

Just curious... what sort of camshafts and carb setups do you guys run that require 8500 rpms all day??

One off cam 310 intake, 314 exhaust on 1.25 rockers, .425 lift.

Split Webber 48 with 41 mm chokes.

Made good power from 5500 to 8000, and just let it run up to 8500 on long straights. Isky lifters would last 4 race weekends.

[Worx_55]

Hi All,
This is an interesting subject, because I’m currently on the lookout for a new crank for my Historic racer here in Australia.

A little bit of background, I had been running an EN40b crank from a supplier in the uk (not Minispares or swiffy) that what supposed to have been machined and so on by arrow, but it has failed by cracking through No: 4 big end following the oil hole to the radius and starting to run around the radius, at first I thought it was a hair, that’s how noticeable it was, lucky I caught it! The sad part about it was the engine its self had only done 6 race meetings! After some close inspection and chatting with NDT people, the crack had started from rough machining on the chamfer on the oil way hole (it had left machining marks running perpendicular with the oil hole) and the angle of the oil way hole was way too close to the surface of the big end journal (1.5mm - 2.7mm material thickness for the first 10mm of the hole). However with further inspection, there had to be something to start the cracking, and it was from a poorly machined 2 piece harmonic balancer that the outer ring does not line up true with the pulley, causing the outer ring to be out of centre with the pulley(one big counter weight at 8000 rpm). When discussions occurred with the supplier the old saying "This has never happen" came in to play, anyway no point bashing my head against a brick wall!

Also on top of that, we have had 3 A....s M.. Billet cranks over here self destruct, 2 straight through the centre main and one the tail came off! And the tail jobbie crank was heat treated that well the owner had no problems filing any part of it!

My question is who does good cranks and balancers that will last longer than my last disaster? I am currently exploring manufacturers in the US but what premade cranks are the better options to go for in the UK?

Just to be clear, was this a) a billet crank and b) nitrided?

My cranks was a en40 forged and nitrided jobbie, the second ones are "CNC machined from steel EN40B billet
Nitride hardened to a depth of .020” as the web site says!

[migliacars]

Just googling snapped mini cranks and found this thread.

Reason is a good friend of mine who races in the same championship as me has snapped yet another 86mm steel crank. billet
one last year one this year.

Ive never been a fan of these en40b cranks, Ive heard of at least 10 snapping in competition use over the last 11 years.

Ive always used the A plus forged crank and never really modified it to death. We have never had a rubber crank fail on us.

[northern monkey]

Awesome thread...now just to add my tuppence to the debate...whenever the subject of forgings or billets came up at work,where anything that could be modified or tuned or improved was leapt on,because true engineers never switch off,and most were serious petrolheads (as far back as my apprentice days) the instructors and older engineers would always say that the only thing to be used for a crank is a well made well treated forging...and nothing else ever.

I was told to think of a billet in terms of a tree branch from which you needed to make a wine glass (very simplistic) so having a grain like wood which is strong ,but allows it to flex,twist etc,,,you then cut it into a new shape (machining) across this grain thus leaving weak spots....and then I was told to draw a wine glass (cross section) outline,with as many ever smaller outlines inside the first outline,now if you were to machine the outer surface to make your wine glass the structure (grain) is still present in a less disrupted manner making it stronger.......well they did have to explain it to 16 year old's

Now even allowing for more modern steels and production methods..which differ vastly from even five years ago,never mind 30..or 40 or more years ago,and also allowing for as people have stated correctly certain processes which have been curtailed by legislation due to health and safety and environmental issues (mostly the chemical aspects in the metal treatment) the advancements in engineering have turned out sometimes to be anything but advancements,and most are mainly due to time and cost alone....A properly forged,properly treated and properly machined and ground forging is the better prospect....your problem will be in finding one.

I think there are still a few firms that manufacture good forgings for crank's and my first port of call would be companies who make Aeroplane race engines (unlimited warbird class)or top fuel Dragsters) then find a group of people who need cranks and order a batch..


P.S. The engineer's who the discussions were held with all worked for a small backwater firm..... Roll's Royce (Aero engine's)