Thread: Steel for a Crank shaft.

John, knowing nothing about this field myself (well, other than turning little model cranks, but they hardly count), I'm fascinated by the process. From my completely ignorant position, the suggestion to modify an existing crank sure seems like a great idea to me. If it's any consolation, even modern aircraft piston engines/props can have horrible harmonics too, so your aircraft/auto engine is in good company there!! Whether you modify of scratch build, I'd be grateful if you could post the process here. Could come in handy next time my, errr "Maserati" needs a new crankshaft.

Pete

Originally Posted by nearnexus

An estimate on the hours would be interesting.

Rob

Mate reckoned under 30hrs, pre-grind, came out under 10 grams on the balance. I expect this thing may be more challenging, probably long stroke to keep revs low and tips of the prop sub-sonic in aircraft use, unless they were using a reduction gearbox.

I do know Crankshaft Rebuilders quoted 4k a pop for 4 cylinder units, quantity three!

Hold breath moment is apparently doing the drillings - and when they intersect!

Originally Posted by bob ward

If the Diatto engine is a WWI design it presumably it has no counterbalances, if they could be included with the new crank that could well get rid of the harmonics of which you speak. (Hudson were the first auto manufacturers to use counterbalanced cranks in 1916. Even Packard were still using non-balanced cranks 10 years later).

Given the price of the raw material, $1400 for a 250dia x 900 or $2000 for a 300dia x 900, I think I would be having serious discussions with the guys who do this sort of thing for a living before I tackled it myself. Yes they will be making a dollar out of you, but you get an item that is absolutely spot on and all the risk is on them.

Bob, have a 1916 Hudson here is a Hudson powered special.[Hudson won Indy 500 in 1916] yes a counter weighted crank beautiful thick chr vanadium rods.Been into the bowels of many of these engines never seen them break a rod nor break a crank. they were splash fed with a piddly piston plunger oil pump ''pilgrim motor cycle type.Cocky beak dippers on the big ends sweep through individual troughs in the oil pan.I the alloy crank case [cast block is separate.,there are troughs and runners for oil to run down to lubricate the mains cam bearings. I have never seen one of these engines without the original factory fitment shims some virgin still with factory fitted split pins.They are 6cyl whopping 53 cu in per cyl 318 cu in all up.A real torquey low revving grunter of an engine. Cheers J A

Originally Posted by steamboatbrucey

Ha

Reinventing the wheel here its a flat plane crank get a profile of it blasted out of some 350 grade plate 75 mm should do it

Hi all thanks again for the input. 1 due to the stroke a substitute crank from other sources rule it out. Re the harmonics,when I first encountered this vehicle and drove it it scared the sh 1t out of me with this 2800 rpm vibe. Consultation with other owners reassured me that this was the norm as they all did it. me personally was not happy,however drove it for many years until the crank broke.2 Fiat engines of the same era had flat plane cranks 4 cyl ones and the shaper or planer marks are visible even get your finger nail into the the finish cut.3 Considered that option as well flat plane with bolt on c weights. John.

Making a crank, a big one....BostCrank - YouTube

Great project. EN 40b was a very popular steel for forged UK cranks, it was then nitrided. If you go with any heat treatment consider when you drill the oil holes etc and they can some times be done after carbonising (if needed) and it means the hardness doesn't follow the holes etc and weaken the crank.

I was only ever involved in turning or more correctly trying to turn a big crank on a lathe (did some small and bike stuff). It was a 350 ci V8 something on a new Visby. It wasn't my project but it was a lot of machining and the offset bit on standard tailstock wasn't fun.

Years later I was keen to have another go and got a large Mazak lathe. I got hold of some taylor chucks and The plan was to also get some counterbalance faceplates off a crank grinder and make a rig up for turning crank blanks. I never finished it so never got to have another go.

good luck and if you do go ahead please take plenty of picks.

Spotted this Youtube video about reproducing a 1914 6 cylinder 2 stroke aero engine. All pretty cool stuff, at about 7.30 they show and discuss the the crankshaft they have made, a 900lb billet reduced to 60 odd pounds.
Benoist 2014 - Roberts Engine Reproduction - YouTube

Originally Posted by bob ward

Spotted this Youtube video about reproducing a 1914 6 cylinder 2 stroke aero engine. All pretty cool stuff, at about 7.30 they show and discuss the the crankshaft they have made, a 900lb billet reduced to 60 odd pounds.
Benoist 2014 - Roberts Engine Reproduction - YouTube

Thanks for the link Bob

Originally Posted by bob ward

Spotted this Youtube video about reproducing a 1914 6 cylinder 2 stroke aero engine. All pretty cool stuff, at about 7.30 they show and discuss the the crankshaft they have made, a 900lb billet reduced to 60 odd pounds.
Benoist 2014 - Roberts Engine Reproduction - YouTube

Good Vid, but I somehow question that he turned that crank on that lathe.

Hi couple of Diatto pic no engine yet cant get the file to open

140.jpg

139.jpg

John, there is Diatto reference a page or 3 in on this web site.

All about Antique, Vintage and Pre-War Cars - PreWarCar

For those with an interest in old cars the site is a real time waster, in a good sense of course.

As is this one. COACHBUILD.com

[QUOTE=bob ward;1693187]John, there is Diatto reference a page or 3 in on this web site.

All about Antique, Vintage and Pre-War Cars - PreWarCar

For those with an interest in old cars the site is a real time waster, in a good sense of course.

As is this one. COACHBUILD.com

Thanks for the link Bob,for any one interested this blue 1922 Diatto 20s roadster is now in UK ex Melbourne. any one been following the tv mini series Underbelly Squizzy Taylor this was alleged to be his car in the 1920's.taylor was small in stature and dressed flashy and drove a big car to suit his ego,definitely a sufferer of the ''small man syndrome''. This car lived all its life in Melbourne and is another loss to the country.