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Strengthen the crankshaft

Kristian Jonsson

Kristian Jonsson

Donation Time
What methods are you using to strengthen the crankshaft? Surface treatment, heat treatment or what is known to be effective?
 
Surface treatments might improve crankshaft durability, but crankshaft strength is mostly a function of the metallurgy which is what it was.
 
Well, I mean durability or sustainability or whatever that will make the chances to survive better under power......hopefully.
What kind of crankshaft disaster or problems has occurred?
 
Barry has stated it correctly. You can toughen a crank with surface treatments, but overall you can’t change the metal and therefore the inner strength.

There is, of course, thermal treatment, and cryo (freezing) treatments have been effective in reducing metal fractures in things such as aircraft parts, but it’s bloody expensive.

All that being said, the most effective thing I’ve done is to be very careful when machining journals... one needs to provide a generous radius at the ends of the journals such that you reduce any right-angles and thereby greatly reduce the chance of fracture.
 
puff4: "All that being said, the most effective thing I’ve done is to be very careful when machining journals... one needs to provide a generous radius at the ends of the journals such that you reduce any right-angles and thereby greatly reduce the chance of fracture."

Right!
 
Kristian Jonsson said:
... will make the chances to survive better under power......hopefully.
What kind of crankshaft disaster or problems has occurred?
Click to expand...
How much HP are you expecting? The most I have seen is about 119HP @6500rpm from a 1725.
I have never seen any broken cranks even when the rods seized to the crank pin. If anything, it will break from torsional vibration because of a cheap torsional damper (i.e., harmonic balancer)
Jan
 
My guess is the original parts, rods and pistons, are too heavy/weak for high rpm use.

The crank is also not really intended for high rpm use, but will last longer with a lighter load, lighter rods and pistons.

Dave Anderson has concluded 7000 rpm is a practical limit for an iron 1725 crank.

I agree with Dave.

For running above 7000, my plan is to switch to a 1592, with it's standard Steel crank.

BTW, when I started Vintage Racing Tigers, it was common in the VR Ford community to loose bottom ends, spin rod bearings and break rods/bolts.

I tried REAL hard to NOT join that parts breaking community.

After 20+ years of Tiger VR and more than 100 Events (with multiple track sessions each event), I have lost a total of one bottom end.

And even that was just a spun bearing under unusual circumstances, I reused the Steel crank.

Granted, I DID use parts and processes that were more than adequate for the job.

And if you think maybe I just didn't race the Tigers very hard, check out my little picture/avatar.

That is the start of a race, where I qualified 2nd and took over 1st place before turn one!

DW
 
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BTW, As far as I know, Carl Christensen admitted to 156 HP @6500 with his overbored and stroked "1725".

Also, as far as I know, he used a cast crank and didn't have a lot of bottom end problems.

BUT, even the BEST cranks have a life span, cast iron, no extra/long lives for them!

DW
 
spmdr said:
BTW, As far as I know, Carl Christensen admitted to 156 HP @6500 with his overbored and stroked "1725".

Also, as far as I know, he used a cast crank and didn't have a lot of bottom end problems.

BUT, even the BEST cranks have a life span, cast iron, no extra/long lives for them!

DW
Click to expand...
There is a member who has turbocharged a 1725 and is claiming a boat load of power. Sorry, but I cannot remember his name or actual hp. His name is Bryan (I think), but I cannot remember his member name.
Bill
 
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A race car in UK

".....carried out in 2009 by Sunbeam Supreme and the car was run by preparation and race support specialists Davron. The impressive specification included but was not limited to an all steel engine, five speed T9 gearbox sporting Quaife straight cut gears, a ‘bullet proof’ disc braked, limited slip differential rear axle well located via a Panard rod and anti-tramp bars, plus double adjustable alloy bodied Koni dampers. The engine inhaled through 45 DCOE Weber carburettors and exhaled through a BTB exhaust system while the lightened body shell sported a fibreglass boot and bonnet.

Chris Conoley of Mass Racing Developments has built and rebuilt the engine several times, dynamometer testing it each time and in 2006 and 2007 it was giving 170.3 and 170.4 BHP respectively. The five speed gearbox was rebuilt in 2011 and the car was run on pretty much an ‘arrive and drive’ basis with full trackside support from Davron."

https://www.berlinetta-auctions.co....t-144-1964-sunbeam-alpine-series-iv-race-car/
 
Looking at the above link, we see this (with great interest):

"in February 2016. Mr Michael returned the engine to Mass for a comprehensive rebuild in July 2016 and this included new pistons, camshaft, steel rods and flywheel while the steel crankshaft required nothing more than a lap. The results were clearly worth it as the dynamometer now showed power to have increased to 175.6 BHP at 6,525 RPM; Mr Michael’s bank account on the other hand, had decreased by £7,493.53."

I have not "run the numbers", but that power at that RPM would suggest something WAY bigger than a 1725.

AND, less than 6 HP for 7500 pounds? ...well, some expensive ponys!

DW
 
Bill Blue said:
There is a member who has turbocharged a 1725 and is claiming a boat load of power. Sorry, but I cannot remember his name or actual hp. His name is Bryan (I think), but I cannot remember his member name.
Bill
Click to expand...

Think it's TIGRETR. (Brian )

Author of this thread.

http://forum.sunbeamalpine.org/inde...lves-seat-and-door-chrome-hinges.29943/unread

He used to have a website with the story of his Alpine but the link I saved seems no longer valid. Very involved and interesting.
 
Getting back to the original question,

I will be tuning up and resizing at least two STD 1725 cranks for the Long rod engines soon.

So, this subject is of great importance.

I will be talking to a few more Crank shops to see what they recommend.

But my current thinking is a Micro polish as a minimum.
 
Seeing I think this is pertinent, I looked at the pictures of that Alpine Race car, linked above.

WOW! ... a STOCK oil pan???

AND, I don't see any extra oiling lines that would suggest an oil accumulator.... Hmmmm....

Paint me skeptical!

DW
 
jumpinjan said:
So, do you believe those HP numbers?
Lets do some math...1725cc = 105.3 cu in
170.4 HP/105.3cu in =1.6 HP/cu in
Do you see where I'm going with this?
Jan
Click to expand...

The car is said to be running with a 1600 engine in a 1600 class. Don't think anyone believe that. With it's steel crank it has to be a stroker engine.
I have tried to get in touch with Devron and MASS Racing who has been involved in this engine but no answer so far. Chris Conoley was named as one of the builder, but he says that they just made some adjustment. If the car is fore sale with all that is claimed in the ad. I could buy it. But what is inside the engine is unknown for my eyes so far.
 
There are so e guys running race 1725s at the moment that are a tad over 1850cc and on twin 45s with lightweight forged rods and pistons and putting down 138 to the wheels on race fuel... So at the flywheel they will be over 150..

That said.. In historic production classes in Australia that would be illegal engine size and carb setup
 
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