Joined: Mar 2021 Posts: 9 Threads: 2
Reputation:
1
Location: England
Car type: Austin Seven
On my way to the VSCC Light car event in Llandrindod Wells my journey came to a sudden and noisy end, followed by recovery to home.
On stripping the engine I found a broken crankshaft but thankfully no other damage. Clearly a new crank is required, but what size should I use?
The car is a 1925 Sports and the crankcase is unique ( well I have yet to find another the same), and has at present an 1 1/8 inch crank. So, do I replace like for like, or upgrade to 1 5/16 crank, and if so why. I am interested to hear any views on the matter.
Colin
Joined: Dec 2017 Posts: 1,160 Threads: 68
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8
Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
Hi, I don’t know if your crankcase will take a 1 5/16ths cranked. Others more informed than me will be able to tell you. The 1 5/16ths crank is stronger and modern ones even stronger made from better steel.
John Mason.
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
Joined: Aug 2017 Posts: 1,337 Threads: 34
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30
Location: Cheshire
Car type: Race Ulster, 1926 Special, 1927 Chummy, 1930 Box
A 1 5/16in crank can be made to fit but really a new smaller crank will do you fine.
Alan Fairless
Joined: Aug 2017 Posts: 482 Threads: 14
Reputation:
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Location: Dunchurch, Warwickshire
If you switch to 1-5/16" you will have to change the flywheel, the con-rods and the rear main bearing & housing. The flywheels are getting hard to find. Unless you're going racing with it, there's no point in fitting a larger crank.
Joined: Aug 2017 Posts: 984 Threads: 6
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12
Location: Scottish Borders
We fitted an 1-1/8" Phoenix crank to our 1929 car as a precaution against breakage. The car still has its original engine which we didn't want to risk.
Jim
Joined: Aug 2017 Posts: 3,391 Threads: 106
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Location: Darkest Bedfordshire
It's more than likely a modern 1 1/8" crank is stronger than the original was when new, and it's certainly 99 years younger! Unless you are using it for all-out racing that would be my choice. Fatigue is the real enemy and any new crank shouldn't have any.
Joined: Aug 2017 Posts: 966 Threads: 117
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Location: Melton Mowbray.
Interesting Colin...and bad luck! In my experience breakages of 1 1/8" cranks are rare. I firmly believe the metal of this type was either of better quality or manufacturing technique than the later larger diameter cranks. Look at the revolutions the cranks were taken up to in the early Seven racers. Like many others here, I would also replace it with one the same diameter.
Joined: Mar 2015 Posts: 5,442 Threads: 231
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67
Location: Scotchland
Both 1 1/8” cranks I have broken have gone through number 3 journal. One took nothing with it, the other damaged the front lip.
Joined: Aug 2017 Posts: 881 Threads: 48
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Location: North Wiltshire
Car type: 1927 Chummy, 1938 Big Seven 1/2 a Trials Chummy
Fitting a 1 5/16" Phoenix crank to an early (1926) mag crankcase is covered on Page 10 of the "Restoring a Top Hat" thread, with photos.
To summarise,
1) drill rear main oil return hole
2) relieve centre camshaft bearing housing to provide sufficient clearance
3) relieve front lip to provide clearance. Crankshaft may have to be relieved as well, so do this before it's balanced.
All the rear main mounting hardware from a 1 5/16" engine is used as well as the rods (obviously!) and the flywheel. 1 5/16" rear mounted starter flywheels are becoming hard to find but a later, 4 speed type can be machined to suit.
Some people have found that the big ends foul the inside of the crankcase, I've done a few of these and not had any problems but it's worth checking.
