Ring-a-ding crankshaft

[Nick Salmon]

Perhaps we could form a 'Crankshaft Orchestra' and in a few week's time perform that seasonal favourite: 'Ding, donk, merrily on high'?

I'll get me coat...

[cardiffrob]

Thanks for the input, everyone.

I scared myself looking at the prices of cranks for a 2 bearing jobbie. I do have one rebuilt engine here with original circa 1930 bits that came with the 'project' car that has an original crank, rods etc but a second set of oil spray nozzles. I did wonder whether to risk using it as-is or to strip it back and re-test everything.

On a side note, what about a new crank with these resized big ends that haven't yet run. False economy?

"Ding, Donk, merrily on high..." I think I could probably supply a big-end drum roll and a crashing Cymbal sound as a rod goes through.

[AustinWood]

If the existing rods have been re-metalled for undersized big ends then they could easily be bored to match a new crank. I had this done on my car and 12,000 miles on it's all fine.
I fitted a new 1-1/8" crank because it's the original engine and a broken crank often destroys the crankcase and sometimes almost everything else.

[Ruairidh Dunford]

I did this very job last weekend - all bored to fit new Pheonix shafts.

   

[Alan]

Generally nothing wrong with Austin rods as long as you don’t want to do more than 5000rev/min. You need to be sure they aren’t cracked from the bottom of the pinchbolt slot and that all 4 are the same weight. - there is considerable variation.

[Ruairidh Dunford]

To add further to Alan’s comment, between a third and half of all the rods I test are cracked, a small number are bent vertically and some have a small amount of twist (both of which can be corrected with surprisingly little force).

I have found that end to end balancing a set of four can be quite tricky to achieve without a large selection, and further work, hence my photo above.

[Bob Culver]

Hi Ruairidh
 
Many with lathes will be interested in your activities. It is a while since you published a photo of the jig used. It could be easily reproduced by any keen amateur. Perhaps time to run the photo again ?
A bit rattled by the extent of cracks found. Yet failed con rods not a major issue on cars reasonably driven. Is there a pattern to the conrod cracks? I presume you mean in the steel and not the whitemetal. If mostly short straight extensions of the slit would seem of little consequence if the bore not distorted. Or are cracks random transverse? Garages and reconditioners used to indent with their straightening jigs. I have detected on other makes by testing at forging flaws.

[Ruairidh Dunford]

The rod boring jig is one produced by Myford based on a earlier design by Drummond - details of it can be found on Tony Griffith's site here: http://www.lathes.co.uk/myford/page3.html mine has a fabricated adaptor plate so that it can be mounted to my Boxford.

   

All cracks I have found are as Alan describes above.

   

[Bob Culver]

Thanks Ruairidh

Presumably the crack only forms if the bolt not tight, in which case would expect the bolt to fatigue and fail?
If the white metal is good and the pin bore and thread OK a wee hole just past the detectable end of the crack would do me!
A local Seven enthusiast also has a 1930s six. One rod was split full length. Welded and still OK years after! (Do not try on much smaller Seven parts)

[Marcus Ling]

Thanks Ruairidh

Presumably the crack only forms if the bolt not tight, in which case would expect the bolt to fatigue and fail?
If the white metal is good and the pin bore and thread OK a wee hole just past the detectable end of the crack would do me!
A local Seven enthusiast also has a 1930s six. One rod was split full length. Welded and still OK years after! (Do not try on much smaller Seven parts)

Hi Bob,

This is the machine which I own and is available for use by Auckland North VAR.

   

Cheers

Marcus