well while the debate on the "hardness test" is going on I thought I might throw some points around with the subjects covered so far.

1 all mini cranks are heat treated either truftriding or nitriding and only the base metals are different.

2 a std mini crank is not well balanced [centripically] and these new 8 web cranks would only partically solve this problem as long as the "balancing " includes the forces from the mass of piston/rod and the frictional load from the piston. This balance has the maximum "out of balance" when the con-rod is halfway down the stroke. It is impossible to get a perfect balanced crank because the balancing is different when the piston is at TDC,or BDC compared with half stroke. This with the acceleration and deceleration of the piston also makes a perfect balance impossible.

3 any centripically balanced crank will help to reduce the magnitude of the forces created by torsional vibration but can not eliminate these forces, unless the engine is NOT firing.

4 a torsional vibration is created also by a cam shaft [I know GR disagrees] but the loads acting either by opening the valves and closing the valves are not dimetrecally opposite and equal in magnitude. Thats why there are some engines that use a balancer on the camshaft.

5 Inregards to a crank damper on a mini crank, any of the short stroke engines did not have one fitted,why, as the stroke increases the T/V increases rapidly. hence long stroke engines have one fitted to reduce the forces on the crank.

6 now the original discussion as to why the cranks break where they do. firstly to fracture a crank in that position the force that causes it is only a twisting force IE torsional . It is impossible to fracture a crank longitudinally because of the main bearings IE bend it length wise for it to crack at that point.

so when you look at the number of problems it all come back to T/V and when a engine power is increased IE higher peak pressure, incorrect timing, too high air comp temp at ignition all create a higher stress load on the crank. The one that I consider is the most damaging on a mini is the "out of balance force" created by the action of the clutch back plate.
With all the associated engine forces when you are at a critical rpm [node point in T/V calcs] and the clutch is used then the crank will start to under go fatigue stress and eventually crack.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

I have had work done by Steve and found him very professional and knowledgeable in his field. I trust him with anything to do with my parts, car or bike.

Cheers.

[quote="david rosenthal"]

5 Inregards to a crank damper on a mini crank, any of the short stroke engines did not have one fitted,why, as the stroke increases the T/V increases rapidly. hence long stroke engines have one fitted to reduce the forces on the crank.

[quote="david rosenthal"]

Ummm you might wanna have a look at some. 998 A+ engines pretty sure they have balancers on them

Beanie

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I am the son of the STIG

HOTBRICKS
http://hotbricks.org.au/

'65 NCF MINI.....
'69 MINIMATIC.... 9 year resto still on the go

So did the 998 Cooper. Also, 970S and 1071 S.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

So maybe we could say that they didn't put ballancers on the earlier ones to make it more cost effective ( cheaper )

Beanie

_________________
I am the son of the STIG

HOTBRICKS
http://hotbricks.org.au/

'65 NCF MINI.....
'69 MINIMATIC.... 9 year resto still on the go

It's been a while since I looked in detail on the small bore engines, but I seem to recall that the Deluxe, and all the post 74 imported 998, up to the pollution models, did not have harmonic dampers fitted. I do recall that Mini K (1100) did and rightly so.

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In my experience it was the 'powerfull' 998s that got them; the Cooper and derivatives (Inno 1001 etc.). I've never driven one, but I guess they reved quite well past 5500 - where my A+ 998 (like almost all fitted with 3,1 diff) allready ran out of juice

Great thread!! I think I learned a lot here - even if I probably only understood half of it

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No speakers, no bodykits, no six-inch spacers, no spak filler, no bullshit

And the other part of the equation is COMP ratio with those engines.
If they had more than 8.3:1 comp ratio or the stroke exceeded 3 " they fitted a damper. Why, because the peak pressure/stroke exceeded the limits of the std cranks.
I think you will find that the A+ engines were a high comp and there would also be a cost factor as well. Standardization for the engine range.

_________________
Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com

interesting, i recall a few years back a mate of mine running a 1293 race engine broke the crank when taking the car from standstill , he was reving a bit because of the taller 1st gear and car uphill , when releasing the clutch it went bang!

Here here! This bloke has only ever drunk Vickers once (yuk, give me Bombay every day) and I couldn't understand why anyone would want a machine which produces the stuff.. but I digress, I agree. Seriously enjoying this thread, fascinating stuff!

(even if I miss the point entirely, which is plainly obvious)

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Simon

The adventures of an owner builder in the Tallarook Ranges

Update, update, update...

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Mr 'Ting, Mr 'Ting, Waiting.......

They said it'd be about 2 weeks, but I'd be adding another week to that (from previous experience) so I'm not expecting to see anything before the end of the week after next.....

So, you'll need a LOT more popcorn to last you until then.......

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Just a small up-date to say, well, there is as yet, no up-date. Spoke with the lab today to see where they are at with it. They do tell me 'it is in the que......'

I did also have some factory info passed on to me regarding the design philosophy of the Cooper S Crank and how they made the them stiffer. It maybe of interest;-

http://www.mk1-performance-conversions. ... folder.pdf

On page 5, the lower 1/3 of the page. Thanks Mark

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Some nice PR speak in that press release, the bits about...

...don't really match up to what really happened in Formula Junior where BMC powered cars were flogged by Ford powered cars.

But it was a press release and I bet they all fell for it.

When did this Forum become "AusSprite"? Maybe next time we can get a Mini crankshaft tested...

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