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Author Topic: The conrod saga  (Read 3286 times)
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welleyes
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« Reply #15 on: 26 May, 2014, 08:30:27 PM »

Regarding the above, would someone like to un-confuse me by giving the sizes of main bearing journals and big ends for the Series One and the Series Two. If anyone else can give me suggestions for shell bearings (bearing in mind we are having new alloy rods made) I would be grateful.

Stuart
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ben
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« Reply #16 on: 27 May, 2014, 11:10:56 PM »

I believe the original S1 crank had 45mm big-ends but the diameter was reduced to 43,5mm when the shells were introduced which was some time before the launch of the S2 engine with its 45.5mm journals.
 The data sheets posted by Blue Sky give the S1 size as 45mm up to engine no 7700 and the first regrind sizes as 43,3mm and 45,3mm for S1 and S2 respectively where the S1 data obviously relates to an original size of 43,5mm. IE both regrind sizes are 0,2mm (or 8 thou' ) down from the originals.
Harry used to use a Skoda shell for the smaller cranks which may now be difficult to source. I would think any crank grinding specialist would have lists of currently available shells with sizes etc that you could choose from.
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welleyes
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« Reply #17 on: 28 May, 2014, 07:39:38 AM »

Thank you, Ben. That makes things much clearer.
Stuart
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welleyes
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« Reply #18 on: 30 May, 2014, 05:27:37 PM »

Courtesy of John Savage, we now have a photocopy of the 1946 Lancia document which Blue Sky showed in his posting. There is a typing error in it or else I am getting confused again.

It has a line title
                                                                                           Engine 97                Engine 99

Diameter of crank journals for engines 97 up to no 7700     44.982-45.000                  _

Diameter of crank journal for fitting first undersize              43.282-43.300         45.282-45.300

                ditto for second undersize                                 43.082-43.100         45.082-45.100


That makes perfect sense as undersizes for 43.5 (S1 with shells) and 45.5 (S2)  What on earth is the 44.984-45.000? It would appear to be the size of the original S1 journal but what is it doing under that heading? Am I being obtuse? (again!)

Stuart

Stuart
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davidwheeler
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« Reply #19 on: 01 June, 2014, 08:50:16 AM »

If anyone is going to break a crank, then, it will be me.  So far, two years on from a major rebalance (they said the engine tried to jump off the rig is was so out of balance with the new heavier rods) I have done many miles, including going from Carlisle to Goodwood and back at full chat down the motorway.  I always drive the Aprilia enthusiastically (that is what it is for) and should the engine get a bit hesitant give it a blast at full revs to clear the plugs.  Have been doing this for 2 years and more, so far so good.

One concern some have (jump in please anyone with more information) with the "vibration free method" is that the correction weight is applied or removed at the ends of the crank on the flywheel and front pulley. The thought is this (insert Have I Got News For You style "allegedly") sets up a twisting vibration or resonance in the crank which may have been the cause of a couple of crank failures.  

They put the engine as a unit on a rig much like at the tyre fitters.  Perhaps think of it as making each end vibrate to counter the internal vibrations so it doesn't jump about on its mountings so much.  Money no object people have a modern style counterbalanced crank made to match the rod and piston combo.

Recent problems might also have been machining of the crank beyond limits, or stress raisers, or going beyond rev limits either on a "motorway" basis or through the gears or with missed changes or too much blipping with no load on it or any one or more other causes.  In one case hanging a supercharger off the front with its pulsing load could have been a factor along side the increased torque it produced.

Perhaps its as simple as a smooth engine with steel rods gets (relatively) thrashed.  Back in the day a week flat out round a banked track day and night to setup records would be considered an extreme test. Now we have the roads to pound along beyond the design limits as a matter of course.

David
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David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
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