chriscook
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| posted on 13/11/07 at 04:45 PM |
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Which crank?
I have 2 XE cranks now and don't know which to go with.
One is an early lighter weight type but is out of my engine that let go. Therefore one of the big end bearing surfaces is knackered but might just
about be regrindable to a -0.5mm size.
The other is slightly later and is the heavier version but is fine but I might treat it to a polish if I go with that one.
The knackered bearing has gone blue on the more loaded side and is very damaged. I've not inspected the fillets closely to see how they look
yet.
Opinions? The lighter one has its obvious benefits but am I asking for it to let go somewhere not very far down the line? The weight difference is
definitely noticeable just by picking them up.
Chris
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ned
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| posted on 13/11/07 at 05:28 PM |
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I wouldn't use it if it has blued from the heat even if you could grind out the damage to the journals.
From working on race engines there is little real world difference between the early and late cranks but obviously the lighter one is normally
preferred.
If getting the crank fully balanced I'm guessing it wouldn't be too much more to get it knife edged or lightened?
Ned.
beware, I've got yellow skin
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chriscook
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| posted on 13/11/07 at 05:28 PM |
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The weight difference is about 2kg (15 vs 17kg)
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02GF74
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| posted on 13/11/07 at 06:29 PM |
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what is important is where the weight is distributed, if close to the centre than not such a big issue.
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chriscook
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| posted on 13/11/07 at 06:31 PM |
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But seeing as i don't have the facility to measure its moment of inertia weight will have to do..... 
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snapper
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| posted on 13/11/07 at 10:31 PM |
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How much will it cost to get the lighter crank back to usable and safe?
Will you always wonder if it will let go?
Build it with the cheaper safer option and have a look at the lighter crank in slower time, always good to have an upgrade ready for winter.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Paul TigerB6
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| posted on 14/11/07 at 09:29 AM |
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Personally i'd be asking why the later version is heavier?? Is there any reliability issues with the earlier type crank?? Is the later version
stiffer??
Could be a case that the slightly heavier, not knackered crank will be the better option for reliability and handling some serious tuning.
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02GF74
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| posted on 14/11/07 at 09:50 AM |
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quote:
Originally posted by chriscook
But seeing as i don't have the facility to measure its moment of inertia weight will have to do.....
You surprise me, I thought we all had these machines - have you looked in the broom cupboard?
Assuming the material density is the same, can you not measure the size of the balancing lugs (if the is the correct term) - the one with larger M.I.
will have bigger lumps at the outer most ends.
If they look the same, then the heavier crank is denser material - that may mean it is stronger, but not necesaarily as it could mean the heavier
material was cheaper.
Have you trawled vauxhall car/tuning sites about this?
Take both cranks for a crank specialist to look at and if the lighter one is deemed good, go for that one would be my advice.
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chriscook
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| posted on 14/11/07 at 09:54 AM |
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The general dimensions are the same so the heavier one will have a greater I. From what I understand the lighter crank has plenty of strength - the
extra material doesn't look like its in particularly load carrying sections. I think the extra weight was so they could lean it out a little for
emissions reasons
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ned
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| posted on 14/11/07 at 10:10 AM |
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I've never seen an early/lighter crank break on a race engine red lining at 7750 and seeing over rev on downshift upto 8200. standard rods
failing or bearings due to oil starvation have always let go first. I've even seen a forged piston and rod in a mess with holes in block/sump
and a standard crank intact.
The heavier crank is chunkier across the journals, not as wasted and possibly the coutnerweights are heavier to match iirc.
ps
late crank:
http://www.locostbuilders.co.uk/upload/img_0338.jpg
early crank:
http://www.locostbuilders.co.uk/upload/img_0354b.jpg
[Edited on 14/11/07 by ned]
beware, I've got yellow skin
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david walker
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| posted on 16/11/07 at 05:00 PM |
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Don't use the blued crank, chances are it's almost certainly bent as well. Don't even think about straightening it.
You'll find/detect no performance differences between the two cranks. These cranks aren't too expensive, throw the damaged one away.
Bottom end failures in XE's usually occur in the following order:
Rod Bolts, Pistons, Rods, Crank - assuming lube, cleanliness etc all ok.
Do you concur Nat?
Dave Walker, Race Engine Services - 07957 454659 or 01636 671277
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