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posted on November 14th, 2013 at 10:46 PM
Crankshaft quality
A long, long time ago, in a machine shop far, far away (I remember seeing that in the cinema......Jeez I'm old! HAHA!), people didn't have access to
4140 and 4340 cranks from the CBs and Aircooled.net's of the world, because there were none.
Instead, they offset ground their cranks using Holden Starfire rods to get 75mm throws, then they even sometimes used the Holden Red 161 pistons in a
honed out stock cylinder (3.375" = 85.7mm ), along with 2 BX
Strommies to give them 1732cc of cheap VW hotrod goodness to keep the Clevo's of the world at bay between the lights.......
Crankshafts, back on the topic at hand.
I thought I'd get my perfectly fine OEM 69mm crank offset ground to 74mm or 75mm, using aftermarket H-beams with chev journals (can you even FIND
Blue or Black motor rods any more?) of course. The reason for this is I would have to properly balance the newly-bought 74mm or 76mm crankshaft units
anyway. Offset grinds are about $300 (rough guess), new cranks are $400+ before freight locally, and I'm dubious about the quality. I have heard
possibly as much as 5% of all "cheap" cranks (eg, not DPR, DeMello or Dave Butler......do you still do this offset stuff Dave?) have index and
quality issues also.
Please don't see this as a slight on the Chinese manufacturing ability, rather see it as a slight on the importers who want their products at a
price-point not a quality mark.
Since I'm old enough to remember Star Wars when new, and I live under a small rock inside a deep cave on the edge of a desert, I figure a few of you
blokes know more about the "new ways" as opposed to the "old ways" like me, and so can tell me if these new 4140 cheaper cranks are good enough to
take a punt on for a 5500rpm streeter in an El Bug, or whether I should just say "Aw, f^&k it", and put 88mm thickwalls on a stock crank and
just call it too hard to make a baby stroker with excellent balancing unless I spend over $500 for a shiny piece of something from someone.
Not trying to be smart, a few of you blokes out there have done it all, but new and shiny doesn't necessarily mean good.
May the Force be with you.
cnfabo
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posted on November 14th, 2013 at 11:39 PM
My first hillclimb sprint engine used a cheaper chromoly crank and it held up,used to rev it to over 7000..but who' to say they would all hold
up...whatever crank you use it should be measured for trueness regardless...but 5500 ppff any crank should do the job...why don't you go bigger
stroke for pretty much the same price and have more torque for the street...
Fabo
modnrod
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posted on November 15th, 2013 at 12:16 AM
Bigger throw is the plan, within other guidelines at least.
Was originally going to get mine offset ground, but it seems most machining companies are busy.........
hence asking about the quality of 4140 cranks, even if they work out more expensive than OEM quality crankshafts it may be my only option.
stoker
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posted on November 15th, 2013 at 06:32 AM
i had a stroker scat crank in our race car for 5 or 6yrs until it cracked and now we have an AA crank which we rev
to 7900 across the line on 20psi boost
i was never a big fan of chinese cranks but i am slowly coming around
just get it crack tested as soon as you buy it even though it is a street car(it could save a lot of tears later)
dangerous
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posted on November 15th, 2013 at 08:50 AM
When you offset grind a crank shaft, it should be nitrided,
since machining will cut through the original VW induction hardening.
Ideally, it should be
#1: pre-ground,
#2 :nitrided,
and then
#3: finish ground.
This will add considerable cost, but is the best way.
For Chinese cranks,
it will also give the opportunity to improve the fillet radii,
which is pretty ugly.
Unfortunately it is very hard to tell the quality of the nitriding,
but having machined a lot of crankshafts,
the Chinese ones are mostly just waved NEAR the oven, and it is very shallow.
For any application that you want to keep for a while,
I would have the crankshaft nitrided by someone who knows what they are doing,
like Rene at Adelaide Heat Treatment Services.
But you must at least have the crank shaft checked for size,
and polished afterward,
or better yet,
do the pre-grind and finish grind process.
The Demello cranks look nice and are apparently heat treated at request,
but are still only a high carbon steel, and not chrome moly.
That being said, they are excellent value and will likely out last most engines.
If it were me Dave(Modnrod),
I would chooses China and get Rene to nitride it properly.
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posted on November 15th, 2013 at 09:28 AM
Gday Stoker, it was a AA crank I was considering.
Thanks for the info Dave. Having to machine a brand new crank to fix things like journals then needing nitriding on top sorta tips the odds in favour
of starting with an OEM crank I already have in my view, if the local machinists weren't flat out. I still have a Wasser 76mm crank in the shed too,
but that entails machining as well (this time on the cases), which is still the difficult bit. 76 stroke x 83-88 bore (all thickwall) is what I'm
looking at.
I'll keep looking at all the options though.
Sides
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posted on November 15th, 2013 at 12:11 PM
I've got a DPR 72mm on the way... which very soon after arriving will be in the hands of Mr Butler.
Will let you know what he says... basically a benefit of being a member of the secret society of Dave's methinks !!!
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posted on November 15th, 2013 at 01:32 PM
Secret Society of the Cranks!?!?!?!?!
I'd probably qualify for that I rekn.......
bajachris88
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posted on November 15th, 2013 at 06:09 PM
I bought a cheap crank from cip1. It was a chinese cw, chromoly 74mm 8 dowell balanced crank. Cip1 advertised it as the ducks nuts.
$345 for crank or so delivered. Firstly, it ended up having a dirty empi label on it.
Ended up needing big ends and mains reground $220, as clearance was too tight and inconsistent.
Ended up spending another hundred or so solving an offset issue with the flywheel/front seal surface.
A complete stuff around.
In total the initial cost doubled (and a bit more) of what i paid to CIP1. They should be inspected rigorously prior to fitting and not trusted.
(ô_!_/ô) (ô_!_/ô)
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New engine in process: 94mm p&bs, 74mm C/w chomol Crank, 35.5x39 SP heads, turbo. Wierd combo, hopeful torque monsta!
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posted on November 15th, 2013 at 09:01 PM
If you aren't fussed about a CW crank then I'd go OEM VW regrind and then nitrided.
Reason being is that unless the crank has been licensed by a company with strigent compound and processing requirements for the chinese factory then
you cannot be certain what the 'new' crank will be like.
Many BMW and Merc parts are made in china but the quality of the components made is far higher then cheaper made aftermarket items. Many pattern parts
are made to barely comply with ISO standards for international sale but will under perform compared to OEM parts due to shortcuts in manufacturing to
keep costs down.
madness is in the eye of the beholder
modnrod
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posted on November 15th, 2013 at 10:06 PM
I'd get a crank from DPR, DeMello or Dave as I said, and I wouldn't even bother checking the thing it would just go straight in. And no, I don't
need CW, it will be balanced anyway.
I have heard of experiences such as BajaChris however, hence checking to see if I was just being a bit up tight about it all I guess. It's like
everthing else, if there is a large market for anything it seems inevitable that cheaper parts will flood that market hoping for a turnover, the VW
world is no different.
Can anyone remember how far is safe to go realistically on the undersize for the offset before the oil galleries end up badly off centre? Chev journal
rods to get 74mm throw on an OEM 1584TP crankshaft OK? From memory we went to 75mm with a smaller journal than that, but I don't rekn life expectancy
back then really mattered a stuff to us!
Maybe try and find another Wasser crank to play with a bit too perhaps?
Thanks for helping me keep awake at nights everyone! HAHA!
dangerous
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posted on November 16th, 2013 at 05:26 AM
If you get the '6 Volt' 69mm crank from something,
then the oil hole will be fine.
We did one once that was 78 stroke with golf rods.
Even balanced nitrided and with big radii,
it breathed past the pulley threads,
but it is still going some 10+ years later.
You will have to modify either the crank end of FW to make a 12V O-ting FW fit.
I have seen a few of the late cranks stroked to 74-76mm with Holden journal,
but the oil hole is close to the cheek,
and more of a problem, it moves closer to the critical under side of the big end.
They will crack here after some time,
but have a look at a 76mm WBX crank and it has a similar oil hole position only not so bad.
), along with 2 BX
Strommies to give them 1732cc of cheap VW hotrod goodness to keep the Clevo's of the world at bay between the lights.......
