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 sander288
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 posted on September 7th, 2010 at 11:41 AM |
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De-stroking? How?
This isn't a thread for engine combos or anythings I simply want to know how a crankshaft can be de-stroked?
ie. can a stock VW crank be de stroked back from 69mm and how?
I've tried googling de-stroking but its usually about V8s putting in smaller cranks etc...
I know to stroke an engine its a matter of a new crank but de-stroking I just don't know if it can machined or a new crank also needs to be
made...
Cheers
Shaun
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 matberry
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| posted on September 7th, 2010 at 12:05 PM |
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It can be done by a crankshaft reconditioner, but only if your willing to go to a different conrod with a smaller bigend. Exactly how much depends on
many components, and what your trying to do.
I destroked a 1600 to build a big bore 1300 race engine, then CAMS changed the rules  .
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bajachris88
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| posted on September 7th, 2010 at 12:06 PM |
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didn't the 1100cc's have smaller strokes? but the issue was in the cam gear drive for a later engine??
Someone can extend on this...
Is this low comp prep for forced induction or sumfin :P??
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matberry
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| posted on September 7th, 2010 at 12:10 PM |
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36hp's have a dimensianally diferent engine, but a 40hp has a smaller stroke ie 64mm, and they fit into a 1600 case.
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
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 vw54
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| posted on September 7th, 2010 at 01:20 PM |
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most people Off set grind the granks usually to 72mm to allow you to build an engine just under 2 Liter to suit a particular racing class
the crank is ground and hard face welded then re ground to suit
What size and purpose do u need
Dangerous on here would be the best guy to talk to as he used to machine cranks for a living
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sander288
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| posted on September 7th, 2010 at 01:36 PM |
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I was thinking of a race engine at 60 (stroke)x92 (thickwall) (bore) which would be 1595cc which is ok for class C tarmac rally cars, where I want to
put the car eventually
The rules state that for Class C (i think i was class c) that you can go up to the limit for the original class your stock motor falls into, ie 1300cc
in the 0-1600 class can go up to 1600cc.
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hellbugged
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| posted on September 7th, 2010 at 02:23 PM |
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got one here ready to go........if youre serious let me know
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Sides
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| posted on September 7th, 2010 at 02:26 PM |
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Shaun... what sort of events are you planning on running in ???
Tarmac Rally regs are a bit fluid to say the least, and realistically unless you're going to do something like Targa or Classic Adelaide then you're
likely better off sticking with 3J. Also Targa is now run under AASA, so as far as I know the CAMS classes are only used as a reference.
My advice would be work out what events you want to run (specifically), identify the guys/cars that would be good to compete with, then build a car to
suit that class. Going up to 1999cc like Dave has suggested for example is a 3J Improved Production trick. BiX did it with his engine, Marcus also,
and pretty sure that Grant Cook's beetle also is a 72mm stroke.
EDIT : Sorry - just realized the "not a combo discussion" at the start... ignore me.... 
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Sides
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| posted on September 7th, 2010 at 02:27 PM |
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Is there anything you don't have there Daimo ???
VWDCQ vice pres & web dude - vwdcqinc.org.au
Join a car club - get car peeps
My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI - http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners |
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hellbugged
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| posted on September 7th, 2010 at 02:42 PM |
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engle KB 435 and titanium valves.......had to order them 
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mactaylor
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| posted on September 7th, 2010 at 05:13 PM |
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you really need to read the regs cause most say an overbore of 1mm max dunno bout your class but if you wana be competitive they may ask you to prove
your combo!!
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sander288
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| posted on September 7th, 2010 at 06:22 PM |
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The 1.5 mm bore was in the majority of classes but rally is alot looser as suggested and there are different levels that you can go to.
Daimo did you say you have 60mm crank!? Dave is right is there anything you don't have....
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hellbugged
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| posted on September 7th, 2010 at 06:31 PM |
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from memory its 62mm
If it was me, id contact matt berry about paul z 77.5mm crank as it is for sale and run 2l
You will need torque for rally
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Craig Torrens
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| posted on September 7th, 2010 at 08:40 PM |
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| Quote: | Originally
posted by Sides
Going up to 1999cc like Dave has suggested for example is a 3J Improved Production trick. BiX did it with his engine, Marcus also, and pretty sure
that Grant Cook's beetle also is a 72mm stroke.
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Not really a trick.......the trick is about building a winning combo that fits within the cc range for the class. Most of the under 2lt class winning
cars were never close to 1999cc.
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Phil74Camper
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| posted on September 8th, 2010 at 08:03 AM |
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VW 1100 used a 64 mm stroke crank (and 75 mm cylinders). Only sold in Australia in the early months of 1954 so you won't see any around.
VW 1200 36-hp (1954-60) also used 64 mm stroke, with 77 mm cylinders. The 1200 40-hp (1960-66) was dimensionally exactly the the same but
redesigned.
VW 1300, 1500 and 1600 all used 69 mm stroke.
You can increase or decrease the stroke of a crank by offset grinding. A crank's (half) stroke is measured from the centre of the main bearing
journal (that is, the crank centre-line), to the centre of the big-end journal. To decrease the stroke, you have to move the big-end journal centre
closer to the crank centre.
To use an example. Let's say your crank is a 69 mm and you want to make a custom version with a 67 mm stroke. You measure the diameter of the big-end
journal, and let's say it's 50 mm across. You have to move the centre of that big-end journal 1 mm closer to the centre of the crank (since half of
the stroke - the complete circle - is the radius). So, you machine the big end into a new circle with its centre 1 mm closer to the crank centre. You
end up with a 48 mm diameter big end, offset 1mm closer to the crank centre than before. And there you have it - a 67mm stroke. The change in big-end
diameter is the same as the change in stroke. Of course you'll need custom rods with smaller big ends and bearings to go with them.
Volkswagen did this trick in reverse with the Type 4 motor when they went from 1800 to 2000cc in 1975. It's the same crank but the big ends have been
offset ground outwards to go from a 66 mm to a 71 mm stroke. The 2000's big-ends are 5 mm smaller than the 1700 and 1800.
Do a Google search on 'crankshaft offset grinding' - it's a pretty common hotrodding trick but probably not financially viable for VWs, given the
ease of swapping cylinders and pistons instead.
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sander288
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| posted on September 8th, 2010 at 08:36 AM |
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wow, cheers phil! great explanation
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