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cmiller95 Samba Member

Joined: August 04, 2010 Posts: 1232 Location: Illinois
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Posted: Wed Jul 27, 2011 1:43 pm Post subject: 69mm crank vs 74 mm crank. |
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My sand rail's engine is 40 years old and has never been rebuilt. I plan on rebuilding it soon and was wondering if it would be worth my time to use a 74mm crank instead of a 69mm. Reasoning for a 74mm crank, its not a huge amount of gain, i don't have to do any clearancing on the case, and its costs just as much as a new 69mm crank (cb performance). I understand ill have to put more spacers between the head and the cylinder. But, if i have more spacer will i have to get longer push rods? And, Will there be a very big difference at all. Will i be able to feel the difference? I understand its only a 5mm stroke gain.
thanks, Colton _________________ Swing axle: Eating tires since 1938
My Rail Build: http://www.thesamba.com/vw/forum/viewtopic.php?t=427627
My Baja Build: http://www.thesamba.com/vw/forum/viewtopic.php?t=466974 |
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jsturtlebuggy Samba Member

Joined: August 24, 2005 Posts: 4599 Location: Fair Oaks/Orangevale, CA
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Posted: Wed Jul 27, 2011 1:57 pm Post subject: |
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More than likely you will have to do some case clearancing even with a 74mm crank. Inside case webbing has changed over the years so sometime even using a stock 69mm crank needs the case clearance.
You will have do some clearancing on the pistons to clear the crank and rod when it at the bottom of it stroke.
Depending on camshaft you may have to clearance center bearing surface and thrust surface of camshaft.
You will notice a difference in power. There will be more torque.
With so much available now then in the early years going to a 78 or 82mm stroke can cost you less in time and labor then it use to be.
What cylinder heads do you plan on using? _________________ Joseph
Fair Oaks/Orangevale, CA
Elrod Motorsports
Motion Tire Motorsports
Having fun with Dune Buggies since 1970
Into Volkswagens since 1960 |
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krusher Samba Member

Joined: September 24, 2002 Posts: 7662 Location: europe
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smitty24 Samba Member

Joined: April 28, 2008 Posts: 2730 Location: Salem, Oregon
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Posted: Wed Jul 27, 2011 2:41 pm Post subject: |
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yep, I still had machining and some hand clearance work to make mine fit. Go 78-82 and call it good. |
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Wayne26 Samba Member
Joined: November 18, 2010 Posts: 284 Location: Houghton Lake MI
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Posted: Wed Jul 27, 2011 3:29 pm Post subject: |
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I just did one going from 69mm to 74, noticed a big difference in the low and mid rpm's.
the only thing that needed clearanced for me was the piston skirts because I went with the shorter 5.325 race rods. it ended up being easy, even though I was scared. but it turned out fine and runs great. http://www.thesamba.com/vw/forum/viewtopic.php?t=472324&highlight=clearanced+piston
my case was clearanced for a counterweighted crank in the past though. |
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[email protected] Samba Member

Joined: August 03, 2002 Posts: 12785 Location: Salt Lake City, Utah
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Posted: Wed Jul 27, 2011 3:31 pm Post subject: |
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if you go with a bigger bore the 74/76 and 5.325" rods works great. If you use 85.5s the skirts need extensive clearancing, which can be a pain. _________________ It's just advice, do whatever you want with it!
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jbbugs Samba Member

Joined: September 16, 2002 Posts: 2179 Location: Behind the wheel
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Mon Aug 01, 2011 6:38 pm Post subject: |
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[email protected] wrote: |
if you go with a bigger bore the 74/76 and 5.325" rods works great. If you use 85.5s the skirts need extensive clearancing, which can be a pain. |
Will the skirts on 94's need clearancing with a 74 mm crankshaft? |
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ralf Samba Member
Joined: July 08, 2008 Posts: 1215 Location: r4
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Posted: Mon Aug 01, 2011 6:56 pm Post subject: |
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i think he said. if u go with a bigger bore.. its fine _________________ Flow Through a Curved Conduit
porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk |
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Mon Aug 01, 2011 7:03 pm Post subject: |
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oops.....so he did....gotta polish up on my reading skills  |
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ralf Samba Member
Joined: July 08, 2008 Posts: 1215 Location: r4
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Posted: Mon Aug 01, 2011 7:21 pm Post subject: |
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reading skills comes later..
just do a build thread now will you
wonder wat u finally decided on !
 _________________ Flow Through a Curved Conduit
porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk |
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DarthWeber Samba Member

Joined: November 24, 2007 Posts: 7543 Location: Whittier,CA
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Posted: Mon Aug 01, 2011 7:45 pm Post subject: |
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ralf wrote: |
reading skills comes later..
wonder wat u finally decided on ! |
Come on Ralphee, read!!
From the Non-stroker motors thread:
I've learned that quite a bit of what I hear on this forum is not worth the time it took to read.....STROKER....gotta build a STROKER.....Lol! .....whatever......1915cc is the way I'm going and I'll be paying special attention to matching everything up with my combo....that's right....it's in the combo..........1915cc....ported 40x35 heads with dual springs....match ported manifolds with Weber 44's...Engle 120 with 1.25 rockers...chromoly pushrods.....balanced rotating assembly and pistons......1 and a half inch merged header with single phat boy muffler to keep good back pressure for the bottom end....Bosch 019 distributor and yes it will have an electronic ignition conversion..(points and condenser will be in the glove box just in case) 12.lb flywheel balanced with the crank and a Kennedy sage 1 pressure plate with stock disc to keep it smooth and not harsh.... _________________
Mitey62 wrote: |
Swapped the Compufire for a Bosch blue and some points I had sitting around, started 1st crank. Took her out for a drive, pulls harder, more RPM, and runs smoother. I think I'll be sticking with points from now on. |
RockCrusher wrote: |
JB weld the case halves....that'll keep the fretting to a minimum.  |
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ralf Samba Member
Joined: July 08, 2008 Posts: 1215 Location: r4
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Posted: Mon Aug 01, 2011 8:38 pm Post subject: |
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ralpheeee ? wrong spelling darthy beibery hahaha
yes saw that thread
but also he wonders of a 74 stroke a 78 an 82 i think and alot
saw ur sad face on the 1807 build bfor.. i guess i should do that LOL to make u smile? hahahaha _________________ Flow Through a Curved Conduit
porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk |
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Tue Aug 02, 2011 2:32 am Post subject: |
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ralf wrote: |
ralpheeee ? wrong spelling darthy beibery hahaha
yes saw that thread
but also he wonders of a 74 stroke a 78 an 82 i think and alot
saw ur sad face on the 1807 build bfor.. i guess i should do that LOL to make u smile? hahahaha |
yes......I'm guilty of waffling........think I should have bought motor parts first instead of the beam, wiring harness, body work...blah blah blah.....too many choices for the motor.....cash for moor partrs will be availale next week so we'll see...gonna be a crap shoot... |
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Tue Aug 02, 2011 2:35 am Post subject: |
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justreally like the old school stuff.......not set in stones but it's probably oing to be a 2054 cc motor......if I remember correcty the 74 crank was one of the first "stroked" hi po motors...reground stock stroke crank....give me about 100 grand and I'll build one of each |
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AlteWagen Troll

Joined: February 23, 2007 Posts: 8697 Location: PNW
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Posted: Tue Aug 02, 2011 2:03 pm Post subject: |
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If you use the Mahle FORGED 85.5 pistons you do not need to clearance the skirt. Any big bore Mahle (90.5, 92, 94) already have the short skirt design.
I love my mini stroker but would put 90.5s if I were to do it again. |
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Tue Aug 02, 2011 2:26 pm Post subject: |
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derluftwagen wrote: |
If you use the Mahle FORGED 85.5 pistons you do not need to clearance the skirt. Any big bore Mahle (90.5, 92, 94) already have the short skirt design.
I love my mini stroker but would put 90.5s if I were to do it again. |
And what about the AA pistons? |
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ralf Samba Member
Joined: July 08, 2008 Posts: 1215 Location: r4
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Posted: Tue Aug 02, 2011 3:13 pm Post subject: |
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as stated by derluft ,
the forged 85.5s have shorter skirts = clearancing not needed
which was already answered by a dashing fellow by the name of John Connoly
90.5s up has shorter skirts, and the B stroke pistons are even shorter..
but the problem with the cast 85.5mm isnt the skirt being long.. its the bore being small so it hits the cheeks of the crank
ever wonder why90.5 A pistons dont hit the crank like a small bore?
the dashing fellow by the name of john connoly also did answer this a few postststs back
HTH _________________ Flow Through a Curved Conduit
porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk |
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fivelugshortaxle Samba Member

Joined: May 13, 2011 Posts: 4263 Location: Aumsville, Oregon
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Posted: Tue Aug 02, 2011 6:22 pm Post subject: |
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ralf wrote: |
as stated by derluft ,
the forged 85.5s have shorter skirts = clearancing not needed
which was already answered by a dashing fellow by the name of John Connoly
90.5s up has shorter skirts, and the B stroke pistons are even shorter..
but the problem with the cast 85.5mm isnt the skirt being long.. its the bore being small so it hits the cheeks of the crank
ever wonder why90.5 A pistons dont hit the crank like a small bore?
the dashing fellow by the name of john connoly also did answer this a few postststs back
HTH |
So.....74 x 94 2054cc won't have piston clearancing problems?......I think that's what I got out of it....soryy, but I'm quite ignorant when it comes to anything other than stock 69mm stroke motors......
which motor, in your opinion, would be easier to build? 74 x94 or 78 x 94 or 82 x 94? |
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ralf Samba Member
Joined: July 08, 2008 Posts: 1215 Location: r4
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Posted: Tue Aug 02, 2011 6:25 pm Post subject: |
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74x94 on B pin height
use 5.5 rods
and ud have about 0.060" deck.. u can turn the barrels on a lathe
to get ur desired deck.. or turn the barrels enough that it would let u use a 0.040" copper headgasket
call it a day..
74x90.5 works too..
ofcourse like most would say. it would make sense to run
78.4-82 strokes its easier..
example
78.4 stroke and using 5.5 rods on B pin height pistons,
ud need maybe 0.050" to 0.060" shims to get to ideal deckheight
so getting a set of copperhead gaskets of that thickness.. would let u have ur deck nice..
ofcourse mocking it up will have the final say on where ur stuff fals.. as far as deckheights go _________________ Flow Through a Curved Conduit
porting my SP head for my brother's project
https://youtu.be/OS_mVjQuqgk |
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