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bartman
Samba Member
Joined: February 22, 2004
Posts: 767
Location: palatka, fl
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 Posted: Wed Apr 14, 2010 6:36 am Post subject: |
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I'm building a 78x94 engine. With the B pistons, i have about .2"
deck. I'm in the process of trying to trade them for A pistons.
This deck is with a stock rod. A longer rod would get it closer to where it should be. I did a pretty thorough search and didn't find the info about 78mm cranks vs B pistons. Some sort of chart to get builders into the ballpark, at least, would be handy.
If you have the clearance and a decent rod ratio, i think you may be better off with the 82. |
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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 Apr 14, 2010 6:42 am Post subject: |
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this is why building with a 78 crank is such a mistake, my opinion.
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Matthew
Samba Member
Joined: January 29, 2004
Posts: 1760
Location: Eastern Tennessee
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| Posted: Wed Apr 14, 2010 8:40 am Post subject: |
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| bartman wrote: |
I'm building a 78x94 engine. With the B pistons, i have about .2"
deck. I'm in the process of trying to trade them for A pistons.
This deck is with a stock rod. A longer rod would get it closer to where it should be. I did a pretty thorough search and didn't find the info about 78mm cranks vs B pistons. Some sort of chart to get builders into the ballpark, at least, would be handy.
If you have the clearance and a decent rod ratio, i think you may be better off with the 82. |
If you use A pistons, you will have huge spacers and a wide engine. Why not face some material from the base of the cylinders to achieve the correct deck with the B pistons?
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1965 Beetle sedan
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grimace007
Samba Member
Joined: August 30, 2006
Posts: 2673
Location: swampville, florida
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| Posted: Wed Apr 14, 2010 8:47 am Post subject: |
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| Matthew wrote: |
| bartman wrote: |
I'm building a 78x94 engine. With the B pistons, i have about .2"
deck. I'm in the process of trying to trade them for A pistons.
This deck is with a stock rod. A longer rod would get it closer to where it should be. I did a pretty thorough search and didn't find the info about 78mm cranks vs B pistons. Some sort of chart to get builders into the ballpark, at least, would be handy.
If you have the clearance and a decent rod ratio, i think you may be better off with the 82. |
If you use A pistons, you will have huge spacers and a wide engine. Why not face some material from the base of the cylinders to achieve the correct deck with the B pistons? |
or for the same price, go 82 stroke and have a stock witdh engine with alot less deck height and easier to assemble
_________________
Brian
68 sedan
Dallas Air Coolers
| perrib wrote: |
Hey It is The Samba where well thought out rational answers can take a while and getting side tracked is normal. I was just lucky this time.  |
| cr@M wrote: |
No one has any personal responsibility these days. This country is sue happy. Intelligence is no longer a requirement, just an accessory. |
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Wed Apr 14, 2010 8:52 am Post subject: |
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| jamestwo wrote: |
No, they did you a favor. With the 78.4 you was heading for all kind of problems setting the deck.
Hp won't be less, it will just come at a lower RPM. |
What kind of problems? That's what I'm working with for my 2017 build, as I was advised it was a good crank to go with due to less clearancing involved, etc. |
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Teeroy 
Samba Member
Joined: April 20, 2003
Posts: 3840
Location: Eastern WA
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| Posted: Wed Apr 14, 2010 8:57 am Post subject: Got wrong stroker crank - What to do? |
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With the 78 you end up with extra deck, not really a problem just an extra step. You need to machine the bottom of the cylinders or deck the case or both if running 94's. Or if you don't have all your parts yet, get longer rods.
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Matthew
Samba Member
Joined: January 29, 2004
Posts: 1760
Location: Eastern Tennessee
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| Posted: Wed Apr 14, 2010 8:57 am Post subject: |
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| grimace007 wrote: |
| Matthew wrote: |
| bartman wrote: |
I'm building a 78x94 engine. With the B pistons, i have about .2"
deck. ..
If you have the clearance and a decent rod ratio, i think you may be better off with the 82. |
If you use A pistons, you will have huge spacers and a wide engine. Why not face some material from the base of the cylinders to achieve the correct deck with the B pistons? |
or for the same price, go 82 stroke and have a stock witdh engine with alot less deck height and easier to assemble |
I agree, I was just working with the 78mm crank as a given. If I had the choice I would go 82 for sure.
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1965 Beetle sedan
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grimace007
Samba Member
Joined: August 30, 2006
Posts: 2673
Location: swampville, florida
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| Posted: Wed Apr 14, 2010 9:31 am Post subject: |
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| Matthew wrote: |
| grimace007 wrote: |
| Matthew wrote: |
| bartman wrote: |
I'm building a 78x94 engine. With the B pistons, i have about .2"
deck. ..
If you have the clearance and a decent rod ratio, i think you may be better off with the 82. |
If you use A pistons, you will have huge spacers and a wide engine. Why not face some material from the base of the cylinders to achieve the correct deck with the B pistons? |
or for the same price, go 82 stroke and have a stock witdh engine with alot less deck height and easier to assemble |
I agree, I was just working with the 78mm crank as a given. If I had the choice I would go 82 for sure. |
well if it was given to you then run it by all means
sometimes you can get lucky in the classified and find someone wanting a shorter stroke in trade for their 82
_________________
Brian
68 sedan
Dallas Air Coolers
| perrib wrote: |
| Hey It is The Samba where well thought out rational answers can take a while and getting side tracked is normal. I was just lucky this time. |
| cr@M wrote: |
No one has any personal responsibility these days. This country is sue happy. Intelligence is no longer a requirement, just an accessory. |
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Wed Apr 14, 2010 10:20 am Post subject: Re: Got wrong stroker crank - What to do? |
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| Teeroy wrote: |
| With the 78 you end up with extra deck, not really a problem just an extra step. You need to machine the bottom of the cylinders or deck the case or both if running 94's. Or if you don't have all your parts yet, get longer rods. |
No one mentioned this to me when I first started asking around for feedback on the build I've got coming together. I kept hearing that a 78.4mm build is a pretty trouble-free route to take, and a good option, but no one ever mentioned anything about deck difficulties. I'd heard about that problem with the 74 and 76mm cranks, but not 78.4 units.
I'm not terribly worried, as I know I can handle getting the deck where it needs to be, I'm just a little surprised this is the first I've heard about it. |
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bartman
Samba Member
Joined: February 22, 2004
Posts: 767
Location: palatka, fl
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| Posted: Wed Apr 14, 2010 6:36 pm Post subject: |
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A 78mm crank (well, my 78mm crank with my case and stock rods) with A pistons results in a deck of about -.2". This requires about half an inch of shims, total.
My combo with B pistons has about .2" of deck. This is only a problem if one lives in a boonfuck town with one machine shop that has no idea what one is talking about when one takes them a jug and asks about taking material off the bottom.
The solution, as mentioned, is to change rod length or take a trip to the big city where machine shops know what the hell they're doing.
IMO, the 82 is a better and easier build. the 78 works if one gets the rod length right.
I have stock rods and I'm considering getting a longer rod and selling my 311b's. In my case, this would probably be cheaper than machine work. I do have a guy that might trade my B pistons for a set of A's. This is the cheapest fix, requiring shimming to dial in the deck. |
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slingblade
Samba Member
Joined: December 18, 2009
Posts: 107
Location: conyers ga.
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| Posted: Wed Apr 14, 2010 7:06 pm Post subject: |
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sweet mistake cb made,,you,ll love the torque
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bugnut68
Samba Member
Joined: June 10, 2003
Posts: 4180
Location: Eugene, OR
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| Posted: Thu Apr 15, 2010 8:47 am Post subject: |
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| bartman wrote: |
A 78mm crank (well, my 78mm crank with my case and stock rods) with A pistons results in a deck of about -.2". This requires about half an inch of shims, total.
My combo with B pistons has about .2" of deck. This is only a problem if one lives in a boonfuck town with one machine shop that has no idea what one is talking about when one takes them a jug and asks about taking material off the bottom.
The solution, as mentioned, is to change rod length or take a trip to the big city where machine shops know what the hell they're doing.
IMO, the 82 is a better and easier build. the 78 works if one gets the rod length right.
I have stock rods and I'm considering getting a longer rod and selling my 311b's. In my case, this would probably be cheaper than machine work. I do have a guy that might trade my B pistons for a set of A's. This is the cheapest fix, requiring shimming to dial in the deck. |
I'd forgotten to mention earlier that I have 'B' pistons... I haven't begun to put this engine together yet, so I guess I'll see where I'm at when the time comes. |
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