Author Topic: Rod piston issue SBC  (Read 1538 times)

Offline tcoupekyle

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Rod piston issue SBC
« on: June 27, 2021, 04:39:01 PM »
Sooo the wrist pins wonít fit through the rods because the top of the Rod hits the bottom of the pistons.
This is a problem lol
So moving forward. How does one go about remedying this?
Itís a 434 with 6Ē aluminum rod and an off the shelf je piston.

Offline THE FRENCHTOWN FLYER

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Re: Rod piston issue SBC
« Reply #1 on: June 27, 2021, 07:03:09 PM »
First thing I would do is measure the thickness of the piston above the rod to see how much material may be removed. Check with your piston supplier on minimum local thickness allowed. I would take material away using a ball nose end mill so there is no sharp edged stress concentration on the underside of the dome. Re balance pistons.

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #2 on: June 28, 2021, 03:21:35 AM »
Ooh good idea Iíll call JE TODAY. Thanks didnít even think about the piston

Offline glofria

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Re: Rod piston issue SBC
« Reply #3 on: June 28, 2021, 09:41:30 AM »
It's been a long time since I've posted here and came across this while killing some time at work.

If you plan on having your rotating assembly balanced, they can take material off of the top of the rod or mill out the bottom of the piston to make it work (before balancing process).

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #4 on: June 28, 2021, 03:29:58 PM »
Sooo. Thank you guys for the replies.
Called JE they said the Piston is like .275 thick (don't remember exactly thickness but it's .200 something) and said don't cut the Piston there's not enough meat. So I kept talking to JE to get a piston that would work and maybe a credit on the brand new set I already have. They basically said don't build a 434 blower motor change to a 3.5 stroke crank instead and buy a different Piston..
 
I called lightning rods who make the aluminum rods I have and he says taking a hundred thou off the top of the rods isn't a great idea. But he said he'd trade my 6 inch rod for shorter ones if that helps.

So that's today's breakthroughs

Offline Paul New

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Re: Rod piston issue SBC
« Reply #5 on: June 28, 2021, 04:17:51 PM »
Sooo. Thank you guys for the replies.
Called JE they said the Piston is like .275 thick (don't remember exactly thickness but it's .200 something) and said don't cut the Piston there's not enough meat. So I kept talking to JE to get a piston that would work and maybe a credit on the brand new set I already have. They basically said don't build a 434 blower motor change to a 3.5 stroke crank instead and buy a different Piston..
 
I called lightning rods who make the aluminum rods I have and he says taking a hundred thou off the top of the rods isn't a great idea. But he said he'd trade my 6 inch rod for shorter ones if that helps.

So that's today's breakthroughs

Yes thatís a tough combination unless you build it as 9.300 or more DH block vs the 9.025 or shorter block we did build one recently but with steel rods they are significantly thinner at the pin end

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #6 on: June 28, 2021, 06:37:21 PM »
Steel rods and it would work I think. But I got an eagle crank so I was going with an aluminum rod to try to be friendly to the crankshaft. Looks like a new crank is in my future...
What stroke you guys recommend with a 6 inch rod and any recommendations on manufacturer that ain't gonna be extremely high dollar?

Offline Paul New

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Re: Rod piston issue SBC
« Reply #7 on: June 29, 2021, 03:11:30 PM »
My favorite combination is 4.125x3.625 stroke but you would clear fine with 3.75 stroke lots of 406 blown SBCís out there

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #8 on: June 30, 2021, 07:17:03 AM »
Paul what's the dimensions on those combinations? I have to buy a crank but I have 6" aluminum rods. And I have to buy Pistons so trying to figure out what'll work.

Offline Paul New

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Re: Rod piston issue SBC
« Reply #9 on: June 30, 2021, 09:13:46 AM »
With your current pistons you probably have a 1.00 compression height with a 3.75 stoke and 6Ē rod you would end up with 1.125 CH and with 3.625 and 6Ē rod 1.185 CH so that would be most likely a .125-.185 more clearance between rod and piston unless they increased the thickness of the top of the piston

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #10 on: June 30, 2021, 05:43:11 PM »
Thanks Paul.
Ended up doing a deal with JE on a custom Piston. Guy over there named Greg was really helpful.

Offline Paul New

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Re: Rod piston issue SBC
« Reply #11 on: July 01, 2021, 05:52:25 AM »
Excellent!  Glad you were able to come up with a plan

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #12 on: July 01, 2021, 12:00:24 PM »
So plan is 3.75 stroke. So I need to buy a crank. Looking at a Howards... Any opinions?

Offline JEFF/21C

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Re: Rod piston issue SBC
« Reply #13 on: July 01, 2021, 04:30:01 PM »
the only crankshaft that wasn't up to spec was Eagle all the other different brands I've used  were what I expected they varied depending on project, never used a Howard you should call and talk to a tech and tell him what you want and ask for his opinion if your not using a snout support go for a bbc snout with double keyways ran a 406, 6/71 30% over  with no problems

Offline tcoupekyle

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Re: Rod piston issue SBC
« Reply #14 on: July 01, 2021, 08:36:30 PM »
I have a snout support but since I got to buy a crank I'm thinking of going with the BBC snout and changing the support.