Connecting rod Diameter spec???
04-27-2008, 05:38 PM
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Car: 87 Firebird,
Engine: lq4
Transmission: gto t56 (mn12)
Connecting rod Diameter spec???
I'm looking for the inside diameter of a connecting rod off a 350 tpi motor. I'm looking for the measurement of the bare rod without the bearing installed. The big end of the rod. Can't find the measurement anywhere thanks!
04-27-2008, 05:59 PM
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Car: 1989-92 FORMULA350 305 92 Hawkclone
Engine: 4++,350 & 305 CIs
Transmission: 700R4 4800 vig 18th700R4 t56 ZF6 T5
Axle/Gears: 3.70 9"ford alum chunk,dana44,9bolt
Re: Connecting rod Diameter spec???
I just ooked in my 89 sevice manual and found nothing on that measurement.
might try calling a machine shop.
might try calling a machine shop.
04-27-2008, 09:42 PM
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Car: 91 RS
Engine: 350 vortec
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Axle/Gears: not the best not the worst
Re: Connecting rod Diameter spec???
ok the connecting rod journal diameter should be 2.0978-2.0998
you are measuring the big end without a bearing installed getting 2.250-2.0978=.1522/2=0.0761-.0015=.0746
with a big end measureing 2.250 and a rod journal measuring on the low you need a bearing thickness of .0746 to provide enough oil clearance what do the old bearings measure?
what are you using to measure +/- .0005? hopefully not calipers...
you are measuring the big end without a bearing installed getting 2.250-2.0978=.1522/2=0.0761-.0015=.0746
with a big end measureing 2.250 and a rod journal measuring on the low you need a bearing thickness of .0746 to provide enough oil clearance what do the old bearings measure?
what are you using to measure +/- .0005? hopefully not calipers...
Last edited by SpitotRs305; 04-27-2008 at 09:46 PM.
04-28-2008, 07:42 AM
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Re: Connecting rod Diameter spec???
The GM spec for the large end of a large journal connecting rod is as follows:
2.2247" - 2.2252" diameter
Taper or out of round not to exceed 0.00015"
No bellmouthing permissible
1976, GM, Chevrolet Power book, 2nd edition, p. 1-16
RBob.
2.2247" - 2.2252" diameter
Taper or out of round not to exceed 0.00015"
No bellmouthing permissible
1976, GM, Chevrolet Power book, 2nd edition, p. 1-16
RBob.
04-28-2008, 05:27 PM
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Re: Connecting rod Diameter spec???
ok thanks for the replies. Im using a telescoping gauge with the auto centering feature. It can hold up to +/-.0001. The out of round spec kills me though. I guess I'll just get a new rod. Thanks for the help I couldn't find that measurement anywhere.
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04-28-2008, 09:47 PM
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Car: 1988 Trans Am GTA
Engine: 350 4BBL
Transmission: 700R4
Axle/Gears: 3.27
Re: Connecting rod Diameter spec???
I've encountered one out of round rod before and it must have been dropped with the cap installed during a previous rebuild. Thank goodness for plastigage!
04-28-2008, 09:50 PM
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Car: '87 IROC/'68 SS
Engine: 5.7L/350
Transmission: 700R4/Muncie 4-spd
Axle/Gears: 3.27 9 bolt / 3.31 12 bolt
Re: Connecting rod Diameter spec???
If you're dealing with a stock rod, try to find one that has the big-end balancing pad close to the same thickness as the original to keep the balance close. (that is, if you're getting a used one and you have a pile to choose from)
I've encountered one out of round rod before and it must have been dropped with the cap installed during a previous rebuild. Thank goodness for plastigage!
I've encountered one out of round rod before and it must have been dropped with the cap installed during a previous rebuild. Thank goodness for plastigage!
04-28-2008, 10:16 PM
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Car: 1988 Trans Am GTA
Engine: 350 4BBL
Transmission: 700R4
Axle/Gears: 3.27
Re: Connecting rod Diameter spec???
If it's wider (bigger) across the parting line of the rod how are they supposed to grind that part of the rod smaller?
\ <--> /
.\____/
I know they resurface the parting areas of the rod and cap, but the bore is vertical there. They would have to grind a bunch off of each to close it up.
I say pitch it!
You can buy a box full of rods at a junkyard for $20.
Or join the people that can't figure out why they have spun bearings...
\ <--> /
.\____/
I know they resurface the parting areas of the rod and cap, but the bore is vertical there. They would have to grind a bunch off of each to close it up.
I say pitch it!
You can buy a box full of rods at a junkyard for $20.
Or join the people that can't figure out why they have spun bearings...
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