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Where do I put the new rods?

General engine tech -- Drag Racing to Circle Track

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Lizardracing
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Where do I put the new rods?

Post by Lizardracing » Sun Nov 03, 2019 6:40 pm

SBC
4.155"x3.75"
406ci
Scat crank 3.75"
Scat rods 6.00"
JE pistons and rings.
Brodix T1x heads
Brodix Intake
Mike Jones SFT cam
Dirt Modified.
7200 rpm chip

I had a blow up. A bad one. All I saved was the crank and 6 rods. I replaced the rods with 2 new ones from Scat. They are 5g heavier total weight. They are lighter on the big end, a little heavier on the small end. I;m going to mix and match as needed to get the pistons/pins and rods as close as possible to the same. The original rods are all identical small/big end and total weight.
The new pistons are 46g lighter. I hadn't planned for a another balance job if I can get it close enough.
Is there a better position to put the new rods? On the ends of the crank? Middle? Same Journal? Trash can? Does it really matter?

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Re: Where do I put the new rods?

Post by Krooser » Sun Nov 03, 2019 7:00 pm

I used to fret about stuff like that until I found myself working as a volunteer helper washing engine parts in a plastic tub in front of a cheesy motel in Wendover Utah while the real crew was putting one engine together from the previous two they blew up on the salt flats. IIRC there were two TRW and four Venolia pistons in the final engine configuration along with a mix of stock and billet rods.

Just shy of 180 mph in a modified roadster and it stayed together for two runs.

My buddy Wes put one Ford piston in his blowed up 383 Chevy and won a feature in a late season DLM race at Hales Corners WI circa 1979.

Wes said he drove so fast the Ford piston wasn't smart enough to know it was in a Chevy engine.
Luxemburg Speedway Hall of Fame Member Class of 2019

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GuysMonteSS
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Re: Where do I put the new rods?

Post by GuysMonteSS » Sun Nov 03, 2019 7:12 pm

Krooser wrote:
Sun Nov 03, 2019 7:00 pm


My buddy Wes put one Ford piston in his blowed up 383 Chevy and won a feature in a late season DLM race at Hales Corners WI circa 1979.

Wes said he drove so fast the Ford piston wasn't smart enough to know it was in a Chevy engine.
LOL :lol:
Guy
'86 Monte SS,513 BBC,AFR heads,Bullet solid roller cam,Doug Nash 4+1 5 speed,Hurst Inline Shifter,Ford 9 inch Rearend.

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Re: Where do I put the new rods?

Post by Lizardracing » Sun Nov 03, 2019 7:41 pm

You’re right about that.
Stupid engineers can’t even decide what’s the where and how much engine balancing even makes a difference.
You always hear about that one guy who claims it shook bad enough to need his dental fillings put back in and at the same time, there’s that one guy who puts together 8 different rods and 8 different pistons and a broken crank and still wins races.
I have an mechanical engineering degree but still not smart enough to stay away from the racing money pit but if I have a choice here, I’m gonna over think it. I ain’t trying to make 900hp and sell it for a profit, I’m also not not running junk yard parts. Their just regular yards parts.
Anyway, I’m just asking for opinions on the theories.
It seems if your gonna have something different, between the counter weights of the crank throws, seems to make the best place to have an imbalance.

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Re: Where do I put the new rods?

Post by Dave Koehler » Sun Nov 03, 2019 8:09 pm

Grab this little program. It will take the pain out of matching light this with heavy that.
Light pistons, are your old pins any heavier?
http://www.maverickracing.co.uk/crankbalsoft.htm
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Re: Where do I put the new rods?

Post by Lizardracing » Sun Nov 03, 2019 8:28 pm

Neat program there.
I didn’t save the old pins. Two were bent and 1 is still MIA.

New Pistons are all within 1.5g. 451g-452.5
New pins are lighter. They are 130.2g-130.6g

Old pistons were 500g +\- 2g
Old pins were 146g +\- 1g

New pistons/pins are 64g lighter.

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Re: Where do I put the new rods?

Post by Geoff2 » Mon Nov 04, 2019 3:16 am

And how much extra weight will the oil on the rods add in a running engine? And the carbon on the piston crown?

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Re: Where do I put the new rods?

Post by Dave Koehler » Mon Nov 04, 2019 7:15 am

Geoff2 wrote:
Mon Nov 04, 2019 3:16 am
And how much extra weight will the oil on the rods add in a running engine? And the carbon on the piston crown?
Stop now. Go get a beer
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Re: Where do I put the new rods?

Post by enigma57 » Mon Nov 04, 2019 7:31 am

Reminds me of the '53 Ford Victoria sport coupe I had back in '68. Seems like every time I worked on that flathead engine, I had parts left over when I was done. And every time I had parts left over, it ran better. :shock:

Looked like this car except I ran chrome reverse wheels and blackwall tires on mine......

Image

Drove her too hard one Friday night outrunning some maniacs in a new Chevy who were dead set on shooting me. Next day, I noticed engine was running hot and missing on 2 cylinders. And water was dripping out the passenger side exhaust pipe (I was running duals and steel pack mufflers on the flattie). Checked fluids. Oil was milky with engine coolant. Radiator was dry. Not good.

Was hoping it was only a blown head gasket, but as it turned out the block was cracked. Pulled passenger side head and 2 cylinders had cracks extending from under exhaust valve seat over to top of piston bore and down to the ridge where the piston rings stopped at TDC. Drivers side water pump was kaput, as well.

That was Saturday morning. Had to be at work Monday, so spent the day working on the car. Couldn't afford a rebuilt engine, so got some Liquid Steel and pushed it into the cracks as best I could, then turned engine over a few revolutions to make sure the Liquid Steel was pushed down enough to allow exhaust valves to seat.

Put the head back on with a new gasket, installed new spark plugs, replaced both thermostats and both water pumps (figured if one water pump was shot, the other probably wasn't going to last much longer), dug out the huge 1950 Lincoln radiator I was going to install in the Ford 'some day' and managed to get it in with a little metal trimming and drilling a few holes.

Let the car sit overnight Saturday and Sunday hoping the Liquid Steel would set up hard. Sunday, changed oil and filter.

Monday morning had to get to work. Refilled radiator with new anti-freeze and water. No leaks. Cranked up the flattie, left the radiator cap loose so there wouldn't be pressure in the water jackets. Fingers crossed, began the 25 mile drive to work watching the temperature gauge like a hawk. Made it OK. Checked oil...... No coolant. Checked coolant...... No oil.

After work, drove home taking it easy. Arrived safely. Checked fluids, all was well. The following day, tightened up the radiator cap and drove the Ford another year before buying another car. :D

Happy Motoring,

Harry

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Re: Where do I put the new rods?

Post by mag2555 » Mon Nov 04, 2019 7:39 am

If you only have a 6 counter weight Crank then put the heavier Rod and piston assy near the front and rear of the motor, not near the center where your missing 2 counter weights !

Also if the Rods your reusing have have more then 4 torque up session on the bolts them then your playing with Fire again blow up wise.

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Re: Where do I put the new rods?

Post by Hrdlx62 » Mon Nov 04, 2019 7:48 am

Maybe turn up some weight slugs to press, Loctite, epoxy into the pins to gain some piston weight. Been there done that.

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Re: Where do I put the new rods?

Post by Baprace » Mon Nov 04, 2019 7:53 am

mag2555 wrote:
Mon Nov 04, 2019 7:39 am
If you only have a 6 counter weight Crank then put the heavier Rod and piston assy near the front and rear of the motor, not near the center where your missing 2 counter weights !

Also if the Rods your reusing have have more then 4 torque up session on the bolts them then your playing with Fire again blow up wise.

This is probably your best suggestion if you are not balancing the assembly, my choice would be 2 & 7. JMHO

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Re: Where do I put the new rods?

Post by Lizardracing » Mon Nov 04, 2019 8:25 am

2 and 7 seems to make sense.

Can you elaborate on the 4 torque up sessions? Are you suggesting the rod bolts are fatigued?

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Re: Where do I put the new rods?

Post by BillK » Mon Nov 04, 2019 9:24 am

Ok, I am ready for the flames but . . . . . you are worried about rods that are 5 grams different and yet you have pistons that are 46 grams lighter and you aren't going to rebalance it ???????

I dont think it wall make any difference at all where you put those two rods.

Just my opinion,
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Re: Where do I put the new rods?

Post by mag2555 » Mon Nov 04, 2019 9:30 am

Yes to that rod bolt potential issue!

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