406 rods to buy?

muzzy · Jul 12, 2013

Hi,Building SBC 406 using factory block and cast crank 3.750 stroke 5.7 length rods and forged pistons.
Do you think I will need stroker clearance rods?
Cam lift is about 510/520.
I realize I will have to check cam rod clearance on assembly,I don't want to get bottom end balanced and then find I have to grind rods for clearance.
Motor for street use and occasion club day drag meet 6000rpm max.
Appreciate all advice and suggestions on what rods to buy.

Thanks for any replies Murray

keithl1967 · Jul 12, 2013

Funny you should ask...

I was just at the machine shop yesterday assembling my motor...a 406, with Scat 5.7 forged rods, and stock crank...

the cam i am using is a Comp XR282HR, with .510/.520 lift.

The machinist had to clearance the #2 rod and the # 6 rod...to clear the cam lobes...

Also turns out the pushrods in the comp cams kit were too short--came with 7.266...I need 7.3inch pushrods...waiting for them to come in...

BPOS · Jul 13, 2013

Mock up engine, check all clearances and adjust as necessary, disassemble, then balance.

muzzy · Jul 13, 2013

That's the cam I was recommended, be interested to hear how the engine goes.
Probably go with the Scat rods,were they the stroker clearance one's?

keithl1967 · Jul 13, 2013

muzzy said:
That's the cam I was recommended, be interested to hear how the engine goes.
Probably go with the Scat rods,were they the stroker clearance one's?

yes:

this is the rod I used:

http://www.summitracing.com/parts/sca-25700

I actually went with Hyper pistons, not forged, as my compression will be about 10:1 static (10.03:1, if the Summit racing calculator is correct)...

http://www.summitracing.com/parts/slp-h615cp30

My heads (DART Iron Eagle--older set, not the new platinums--200cc intake runner) cc'd at 65.5, rather than the advertised 64...

Felpro head gasket 1014

Hopefully will finish the assembly next Thursday when the new pushrods come in, and install the following weekend..

68rs406 · Jul 13, 2013

2 and 6 are the usual culprits, but it will depend on cam base circle and profile. As you said you will have to check.
But that said, the amount you may or may not have to clearance won't be enough to affect balance, with a 5.7 I beam rod you just have to touch up the shoulder of the rod at the bolt.
The Scat I beams with the cap screw are said to be good rods and pretty forgiving to cam clearance, so you could go with them and may not have to do anything.

Either way don't worry too much about it, 5.7 rods and a mild cam like that shouldn't give you too much grief, just check during assembly and you will be good.

keithl1967 · Jul 13, 2013

68rs406 said:
But that said, the amount you may or may not have to clearance won't be enough to affect balance, with a 5.7 I beam rod you just have to touch up the shoulder of the rod at the bolt.

I'm glad you said that--This thread got me thinking about it--my assembly was balanced prior to having to machine the rods...glad to hear it should not affect the balancing...

mark191 · Jul 13, 2013

My 406 build either required grinding on the scat h-beam rods or going small base circle cam (605 lift solid roller). Went small base and no problems. Also running 5.7 rods.

muzzy · Jul 13, 2013

What is the recommended clearance between cam and rod?
Thanks for the good replies.

mark191 · Jul 13, 2013

I'm at .060 on the tight spots and have zero problems.

keithl1967 · Jul 13, 2013

mark191 said:
I'm at .060 on the tight spots and have zero problems.

X2...my machinist, after taking some off, I reinstalled, tested, and wa sonly at about .050...had me take it back out, so he could take some more off to get to .060 at least...

68rs406 · Jul 13, 2013

I went to .060 and maybe just a bit more and all was well. I had to clearance more than just 2 and 6 with mine also (there are 1 or 2 more typical rods, forget which now), the cam was 1.000 base circle and had a decent sized lobe on it.

Nothing wrong with a reduced base circle, but I'm not a fan of the pencil thin base circles you see sometimes.

zdld17 · Jul 13, 2013

I selected my cam first from UDHarold. He recommended a .750 billet base circle, this took care of much worry as my cam was slightly larger , 282/290 , 550" billet x 112° lsa. Cam uses his Everwear cam gear for stock distributors.

One thing I did notice during mock up, this moved my retro roller Comp 853 rollers further down the lifter bore .250. I made it a point to check each oil galley passage in the block to make sure that lifter grove was well within the oil galley. This did cause the need for longer push rods to make the rocker arm geometery correct. I used 7.450 length, same as the LS motors.

Using the Compstar 6.0" rods, I touched the outer oil pan rails with a grinder , to get a comfortable clearance between the cap screws and block. I allowed .100 clearance every where else.

Vintage 68 · Jul 13, 2013

Be sure to check/re-check clearances with, or after, cam is degreed to it's final installed setting.
Advancing cam timing can close up clearances vs. a 'straight-up' install.

406 rods to buy?

muzzy

keithl1967

BPOS

muzzy

keithl1967

68rs406

keithl1967

mark191

muzzy

mark191

keithl1967

68rs406

zdld17

Vintage 68

Top Contributors this Month

Recommended Communities