Connecting Rod and/or Piston Machining

[CTX-SLPR]

Howdy,

I'm sure many, if not most, of us have tried something only to have the "right" way to do it be painfully expensive and out of budgetary reach. That's kinda where I find myself now.

I've agreed to buy an old BMS (Buick Motorsports) 2.66in stroke Odd-fire forged crank that is set up for 2.100x0.940in big end SBC rods. The problem is that with a 0.740in bank-bank offset on the Buick V6, even with 0.030-0.035in offset SBC rods the rod centerline is 0.130-0.135in offset to the outside of the bore on each journal pair. With only a 1.150in gap between the pin bosses and a 0.900-1.060in wide pin end on the rod, they run afoul of each other. From quotes from R&R and Carrillo, a custom set of rods is $1300-1800! That is just beyond my budget right now.

From looking and thinking, especially with my 350hp at the crank limit, I see a few options.

1. Find a cheaper maker of custom rods and get a set of 6.350in long SBC rods with a 0.100in offset
2. Spot face the sides of the pin end of the rod down to just under 0.900in wide then clearance the piston pin bosses to allow for ~0.015 clearance on one side and machine the other to match
3. Machine the outside side of the rod down so that the pin end is in the middle of the pin bosses

Honestly I'm likely to go with 2 since a 0.900in wide pin end does exist on "lightweight" SBC rods already (not sure about the K1's that exist in 6.300 which is close enough for using a production block to start with) and It means that I'd only need to take ~0.020in out of the insides of the pin bosses to make it work.

That being said, anyone know of a good custom rod maker for a set of 750hp at 7000rpm rods at around $800 for a set of 6?

[Barry Donovan]

offsets..v6.
I'd cheat none.

90 degrees and a six that pounces every casting.

the 2.66 inch stroke and long rods caught my attention. That ought to be a screamer.

a machinist is probably giggling the 3 dollar route if to read your request...not a big problem there.

[Beagle]

Did you ever talk to the guys with the 6.350 long 2.1 BE x BBC pin rods? They were like 440.00 for a set of 8 iirc. You could tweak and bush them probably.

2 sounds doable.

Custom pistons sound cheaper than the rods you're looking at, maybe find a more standard size rod like a 6.250 Chevy rod that there are a million of and go for the custom pistons instead.

[TC]

That is what I was thinking custom pistons......

[CTX-SLPR]

All that would do is make things fit without me modifying anything... the real problem is that the rods aren't running up the center of the bore. Doing custom pistons leaves me with spending money on custom pistons and still leaves me with rods that are in the wrong place for an ideal combination. Besides, if all I'm doing is making the pin bosses narrower, I can do that at home for free.

Beagle,

The BBC rods are 6.385in long which is too tall for my combination without shaving the piston crowns (doable) but more importantly they have 0.990in pin bores and with a 0.025in initial bushing and then needing a 0.940in at the largest pin bore, that's a 0.050in thick bushing that I don't think bronze is going to hold up to the strain of slinging a heavy piston around at elevated RPM's. If they made a 0.030in steel bushing with a 0.265in bronze bushing in the center, that would be more comfortable but heavy since you've got the rod's structure for a 0.990in pin then more steel to bush it down. The rods would work if the pin issue could be resolved.

[CTX-SLPR]

Think you can open up a big end of a rod 0.105in? NASCAR rods typically use a rod bearing housing of 2.015in when I'd need a 2.225in housing.

Thoughts?

[cstmwgn]

Think you can open up a big end of a rod 0.105in? NASCAR rods typically use a rod bearing housing of 2.015in when I'd need a 2.225in housing.

Thoughts?

that the math does not add up for me. 2.225 - 2.015 = .210

[BOSSMAN]

Think you can open up a big end of a rod 0.105in? NASCAR rods typically use a rod bearing housing of 2.015in when I'd need a 2.225in housing.

Thoughts?

I'm gonna say NOPE! The material just isn't there (I have a few sets) and I believe to bolts are also located closer together since the bore size is smaller. Better off just getting the correct part for the job OR look at another avenue if custom.

[CTX-SLPR]

I'm gonna say NOPE! The material just isn't there (I have a few sets) and I believe to bolts are also located closer together since the bore size is smaller. Better off just getting the correct part for the job OR look at another avenue if custom.

I can believe that, just visualizing the 0.105in made it borderline. While I'm sure the NASCAR rods are of good material, they do seem to be pared down to the minimal weight to begin with so I doubt there is extra meat in the BE

that the math does not add up for me. 2.225 - 2.015 = .210

Yeah, but I skipped to the material removed so 0.105in all around.

[Hemi Joel]

The piston rod DOES NOT have to be centered in the bore, and the piston does not have to be ballanced from one side to the other. If there is enuff meat there, just cut the pin boss on one side for clearance. If you are not sure that there is enuff structure there, cut one side of the rod a little.

[jlmccuan]

I have a set of Carrillo's that are 6.35" center to center, but don't know the offset. They would need the 1.850" rod journal or 1.889" depending on the bearing used. Are you willing to turn the crank to the Honda journal? I'm willing to cut a deal on them.

[CTX-SLPR]

I have a set of Carrillo's that are 6.35" center to center, but don't know the offset. They would need the 1.850" rod journal or 1.889" depending on the bearing used. Are you willing to turn the crank to the Honda journal? I'm willing to cut a deal on them.

Potentially willing to turn the crank to the larger of the two IF the rest of the stuff makes it a good fit.

Pin size:
Pin End Width:
Big End Width:
Offset: (lay the rod cheek flat on a surface then measure the height to the beam, flip over and repeat; the difference is the offset)

Thanks,

[CTX-SLPR]

Assuming that JLMCCUAN's rods (or a similar set of rods) don't appear I've done the math on the various different combinations of parts. I'm only shooting for 350hp right now but with good pistons and crank, I'd rather not spend significant money on something with only half the power capacity in the middle of them and kill the good parts. The block will only take 400-450hp for the length of time I'd need to run it anyway so I'd like to put the whole rotating assembly in a Stage I/II block later.

It's about $1000 for all parts to make the BBC 6.385in rods work between getting custom 0.0215in steel bushings, Crower 0.035in bronze bushings, rod narrowing, and piston shaving if I farm out doing the machine work. Maybe a few hundred less if I buy the tooling and try to do it myself on my own mill. This option would give me almost exactly the compression I was after and rods down the center of the bore. However it makes the pistons as thin on the crowns as I'd be willing to go so deck height changes would have to be compensated for in gasket thickness and the combo would be heavy with the BBC pin end filled in with more steel. HP limit: with the weight these would probably cap out around 650hp at 7000rpm, maybe more since the bushing is steel and they are ment for swinging much heavier pistons.

To make the 6.300in SBC rods fit (not work in the sense of getting them in the middle of the bore) it would be fairly cheap to machine (potentially do it myself with a fly cutter or face mill) the rod pin end down and then open up the pin boss with a ball nosed end mill. Total cost around $650-700 but my compression is about as low as I'm willing to go with the thinnest gasket available and the rods are still way off center in the bore. HP limit: I don't think I'd want to push these past 650hp at 7000rpm.

Custom rods from R&R would of course be perfect dimensionally and give my both the rod up the middle of the bore and compression. The are however $1300 unless a vendor (not the mothership) can get a discount on 6 custom rods. HP limit: 1000hp or whatever they quote as the 7000rpm limit.

I think I can throw out the BBC rod idea since it's got a ton of work and puts me in a bind for future work. Getting the SBC rod to fit sounds great but at over half the price for around half the rod with compromises on compression and bore centering, I'm not sure if it's a good enough deal to justify it as an interim solution. Even with my recently improved funding situation, it's more than half my remaining budget for the R&R's and I still need to get pretty much an entire set of rebuild supplies such as bearings, rings, timing chain, lifters, push rods... and the list goes on and on...

I hate buying a half assed solution and hoping it doesn't bite me but I might have to get something done at all.

[Huskinhano]

I don't know how use full this is but maybe give Howards Racing a call. They sell a lot of powered metal rods for racing purposes. Maybe something off the shelf could be custom made for a reasonable cost since this is not a super high HP motor.

[CTX-SLPR]

Not sure these rods were ever run but holy crap check out the bushings!!! http://www.ebay.com/itm/NASCAR-NEW-L...071c44&vxp=mtr
0.927in bores bushed down to 0.787in, that's a 0.070in wall thickness bushing and it looks to be all bronze too! I suspect if that's a legit NASCAR or similar rod and bushing setup and they have been run at 10mil RPM for 500+ miles that I can run something similar to 7000rpm for 3miles repeatedly. More food for thought

Tom,

I'll see what they say, I already have expensive on the list so similarly expensive is just another refference...