Packard Forum Index » Modification Discussion

Craig. I'm impressed with your findings on the rods and pistons. Most likely the way i will go for long term keeper engines.

The point i am trying to make relative to the pistons is that a wider variety of oversizes (not just up to .030 over) and wide continuous availability into the future mite well be worth the added expense of the rods that u have discovered.

The only question now is one that JV brought up about the width of the big end of the rod.

PackardV8 wrote Quote:
The width of the big end of a BBC rod is 0.995 according to my source. I don't know what the width of one of the 7.100 rods measure. A Packard rod I have handy measures 1.050. As to whether this difference will be a problem or not, I'll have to check. If someone gets serious about this rod/piston combination, then exact measurement of everything would be in order.

If this combo does work, the rods will outlive 3 engines.

Craig

Update on the rod side clearance difference.

I cannot think of any reason why extra rod side clearance would be a problem, even 0.100. The oil flow is determined by the bearing clearance, not the rod side clearance. Both the pin end and the bearing end are floating, so they are NOT dependent on the side clearance for anything but keeping the rod somewhat captured within its nominal position.

For instance one source I found on the internet says:

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On edit: "pin guided" probably means that the rod bearings are pinned rather than using normal end slots. For a HiPo street engine, pinned rod bearings are not needed.

A call to Eagle or one of the other manufacturers would be in order to help resolve this question.

Craig

Quick, dumb question. Does this mean that it's possible to use different rod bearings in the Packard rods that are narrower than the original bearing?

TurboPackman wrote Quote:
Short answer: yes. If the BBC big end rod bearing (which is narrower than a Packard) will withstand 1,000HP, then it will withstand anything a Packard head/intake/exhaust can throw at it.

Craig

FYI: Packard service manual indicates .003 to .011 inch sideplay for the rods. The .003 seems a bit tite to me.
I'm not sure about that .100 inch sideplay tho. Seems like too much.
I suppose one could cut the top out of a scrap piston and mock it up to see if the top of the rod is getting too close to the piston pin bosses and for general centering analysis.

PackardV8 wrote Quote:

Maybe not. Until you ran it at 12,000RPM for 500 miles, who can say?

Craig

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Not quite. The "pin-guided" rods referenced is when the piston top end clearance between the rod small end sides and the piston pin boss is reduced to less than .003" per side. The tight clearance between the piston and the rod small end keeps the rod big end from moving side-to-side on the crankshaft. Thus, the rod is pin-guided instead of big-end side clearance guided.

The Packard V8 con rod big end width is 1.060" and the BBC is .990". The real concern is when the crankshaft diameter is reduced .050" to fit the BBC bearings and the side clearance is opened up to .150" will the oil holes in the rod throws be uncovered?


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Yes, theoretically possible. See above - will a narrower bearing uncover the oil passages?
No, it's not that easy. Most BrandXYZ rod bearings of the same nominal 2.25" crank diameter are a different outer diameter as well as being narrower. This would require a careful re-manufacturing of the rod bore ID, as well as sometimes cutting a new tang locating slot. Major, expensive machining operations.
Maybe, until we start breaking a lot of Packard rods with high RPM and high horsepower, we don't yet really need to swap out bearings and rods.

thnx, jack vines

thnx, jack vines

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Now why would you drive that fast if your car had a Treadle-Vac Brake system? (Sarcasm- Runs for cover)

Keith doesn't have a BTV in his car, he came to his senses long ago.