Packard Forum Index » V-8 (1955-56)

For fifty years, the small block Chevy turned relatively high RPMs and never had a main bearing issue. Then, GM went to lockup converters with EFI and computer controlled ignition. This search for fuel economy led them to hold the lockup and put the engine in a hard pull at large throttle openings down in the 1500-2000 RPM range. At the same time, they were using the SBCs in Suburbans and 6,000# pickups The SBCs so equipped began to show main bearing problems.

What if our Packard V8s were experiencing the same conditions; pulling hard in a heavy vehicle against a locked converter? Main bearing issues wouldn't be a surprise.

Yes, the oil pump problems manifest as lifter clatter at idle, but what if the lockup converter is as much the cause of the main bearing wear?

Yes, I'm also investigating some crankshaft design issues. One of the top crankshaft builders in the country is modifying a forged crankshaft for me with radically different counterweights.

jack vines

I also suspect that many of the main bearing troubles come from the very low lockup speeds that Packard specified. I believe that was some thinking left over from the high torque at low speed engines from the thirties. Those engines had far lower unit bearing loading than the v8s. The customer base seemed to expect direct drive at low speed as suggested by the change in mid 55 to lower the direct engagement speed. The crankshafts don't like it and the trans don't much care for it either. It is not unusual to get torque agony pulling a hill at low speed in direct

On the winding hilly roads around here those low engagement speeds are purely annoying and lead to lots of lugging and then kickdowns. That is why I raise the direct engagement speed quite a lot on all the trannys that I build. My 56 Packup will go direct at 28 at light throttle. With a 3.07 rear, that is still a bit too slow in many instances and I will bump it up a bit more the next time I have the pan off.

No main bearing problems with the stick shift transmissions???

So i very much doubt that either the SBC main failure had anything to do with the lock-up or overdrive.

Furthermore:
It is my understanding that the Packard V8 wears the MIDDLE (#3) main bearing faster than any of the rest. So that would contradict any chaances of the lock up converter to cause any premature wear. No??


As for the SBC reaar main wear we have to keep in mind that GM went to shit over the last 20 years. So without some indepth analysis of the modern SBC vs the first 35 to 40 years of SBC and any changes (incl metalurigacal) then no determination can made about the wear.

Quote:

The '56 Studebaker Golden Hawks with the standard transmissions are more likely to drop a valve or crack a piston from being over-revved.
Quote:

The analysis of SBC main bearing wear comes directly from the American Engine Rebuilders Association and is confirmed by the local rebuilder to whom we sell core engines. They build a dozen SBCs every week, so they see the post-mortem when cleaning the core, so it's not debatable.

jack vines

Quote from above post:
" e American Engine
Rebuilders Association and is confirmed by
the local rebuilder to whom we sell core
engines. They build a dozen SBCs"

Meaning what???? That SBC's with MANUALshift trans does NOT have such main bearing failure?????

Depending on how they're driven. Some of them have a skip-shift solenoid which forces shifts from first to third around town unless a lot of throttle is used. The .67 overdrive with 3.23 gears has them pulling really low RPMs. The driver can choose to override and if more R's are used, there's less main bearing trouble.

The above mainly applies to Corvette/Camaro. There's not been a manual Suburban in the modern era and very, very few manual pickups.

jack vines

I'll have to admit that i am not familiar with much of any vehicle built over the last 20 years.

However, Is this main bearing failure chronic among the SBC engines and does NOT appear in any OTHER mass pproduced engines such as Ford or Chrysler or MB or any other vehicles????


Maybe SBC"s are the ONLY engines coupled to lock up converters and overdrive etc and thus turning such low rpm at low speeds???

Maybe so. I don't know. But i doubt it.

If only my two Packard 374s had the performance and longevity of our family's several dozen Chevy small block V8s, I could die a more satisfied man. Currently, my most primitive SBC is a fifty year old Corvette 327 that has not had the engine opened up in the 35 years I have owned it. Next come at least fifteen Chevy/GMC light trucks, ranging from 1988 to 2008, both SMC and Big Blocks, all with engine miles somewhere between 120 and 600 thousand miles with remarkably trouble free performances. Of course, they have regular servicing, but still our experience is almost Corolla-like.

Two of my newer Corvettes have the skip-shift manual transmission feature mentioned that would force first to fourth gear shifts at any throttle position less than 30%, but I found it both annoying and dangerous. I easily disabled both with an inexpensive (less than $20) clip in wiring defeat device. Their 6 speed transmissions now do as I say, although the dash instrument light still shows me what EPA would prefer.

Conversely, my two 1956 Ultramatics still lock up sooner than I would prefer, and one leaks enough F-type if it sits too long to be embarrassing. That alone is enough to make me drive both at least once a week when conditions are favorable. Now if I could get GM transmission life, usually north of 200 thousand miles before rebuilding is necessary, out of these Packard beauties, the world would be prettier. My last remaining two speed PowerGlide just turned 51 years with only seven fluid changes recorded since new. Still on the job with no complaints other than a bit too slow behind a six. If it were in a SBC, there would be no complaints at all.

On your too soon shifting Ultramatic, follow the service manual to increase the lock-up shift point... You can adjust the ultramatic link on the carb linkage and/or move the link to a different hole. A 10 minute fix.

On the leaking while sitting, it is probably from converter leakdown which is a big job. Often just replacing the throttle shaft seal will eliminate the leak. A 1 hour job.

About the 200,000 life, sorry.......