L31MaxExpress
I'm Awesome
I Had Rhoads V-Max lifters in this engine. They worked too well on the small camshaft.
Head scratcher
- Thread starter L31MaxExpress
- Start date
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Too well?
L31MaxExpress
I'm Awesome
Pushed the cranking compression up a full 20 psi.
With Rhoads V-Max lifters, 0.020" off the bottom of the lifter travel.
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With GM LS7 lifters
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And that's a bad thing? Created too much overall compression?
L31MaxExpress
I'm Awesome
Made it much more prone to pre-ignition or pinging.
Good call. That would almost exactly duplicate what they used to do back when all this technology was new,
when parts were relatively expensive and the labor was cheap. Here's a photo from the 1951 Buick FSM
about how to test the bleed down rate of this new technology:
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(credit: Read the entire procedure here: 1951 Buick hydraulic lifter test procedure)
This piqued my curiousity. Was this ever mentioned in any of the GMT400 FSMs?
And if so, what was the most recent reference made?
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(From the '94 Unit Repair Manual, see upper LH corner for specifics. NOTE: Passing the lifter test was if the leakdown took between "12 & 90 seconds" w/special test fluid.)
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The bottom line? The more I try to get hydraulic lifters to work the way I want them to, the
more I like the sheer repeatability / simplicity of solid lifters. Especially with the new tight lash
solid lifter cams.
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I'm thinking the best way to get that repeatability is to run them just off the bottom. .025" should allow for any seat settling and temp changes.
I wonder what the "special" oil is. Possibly straight 30w?
According to the '51 Buick FSM it's a lot thinner than that. The mechanic is instructed
to get an exact 1 gallon container, (preferably glass) add 12oz of 10-weight oil, and
fill up the remainder of the container with kerosene. (I love the common sense directions
in the old manuals -- they state that a 6 oz Coca-Cola bottle is a convenient measurement. :0)
In other words, 12 oz of 10-weight oil + 116 oz of kerosene. (See attached.)
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That's the short answer. In '54 there was Buick Service Bulletin about a new test fluid that
should be used for hydraulic lifter leakdown testing. (Kent-Moore J-5268) FWIW I've scraped the
interwebs, and I can't find any recent links to this fluid. But I've attached a screen grab of that
service bulletin, mostly to show just how fussy you have to be in terms of cleanliness in order
to get good go/no-go test results.
Moving forward in time, an elder was talking about a bad batch of noisy hydraulic lifters from
the factory in the (brand F) '67 390 V8s. And that he used the Kent-Moore J-5790 leakdown tester
tool to ferret out the bad ones. The cool thing is that he shared a couple of actual photos of his
test rig:
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And to wrap this up, the '94 GM Unit Repair manual mentioned in reply #86 specifically
refers to the J-5790 tester. And that's pretty much the sum total of what I could find in terms
of calibrated hydraulic lifter leakdown test equipment that used to be used by auto/truck mechanics
in the field. Obviously we are closing in on the end of an era.
NOTE: All this careful analysis & testing in the service areas was pushed to the wayside as labor costs
kept rising and parts prices kept coming down. Good parts were cheap & plentiful, so why waste time on
all this stuff? But times have changed, and some of this style of repair may come back into vogue.
(ie: Keep the original bits working as long as possible.)
As always, food for thought. At least we have a good idea of what they were trying to achieve
during diagnostic testing. All I know is that it doesn't take much dirt, varnish, or wear for these
super close-tolerance devices to start drawing attention to themselves in a ticky/clattery way.
FWIW --
EDIT: I happened to find a .pdf of an old J-5790 brochure. Pretty cool - I enjoy old technical
features & benefits artifacts like this. Anything that helps me better understand the mindset
of the folks who were involved with this all-but-forgotten test apparatus.
Attachments
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Found this one on evilbay,
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Great posts, everyone.This thread is a great read/look over your shoulder. I really enjoy the ongoing analysis of internal oil control with the goal of optimizing
your powerplant's oil consumption vs the more often seen "It is what it is / If you're gonna play you gotta pay / I can't be bothered"
school of thought.
This thread reminds me of all the hubbub back in the day that surrounded the excessive oil consumption of the LS1 & LS6
engines that a small but vocal minority of Corvette owners were experiencing. Eventually the GM powertrain engineers figured
out what was going on, and based on their understanding were able to come up with a genuine fix for the owners with driving
habits that stimulated the problem:
(John Juriga on the 4 forces of ring flutter: Combustion pressure, Ring inertia, Ring's radial expansion pressure, Crankcase Pressure)
So the near-term warranty fix was the revised ring package for the small pool of drivers that could stimulate the excess oil consumption.
IIRC, the long term fix was some kind of internal block windowing that the engineers added in order to reduce
the 4th variable -- crankcase pressure pulsations. (And no, I'm not confusing this with the controversial Olds 403
block windowing.) Unfortunately, I can't seem to dig up the article describing the long term fix?
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Given all of the above, I don't think that a discussion about oil consumption, catch cans, and ring flutter is an over the
top geekfest when thinking about what's going on inside a hard-working wet-sump V8. Like what L31MaxExpress is
debugging/documenting for our viewing pleasure. It's leading-edge effort like this that allows you to not have to
apologize for still enjoying a 1st-gen SBC in a sharp state of tune.
New guy here- In all humility, this is a subject I'm passionate about and want to share without sounding like a pompous know-it-all:
The once upon a time answer from piston manufacturers (when we were making less than 3 hp/c.i.) was the "accumulator groove" between the top compression and bottom rings and managing the second ring gap. I quickly found out that it helps, but is not the end-all to the issue; which is why I always use either PCV with a vacuum pump and air/oil seperator (N/A) or something similar with a check valve for boosted applications. I've used GM 24505066 air pump (converted for vacuum) for 95 Corvette and GM 12117025 Pigtail on any engines I've assembled making steam, from Subarus to BBCs, boosted or not. Plugs are cleaner, oil is cleaner, idle is smoother. People used to comment on why my engines sounded so much different, even when the same parts were used. I'd reply that it's ring seal and lack of crankcase pressure fighting the ring pack. I've used Total Seal (Gas-ported are my favorite) for a long time.
I've never been a fan of the "replace the PCV with a catch can" advice so prevalent nowdays. The ring pack doesn't like the pressure from underneath, or between. The more differential pressure you can create, the better everything works.
Thanks for all the insightful and helpful info.
