[DeTomaso] NPC - Machine Shop Practices
Timothy Meyer
fordmachinist at gmail.com
Wed Nov 11 13:40:40 EST 2015
We balance a street engine to be below 3 grams tolerance,
racing, we shoot for below 1 gram tolerance.
The balancer or flywheel off the shelf may be within 5-10 grams to each other.
Good enough for the factory.
But if you had an engine balanced to a perf level and had an issue.
I would purchase the new parts and have a machine shop match the imbalance to get it as close to the original.
Tim Meyer
TMeyer Inc
www.tmeyerinc.com
-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Guido deTomaso
Sent: Wednesday, November 11, 2015 12:20 PM
To: detomaso at poca.com
Subject: Re: [DeTomaso] NPC - Machine Shop Practices
Okay, the thread's gone in a different direction ... how precisely are these flywheels and vibration dampers providing that 28.2 oz-in, can you swap these parts later without throwing off the crankshaft balance?
Or do the vibration damper, crank and flywheel become a "set" once balanced?
Alternately, can that 28.2 oz-in be verified on the flywheel or vibration damper alone?
Maybe the biggest problem, I can easily imagine the guy behind the counter not grasping any of this...
Thanks,
GD
From: Daniel C Jones <daniel.c.jones2 at gmail.com>
To:
Cc: "detomaso at poca.com" <detomaso at poca.com>
Sent: Wednesday, November 11, 2015 6:39 AM
Subject: Re: [DeTomaso] NPC - Machine Shop Practices
A
A No.A It's a balance factor with the units of oz-in and is the
product of a mass and a distance (radially away from the crank
centerline).A Also, it's 28.2 oz-in at each end.A When someone says
my flywheel balance is 28 ounces it sounds as moronic as saying I have
450 feet of torque :-)
A
A Dan Jones
On Wed, Nov 11, 2015 at 8:01 AM, Sean Korb <[1]spkorb at gmail.com> wrote:
A A Always wanted to know, but was afraid to ask... and this seems
like the
A A place to do it:
A A If my motor is 28oz external balance, is that 14 at the
harmonic
A A balancer and 14 at the flywheel?AA Could you put all 28 on one
end or
A A is that a "bad thing"?AA Asking for a friend ;)
A A sean
A A On Wed, Nov 11, 2015 at 6:51 AM, JEFFREY COBB
<[1][2]jeffcobb1 at me.com>
A A wrote:
A A A GD, you are correct that machining a block and crank based
on known
A A A piston and big end size is the best and most intelligent way
to
A A A create a tight fast and secure short block.
A A A AA A So it appears that the margin of error needs to be in
place so
A A A as to support the reality of new bearings and cranks having
a
A A A tolerance variation which as Tim says, stacks up to your end
A A A clearance and production run variances, I agree to that.
A A A Of course it is better to machine a crank and block to its
recip
A A A parts; pistons and big ends.
A A A AA A Though that creates a problem later on if rework
without
A A A machining is done and diff brand parts are used that will
then
A A A damage your initial perfect job clearance results, now too
loose or
A A A tight.
A A A AA I have found with our matchining that the clearances
made no real
A A A difference unless it was on a Benz turbo diesel or a high
output
A A A high rpm engine. The oil pump, oil and block temperature
tends to
A A A cover different clearance issues until you stress it out and
the
A A A ugly knock or bang changes your day.
A A A AA A So in closing, we always machine our block and crank
according
A A A to known static size values because we care about this
engine today
A A A not a run of production engines tomorrow.
A A A AA A And the best of clearance jobs will always be
destroyed by a
A A A not perfect balance of reciprocating mass. Balance is
critical,
A A A maybe more than clearances.
A A A AA A Static neutral balance is the first and only step way
to go if
A A A then the rotating mass is spun to check out its dynamic
secondary
A A A harmonic balance results. Which can then be fine tuned.
A A A Now your have proper dynamic balance spinning in its own
correct
A A A clearances. She will last a long time.
A A A Bad harmonics, just like how an off key tenor will kill a
Pucinni
A A A opera, will also kill a fine engine.
A A A Take care,
A A A Jeff Cobb- I pad
A A A W-[2]225-343-7525
A A A C-[3]225-907-4514
A A A Jeff Cobb Auto Works
A A A 1316 S. Acadian Thruway
A A A Baton Rouge, La.
A A A 70806
A A A [4][3]www.LiveOakConcours.org
A A On Nov 10, 2015, at 9:51 PM, [5][4]fordmachinist at gmail.com
wrote:
A A > We will grind a crankshaft at time with the bearings
installed in the
A A block and the rods. There are time we see tolerance stack.
A A > But true, most shops will grind a shaft according to the spec
size.
A A Typically +/- .0004"
A A > Performance may favor the low end of spec. But see do see
that many
A A aftermarket cranks are not that great.
A A > Start miking the bearings. That starts to get scary. we will
find
A A .0002-.0004 difference in brands.
A A >
A A > I worked for a production builder, and I bored blocks all
day.
A A > Didn't have any pistons in my hand. Just bored it to a
nominal size
A A plus maybe .0005" and that was it. Never saw an issue.
A A >
A A > Neutral balance does not require balancer or flywheel. All
the weight
A A is on the inside.
A A > If the engine was a neutral balance design, you would balance
the
A A rotating assy first, then add the flywheel and balancer. If it
is
A A neutral balance, the balancer and flywheel could be balanced
all by
A A them self also.
A A >
A A > Tim Meyer
A A > TMeyer Inc.
A A > [6][5]www.tmeyerinc.com
A A >
A A > Sent from my iPad
A A >
A A >> On Nov 10, 2015, at 8:04 PM, Guido deTomaso
A A <[7][6]guido_detomaso at prodigy.net> wrote:
A A >>
A A >>AA Not sure why this is on my mind today, but:
A A >>AA It's common in my experience to provide a piston when a
cylinder
A A is
A A >>AA bored, so the bore provides a known clearance to that
piston.
A A >>AA Does anyone do this with crankshafts, use the actual
connecting
A A rod
A A >>AA bearing ID and turn the crank to match?AA By the time
you get out
A A the
A A >>AA plastigage, it's too late if the clearance isn't what you
A A wanted.AA But
A A >>AA I've never heard of anyone doing anything with a
crankshaft other
A A than
A A >>AA turn it down to some arbitrary diameter.
A A >>AA Similarly, from what I've observed on YouTube, it ought
to be
A A >>AA technically possible to balance a crankshaft alone, then
add
A A flywheel
A A >>AA and balance it, then the pressure plate, then the
harmonic
A A balancer.
A A >>AA This would make all those bolt-on items "neutrally
balanced" and
A A they
A A >>AA could be replaced or swapped from engine to engine.
A A >>AA What I suspect usually happens instead is, all the parts
are
A A bolted
A A >>AA together and balanced in one shot, making a set which
cannot be
A A broken
A A >>AA without upsetting the achieved balance.
A A >>AA So, if I asked that a crank be turned to match the rod
bearings,
A A or
A A >>AA that the bottom end NOT be turned into a matched set, am
I likely
A A to be
A A >>AA shown the door?
A A >>AA Thanks,
A A >>AA GD
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A A Sean Korb [14][13]spkorb at spkorb.org
[15][14]http://www.spkorb.org
A A '65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71
Pantera
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References
A A 1. mailto:[15]jeffcobb1 at me.com
A A 2. tel:225-343-7525
A A 3. tel:225-907-4514
A A 4. [16]http://www.LiveOakConcours.org/
A A 5. mailto:[17]fordmachinist at gmail.com
A A 6. [18]http://www.tmeyerinc.com/
A A 7. mailto:[19]guido_detomaso at prodigy.net
A A 8. mailto:[20]DeTomaso at poca.com
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A 15. [27]http://www.spkorb.org/
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