[DeTomaso] NPC - Machine Shop Practices
Tim Meyer
fordmachinist at gmail.com
Thu Nov 12 19:32:37 EST 2015
By using a machine. You would spin up the original part and measure the exact amount of imbalance. Then spin the replacement part and make the balance from the original part.
Tim Meyer
Sent from my iPhone
> On Nov 12, 2015, at 5:26 PM, Guido deTomaso <guido_detomaso at prodigy.net> wrote:
>
> "have a machine shop match the imbalance ( vibration damper, flywheel,
> flexplate ) to get it as close to the original"
> How common a request to the machine shop is this? How would it be
> done? Not with a bubble balancer I suppose ... maybe with a dummy
> shaft or a known balanced crankshaft in the balance machine?
> I've heard repeated reports of guys asking for a 28 oz-in to be
> rebalanced to 50 oz-in, only to be told "can't be done without the
> crank, rods, pistons".
> Thanks,
> GD
> __________________________________________________________________
>
> From: Timothy Meyer <fordmachinist at gmail.com>
> To: 'Guido deTomaso' <guido_detomaso at prodigy.net>; detomaso at poca.com
> Sent: Wednesday, November 11, 2015 10:40 AM
> Subject: RE: [DeTomaso] NPC - Machine Shop Practices
> 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:[1]detomaso-bounces at poca.com] On Behalf Of Guido
> deTomaso
> Sent: Wednesday, November 11, 2015 12:20 PM
> To: [2]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 <[3]daniel.c.jones2 at gmail.com>
> To:
> Cc: "[4]detomaso at poca.com" <[5]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][6]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][7]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][8]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][9]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][16]spkorb at spkorb.org
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> A A 4. [16][19]http://www.LiveOakConcours.org/
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