[DeTomaso] NPC - Machine Shop Practices

Timothy Meyer fordmachinist at gmail.com
Wed Nov 11 09:17:17 EST 2015


28 oz imbalance is at each end.
It is possible to balance one end at neutral and leave the other end at the 28oz.

We have circle track engines that will do that. 
Due to no flywheel, just a drive hub.
But then if that is the case, spend the extra money and finish the job.

Tim Meyer
TMeyer Inc
www.tmeyerinc.com



-----Original Message-----
From: DeTomaso [mailto:detomaso-bounces at poca.com] On Behalf Of Sean Korb
Sent: Wednesday, November 11, 2015 8:01 AM
To: detomaso at poca.com
Subject: Re: [DeTomaso] NPC - Machine Shop Practices

Always wanted to know, but was afraid to ask... and this seems like the place to do it:
If my motor is 28oz external balance, is that 14 at the harmonic balancer and 14 at the flywheel?  Could you put all 28 on one end or is that a "bad thing"?  Asking for a friend ;)

sean

On Wed, Nov 11, 2015 at 6:51 AM, JEFFREY COBB <jeffcobb1 at me.com> wrote:

> GD, you are correct that machining a block and crank based on known 
> piston and big end size is the best and most intelligent way to create 
> a tight fast and secure short block.
>
>    So it appears that the margin of error needs to be in place so as 
> to support the reality of new bearings and cranks having a tolerance 
> variation which as Tim says, stacks up to your end clearance and 
> production run variances, I agree to that.
> Of course it is better to machine a crank and block to its recip 
> parts; pistons and big ends.
>
>    Though that creates a problem later on if rework without machining 
> is done and diff brand parts are used that will then damage your 
> initial perfect job clearance results, now too loose or tight.
>   I have found with our matchining that the clearances made no real 
> difference unless it was on a Benz turbo diesel or a high output high 
> rpm engine. The oil pump, oil and block temperature tends to cover 
> different clearance issues until you stress it out and the ugly knock 
> or bang changes your day.
>
>    So in closing, we always machine our block and crank according to 
> known static size values because we care about this engine today not a 
> run of production engines tomorrow.
>
>    And the best of clearance jobs will always be destroyed by a not 
> perfect balance of reciprocating mass. Balance is critical, maybe more 
> than clearances.
>    Static neutral balance is the first and only step way to go if then 
> the rotating mass is spun to check out its dynamic secondary harmonic 
> balance results. Which can then be fine tuned.
> Now your have proper dynamic balance spinning in its own correct 
> clearances. She will last a long time.
>
> Bad harmonics, just like how an off key tenor will kill a Pucinni 
> opera, will also kill a fine engine.
> Take care,
>
> Jeff Cobb- I pad
> W-225-343-7525
> C-225-907-4514
>
> Jeff Cobb Auto Works
> 1316 S. Acadian Thruway
> Baton Rouge, La.
> 70806
>
> www.LiveOakConcours.org
>
> On Nov 10, 2015, at 9:51 PM, fordmachinist at gmail.com wrote:
>
> > We will grind a crankshaft at time with the bearings installed in 
> > the
> block and the rods. There are time we see tolerance stack.
> > But true, most shops will grind a shaft according to the spec size.
> Typically +/- .0004"
> > Performance may favor the low end of spec. But see do see that many
> aftermarket cranks are not that great.
> > Start miking the bearings. That starts to get scary. we will find
> .0002-.0004 difference in brands.
> >
> > I worked for a production builder, and I bored blocks all day.
> > Didn't have any pistons in my hand. Just bored it to a nominal size 
> > plus
> maybe .0005" and that was it. Never saw an issue.
> >
> > Neutral balance does not require balancer or flywheel. All the 
> > weight is
> on the inside.
> > If the engine was a neutral balance design, you would balance the
> rotating assy first, then add the flywheel and balancer. If it is 
> neutral balance, the balancer and flywheel could be balanced all by them self also.
> >
> > Tim Meyer
> > TMeyer Inc.
> > www.tmeyerinc.com
> >
> > Sent from my iPad
> >
> >> On Nov 10, 2015, at 8:04 PM, Guido deTomaso 
> >> <guido_detomaso at prodigy.net>
> wrote:
> >>
> >>  Not sure why this is on my mind today, but:
> >>  It's common in my experience to provide a piston when a cylinder 
> >> is  bored, so the bore provides a known clearance to that piston.
> >>  Does anyone do this with crankshafts, use the actual connecting 
> >> rod  bearing ID and turn the crank to match?  By the time you get 
> >> out the  plastigage, it's too late if the clearance isn't what you 
> >> wanted.  But  I've never heard of anyone doing anything with a 
> >> crankshaft other than  turn it down to some arbitrary diameter.
> >>  Similarly, from what I've observed on YouTube, it ought to be  
> >> technically possible to balance a crankshaft alone, then add 
> >> flywheel  and balance it, then the pressure plate, then the harmonic balancer.
> >>  This would make all those bolt-on items "neutrally balanced" and 
> >> they  could be replaced or swapped from engine to engine.
> >>  What I suspect usually happens instead is, all the parts are 
> >> bolted  together and balanced in one shot, making a set which 
> >> cannot be broken  without upsetting the achieved balance.
> >>  So, if I asked that a crank be turned to match the rod bearings, 
> >> or  that the bottom end NOT be turned into a matched set, am I 
> >> likely to be  shown the door?
> >>  Thanks,
> >>  GD
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--
Sean Korb spkorb at spkorb.org http://www.spkorb.org
'65,'68 Mustangs,'68 Cougar,'78 R100/7,'60 Metro,'59 A35,'71 Pantera #1382 "The more you drive, the less intelligent you get" --Miller "Computers are useless.  They can only give you answers." -P. Picasso





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