[DeTomaso] NPC - Machine Shop Practices
Sean Korb
spkorb at gmail.com
Wed Nov 11 09:01:07 EST 2015
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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> >
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> >
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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
-------------- next part --------------
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?A Could you put all 28 on one end or
is that a "bad thing"?A Asking for a friend ;)
sean
On Wed, Nov 11, 2015 at 6:51 AM, JEFFREY COBB <[1]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.
A A 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.
A A 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.
A 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.
A A 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.
A A 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.
A A 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-[2]225-343-7525
C-[3]225-907-4514
Jeff Cobb Auto Works
1316 S. Acadian Thruway
Baton Rouge, La.
70806
[4]www.LiveOakConcours.org
On Nov 10, 2015, at 9:51 PM, [5]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.
> [6]www.tmeyerinc.com
>
> Sent from my iPad
>
>> On Nov 10, 2015, at 8:04 PM, Guido deTomaso
<[7]guido_detomaso at prodigy.net> wrote:
>>
>>A Not sure why this is on my mind today, but:
>>A It's common in my experience to provide a piston when a cylinder
is
>>A bored, so the bore provides a known clearance to that piston.
>>A Does anyone do this with crankshafts, use the actual connecting
rod
>>A bearing ID and turn the crank to match?A By the time you get out
the
>>A plastigage, it's too late if the clearance isn't what you
wanted.A But
>>A I've never heard of anyone doing anything with a crankshaft other
than
>>A turn it down to some arbitrary diameter.
>>A Similarly, from what I've observed on YouTube, it ought to be
>>A technically possible to balance a crankshaft alone, then add
flywheel
>>A and balance it, then the pressure plate, then the harmonic
balancer.
>>A This would make all those bolt-on items "neutrally balanced" and
they
>>A could be replaced or swapped from engine to engine.
>>A What I suspect usually happens instead is, all the parts are
bolted
>>A together and balanced in one shot, making a set which cannot be
broken
>>A without upsetting the achieved balance.
>>A So, if I asked that a crank be turned to match the rod bearings,
or
>>A that the bottom end NOT be turned into a matched set, am I likely
to be
>>A shown the door?
>>A Thanks,
>>A GD
>> _______________________________________________
>>
>> Detomaso Forum Managed by POCA
>> Posted emails must not exceed 1.5 Megabytes
>> DeTomaso mailing list
>> [8]DeTomaso at poca.com
>> [9]http://poca.com/mailman/listinfo/detomaso_poca.com
>>
>> To manage your subscription (change email address, unsubscribe,
etc.) use the links above.
>
> _______________________________________________
>
> Detomaso Forum Managed by POCA
> Posted emails must not exceed 1.5 Megabytes
> DeTomaso mailing list
> [10]DeTomaso at poca.com
> [11]http://poca.com/mailman/listinfo/detomaso_poca.com
>
> To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
_______________________________________________
Detomaso Forum Managed by POCA
Posted emails must not exceed 1.5 Megabytes
DeTomaso mailing list
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To manage your subscription (change email address, unsubscribe, etc.)
use the links above.
--
Sean Korb [14]spkorb at spkorb.org [15]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.A They can only give you answers." -P. Picasso
References
1. mailto:jeffcobb1 at me.com
2. tel:225-343-7525
3. tel:225-907-4514
4. http://www.LiveOakConcours.org/
5. mailto:fordmachinist at gmail.com
6. http://www.tmeyerinc.com/
7. mailto:guido_detomaso at prodigy.net
8. mailto:DeTomaso at poca.com
9. http://poca.com/mailman/listinfo/detomaso_poca.com
10. mailto:DeTomaso at poca.com
11. http://poca.com/mailman/listinfo/detomaso_poca.com
12. mailto:DeTomaso at poca.com
13. http://poca.com/mailman/listinfo/detomaso_poca.com
14. mailto:spkorb at spkorb.org
15. http://www.spkorb.org/
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