ENGINE BUILDERS,, How is this possible, and what would you recommend
10-05-2010, 09:52 PM
#1
ENGINE BUILDERS,, How is this possible, and what would you recommend I am putting my 383 back together and my question is this, I had a buddy of mine who is a machinist for over 20 years, measure my crank main and rod journals, along with MY main bearings installed (which were torqued to spec, and my rod bearings installed (also torqued to spec). Using his measurements My clearances are way to big,
EX.
my crank main journal measuring at 2.5590
and my main bearing measuring at 2.5626 leavin clearance at .0036 TOO big my GM book says max is .0021.
HERE IS THE DILEMA I put the crank in to check the clearances with plastigagt also to double check. torqued crank in to spec and the clearances are within spec.
EX. no.1 main .0015 SO how is it possible to have the two different measurements? What gives, Which way would you recommend to follow as the best and most accurate? Its the same deal on the rods, I am certain that he measured correctly because his measurement of 2.5590 is exactly what is in My GM service manual.. Please Give me your EXPERIENCED advice. Thank you
EX.
my crank main journal measuring at 2.5590
and my main bearing measuring at 2.5626 leavin clearance at .0036 TOO big my GM book says max is .0021.
HERE IS THE DILEMA I put the crank in to check the clearances with plastigagt also to double check. torqued crank in to spec and the clearances are within spec.
EX. no.1 main .0015 SO how is it possible to have the two different measurements? What gives, Which way would you recommend to follow as the best and most accurate? Its the same deal on the rods, I am certain that he measured correctly because his measurement of 2.5590 is exactly what is in My GM service manual.. Please Give me your EXPERIENCED advice. Thank you
10-05-2010, 10:00 PM
#2
Staging Lane
Join Date: Jul 2010
Location: Maine
Posts: 62
Likes: 0
Received 0 Likes
on
0 Posts
One measurement was done with a micrometer, and one was done with plastigage, is that what you're saying? It could be a few different things. Even oil residue can change the reading. I'm not an experienced engine builder, but I know enough that this is interesting.
10-05-2010, 10:15 PM
#3
Yes, The measuerments were made with a set of micrometers on the crankshaft, and the bearing I.D. measurements were done with internal bore mikes. Those were the measurements that are way big..
The ones that are OK were done with Plastigage. BTW the crank and bearings were clean no oil or residue.
The ones that are OK were done with Plastigage. BTW the crank and bearings were clean no oil or residue.
10-05-2010, 10:17 PM
#4
Measure in a few spots make sure the crank is not out of round. You might have to get different bearings to accommodate if it is too big. You need to be in between .0015 and .0020. I am assuming the is an aluminum block correct? Number 3 can be a bit looser than the rest which is the thrust bearing but the others should be within that range.
10-05-2010, 10:27 PM
#6
Staging Lane
Join Date: Jul 2010
Location: Maine
Posts: 62
Likes: 0
Received 0 Likes
on
0 Posts
Yeah, but the problem is he is not even getting consistent readings. You may be not measuring in enough places as was stated, and I also agree that you need to check for taper and out-of-round. If it is tapered or out-of-round, and you measure in a "narrow" spot, and he measures in a spot with a "wide" OD, this would be the result. Does that make sense? In how many places was each journal measured?
Edit: Oh, ok, I took a minute to write my post. How many places? I say keep measuring.
Edit: Oh, ok, I took a minute to write my post. How many places? I say keep measuring.
10-05-2010, 10:56 PM
#7
Well this is what i would do before i started spending a lot of money. Sometimes when you drop tools like micrometers and such they sometimes don't read like they should, so if you could get something to verify that its accurate and if it is your going to have to get bearings that will close that gap to get you into the desirable range. I would not run the motor that loose either your just asking for trouble and will trash the motor very quickly. So get it right the first time that way you can enjoy it.
Trending Topics
10-06-2010, 07:04 AM
#8
0.0020-0.0025" is best, with 0.0030 being tolerable with an HV oil pump.
The micrometers always come with a standard, so you can check them if they get dropped. The mic should read 0 on a 2" standard.
People tend to have different feel for mics, and this tends to have more error than plastigage.
I've assembled more hundreds of stock-rebuild engines than I can count, and I've never once been bitten from believing the plastigage over the mics. Not one come-back, and not one complaint.
Just be sure the plastigage isn't stale. When it becomes brittle, it doesn't crush right.
The micrometers always come with a standard, so you can check them if they get dropped. The mic should read 0 on a 2" standard.
People tend to have different feel for mics, and this tends to have more error than plastigage.
I've assembled more hundreds of stock-rebuild engines than I can count, and I've never once been bitten from believing the plastigage over the mics. Not one come-back, and not one complaint.
Just be sure the plastigage isn't stale. When it becomes brittle, it doesn't crush right.
10-06-2010, 09:51 AM
#9
ok, the mikes are not the problem, everything is the mitotoyou (not sure how to spell the brand) brand. the bore mikes have three legs that expand out and then when tightened a spring clicks so no feel needed. they are scaled to .0002. this is not a measuring problem. the guy measuring has been a machinist for over 20 years and these are his tools. the measurements are taken in various locations and are consistant to within .0001. and the clearances end up being over .003 on every main. However when done with the plastigage everything is within spec. If the crank was out of round or tapered then i would have different readings, not to mention i had the crank checked by a shop when bouhgt. I called my local builder and asked him about this and he said they always go by measurements, and that PLASTIGAGE WAS NOTHING BUT A GUESS. but i know people have been using it forever.
10-06-2010, 09:59 AM
#10
The big name engine builders that everyone has read about in Hot Rod, they have to say believe the mics over the plastigage, for several reasons. But most volume rebuilders, who mostly do stock rebuilds, have wildly varying approaches. I've worked for several, and visited many others. In the early days of plastigage, the consistency was poor. But their quality control has progressed along with their newer manufacturing equipment, and even the formulas have been revised.
That early inconsistency was good reason for builders to shun it. But the reasons that were very valid back then are only vague memories now.
Even the best old builders will feel the mic differently if they suddenly hear the telephone , for example. The plastigage doesn't respond at all to the phone.
These days, it's no different than Coke versus Pepsi: personal preference. You'll get vehement arguments both ways, but in the end, it's your money, so it's on you to decide.
That early inconsistency was good reason for builders to shun it. But the reasons that were very valid back then are only vague memories now.
Even the best old builders will feel the mic differently if they suddenly hear the telephone , for example. The plastigage doesn't respond at all to the phone.
These days, it's no different than Coke versus Pepsi: personal preference. You'll get vehement arguments both ways, but in the end, it's your money, so it's on you to decide.
10-07-2010, 08:25 PM
#12
TOOK EVERYTHING TO THE MACHINE SHOP TO HAVE IT ALL CHECKED,, after taking measurements using his micrometers and then setting his dial bore indicator to it, main clearances and rods were in spec, all on the big side but still within range,, So the problem is using two different micrometers, Have to use the same one, NOW WE KNOW.
10-07-2010, 09:42 PM
#14
On The Tree
iTrader: (5)
Join Date: May 2004
Location: Iowa
Posts: 109
Likes: 0
Received 0 Likes
on
0 Posts
TOOK EVERYTHING TO THE MACHINE SHOP TO HAVE IT ALL CHECKED,, after taking measurements using his micrometers and then setting his dial bore indicator to it, main clearances and rods were in spec, all on the big side but still within range,, So the problem is using two different micrometers, Have to use the same one, NOW WE KNOW.
A long time engine builder I know has said he will try several different bearings all of which are suppose to be the same size, part # and brand and will get different readings for each one
. What he will do is swap them in until he finds the specs he is looking for. Kind of expensive but he has dozens and dozens of bearing on the shelves and continues to swap them until he is happy. At first I thought he was a little crazy until I seen this in practice.GL with the build.
10-07-2010, 11:25 PM
#15
TOOK EVERYTHING TO THE MACHINE SHOP TO HAVE IT ALL CHECKED,, after taking measurements using his micrometers and then setting his dial bore indicator to it, main clearances and rods were in spec, all on the big side but still within range,, So the problem is using two different micrometers, Have to use the same one, NOW WE KNOW.
I've just recently been building an LS6 for a friend and with STD ACL main bearings the clearance was .003-.0032". Since the housing bores were on the high side of the spec (2.7515"), I align honed the block to the low (2.7509") and that alone got the bearing clearance to a more ideal .0024-.0026".
I'm just saying, don't assume your measurements are correct because they make you happy. You may have gotten the measurements right the first time.
