Crank Question - Team Camaro Tech
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post #1 of 24 (permalink) Old Apr 9th, 02, 03:35 PM Thread Starter
 
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I am having my engine put back together and the mechanic told me the crank was not balanced properly and did not fit (tight). He said the rod journals were 29.5/1000's and they needed to be 30/1000's. I am probably not saying this stuff right but it was something like that. They need to be ground very slightly or sometihng.

I then had my son bring the crank to the machinist since I work in Houston during the week and cant do this and he told my son that it was machined properly and that its within tolerance. The mechanic of course says there is not a tolerance here and the crank does not fit or is too tight. The machinist says get a new mechanic. Maybe I need both to be replaced but would like to understand what the hell is right or wrong so I can sound intelligent when I get rid of the one who is wrong, unless both are right???

Any advice would be appreciated.

Ken
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post #2 of 24 (permalink) Old Apr 9th, 02, 04:01 PM
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If the crank's out of spec, as in worn, it should have too much clearance and be too loose...but I don't understand where all this tightness your mechanic talks about is coming from...looks like the crank would go back in the block regardless of rod journal condition. Ask your mechanic if he or she actually measured the journals as well as the inside diameters of the main caps and rod caps after torqued to spec with the bearings in place. The crank could be bent which would prevent it from rotating easily, but that doesn't sound like the tightness your mechanic was running into. Maybe the bearings are undersize and don't jive with the crank? Are you using a crank from another motor? Sounds strange.

[This message has been edited by Glenn1018 (edited 04-09-2002).]

[This message has been edited by Glenn1018 (edited 04-09-2002).]
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post #3 of 24 (permalink) Old Apr 9th, 02, 04:18 PM
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Ken,
I dont know how a "mechanic" could determine if the crankshaft was not balanced properly. The only way to do this is on a crankshaft balancer with bobweights clamped to the crankshaft.
As far as the size range on the crank journals, there is a range of allowable sizes. Most crankshaft grinders try to grind the crankshaft in the middle of the range. This will generally give you ideal clearances if everything else in the motor is correct. Ask your "mechanic" exactly what size the crankshaft is and post his answer, I would like to see it. Like Glenn said...has he actually measured the clearances ? If so, how ? Ask him these questions and see what type of answers you get. If he has not actually measured the clearances, then he does not need to be assembling an engine for you in my opinion.
I am a bit biased, and probably leaning towards the machine shop's side, but there are many things that can make a crankshaft tight, your "engine builder" should know how to check these things. He should be able to explain to you exactly how he checked them and what his results were. I am not going to give any clues, he should be able to give you the answers.
If you don't trust the machine shop as to the size of the crank, get a second opinion. Mistakes can happen. Most machine shops will probably check a crank for you no charge, I know I do most of the time.
Let us know what you find out,

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post #4 of 24 (permalink) Old Apr 9th, 02, 04:28 PM Thread Starter
 
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I will get the info in the morning and post. I do know the mechanic had the crank measured at a machine shop in Briston Pa and that is where he did get the info from. I will post tomorrow and appreciate the guidance.

Ken
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post #5 of 24 (permalink) Old Apr 10th, 02, 04:13 AM
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I,m not sure around your neck of the woods but around here the machine shop that does the machine work usally puts the mill together and guarentees the work, sounds like your mechanic is not sure of himself and leaving himself a OUT if the motor screws up.
I would be pulling the entire engine from the shop and let the machine shop assemble, The mechanic can then install the motor in the car for you. I would want to close by when it gets time for fire up, the mechanic should know what the oil pressure will be, he will do this manually befor the distributor goes in, also he should have the timming so close to spec, if not by the time he screws around setting the timing, the cam could suffer damage, the engine should run 1500 -2000 rpm at intial start up for several minutes.

How about it Bill K. do you agree?
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post #6 of 24 (permalink) Old Apr 10th, 02, 07:28 AM
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Rob,
I agree with the installation process, but as far as the machine shop assembling the motor....you would be surprised at how many machine shops do not build motors. I do very few myself anymore....I am too busy with machine work and most customers do not want to pay the price to have an engine properly assembled. I know of several shops in my area that just plain will not assemble engines...period.

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post #7 of 24 (permalink) Old Apr 10th, 02, 01:39 PM Thread Starter
 
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Bill/Glenn.

The measurements as told to us by the one machinist:

Crank Shaft= 29,000 Actual= 29,000
Bearings= 30,000 Actual= 30,000
Main Journal= 29,500 Actual= 30,000

Clearances were too tight I was told. It did not spin properly or something.
Measurements provided by the mechanics machinist.

Sorry if this is not good info as I am lost in space on this stuff. But hey I do know how to manufacture apparel.

Thanks and I hope this does help.

Ken
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post #8 of 24 (permalink) Old Apr 10th, 02, 01:40 PM Thread Starter
 
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Ken Miele:
Bill/Glenn.

The measurements as told to us by the one machinist:

Crank Shaft= 29,000 Actual= 29,000
Bearings= 30,000 Actual= 30,000
Main Journal= 29,500 Actual= 30,000

Clearances were too tight I was told. It did not spin properly or something.
Actual measurements provided by the mechanics machinist.

Sorry if this is not good info as I am lost in space on this stuff. But hey I do know how to manufacture apparel.

Thanks and I hope this does help.

Ken
<HR></BLOCKQUOTE>

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post #9 of 24 (permalink) Old Apr 10th, 02, 02:22 PM
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Ken, what size motor is it? I'm lost as far as those figures go, and I'm not familiar with the "Actual" size the machinist was talking about. I think a rod journal (aka crankpin) on a large journal small-block crank should be between 2.0985-2.1000 to be used with std size bearings. I mention that because it sounds sort of like the "29,000" (twenty nine thousand/two and 900 ten thousandths)your machinist cited. Maybe those figures will mean something to someone else who can help you.

[This message has been edited by Glenn1018 (edited 04-10-2002).]
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post #10 of 24 (permalink) Old Apr 10th, 02, 03:01 PM
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Ken,
Like Glenn said, the measurements you are stating make no sense to me, and I run an automotive machine shop ! If this is a 350 motor, the crank should measure between 2.4484 and 2.4493 on the mains and 2.099 to 2.100 on the rods. You would subtract .010" from those measurements if the crank was ground "10" under etc. I think someone is trying to baffle you with "male cow manure", or not really communicating properly. Ask the guy to put the size of the crank in writing and let us know what it is. Where abouts are you located in NJ ?

------------------
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Owner
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Waldorf Md
1971 Chevelle "Heavy Chevy" original owner
1973 Z-28 ..one family car...Brother bought it new in 73
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post #11 of 24 (permalink) Old Apr 10th, 02, 03:07 PM
 
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As a machinist by trade,let's talk about
these #'s.I'm going to assume 29,000 means
29/1000, or .029" and so on.
Maybe what he's telling you is that the crank
has been re-ground undersize .029"-.030" on
the journals.Or,the crank is standard and the
bearings are intended for a crank that's ground,meaning the bearings would be too thick for proper fit.Let us know when you clear this up.

------------------
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post #12 of 24 (permalink) Old Apr 10th, 02, 03:52 PM
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Been watching this thread for awhile and got to thinking about the information. At first it didn't seem to make any sense - but then I wondered if he isn't giving the clearances of the crank and rods to Ken in thousandths (0.0029?).
If it is the 'clearances' he's ckecking, by Plastigauge or some other method, they would seem to be a little on the loose side - not tight.
I would generally like to see a reading on the plastigauge of around 0.0025 or so for a 350.
You might want to ask if these are the readings he is giving you and recheck the spec.s he is shooting for on your engine.
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post #13 of 24 (permalink) Old Apr 10th, 02, 04:19 PM
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Just as an afterthought, who decided on what size bearings to get and why? Was the crank turned after the bearings were already bought?
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post #14 of 24 (permalink) Old Apr 11th, 02, 04:46 AM Thread Starter
 
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Hello all and thanks for your help.

Ending 350 9:5.1 bored over 30.

Numbers provided were in thousandths.

I am located in Central Jersey near Trenton.

I will get the crank size in writing.

Yes the crank was reground to .029 on the rod and main journal while the bearings were .030. This is where the mechanic is saying its too tight and does not turn or something.

Will try to secure more infomation soon.

Ken


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post #15 of 24 (permalink) Old Apr 12th, 02, 04:41 PM
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Ken,
Did you get any more info on the motor ?? Just curious.

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1971 Chevelle "Heavy Chevy" original owner
1973 Z-28 ..one family car...Brother bought it new in 73
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