1quickTransAm

iTrader: (4)

I am building my first engine (LT1 383) and picked up my block and rotating assembly from the machine shop (well respected performance shop with a lot of experience). They speced the bearings and I have the measured clearance of each individual bearing and not just a general number/range.

Considering that, do you think I should still plastigage them to double check? I had originally planned to, but in thinking about it their measuring tools were clearly superior and they know what they're doing.

Thoughts?

hrcslam

Plastiguage has nothing on the tools they use. What were the specs?

If you do want to double check then use bore gauges and a micrometer that reads to the 10 thousands of an inch.

1quickTransAm

iTrader: (4)

Front two mains were .0021 and back two were .0025. Rods were all between .0022 and .0025.

ACE1252

IMHO...

Bore gauges and micrometers are what is best(with the proper resolution), but plastigauge is better than nothing to do a double check(....and as with a bore gauge, you must use it properly). After all, we are all human and we do make mistakes from time to time. Better to double check now than find out later with engine trouble.

For what it's worth, the GM factory F-body manual(1996) specifically states(page 6A3B-24) to use plastigauge to check the main/rod bearing clearances. It does not mention anything about using a bore gauge. They didn't call it plastigauge though, they called it "gaging plastic". So...for them not to even mention bore gauge tells me that there is validity in the measurement method.

I used plastigauge to select the new bearing shells when I replaced the rod and main bearings in my LT1. I must have done something right as I still have 25-30psi at idle 3+ years later(and many, many track passes). I also had no trouble with my crank being out of round/spec either(I verified that with a micrometer).

Plastigauge is something I would not expect a performance engine shop to use as the defacto measurement standard for checking clearances. However, it does have it's place as being useful for those of us who do not build engines on a day to day basis.

ACE1252

Just for reference, here are a few threads on what I went through a few years ago when working on the bearing replacement for my LT1...cam, rod, and mains(and why I replaced them).

http://www.camaroz28.com/forums/lt1-...ctures-713070/
http://www.camaroz28.com/forums/lt1-...arings-746672/
http://www.camaroz28.com/forums/lt1-...arings-749300/

myltwon

iTrader: (1)

I think this poster means tenths of an inch (0.0001") not to be confused with 10 thousands of an inch (0.010"). digital mics will be preferred, a standard analog can be a little bit up to interpretation when it comes to reading in such fine measurements in regards to a mic.

lt1-xjs

If you are assembling the motor I would check and compare it to their measurements. And I would use plastigage at the very least. Just for the piece of mind.

hrcslam

I meant to the ten thousands of an inch. Like 0.000X". A tenth of an inch is 0.X". What you typed was 10 thousands inch or 0.010", also known a hundredths of an inch. Versus to the thousandth of an inch which is 0.00X". If someone says 25 ten thousandths inch they are saying 0.0025". If they say 25 thousandths inch they are saying 0.025". Make sense? Bearings should have clearances to the 10 thousandths of an inch.

hrcslam

I agree with everything you said here. The Plastiguage is a very useful tool. But I certainly wouldn't use the plastigage as a correction to the machine shop and their much more accurate tools.

I used both the plastigage and bore Guage with a Mic on my build. I went with the bore guages for my official measurements. For a stock rebuild, I wouldn't bother with bore guages.

Shownomercy

iTrader: (1)

No offense to OP, but if you have never used a bore mic or regular mic, learning on your engine prob isn't the best choice.

In this case, plastigage it for peace of mind and then call it a day.

Puck

iTrader: (17)

If you don't trust your machine shop to set up your clearances correctly then you shouldn't be using that machine shop.

SS RRR

iTrader: (2)

Exactomundo. Machine shops should be chosen or avoided on their reputation. If you are going to take caps off and measure you might as well build the thing yourself.
OP, if you are on the east coast near Maryland I can recommend a shop that has done many LTx/LSx platforms.

lt1-xjs

The motor is not assembled according to his post.

SS RRR

iTrader: (2)

Whoopsie.



If the caps are off go ahead and check them anyway if it will give you peace of mind.

WE TODD DID

iTrader: (2)

Never trust anyone's word. They can make a mistake, could have set-up their dial bore gauge incorrectly, etc... In the end, if you are the assembler, you are responsible for everything being right.

ringmaster72

iTrader: (8)

SS RRR, what is the machine shop in the Maryland area you are referring to? I am in process of getting a 383 LT1 together.

SS RRR

iTrader: (2)

Burtonsville Performance Machine

https://www.facebook.com/pages/Burto...54349891267211

myltwon

iTrader: (1)

Tenths of thousandths of an inch, I forgot to include the "of thousands" portion. In machining a tenth is short hand for this, almost never will anyone refer to a tenth as 0.100" unless they've not been in the environment long, and almost as unlikely will anyone call it by its longer name. I've yet to hear anyone refer to 0.0001" as 10 thousandths of an inch. If someone called out a true position of 10 thousandths on a hole position, you'd think you had a pretty wide open geometric tolerance, not butt pucker tight 1 tenth. You might be thinking of 1/10 of a thousandths of an inch (aka 1 tenth to a machinist/engineer/drafter).

Since this topic refers to automotive machine shops and machinist inspection tools, machine shop nomenclature is what takes presidence.

Shownomercy

iTrader: (1)

geo position of 1 tenth? lulz at that bill... machinist may scream bloody murder too.

With a positional tolerance of a tenth or two, you would have a damn perfect hole diameter as well, .000001 status lol

hrcslam

Point taken. We refer to these measurements differently in aviation then. 0.0001" tolerance would be referred to the ten thousands of an inch since it's called 1 ten thousandths of an inch. Bearing clearances between 0.0035" and 0.0025" would require a tool tolerance to the ten thousandths of an inch.