Zigroid

I used a bore gauge on my newly machined 4 bolt main LT1 block. I took 3 measurements at bottom, middle, and top of the bore on 2 different axis for each cylinder. I set the bore gauge as close to 4 as possible. these numbers are not exact but are used as a reference to get the difference.

#1
bottom: 4.00025", 4.0006",
.00035" out of round
middle: 4.0003", 4.001",
.0007" out of round
top: 4.0006", 4.0011",
.0005" out of round
total: .00085" (difference between highest and lowest regardless of top, middle, or bottom)

#2
bottom: 3.9999, 3.9998"
.0001"
middle: 3.9999, 4.0002
.0003"
top: 4.0003, 4.0007
.0004"
total: .0008"

#3
bottom: 3.9995, 4.0006
.0011"
middle: 3.9996, 4.0011
.0015"
top: 4.0002, 4.0011
.0008"
total: .0016"

#4
bottom: 3.9989, 3.9999
.001"
middle: 3.9989, 4.0005
.0016"
top: 3.9999, 4.0006
.0007"
total: .0017"

#5
bottom: 3.9996, 4.0008
.0012"
middle: 3.9997, 4.0011
.0014"
top: 4.0008, 4.0014
.0006"
total: .0018"

#6
bottom: 3.9992, 4.0000
.0009"
middle: 3.9999, 4.0006
.0007"
top: 4.0000, 4.0008
.0008"
total: .0016"

#7
bottom: 3.9994, 4.0002
.0008"
middle: 3.9996, 4.0006
.0010"
top: 4.0004, 4.0009
.0005"
total: .0015"

#8
bottom: 3.9996, 4.0003
.0007"
middle: 3.9988, 4.0006
.0018"
top: 4.0000, 4.0008
.0008"
total: .0020"

as per the how to rebuild LT1/LT4 engines book
out of round production limit is .001"
service is .002"

taper production is .001", .0005" on thrust side
service is .001"

Is this block unacceptable to use in its current form?

Joe Urban

In the CNC machine shop where I work we use bore gages all the time. You were quoting some half-tenths, so I'm guessing you might be using a very expensive electronic gage, or that you have lots of experience with dial bore gaging. Even with electronic gages operator technique plays a role.

No offense, but were the bores finished with a deck plate or "torque plate" installed? Were the mains installed and torqued to spec also? Were the bores the last thing to be machined? If they were, did you measure the bores with the same plate and gasket and bolts or studs installed at the same torques and with the same torque on the mains? If not, I would expect the bores not to be perfectly round when measured in the unrestrained state.

I found that to be true in CNC machining of any parts. The chucking or clamping of the part into the machine can distort the part enough that a hole or bore that is round to less than .0001 when chucked may go out of round many times more than that when unclamped. We are talking tenths here which many people cannot even visualize. .0008 is only 2/100 of one percent of a 4 inch bore.

Again no offense, but did you discuss this situation with the people who did the work? I always appreciate it when QC or a customer discusses my machining with me before rejecting the part. I'm lucky because our customers don't go online with problems they think they find in our work. In my lurking on this type of message board I found many cases where the customer goes public before contacting the shop which did the work. Sadly sometimes there was no actual problem but you don't find that out until many pages into a thread.

I hope this works out for you.


Joe Urban

ssclone

from my knowledge, and ill let Pete answer fully.
he took the block to another machine shop to get a second answer of the work that was done, and they were the ones who told him the problems with the motor.
i also questioned the tq plate honing.


i hope he is able to use the block. i would love to see the car back on the road, just as much as he would. it would also be a shame to **** all that money away.

aaron

Zigroid

I took the block to a separate machine shop, he is the one who brought it to my attention and I double checked it. both our findings match. I know there was no CNC machinework as the shop does not have one. I can't say about the deck plate, I doubt it was used though.

I didnt mention any names in my post, just my findings.