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1968 Pontiac Firebird Engine Assembly Mistake

Now I am a very picky person when it comes to my car build. You can tell that from my other documentation
pages on this site. I double-check and research ( I thought) just about everything. I built this engine
very carefully and tried to make sure I did not make any mistakes. But even with all that effort all it takes is a moment
of thinking you know what you are doing, without checking with someone who KNOWS what they are doing first....

After no more than 500 miles of driving and enjoying my new engine, I started to hear a knocking noise. I thought
it was something minor at first, and checked all over for something loose or touching something..but soon enough
I figured out it was happening only when the engine was under load and it was getting worse fast. I had several friends
listen to it at a cruise night and from the looks on their faces, I knew I was in trouble. So with the help of a good friend Dion,
we pulled the engine and this is the sight that greeted me when I lowered the pan after getting it on the engine stand..

yep those are chunks of bearing in the oil pan. and yes the oil is green. It is Brad Penn High performance
"Green Oil" ( nothing to good for my baby..:-)

if that was the bottom of a Klondike gold pan, it would be a great site, but in the bottom of your oil pan..
nah, not so hot.

Knowing I had major problems I removed the intake, valley pan, timing cover, and heads.
flipped it over and wiggled connecting rods, which should not wiggle. and sure enough, Number 7
or what I thought was number 7.... moved. (read on)

so here is the story.

I do not have a lot of previous engine building experience but in my previous 2 attempts, one chev and one ford,
I remembered that I needed to make sure I identified the rods as they are removed so they can be put back
in the same spots. As I tore apart the original 455 engine, I stamped the cap and rod from 1 to 8 starting
at the first rod in the line and heading to the back. (some of you old -timers may know where this is going already...)

the rest of you have to keep reading to figure it out.

My machine shop checked out my crank and found it's journals still within tolerances so a good
polishing was all that was needed. They also checked and did a block crank main hone.
I also sprung for a full rotating assembly balancing job.
here it is below after getting ready to re-assemble. I used ARP studs to replace the original main bolts.

rear main seal in and the caps all torqued down.

I also had the machine shop check all my rods and press the pins on the new pistons,
and install new ARP rod bolts

and here is where the wheels fell off. I replaced the rods in the same order I took them out
from 1 to 8 from the most forward cylinder to the rear... Not realizing that the Machine shop installed
the pistons on the rods using the proper technique of numbering the rods/pistons by the firing order
of the chambers.. And on pontiacs the farthest forward cylinder is actually the number 2 in the firing order.

Number one is the second cylinder in order of farthest from the front of the engine.

Here is a diagram I found on the internet of the con rod/crank throw assembly .

1.Split in bushing 7.Connecting rod bearing-lower
2.Connecting rod 8.Washer
3.Crankshaft 9.Connecting rod bearing cap
4.Crankshaft fillet 10. Large chamfer side
5.Bearing 11. Small chamfer side
6.Connecting rod bearing-upper 12. Bushing

Crankshafts have a fillet on them where the journal meets the crank throw (no 4 above).
Connecting rods have a large chamfer on one side that corresponds with the fillet on the
crank throws.(no 10) And the connecting rod bearing shell actually sits slightly off -center
so it does not rub against the fillet on the crank as well... I installed every one of my
connecting rods in the wrong position. They should have been 2, 1, 4, 3, 6, 5, 8, 7
according to how I had them stamped. I did not know this and I also should have noticed
the chamfer on the rods going the wrong direction as I installed each one....

I found this picture below that actually clearly shows my screw-up. You can see the chamfer around
the rod beside the bearing shell as it is about to be installed up against the other connecting rod
INSTEAD of up against the fillet between the journal and the crank throw where it should be.
I labeled it for your viewing pleasure.

and here it is snuggling up to it's new home, the WRONG position that is....

here they are all nicely installed numbered from 1 to 8 in a row.... arrgh.

My machinist noticed the abnormal wear on the rod bearings that were not destroyed right away
and asked me which order I had put them in. The failure happened no doubt due to the stresses
placed on the bearing shells by the fillets on the cranks. One eventually pushed over, spun and wore
out quickly. I now am faced with either turning the crank for $250 or buying an aftermarket one for
$290. I am going to go with the new aftermarket eagle cast crank. I briefly toyed with a new scat
forged unit but they just come in 3" mains for 400 blocks. and I will not be subjecting the engine
to full blown racing. I am also going to get a new set of forged rods. I have to replace all the
bearings in the engine as well including cam tunnel. new lifters also. I think I am going to look at a
few oiling upgrades as well.

Kind of a costly blunder but $#!% happens right?



I hope by posting this and you reading it , you or any of your friends that are building a pontiac
powerplant will not make the same mistake. I do not regret building the engine myself as it was
great experience and I enjoyed every minute of it. so much so, that I am going to do it again...

A member on the First gen site (Kyle) took some great pics of the correct installation of the
connecting rods and shells and posted them to the first gen site. Click this link to go directly
to those pics. Thanks Kyle.


Main Block
Cylinder Heads
Intake Manifold
Rope Seal Tech Bulletin
Rotating Assy
Valve train
Final Assembly


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