'72 Engine Problems

In the quest for more power and quicker times, I bought (in early 2000) a new cam, carb, converter (used), and main studs (to help the motor withstand 6500 rpm shifts).

The Damage:
When I tore my engine down to install the cam, main studs, etc., I decided as long as I was that far into it, I should check my main bearings (since the main bolts were off anyway). The bearings were horrible. The outer two (#1 and #5) were tolerable, but the middle three were worn down to the copper layer after only 17,000 miles.
Here's one of the mains:

You can see where it's worn to the copper, right? Two others were just as bad. I had no idea what to do. I figured I needed to replace the bearings, and to do that, the crank needed to come out, and to do that, the rods and pistons needed to come out! What a drag. So I look at the rod bearings and #1-#4 are poor, but not horrible, but #5-#8 are really bad!

The Cause:
Soooo, what could be the problem? I asked around and got several theories.

The Solution:
I had a spare crank, so I brought that and my block into the machine shop to eliminate as many of these possiblities as I could.

They turned the crank (eliminating a bent/warped crank as a possible cause of future problems).

They decked the block (giving a higher compression ratio but also better quench, and hopefully better combustion).

They align-honed the mains ensuring the crank would stay put.

I also purchased a 7-quart Moroso oil pan, pump pickup, scraper, windage tray, pan baffle, Melling M55A oil pump, and an oil temp gauge, so that should eliminate any worries about the oiling system.

I installed a bigger Comp XE274 cam, so that should bleed off a little cylinder pressure.

Also, as mentioned earlier, I'm putting oxygen sensors in my headers to monitor the air/fuel ratio as I drive.

The only unaddressed possible cause on my list is the balance of the rotating assembly, but since I only need this motor for 2-3 years and I really don't think that was the cause anyway (and it's expensive), I decided to skip the balancing this time.

Here are pics of the crank in the block and my new oil pan.

More Problems:
I found out my stock replacement harmonic balancer I had purchased 2 years earlier had cracked, so here's the 6-3/4" StreetDampr I got from Summit. Beautiful, ain't it? It was a shame to paint it. I wanted the 8" Fluidampr, but that was twice the price.

Finally:
Here's the motor on the stand:

Installation:
I finally got the motor installed on May 23rd, 2000, all hooked up on the 24th, and fired it up on the 25th for the cam break-in. We had a few minor problems, but eventually it all worked out. It ran great during the break-in, no leaks or anything, just burned lots of the POR-15 off the headers. No surprise. It's got a nice, lopey idle and will run at 700 rpm, lower than I thought. I love it!

Results:
The motor gave me 13.3s @ 103.2 mph in the quarter. I think it's strong enough for very low 13s but I need a looser converter, the Holeshot 2400 is just too tight to let me get into the powerband.

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Copyright © 2009 Bruce Johnson and Craig Watson