Twisted Merlin Plus Allison Adventures

[GregP]

Some time back I mentioned that it was found that the Merlin out of Dago Red was twisted due to power output levels. Many people chimed in and doubted it, somewhat understandably so.

Well, we measured it and it is defintely twisted. Nothing taht can't be fixed by decking it, but the left front of the left cylinder bank is 0.007" lower than the left rear, and the right front is about that much higher than the right rear.

Again, I want to emphasize, it can be returned to straight with some effort. The person doing the "fixing" knows what he is doing.

Aluminum is Aluminum, and it does apparently bend, cast or not.

While I was there, I got to disassemble the front gearcarse on an Allison. Very interesting and a wake up call for modern engine builders. The front two seams on an Allison are metal to metal joints, and they don't leak a drop until you crack the cases apart.

Then we took the two cylinder banks and cleaned up the bores on a boring machine. Well ... ONE bank cleaned up. The second one will need a few cylinder liners replaced. But everything else looked good (measured within spec). Went through $100 worth of honing stones to get the first bank into good shape. I am beginning to see why these things cost so much!

[Sid447]

That's something!

So if the decks were seven thou out, how much was it actually twisting when at full power for it to be that much out when "static."
Makes you wonder! :)

I remember reading a book by David Vizard who reckoned production Chevy small blocks (cast iron as you know) twisted around 3/16" when making more than production power levels and that was the reason they brought out the much heavier and thicker cylinder walled Bowtie racing blocks. Also they poured "concrete" into the blocks up to the freeze plugs level, to help stop the twisting.

[GregP]

Good question about the twist while running!

To fix, you deck the Merlin block flat, bolt on the cylinder head (which is VERY stiff), and then mate up the center bearings and rebore them straight. It's a lot of trouble, but not as expensive as a new block.

As for high-horsepower V-8's, they DO flex. A Top Fuel drag racer making 7,000 HP from an 800 cubic-inch engine (13 liters) experiences the engine block "breathing" it "puffs up" and "relaxes" as it pressurizes and depressruizes. It's almost scary to watch it in slow motion!

My bet is that an Aluminum block engine designed for 1,700 HP flexes quite a bit when making 3,800 HP!

In any case, the engine is salvageable, but now we KNOW it takes a LOT of stress. We knew that intrinsically before, but enough to twist the block makes you think, huh?

[Sid447]

Hi GregP,

There was a very good article on the supercoolprops.com site here

http://www.supercoolprops.com/articles.php (page down to the articles entitled "Reno For Gearheads")......

In one of those two articles it talks about the racing merlins needing braces to help keep the supercharger on as with the boost levels being used the whole casing wants to pull off from the back of the engine.

Nice write-ups but are a few years old now.

Regards, SS. :)