Need help identifying 289 components...

[Dangerous Doug]

Just bought a 289 for rebuiding. It's a 1965 date coded block, so I'm good for CA emissions when I go to register.

I'm trying to id the pistons to determine if they need replacing. They are dished with a protruding wedge, and have the marking "L2249N". Can anyone id these pistons? I know they are obsolete TRW, but I'm trying to determine what compression ratio they will yield with stock or aftermarket heads (GT-40 heads).

Also, the oil pump has a tag on it that reads "68HV". Is this a high-volume oil pump?

The fun begins!

[blykins]

68HV is a Melling part number. It is a high volume pump.

[Dangerous Doug]

Blykins: Thanks for the help on the oil pump.

Anyone have info on the pistons? How do I determine the compression ratio for these pistons given a standard chamber head?

Dangerous Doug

[Dangerous Doug]

This is all I've found on google:

"78 Mustang II King Cobra with a 302 (10.5:1 comp. (pistons are actually the L2249N 12:1 pop ups but I put a set of shXXy late 70s 351w heads on it), high lift cam, headers, Holley 600vs, "

This would lead me to believe that the pistons are 12:1, but with larger chamber heads can be brought down to 10.5:1.

Any comments?

DD

[blykins]

It's not easy, but you could estimate the dish or dome in the pistons in a volumetric measurement....

With that info and your combustion chamber volume, I could give you a very good estimate.

[Dangerous Doug]

I'm picturing using modeling clay, water, and a graduated cylinder. Is that what you had in mind?

I haven't purchased heads yet (though, a stock pair came with the engine) so I do have some flexiblity in the chamber size, restricted, of course, by what is readily available on the market.

What's the calculation? I figure the ratio of cylindrical volumes, V1 being the chamber volume with the piston at the bottom of the chamber, and V2 being the chamber volume with the piston at the top of it's stroke? (V1-V2)/V2?

[Fox]

This might help...


Compression Calculator

Here is a listing for their other calculators.

Car Math Calculators

Good luck...

-John

[blykins]

The ratio would be the volume at bottom dead center divided by the volume at top dead center.

I would just use some modeling clay to fill in the dish....then see what volume that clay displaces.

If you calculate by hand, be sure to figure in the head gasket thickness and diameter, and deck height.

[Dangerous Doug]

How do I measure deck height? Relative to what?

Novice questions, I know, but that's how you learn...

[blykins]

Yep. That's how you learn.

There's actually two types of deck heights when talking about engines.

The first one is the distance from the crankshaft centerline to the cylinder head deck. For instance, it's 9.503" for a 351W. It's 10.17" for an FE.

The second deck height is the distance from the piston at TDC to the cylinder head deck.

For instance, if your piston sets .015" (distance from the very top of the piston to the head deck) down in the hole at TDC, you'd have a lower compression ratio than if the piston sets flush with the deck (called a 0 deck).

You can use a dial indicator with a magnetic base sitting on the cylinder head deck to get perfect piston TDC. Then you can use the same dial indicator or even a pair of calipers to get the distance from the piston to the deck.

[Dangerous Doug]

More novice questions:

So, for the crankshaft centerline to the deck height, this should be standard for an engine type, correct? In other words, a 289 deck height will always be the same (i.e. the deck will not get machined down for any purpose?)

Dangerous Doug

[blykins]

No, the deck will get machined down.

Sometimes the decks will be warped....sometimes they will just need a cleanup pass on them to take some pitting out.....but if you rebuild an engine and have all the machine work done, chances are it will be decked....even if it's a couple thousandths.

If your 289 has been worked on (chances are it has considering it's got aftermarket pistons in it), I'd say it's a very good bet it's been decked.

That will affect your compression ratio too....it's the same affect as shaving the heads.

Now instead of the piston deck height being .015" in the hole....it could be .010" or .005" in the hole.

[Dangerous Doug]

Hhmmm, I'm beginning to wonder if finding out about these pistons is really worth my time. I could pick up a set of Keith Black pistons from Summit for a couple hundred dollars and have a known quantity...

blykins: you sound like you know your stuff. If you were in my shoes, would you simply replace pistons, cam, and rods, or try to salvage them?

DD

[blykins]

I've only assembled one complete engine by myself. I'm starting on #2....a 406ci FE. So I'm not the best one to ask for advice or really technical stuff. But I'll do my best and give you my $.02.

If it were me, I'd take a look down the road and see what you're planning to do with the engine. If you're looking for high revs and high horsepower, then the stock stuff just won't do in my opinion. Well, it might do...but it's not bulletproof. You know what I mean?

Like you said, pistons are somewhat affordable these days. Buying a new set would allow you to get a good set of forged pistons...and then you would know exactly what compression ratio you have, compression height, etc.

Before you order a set though, you'll need to have your machine work done. It's almost a waste to put a brand new set of pistons and rings in a block that has not been bored/honed. Cylinders develop taper after awhile....You'll need to have the block bored. Do you have any idea on how this engine has been run in the past.....or even how long it's been run? There could be some underlying problems there that will need to be fixed before you sink a lot of money into a refresh.

Once it's bored, decked, and cleaned...then you can decide on what piston you'll need. Chances are, you'll need an overbore piston. You can buy off the shelf stuff....you'll just have to make your other components work around it.

You really need to figure out what you wanna do with the engine before you order parts. Every part you order will affect the buildup of this motor.

This is what I would do....take the block and have it checked and machined. When the machine shop tells you the bore and block deck height, then it's time to decide what cam you want to run and what compression ratio you want. If you have a set of heads you wanna use, then find out the combustion chamber size. That will greatly affect your compression ratio decision. Then when you decide on that aspect, you can pick out a set of pistons.

Bottom line....I would not reuse pistons/rings. If this engine has anything but just a few miles on it, you'll be tearing it back down later on....especially if it's had a rough life.

I would consider reusing rods. If they're straight, and you don't plan on revving this thing until it sings, then you should be fine. But if you're really wanting some power and bulletproof-ness, then I'd go ahead and spend the extra couple hundred bucks for a good set of I-beam or H-beam rods depending on your application.

Cam.....nah....ditch the cam. They're pretty cheap. Again, this engine may have had a really rough life....You can buy a solid lifter cam and lifters for under $200. That's cheap insurance.

Strip her down and take the block to a machine shop. You never can tell...it may go another round with standard bore and no machine work. But if it needs it, you'll have ease of mind later on...knowing everything is in tip-top shape.

Let me know what else I can do to help.

[Dangerous Doug]

Sound advice. Time to contact the local machine shop. I'll let you know how the build goes.

DD

[blykins]

Yeah, keep us informed on what the machine shop says.....

If you're like me, you'll have a blast doing this build....gives you a good shot of confidence too....

[Woodz428]

According to an old TRW catalogue, these are 12.4-1 pistons and .030 versions are 12.6-1.

[Dangerous Doug]

Thanks, Woodz428. That's the info I needed. I now need to take a second look at those heads to see if they are of a larger chamber size to accomodate the pistons.

[foxtailracing]

Hi I am a High School Auto Instructor at Seneca High School. Our auto club races a 1979 Mustang that just had an engine failure. We damaged a TRW 2249n .030 over piston. Are the pistons that you have 30 over? If they are would you be willing to donate them to to are club? Call me for addl. information. Ron Jensen 815-378-2941 or e-mail me at nada5078@yahoo.com thanks for reading my post.