Technical Pulled this crank out of a 283, but casting # doesn't compute!

that sounds like a good, practical engine that should have no issues.I am curious about the 305 heads.Do you not have the original heads?

 

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Image from 1955 265 SAE paper showing -
- rods without reinforcement at the rod bolt notch
- standard issue pistons with steel (anti) expansion inserts and deeply slotted oil ring groove that makes the skirt more independent from the head expansion.

 

Yes, I have the “power pack” heads but they have smaller valves and a larger combustion chamber, I am using the 305 heads to raise compression and intake flow, 1.84 vs 1.72.

 

That sounds real sensible, to often things get out of hand. Go for it and good luck.

Pat

 

Eaton makes a posi unit for our original axle, but nearly $500 for it means it is in the future sometime.

 

Contrary to popular belief they came both ways. I am not sure that I have seen a notched steel crank but I am not sure that I have paid that much attention. LOL

 

As I was reading this I was thinking you'd suggest dropping the crank on the floor to hear the sound.......

 

FWIW, I pinged it with a tiny ball peen and the crank rang like a tuning fork.

 

A cast crank rings too, just not like a forged crank. Yours is cast.
Forged on the left, cast on the right.

 

The only time either one of them doesn't wring is when it is cracked.

There is no doubt a proper test to distinguish cast iron from forged steel, and I cannot suggest that anyone do this with a crank but a simple test is to drill a small hole, steel with throw chips and cast iron will throw dust. LOL

 

These are the pistons I intend to use; flat top cast aluminum.

 

If you had a forged and a cast crank side by side and tried that test, you'd hear a definite difference.

 

has a thin parting line...cast for sure.....forged parting line about 1/4" wide

 

If you are looking for compression be sure to check the pin height on the new pistons against the old ones.It is very common for aftermarket rebuilder type pistons to have lower decks than OEM,usually by about .025" or so.If you know about it you can deck the block to allow for it.The last set of speed pro cast 4 valve relief pistons I bought were that way.That was last year so they are still doing it that way.

 

@steinauge, well that raises a conundrum; do I get the block decked while they are already boring the block, or wait until I have the pistons? I'm inclined to at least try to contact the piston supplier to confirm what you say. That to me is a priceless bit of information you gave me. The whole point of adding the 601 heads was to raise compression, and that would have been for naught because that .025 is a lot really. I guess what I need to do is talk to the machine shop and find out what they suggest I do about decking in advance as well. I did a tour of the one I want to go to and it was a really nice one, clean and organized, lots of sbc's so I reckon they know what to do. When I spoke to the old salt at the counter he seemed satisfied with what I had planned for the 283.

 

I always take the pistons when they bore the block anyway. It sure doesn't hurt to check clearances before you start.

On performance builds, I usually have the block "0 decked". You need one of the piston/rod ***emblies and the crank that you are going to run to do this. If you 0 deck a block your piston/head clearance is set with your head gasket compressed thickness, so you need to do some research there.

 

Quoth Federal Mogul:

"Our 235NP-30 is destroked .020". Compression distance is between 1.779"-1.782"

The pistons in question are the cast aluminum .030 over flat tops Summit sells.

 

Squirrel is correct. The GM 25 is the pattern number, the rest is casting number. It is a casting. The N stands for Nodular Iron. As ****** said, both will ring, unless cracked, the ring will be different, but they both ring.

 

It's kind of hard going by compression distance without knowing if the block has been milled or not. Bottom line is put the piston/rod/crank ***embly in the block and measure it. I think the pistons you're buying will put the piston .020 deeper in the cylinder than stock pistons. That's not a bad thing, if the block has been milled a time or two, but you have to measure to see where you are to start with.

I said in the post above that I zero deck performance stuff, but that doesn't leave you any room for another cut without using thicker head gaskets. So, for a street engine, you might leave the pistons a little farther down in the hole to give your block another cut in case it needs it.

And you have to take into consideration what head gasket you're using. Chevrolet says you need a minimum of .035 clearance between the top of the piston and the cylinder head. When I zero deck a block, I use a .041 compressed thickness Fel Pro composition head gasket to get the right clearances. If you use a steel shim head gasket (.018/.020 or so), you probably need to leave the piston .020 (or more to leave enough material for another cut in the future) in the hole to get the right clearances.

BTW, that's not the end of it. The more you mill, the farther off the alignment of intake/head is. On a performance engine that has been milled a lot, you usually have to check the fit and port match the intake to align with the heads again. Bolt holes and end seals are also affected.

 

I see what you are saying; but does that mean the 3.00" stroke would go down to 2.980" with a loss of compression? Granted, I'm not building a stump puller here, but an engine that will deliver in the neighborhood of 300hp. I'm searching more for an engine I can count on to be reliable and give better performance than stock, otherwise what is the point? I value your input as it seems really reasonable. I don't have a bore gauge but my tape measure said it was 3-7/8, so that should be 3.875. Given what I have been told about the pistons I showed and the connecting rods and crank, this may be the first time this engine has been apart.

 

I think I see a steel strut thru the wrist pin bore in the piston picture in post 41.

Yes, the shop should have the actual pistons before finish honing. And the actual ring type.

To avoid decking the block after the cylinders are finished is a little complicated, but tight squish is worth it.
The attached image is Chevy's design squish/quench according to the 1955 SAE SBC paper.
0.045". How about that !!
I'd try one old rod and piston in all four corners of the block and measure the deck height to figure out what is there now for height, as well as how square the decks are to the main line (ignoring crank stroke variations, but it sounds like you are reusing the crank anyhow). Then measure and record the CC of the used rods (especially the test rod) before and after rebuilding.
Then, the minute the new pistons come in I could measure the comp distance and know what I wanted to do with the block even before it is bored, etc. Careful work with a dial/vernier/digital caliper would be sufficient for the C-C etc measurements.

Do you know how the shop is going to resize the cylinders, especially if their boring machine references off the deck ?

 

No, I do not. What should I look for?

I must say, I have learned quite a bit in this thread; there is certainly more to figuring out a good performance rebuild than reading a magazine or looking at a parts catalog.

 

They aren't really destroking the engine. Actually the pistons would work with engine that was stroked, not destoked. But that's all moot. You will loose a slight amount of compression with the piston .020 deeper in the cylinder, but not enough to notice in the seat of your pants.

If it were my build, I'd probably have the block decked enough to make sure it was level and not warped and run the steel shim headgaskets. The only down side to running them is that you'll need to retorque the heads after you get the engine running. But that's more of a theoretical deal, than a MUST do thing.

Most modern machine shops run boring machines that index off the main bearing bores and not the deck surface. If your machine shop has one of those (Cylinder King is a typical machine), it doesn't really matter if the deck is surfaced before or after the engine is bored. If the boring bar indexes off the deck surface, it probably wouldn't hurt to deck the block before you bore the engine.

 

Larry, my plan was that too, also align bore and hone the crank journals, balance rotating ***embly. I want this to last.

I will say that my greatest trepidation is breaking in the camshaft. I hear so many stories about a cam lobe going flat or a lifter not pumping up, etc., and then having to fight and lose the battle with the cam company because you can't prove it was the cam. It scares the bejabbers out of me, really it is the only thing I am afraid of screwing up.

 

Again, if it were mine, I'd let the machine shop check the main bearing saddles and see what they say about needing align honed. 99% of the engines I've rebuilt (I've been doing it for a living since the early 70s) don't need the main honed, unless you're planning on spending much time on the ragged edge. Balancing is always a good thing.

As far as the camshaft goes, be sure to use a good break in oil with high zinc content. Also Comp Cams will Parkerize a camshaft, which will help a lot with break in. I'm sure some of the other companies will too.

I went to a seminar Sealed Power put on years ago and they said that prelubing an engine would add 20,000/30,000 miles to the life of a freshly rebuilt engine.

 

Agreed Larry, those machine shop guys forgot more about what needs to happen than I know about what they do.

 

I know Keith Black makes some hypereutecic pistons that won't have the .020 off the tops, so you may not need to deck your block. By the time you figure block decking costs ($$$), with getting a better piston design (probably with ONLY 2 valve reliefs), costs are probably about the same. I personally don't care for Keith Black pistons, but many swear by them. I watch E-Bay for NOS parts for the 265/283/327 engines, and I have a ton of it. I can only justify it by saying, "they don't make them anymore". You should try that if you're not in any great hurry to ***emble your 283.
Pistons, rings, bearings, gaskets,etc can be had pretty cheap. I am Butch/56sedandelivery.

 

It does not change the stroke you can only change the stroke with the crank shaft. Destroking in this situation should me that with a stock block stock rods and crank you should be about .020 down the hole. That couldn't be very accurate as your compression height gives you a range .oo3 so you could be from .0215 to .0185 down the hole.

Anyway when Larry T suggests getting your block zero decked that should take care of that problem for you then use the compressed thickness of your head gasket to set your *quench. If it were my engine I would want it to have a .040 quench. Someone else will tell you something different.


*quench the distance from the top face of the piston to the mating face of the head.

 

Yeah? Got a set of .030 to sell?

 

Thanks ******.

You know, if I'm not careful I will price myself out of the build. Must resist temptations that won't give me much in return.