my 340..3 cars, 34 years, 1 family. where to go from here

-
C

Challngd73

Well-Known Member
Joined
May 17, 2012
Messages
587
Reaction score
895
Location
Upstate ny
Ok so here is my 340's story.. It was taken out of a 71 cuda my uncle had, and given to another uncle back around 1980. He went through the motor and ran it in his 65 barracuda. He rebuilt it a 2nd time back in the fall of 1987, but died a little over a year later. It sat in that 65 cuda for a few years until my father took it out and put it on an engine stand and manually turned the crank every so often. Back in 2006 my father took the motor to a machine shop and had them build it. The motor was bored .60 over, new crank, new pistons, the whole deal. My father let them choose the cam. He put the 340 back into his 66 barracuda, and it never ran right from the start. It didnt run bad mind you, but had no where near the power it had back in the 80's when my uncle had it. I was convinced a poor cam choice was the downfall, but no one knew what was in it. My father took the 340 out of the 66, and back on an engine stand it went. Fast forward 8 years....I bought my fathers 66 and the 340, which had only about 1000 miles or so on it since its rebuild, but hadnt been run for those same 8 years. I decided to tear into the motor last night and this is where i am at today...



 
I discovered the cam is a crane cam, a 284 h12 that crane lists the "operating range" as 3,000-6,200 rpms. I dunno, I think that is a very poor operating range for a street car in my opinion this contributed to the poor performance. What do you guys think of this cam, as i am far from an expert. Also I found 2 cylinders with condensation in them, one not too bad, one not good. You can see from the cylinder head picture the price of condensation. Can anyone tell me what part number im looking for on the pistons to get more info from them? I assume the block and heads have to be gone through now? Opinions? thoughts?
 
I can't see the pictures - but i'm a big fan of Crane. There's a lot of things that can make an engine run poorly. Might have been to combination of parts (cam choice), might have been bad parts (mismarked timing set or not degreed), could have been people's memory (fairly common)...
 
Any broken rings? I took apart a 340 I bought and found all 8 pistons had the top ring broken and one piston with the second ring also broken. No wonder why that engine was parked.

I can't answer your cam question, but there are many things that can negatively affect performance. For example: improperly degreed cam, too much ring gap, timing way off, etc.. Did the person who worked on the engine know what they were doing?
 
I agree with the memory sometimes being better, but none the less, a light car like a 66 barracuda with 3.55 gears should have no issue breaking the tires loose, and that wasnt the case after the rebuild. I believe my father said the machine shop had to sleeve some cylinders... .60 over is about the limit for a 340 right? Can they resleeve the damaged cylinder? This motor has too much family history to give up on.
 
68gtxman said:
Any broken rings? I took apart a 340 I bought and found all 8 pistons had the top ring broken and one piston with the second ring also broken. No wonder why that engine was parked.

I can't answer your cam question, but there are many things that can negatively affect performance. For example: improperly degreed cam, too much ring gap, timing way off, etc.. Did the person who worked on the engine know what they were doing?
Click to expand...

They are a respected machine shop in my town, but they also work with mostly gm i believe.
cam specs: duration @ .050" int 228 exh. 228, advertised duration int 284 exh 284, lobe sep 112, valve lash int .000, exh .000, gross valve lift int .480 exh .480
 
Challngd73 said:
pistons have "951 p" stamped in them.
Click to expand...

How far up did the pistons stick? If they are lower than the block's deck, then it had a low compression ratio to start with. Plus with two cylinders with internal rust issues, it probably had a leaking head gasket.
 
68gtxman said:
How far up did the pistons stick? If they are lower than the block's deck, then it had a low compression ratio to start with. Plus with two cylinders with internal rust issues, it probably had a leaking head gasket.
Click to expand...
Its a 71 340, so it should be 10.5 to 1 stock right?
 
Stock rated, yes, but I believe the stock pistons were forged (and very heavy). The ones pictured are castings with the captive ballast weights...and that 10.5:1 number was just a factory optimistic rating. Unless the decks have been cut, it's probably closer to 9.5:1...which is still plenty compression for that crane 284 cam.
 
Whats the top look like? a 951p is a common number for a federal mogul/ sealed power chevy piston. i doubt that is right.
 
txstang84 said:
Stock rated, yes, but I believe the stock pistons were forged (and very heavy). The ones pictured are castings with the captive ballast weights...and that 10.5:1 number was just a factory optimistic rating. Unless the decks have been cut, it's probably closer to 9.5:1...which is still plenty compression for that crane 284 cam.
Click to expand...
What are captive ballast weights?
 
Here is a pic of a stock high compression piston
 

Attachments

  • piston.jpg
    26.4 KB · Views: 377
That is what most of them look like that I have seen, do you know if the pistons were above or below the deck before you took them out?
 
The cam is profiled after the "HEMI" grind from MoPar Performance.
I used one in a 1972 340, same pistons you have, stock intake, T-quad carb, 4-speed & 4:10 gear.
It was in a '69 Dart, ran 13.60's.
This was the first engine I ever built, circa 1977.

Need to get everything checked for wear & cracks.
If ok, ring & bearing it, degree the cam & Spend some money on the heads.
 
Challngd73 said:
What are captive ballast weights?
Click to expand...

Factory high compression pistons like the two valve relief one pictured above are forged, therefore a little heavier than standard castings...your pistons are low compression, and because cast slugs given the same architecture are lighter, piston manufacturers used to cast weights in them to match the weight of factory pistons so the balancing would be in normal limits. Take them out and your cast pistons would weigh probably a couple dozen grams less and would require some weight to be taken out of the crankshaft counterweights.
 
Those may help with weight, but they are steel limiters to control piston skirt expansion.
Better cast pistons will have them.
OEM 340 (low/high comp) pistons were all cast pistons, no forged used.
 
I have to take the block to a shop and have them look it over. I am hoping that one cylinder isnt too bad. its already .60 over, dont think i can go more than that...
 
mikedevore said:
Those may help with weight, but they are steel limiters to control piston skirt expansion.
Better cast pistons will have them.
OEM 340 (low/high comp) pistons were all cast pistons, no forged used.
Click to expand...

im sorry, but i know that stock high compression 340's had forged trw pistons in them.
 
10.5 340s had cast pistons from the factory......8.5 340s had cast pistons from the factory...
 
You must log in or register to reply here.
-

Back
Top