Decoding a 655 block

[61belairbubbletop]

I've got a 655 "X" block in my 61. I plan on pulling the motor to make some upgrades, but for now, I'd
like to know a little more about the short-block. Don't know what's inside of it yet. It's a fresh build,
but I don't know (neither did the guy I bought it from) what the internals consist of. I did get it running,
and it has a smooth idle. It has 379 heads, with the stock rocker arm assembly. The intake is a single aluminum 4-barrel #3797776, and the carb is #3270s. This, I discovered is for a 61 360HP 409. That's
good, I'm just wondering about this short block.
On the back side of the block, passenger side, is 268 cast into the block. There is no stamping on the
front pad, passenger side. Either the block has been decked, or was a factory replacement block ?

What got this all going with me was my reading the post about the 61 409 block on ebay. Phil said that
the 3707776 intake, and 3270s carb is the same set-up for the 09.
I'm just wondering about my 48, short of dismanteling. Of course, if someone got into the shortblock,
there could be anything in there for pistons, etc. But, if it's factory built, I'm wondering what pistons
I should expect to find upon teardown.

 

[BSL409]

if it was a replacement block and still stock 7.75 Comp

 

[61belairbubbletop]

Thanks. Well, if that's what's in there, I might as well build this 656 that I've got. If it comes down to buying
pistons I might as well use the 09. Just didn't want to get into a high performance build right now.

What does the 268 cast into the back passenger side of my 655 block stand for ? Is this a Julian date code ?
The engine is in my car, so it's hard to get to the area. I looked at the chart here, but I'm having trouble figuring
out what the 268 means. 62-65 production date ?

 

[petepedlar]

The only way to know what you have is to take it apart.

Dave

 

[oldskydog]

The 268 is a julian date....the 268th day of whatever year it was cast.....probably 64, could be 65.

 

[61belairbubbletop]

Thanks, Cecil. That's what I thought, but wasn't sure.

 

[1960impala283]

The factory truck piston has a 3/16 ridge that runs all the way across, about 1/3 of the piston is raised to create a quench area. It would be very easy to see or feel this with a "wire" thru the spart plug hole. The cast 9.5:1 piston has a pyramid shape with no cut outs for the valves. 11.5:1 cast and forged pistons have cut outs for valve clearance. Put the piston on bottom dead center and have a look.

 

[61belairbubbletop]

Ian,
That's a good idea. I borrowed a "Rigid" brand camera probe from my job but it was just a little too big to go
thru the spark plug hole. I just don't have the time right now to tear into this motor. But, I've been wondering what pistons are in it.

 

[Don Jacks]

If it has 7.5 truck pistons,with the "379"heads on it,the actual compression should be in the 8.75 range ,due to the fact that the "333's " had a combustion chamber of about 20 cc.'s wouldnt it?It could still be a fun little cruiser motor with a little cam thrown in.

 

[62impala409]

A truck motor in a car works just fine for cruising. We all need to remember that these motors were fully capable of moving large trucks down the highway all day long. My motor originally came out of a garbage truck! I drove a tractor in the early seventies hitched to a fully loaded semi trailer. Got down the highway pretty good. I know a guy that put an all stock 409 truck motor into his '62 Impala 20 years ago and is still driving it. The reality is that most of us can't leave them along. We all want much more. I have had mine apart 3 times already and may not be done yet. Leo

 

[1960impala283]

Should be easy to feel the ridge of the truck piston, It's very obvious. Interesting is the weight of these slugs. Almost 2 1/2 pounds.:eek

 

[1960impala283]

Another view of the pistons.

 

[61belairbubbletop]

Ok. I took a 3/16" dia. steel rod and used that to "feel" the piston top. No ridge. Pyramid shape. No valve relief. I could see the piston top by shining
a light into the spark plug hole. Clean aluminum, I could see the peak at center, smooth top, no valve reliefs.

So, I guess it's got the 9.5:1 cast pistons. I wonder if I could put a lumpy cam in so I could have some fun with the car while I'm building the
656 for some serious HP?

 

[1960impala283]

There is not much room for Intake valve lift with the 9.5 cast piston. I had to degree the cam and have the valves sunk a bit into the head to get the room I needed. I used the smallest Isky cam. I wish that I had purchased pistons with valve reliefs, would have been about the same cost in the end, without the grief.
It looks like the previous owner had a complete rebuild done, The 379 heads are better suited for cruising as well. I would just enjoy as is.

Buy the 656 pistons

 

[61belairbubbletop]

Yeah, it's got the pistons like the one you show on the left, first image. Thank you. I don't know what I'm going to do. I can't stand that smooth idle.
Heck, my plow truck has a rougher idle !

 

[oldskydog]

10.5 cast pistons are about $260. They are configured just like the 340 hp pistons with valve notches and are probably just fine for street use with a more interesting cam. I have them in one of my builds, but haven't chosen a cam yet and haven't run it.

 

[61belairbubbletop]

Cecil,
I looked at pistons last night. I will look some more. I may just put some pistons & a cam in it to make it more
enjoyable driving while building the 656. Showcars, Egg, and I don't know where else, yet. Last night I also
seen a used set of 11:1 cast pistons on ebay at .040 over. They were at $40.00 then. I don't know yet what my
cylinder size is. Guess I'll have to remove the engine & pull the heads.

What brand pistons do you have for $260 ? Is there a metal support / reinforcement when looking up into
the bottom ?

 

[oldskydog]

http://cgi.ebay.com/ebaymotors/64-6...r_Truck_Parts_Accessories&hash=item254beb126c