Engine ID. A little help please.

[Donzie]

I was told that the engine in my '49 Chevy is a '70 250 (straight 6). It's been running rough so I went to buy some new plugs for it. The ones that they sold me are smaller than the ones in it. Maybe the motor is not what I think it is, how do I find out? Where do I look for the numbers?
Also, as I said it's been running rough. It seems to only do it after it's been driven a while and in town, not on the highway. It acts as if it's loading up. I pulled the plugs and they all look clean. I pulled the cap and the points and rotor look new.
Ok, here's what I can't figure out. I took a little sand paper and sanded the contact on the inside of the cap. Now I can't even get it to fire! All the wires are in solid, I've pulled the cap several times and I can't see anything wrong. Did I damage the cap by sanding that contact?

[Bruce Lancaster]

Chevy went to smaller plugs I think in 1969--you may have an older head.

[Fat Hack]

Which contact(s) did you sand?

If you went apeshit with some super coarse paper, you COULD have screwed it up...but I've cleaned up a few cap contacts in my day with a piece of fine emery cloth and had no problems.

Possibly, some debris fell into the points?
Wire (to the points or coil) came loose?

Take a test light and check for power to the coil when the key is switched 'on' (to "run").

Might be a good time for a tune-up...bust out your piggy bank and grab a new cap, rotor, points and condensor to go with the spark plugs. Might as well while you're down this far!

If your engine IS older than about 75 or 76, it will have a bolt-on intake manifold. (Later ones had the intake manifold cast right into the head). These old bolt-on intakes LOVE to develop vacuum leaks...I've had SEVERAL of these engines and they ALL did it. Usually minor leaks that allow the motor to run fine when it's cold (choke on), but makes it idle progressively worse as it warms up.

Tighten the intake bolts...like every day or two. It's really just a piss-poor design...that's part of living with it. I got REAL ambitious with one of my old six bangers and put a new gasket on complete with a good film of sealer. Cranked the bolts down and made a support brace that went from the motor mount bolt to the intake to releive some of the stress on it. Worked real well, but I'm still a fan of the later 'integral head' if you're only gonna run one carb...and the newer head will bolt right onto an older engine.

Also, check your carb base gasket and PCV hose for vacuum leaks.

250 Chevy sixes are among the most reliable engines ever produced, and they're stupidly simple to work on. You can rebuild thos Monojet carbs blindfolded even if you've never done one before, and everything else is self explanatory.

One other side note...does the engine 'tick' when warmed up? It's SUPPOSED to make some noise...but collapsed lifters are fairly common on hydraulic cammed 250s. Just something else to be mindfull of...and you can easily change lifters on one!

[Donzie]

I'll do some more checking.
I tried a new cap, didn't make any difference.
Yes, it is a bolt on intake.
Generally, it only runs rough after it's been driven a ways. Again, it runs fine at 50/60 but develops a stammer at low speeds and idle.
I'll check the vacumn lines.
Thanks for the info.
I'll still like to know for sure what year it is. Where do I look for an ID #?

[TooMany2count]

[ QUOTE ]
Where do I look for an ID #?

[/ QUOTE ]

6 cylinder engines are stamped on the passenger side of the block behind the distributor

Casting Date Example: E038 - (E = Month, 03 = Day, 8 = Last digit of model year (1978)).

Month: A = Jan, B = Feb, C = Mar, D = Apr, E = May, F = Jun, G = July, H = Aug, I = Sep, J = Oct, K = Nov, L = Dec

[Rocky]

If you have a tough time deciphering the date code, that same machined pad next to the distributor will have a series of stamped letters and numbers. 69 and earlier engines will have a 2 digit letter code that I can decipher with my Hollander manuals. If it's 70 or newer, the letter code will be a 3 digit code. It'll be something like an FO or CDR...tell me what it is and I'll tell you what engine you have, it's horsepower rating, what car it came out of and what tranny it originally came with...