Thread: Carbon build-up

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On my shortblock 350 there is a buildup of carbon on the pistons and a small lip on 3 of the cylinder walls. What would be the cause? Should the block be torn down and redone? I have all new parts for the top end and I want to put it together this weekend but someone said be "leery" of the build-up.
What to do?

You didn't say how many miles you have on your engine - but here's a run down of what you may be faced with.

The "carbon build-up" on the top of pistons is a normal by product of the oils and solid deposits that will, over time, find their way into the combustion chambers of any engine. As your engine wears, the rings and valves allow oil to pass and it coats the piston. The build-up doesn't burn clean and continues to accumulate. Modern gasoline may contain additives to help this condition, but eventually all engines develop this condition. High speeds and long, hot run times help, i.e., better to drive a lot of freeway miles than a few "around town" trips.

The lip you are feeling is called a ridge and it is a result of the piston ring wearing the cylinder down. Again, normal in all engines and eventually results in a loss of compression along with allowing oil to pass.

You may be disappointed rather quickly if you rebuild just the top-end (heads) of your engine. New (or rebuilt) heads will have tight seals and valves which will cause pressure to be forced back into the cylinders (past the worn rings) and cause undue pressure in the crankcase. This will be readily visible as smoke coming from the breathers

I think you would be well served to take the time and spend the money to do the entire engine. The results will be better and in the long run, you'll be a lot happier with the performance of your car.

Good luck and let us know what you decide.
Glenn

That's the best advice you're ever gonna get.

Ok, here's another question-I know someone with a 327 block that has been completely remachined, bored .60 over with no crank or cam. I can get it for REAL cheap. Would it be in my best interest to do this and will my components (crank, cam, pistons, lifters etc) work with this block?

Got to go with glenn and tech on this one. in a perfect world maybe.60 over is large will you be throwing boost at it?Not sure on the components

I was just trying to avoid the cost of re-doing my 350 block. I'm stumped guys. There will be NO boost. Just wondering (in the long run) what would be the better option of the two (the refinished 327 or the needs to be re- finished 350)

Need the casting numbers on the 327 block.

What are you going to do with this engine? How was it running before the tear down, smoking, rough idle, etc?

I bought the block from someone who said it "only" had 10,000 miles on it. The top end I bought and had completely redone. I was told it ran great before tear down.

also just talked to the guy with the 327-it came out of an older vette. Will have casting # s tonight. Don't know if that helps.

OK, here are the 327 casting #s; 3959512. I'm trying to figure out which block to go with.

The 327 you have is a 2 bolt from 1962-1963. Should be a good one to build from however, it's a small main journal, as 1968-69 were the only years for large journal in the 327. As such, this may not be a good choice unless you have (or can procure) the proper crankshaft and rods. Another key measurement with installation of a 350 crankshaft in an early 327 block is clearance – see Handy Little Small Block Table below.

All 1st generation small blocks used a 5.7” rod length except for the 400CID engine which used a 5.565" rod length.

Chevy small blocks have a deck height (centerline of crankshaft to cylinder deck measured along the centerline of the bore) of 9.025" and a height (centerline of crankshaft to top of engine along the center of the V) of 9.805". Cylinders are spaced on 4.40" centers on each bank and the centers of cylinders on the two banks are offset to accommodate the two connecting rods on each crank journal.

Hope this helps,
Glenn

Thanks Glenn. I think I'll probably just redo my 350. It is a good block and much easier to work with. Again, thanks for all the info. You guys amaze me every time.