Dirty Spark Plug

[dmcclanahan]

I had a cylinder that was not firing, so I changed the spark plugs and noted that cylinder #5 was the corporate. What causes the gum up on the spark plug? Did the value go bad or is it the piston rings?

(Note: I do put 1/2 qt of oil in it ever 3 to 4 days)

[James McClure]

D, What color is the deposit? Tan\white is normal, black powdery thin deposit is excess fuel and black crusty heavy deposit is oil. Does it smoke? A little smoke on start up is OK for the most part. Key word there is little. Blue smoke (oil) under heavy acceleration is usually rings, blue smoke on deceleration is usually valve guides. jim

[njlimbaugh]

If you only have one plug that's oil fouled and you're using that much oil my guess would be a broken ring on #5 piston. You need to check that because a broken ring could eventually score the cylinder wall which, with time, could cut into the water jacket and completely trash your engine.

[dmcclanahan]

James,
I think it's a mixture of thin and heavy deposit and it only smokes on start up.

[dmcclanahan]

question regarding piston rings? Can one pull piston from the bottom and then reinsert them from the bottom of the block?

['76 Big Block]

I'M almost certain that pulling a piston from the bottom isn't possible---there's just not enough room to manuever the rod, and piston past the crankshaft. IF you were able to pull it that way, reinstalling would be a real bear, because you'd have to compress your rings somehow as you were pushing the piston back into place.

[dmcclanahan]

what is the best way to pull a piston? push from the bottom to the top? or push down from the top? I have a 305 that sounds like i need to rebuild.

['76 Big Block]

I'm assuming you're wanting to do this with the engine still in the vehicle, right?
Not sure about your application, but I've tried to do this once, and the hassle of dropping the oil pan, getting it clear of the suspension, hoses, exhaust, etc,etc will make you learn a whole new vocabulary.
That said, it's possible to deal with one cylinder, but you'll have to pull the head on that side. I've seen guys even leave the intake in place. Once the head's off, and the oil pan's dropped, you take the rod cap off, and push the rod and piston through the top---if there's any ridge around the top of the cylinder, you'll want to ren or buy a ridge reamer, and cut that off before reinstalling your fresh piston/ring set, or you'l most likely break them going back (don't ask me how I know)...
305s are common enough that you may want to look at either getting a short block or one from a donor vehicle, depending on how much time you have or how deep your pockets are.
Good Luck!

[dmcclanahan]

Thanks for the great info. I think that I will limp this 350 tell I get the my 305 rebuild. If it goes south fast, then I will rering my number 5 piston. I didnt know that you could leave the intake and still pull the head. Great idea.

[njlimbaugh]

You can probably pull a head without removing the intake manifold but in order to do the job right and get everything to seal, especially the cooling system, you need to pull that intake. You also need access to clean the gasket surfaces and that's damn near impossible to do right with the manifold in place.

['76 Big Block]

Originally Posted by njlimbaugh

You can probably pull a head without removing the intake manifold but in order to do the job right and get everything to seal, especially the cooling system, you need to pull that intake. You also need access to clean the gasket surfaces and that's damn near impossible to do right with the manifold in place.

Re-read my post--- I didn't say I would do it that way, I said I'd seen it done.
Obviously, you'd need to pull the intake to clean gasket surfaces in order to get a good re-seal, and, personally speaking, I'd never consider pulling just 1 piston (which was how the thread got started anyway).

[dmcclanahan]

Thanks guys for the great info I think that Im going to leave the 350 in the truck and pull the intake, head and replace the #5 piston ring. then replace all the gasket and put back to gather.

[njlimbaugh]

My comment wasn't directed at you, '76 Big Block, it was for dmcclanahan who was asking for advice. My next comment would have been about the ridge reamer, but you beat me to it so you have obviously done this before, as have I. I wasn't trying to step on any toes here, just trying to be helpful.