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1968 Buick Electra 225

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I bought this thing the other day. It has a 430 big block, but I'm having compression issues on cylinder #4. It has about 65 PSI (cold compression test). With oil, it jumps to only 73-75PSI. I believe the rings are good. The heads have recently had work done on them, along with a new camshaft. I'm leaning towards the camshaft being the issue here or a lifter issue (hydraulic lifters).


I did a 'leak down' test where I shot about 100 PSI of air into cylinder #4. The air was only escaping from my air fittings and not from anywhere else. I felt a vacuum on both the exhaust and the oil filler in the valve cover.


I can't tell if any of my push rods are bent at first glance.



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To have low compression a valve (possibly) would not be closing all the way. A bent pushrod would prevent it opening all the way... the exact opposite.


If you had 100PSI in the #4 cylinder and there was a bad valve, you would hear hissing air at the carb (intake) or the exhaust pipe outlet (exhaust) Do this again. You say a valve job was done so this is likely the cause.


Have someone crank the engine over (with the starter) and watch the #4 valves. Compare them to the other valves as they open and close.




If the valves are sealing, the only way to have that low a compression is a hole in the piston.... and nice boat BTW. Bet you have to shut the engine off when re fueling or you can't fill the tank.

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  • 4 weeks later...

Got me a 455 to put in there. I'll redo the 430 later on.





It runs. Just needs new exhaust bolts. Broke one of them off. And then there's the mangled flange ear:





The previous owner looks to have just used a smaller bolt with a nut on the end of it.

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I did another leakdown test. This time, I used my regulator on my compressor to lower the psi to about 20. I was able to hear where the air was escaping a lot better. Definitely coming out of the tail pipe and through those exhaust port/heat crossover things shown above (sooty circles).


I thought I had a cut and dry case of a burnt valve or something.


Removed the head today. Didn't see a burnt exhaust valve. All pistons have carbon sooting on them and look normal. The only thing I can see is that there's a bit of dark carbon trailing around the offending valve. 






That little chip looking detail on the piston just indicates where the piston is supposed to be orientated. I think.

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Turn the head valves up and fill the combustion chamber with diesel fuel (less explosive) enough to cover them. If the valve and seats are good enough, nothing will leak out the ports over night.







That little chip looking detail on the piston just indicates where the piston is supposed to be orientated. I think.

It's for chucking in the lathe when making them?

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Yeah, those are all facing the front. I think datzenmike was looking at the piston titties.


That purple power didn't work out too good. Went with diesel fuel as suggested. Only one cylinder leaked all the fluid overnight. With purple power, all but one chamber leaked out.

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I got this thing running a while back. I opted to stick with the original 430 motor. After fixing the leaking valve, the only problems I ran into were breaking a rocker arm bolt off and sealing up the exhaust manifolds. I have a divorced choke that works pretty decent. Can't drive it at present as I am hoping to hear back from a potential employer. Otherwise, I have no funds. 

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Owned a 1970 Buick Electra Limited with the 455 engine. The "imited"was an early boat with almost all the accessories used to debugthe line and had the air suspension option. The only thing not included was a tape deck! A beautiful car! I sold it when my son made the mistake of telling me how he had out run a Porsche.

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