Thought I would take a little time today to see why my 305 in my avatar truck is puffing a little smoke on startup and I started with a compression test. Surprised to find all 4 rt side cylinders at 158- 162 and all left sides at 118 -122. Puff is from left pipe also. Question is why would all 4 be so different from rt. Squirted oil in cylinders but made only 2 lb difference. Truck burns no oil between changes to measure. All 8 plugs were coated with soot when I pulled them. I'm thinking the puff may be fuel?? Real question is why the difference in pressure. I'm hoping someone can offer some help. Thanks Ralphie
If you oil it and the pressure didn't come up that suggests a head problem as opposed to a ring problem. Loose guides or bad seals will cause one to puff on start up but bad seals won't cause low compression where loose guides will. I would try a leak down test I think you will find that the left side doesn't hold compression. if it works out to be heads do both and not just one because if one is going the other is not likely to be far behind. SBC are bad to loose the left bank first by the way. I have no idea why, it is just a quirk that they have always had.
I wouldn't question what Beaner said about one side wearing out first. But, is it possible 1 head was replaced some time in the past, or a pair of mismatched heads installed?
Thanks for the replys so far. If I pull the covers and can see a head # are L&R heads the same#. Are they interchangeable?? I didn't say but I guess you figured out this is a SBC. Thanks Ralphie
I always thought that the SBC ran inherantly hot on the left side because of the bypass in the stock water pump to the right side into the head. In time that wears out the left bank rings first. #5 and #7 always seem to run hottest and wear out first, because of the unbalanced water flow favoring the right side. #5 is usually the first one to ping or detonate when the timing is too far advanced or the fuel is not enough octane. Don't ask how I know... Edelbrock and Stewart have balanced flow (no bypass) water pumps that seem to correct this problem. Plus, 305's are known to have soft castings and wear out the rear cylinders first, also compounded by the unbalance of the stock water pump. My 2 cents...
I would oil those cylinders and do a wet compression test. If the numbers improve significantly, motor. If not, head.
When I worked in the machine shop years ago, we had a fixture to deck blocks off the crank centerline, and I did a few 350s...I was amazed at how far off they were, from the factory. Maybe one deck is way taller than the other?
SBC heads will swap from one side to the other no problem. Monday and Friday blocks are the worse. LOL I have seen as many on here have some real atrocities on assembly line motors, 4 bolt blocks with 2 bolt caps, motors with one larger bolt than the rest in the line up, soft plugs glued in because the core holes were too big, decks so far out of align that I could not figure how the intake ever sealed. Oh and who can ever forget the over bored 396s, uh I mean 402s. LOL Jim could be onto something here for sure.
305's also have light weight heads and are prone to warp and crack easily from running hot. Sorry to be the bearer of bad news about 305's.
squirrel, we ran into the same problem with our 377 dirt modified engine one side was .010 higher than the other bank. It could be that the right side head was rebuilt at one time. Working in a machine shop we were always surprised when someone brought in one head of a V8 to rebuild.
I was thinking about the head being milled also...and maybe a shim gasket on one side, composite on the other..you never know
IMO, if a wet test made little difference, diagnosis is only going further with the heads off for comparison and inspection.
I had a chance to pull the covers, both heads have same #, but that's all I've had time for. Thanks again Ralphie
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