Here's the background: 1968 GS350. Fresh rebuild, 8,000 mi., steam from the left bank. Dry compression test shows one cylinder -15 psi. with water noted on test gauge. Pulled the head, gasket appears intact, no cracks noted in the head. Block looks intact also. NEVER got hot. Where do I go from here?
I may be wrong but.... Are these 68 heads, or a later year? I know there were differences in the oiling passages back then, is it possibe the same holds true for the coolant passages? Maybe two different style gaskets? Like I said, I could be totally off base but just an idea here? Jon
Have the heads been pressure tested? It isn't possible to see all cracks that might possibly occur. I'd hate to wonder how many heads I've pressure tested - you'd be amazed at how many different spots different heads will crack or just plain leak from a porosity problem!!:eek2: Although I haven't seen it on a Buick engine, I've seen other makes have 'pinhole' leaks in a cylinder after boring only .030"! I highly doubt that's the case with yours though. If the head(s) check out OK, you may have to consider having the block magnafluxed or some other form of crack detection! Lastly, has the top of the block been decked or at least checked for warpage, pitting, etc.?? Hopefully, it was just a gasket problem or something simple!
Your local machine shop would have to do it. This isn't one of those things that just any of us can do in our garage. The head is put on the 'pressure bench' and then a big plate with rubber on one side (to seal the head) is placed on the head. The head is then clamped down and all other water passageways are blocked off. An air line is hooked up to one of the block-off plates and then the entire cooling passageways are pressure-ized. Now the head gets sprayed with a soapy water solution. If there are cracks the soapy solution will bubble up rather quickly! I've found cracks after pressure testing heads that 'passed' with just magnafluxing. Magnafluxing iron heads is much quicker and catches most all cracks - but not quite as accurate as pressure testing! It's almost impossible to detect an internal crack by just mag'ing the head. Hope that clears thing up a little.:grin:
Thanks for the input. I may run the heads to the other machine shop (not the one who rebuilt the engine) and have them checked out. Or I may just look for a good replacement engine and deal with this one later on. Thanks for the input, I really appreciate it. JT:TU:
O.K., it's time for dumb questions: How do I identify what year heads I have? Do they differ in the oiling/cooling passages? Did chamber sizes or shapes change over the years? I find it hard to believe I have a head leak after 8,000 mi. and never overheating. Thanks for your input. JTo No:
casting numbers on the heads since the blocks didn;t change over the years i'd have to think that the oiling didn't either chamber size changed from 48cc , 51cc and 58cc (at least thats what I've seen), shape has remained constant the heads do crack, your machinst should be able to confirm or deny a crack I'm sure someone will reel me back in if i'm off on the above
The results are in... Yep, cracked head. Thanks for the information. My better instinct tells me it's time for a new engine. That's what I have planned. I just hate to trash a rebuilt engine with only 8,000 miles on it. The "El Cheapo" side of me tells me there's got to be a way to repair a head. Is there? (humor me). "warning Will Robinson, danger, danger..."
heads are cheap and easy to find, you should be able to get a new one in runnable shape for less than $75, head gasket, some greasy hands and you are on your way
