Low compression(?)-Buick straight 8

Gents: I have a '48 Buick w/ 248 straight 8. The car sat for a long time before I got it and blows a fair amount of blue out the back. Just installed a PCV, and it's helped with the blow by up front. However, the compression in all cylinders is around 90-95. Have done a leakdown test w/no change, so the good news is it's likely not rings. Any idea what compression these straight 8s should have, and what is an acceptable range for this engine? I'm pretty sure the engine needs a valve job, but I'm trying to be optimistic and hope that with a few hundred miles things might loosen up a bit internally and increase the compression and overall engine health (doubtful, I know). I've put Marvel in the gas and oil, but if things don't improve, and to avoid the $$$ for a valve job, I've heard umbrella-type valve seals may be an option, The question is where would I find some for a Buick straight 8. I've checked with Bob's Automobilia and other dealers, and have come up with nothing.
Any thoughts/advice on this situation?
Thanks in advance.

 

does it blow blue smoke at idle (high vacuum) or at road speed (low vacuum)?

 

www.teambuick.com has a forum that is full of buick info especially on straight 8s.

 

Smoke seems to be there at all speeds....worse at start-up, I guess. I should mention we've just adjusted the valve lash as well...it was out quite a bit.

 

i know this sounds like a very low tech solution. but my 48 roadmaster with the 320 was pretty smoky. i hit it with some sea foam (yeah i know) and it runs great now.

 

Your comp. is not to far off the mark. My old Motor's shows 6.5 ratio and that would be in the 105-110 range. Get a couple of hundred miles on it and see what things look like. As far as valve seals we always used 50s-60s Ford umbrellas

 

***These are the specs for a 248:

<TABLE cellPadding=2 border=0><TBODY><TR><TD bgColor=#ffffff>Valve Location: In head</TD></TR><TR><TD bgColor=#ffffff>Bore and Stroke: 3-3/32 x 4-1/8</TD></TR><TR><TD bgColor=#ffffff>Piston displacement, Cubic Inches: 248</TD></TR><TR><TD bgColor=#ffffff>Compression ratio: 6.3</TD></TR><TR><TD bgColor=#ffffff>Maximum Brake Horsepower: 110 @ 3600 RPM</TD></TR><TR><TD bgColor=#ffffff>Maximum Torque Lbs.Ft. @ RPM: 206 @ 2000 RPM</TD></TR><TR><TD bgColor=#ffffff>Normal Oil Pressure Pounds: 45</TD></TR><TR><TD bgColor=#666666>TUNE UP SPECIFICATIONS

</TD></TR><TR><TD bgColor=#ffffff>Spark Plug Make: AC 48</TD></TR><TR><TD bgColor=#ffffff>Spark Plug Gap, Inch: .025</TD></TR><TR><TD bgColor=#ffffff>Firing Order: 16258374 </TD></TR><TR><TD bgColor=#ffffff>Ignition Timing: ADV. Timing mark on Flywheel</TD></TR><TR><TD bgColor=#ffffff>Engine Idle Speed, RPM: 450</TD></TR><TR><TD bgColor=#ffffff>Cylinder Head Torque Lbs.Ft.: 65-70</TD></TR><TR><TD bgColor=#ffffff>Compression Pressure & Cranking Speed: 112 Min.</TD></TR></TBODY></TABLE>

***It's the spec above I'm worried about...my readings of 90-95 are low, are they not? The good news I guess is that all cylinders are showing fairly similar compresssion...

 

6.3:1 standard 6.9:1 hicompression models

 

6.3:1?! Jesus! Somebody slap a supercharger on that thing! hahaha

 

-Yeah, well, it is what it is. LOL.

 

have you had a vacuum gauge on it yet? a low reading could indicate rings. since you did state that it's worse on startup i would think about pulling the head for a valve job. spend the money and have guides put in it, don't have them knurled. see if your machinist can recommend an umbrella seal that can fit inside the buick's inner valvespring. check the ridge in the bore when the head is off. partly fill the bores with some a mixture of kerosene and marvel when the head is off if the ridge is not excessive. this will help dissolve carbon in the ring lands. once dissolved, flush that crap out and re-oil each bore with clean dexron atf on a clean lint free rag before re-assembly

 

Vacuum was not too bad...around 20/21 or so. I think we're leaning towards valves, too...just have no idea what umbrella seals would work on an old straight 8. Hopefully someone on here can give some suggestions...a previous poster on this thread said 50s Ford umbrellas but where would you get them?

I posted this question on the teambuick website and some of the guys on there said my compression was not really worth worrying about. However, I could do without the cloud of blueish-white exhaust...

 

Put a quart of MMO in the pan and run a few hundred miles on it before yanking things apart. Try to put 50 miles on it at a time to get things well warm and let the MMO do it's thing. Then take a warm comp test and see what you have. Still under a 100 put a bit of oil in each cylinder and take the comp test over ,if it comes up 10 psi or so rings may be a bit tired. But smoke on start up points at valve guides. Any auto machine shop should be able to come up with some umbrella seals

 

i think the buick s-8 uses a .375" diameter valve stem. i'd investigate the 440 mopar viton seals

 

btw, the buick s-8 will tolerate a cut of .100" on the cylinder head, since you are considering a valve job. that will help raise your compression considerably

 

Thanks for the information everyone. I've got Marvel in the gas and another top end lubricant in the oil. We did both dry and wet compression tests...put about a half a cup of Marvel into each cylinder overnight before the wet test, but nothing changed...all cylinders were reading around 90 psi.