Does anyone have or know where I can find out what the compression should be on a stock 69 - 350?

Thanks!

Mark 66SS

http://www.yearone.com/updatedsinglepages/Id_info/gm_engine_id/gmidimages/chevelle69.jpg

Thanks Mike! I am looking for what the actual compression should be not the compression ratio.

Mark 66SS

Mark,you have to tell us which motor you have before we can tell what the approx the comp should be along with if it's bone stock or has had any mods/perf cam/pistons/heads/etrc.

scott

Scott, It's got stock heads and stock cam, Hi-Rise manifold, Holley 570 Street Avenger, and headers. I believe it's the 255 H.P. motor. Here's why I'm asking. Right now I have between 118 and 120 lbs. in all cylinders. It puffs a little blue smoke after you get on the gas hard and let off. Someone told me that the compression is good and that it's probably the valve seals causing it to smoke.

Any thoughts?

Thanks!

Mark

If all the cylinders are close to the same, you are good to go.

Mark ,try this -(I've not checked it out yet):
http://www.not2fast.com/turbo/compression/cranking_pressure.shtml

It's good that the compression is similar for all cylinders though the actual numbers sound a little on the low side. Bad valve seals will typically cause blue smoke when you start the engine. Blue smoke when you let off the throttle could be either rings or valve seals but tends to indicate worn rings more than worn valve seals.

Squirt a little oil in one of the cylinders through the spark plug hole to temporarily help the rings seal (squirt the oil, about a tablespoon's worth in all, toward the top of the cylinder so it will run down around the circumference of the cylinder) and then try your compression test again. If the compression reading goes up, your rings are worn. Also, when measuring compression, turn the engine through 4 entire 4-stoke cycles (eight crankshaft revolutions) and take the highest reading as your compression reading.

The '69 chevy Service manual says 160 for both 255 and 300 hp 350. Make sure the primary throttle blades are blocked open while cranking.

Thanks everyone!

Imho, you should have a stock static compression ratio w/i a 1/4 of a point from spec's!

In other words, an un-blueprinted engine will come in right at 10 to 1 CR if it is an old '67 350SS 1st Gen. Camaro L-48 350 spec'd at 10.25 to 1.

This is why some of the stock engines ran better than others b/c they just happened by the luck of the parts draw and the day built to hit closer to that 10.25 to 1 CR. spec!

pdq67

Imho, you should have a stock static compression ratio w/i a 1/4 of a point from spec.!

In other words, an un-blueprinted engine will come in right at 10 to 1 CR if it is an old '67 350SS 1st Gen. Camaro L-48 350 spec'd at 10.25 to 1.

This is why some of the stock engines ran better than others b/c they just happened by the luck of the parts draw and the day built to hit closer to that 10.25 to 1 CR. spec!

pdq67

Also remember you can have decent compression meaning compression rings are ok but the oil rings can not seal as well resulting in burning oil so keep that in mind.

It would not hurt to try new v-seals because they are cheap and it could reduce the oil use some but there is likley worn rings mixed in with the oil use issue too when your getting blues oil smoke when you let off after getting on it,that can be seals & guides and rings that situation.

Your approx 120 psi all the way arround is a tad low even for a 9:1 com motor but if you didnt have the throttle wide opne when doing the test that can make a few lbs perf cl difference too.

But the test even though a tad low still showed consistancy between all cyls which is a good thing in your case,no bad valves.

Scott

Thanks Scott! I did have the throttle wide open while taking the compression. I borrowed the guage and had some inconsistant readings with it at first so I may buy one and test it again. Will try the valve seals as well. Are there any particular seals that you would recommend?


Mark

Well,who knows what if anything has ever been done to the heads so they could have unbrela seal,stock little o rings that go in the retainers,or selas that rsquire machining the guides to use them.

So you may need to pull the v-cover to see if you can see well enough the a light thru the springs t see what seals the heads are running.

If you can see then pull a couple springs and see whats there and then just go out and get the same type and give them a try.

But be very carefull not to put toomuch pressure on the valve stem with spring off when using compressed are to hold valves in head so you dont accidentially drop a valve.(YIKES!!!!)

Scott

Back in the day we installed both o-ring and umbrllas on engines with alot of miles.

At minimum o-rings are best for small blocks that have factory spring retainers.

jim

for those of us who happen to have bad luck a way to insure you don't drop a valve is to rotate the motor around to every cylinder one at a time on the compression stroke until its a couple of inches down in the bore then feed in about 2 feet or more of nylon 3/8 cord ... tie a Knot in the end so it can not fall into the cylinder !! then slowly rotate the piston up BY HAND to close to TDC now you can remove the retainers / springs & replace the seals with out worry of dropping a valve .... once seals are done rotate the motor again by hand the other direction to relive the pressure on the cord & remove it ...... repeat on 7 more cylinders :D