Vac Gauge diagnoses, confirm my thought here

[usar17]

So i went out and bought a vacuum gauge to see what is going on and confirm some suspicions with my current 305 after reading the thread on vacuum a couple times.

Readings:
Manifold Vac = 17inches
PCV port on carb straight to gauge=20 inches
Gauge in line with PCV port on carb to PCV valve=12 inches
Breather hole on opposite valve cover=0 inches

All of these readings were steady.

Safe to assume this is definitely the cause of bad rings? I'm assuming this is the reason i have oil in my breather filter. I don't see where else i'd be loosing vacuum to my PCV

 

[89Suburban]

Check out this thread:

http://www.gmsquarebody.com/forum/showthread.php?t=1570

 

[usar17]

ya thats what i'm basing this on. Just wanted to make sure i was doing it right

 

[Swims350]

IMO if you doubt it rebuild it.

doing rings aint terribly bad, and it's fairly cheap.

I'd ring it, throw in new bearings, oil pump, timing set, and inspect the cam and lifters for wear and change if need be, then new gaskets and be done.

rings run around $20 or so a set,
timing set is around the same, so is an oil pump.
a new cam and lifter set is like $50-300 depending on brand and if you get a big cam or stockish one.
gasket sets run from $40-100 or so for a complete set,
then if your crank is good, have i tchecked to be sure and to know the bearing size needed, mains run like $30-50 a set I think maybe less, and same for rod bearings.

Then you need a honer, which you can rent and also ring compressor which you can rent for like $10, or you can have the machine shop check it and maybe hone it for you.

only real thing left is heads, either machine shop for full valve job, or get some valve grind compound and use a drill on the valves to seat them in good and clean it all up. That's all we ever do.

 

[usar17]

....lol well this is just my temporary motor till i get a 350 rebuilt to drop in. But since i just broke the drivetrain somewhere last night i maybe doing a full swap sooner then i anticipated.

 

[89Suburban]

....lol well this is just my temporary motor till i get a 350 rebuilt to drop in. But since i just broke the drivetrain somewhere last night i maybe doing a full swap sooner then i anticipated.

Towman is from the same area as you, maybe he can help ya out with things.

 

[Jims86]

....lol well this is just my temporary motor till i get a 350 rebuilt to drop in. But since i just broke the drivetrain somewhere last night i maybe doing a full swap sooner then i anticipated.

IIRC, the manifold vac port is only over 2 cylinder runners, and may be why you are getting a lower reading. The PCV valve port would be best, because it is giving you a total vac reading. One thing you can do to see if you have real bad blow by, is to seal off the dipstick tube, the oil filler hole, and the breather, and hook a pressure gauge or boost gauge to the PCV line coming from the valve. Run the engine up to 3000rpm or so, and see if you get a reading.

steady 20 is a DAMN GOOD reading at idle.....17 is more normal. I have had to re tune the chip in my TBI because My cam is only pulling 15 at idle in drive.