need some major help.....please

[77chevypu]

Newbie here,

I recently purchased a '77 SWB PU, 350 sbc, 2pc rear main. For the most part, the engine runs fine. No noticeable miss while idling or cruising down the road. No loss of water/antifreeze or mixing with the oil.

i decided to do a compression check after I changed the plugs and noticed the #5 (3rd on the drives side) plug looked a little rough. Below are my results:

#1 - 130-132
#3 - 133-134
#5 - 0 (yep, you read that right, a big fat ZERO)
#7 - 125
#2 - 122-123
#4 - 122-123
#6 - 133-134
#8 - 126-128

All in all, they are all very close, minus #5. I checked #5 3x just to be sure. Any suggestions? Am I looking at pulling the engine completely out?

I am thinking it could be the following:

Valve guide
Valve spring
Head gasket
Lifter
Piston rings (Distant possibility)

I know, I really won't know till I pull that valve cover, intake off and inspect it.

Thanks in advance for any assistance.

[Blue 82]

A few years ago i had the same prob in 2 cyls
one one each bank
no water in the oil
no oil or water usage


turned out to be the rings were glued in the piston
with a clear golden epoxy like substance
The pistons fell out of the block
and would slip right back in, even with the rings on


Having used valvoline oil since the day it was built
I contacted valvoline
offered to send em an oil ring
they declined to accept

you may have other problems
does it use oil or water?
do you have excessive blowby?

Check this out
you may want to consider making one or buying one
http://www.carcraft.com/techarticles/116_0406_cylinder_leakdown_tester/index.html

[VileZambonie]

Do a cylinder leakage test on #5 cyl at tdc compression. if you don't have a leakdown gauge just put some regulated air in the cylinder and listen for where the air is coming out. ex. intake, exhaust, cooling system, crankcase...

[77chevypu]

Thanks for the suggestions thus far,

There is no noticeable oil/water loss. I do have an oil pan gasket that is leaking, so it is hard to tell if I am losing oil any other way. I do know that it does not smoke, when first cranked or when driving it around.

One thing I have noticed also is, after I shut the truck off, I hear this "hissing" sound coming from the crankcase breather that is in the driver side valve cover. The "hissing" lasts for a good 3sec or so after the truck is off. I firmly believe this is my needed compression for the #5 cylinder...

So I am strongly leaning towards it being something in the valvetrain (busted valve spring/guide/lifter/etc).

Thoughts?

[VileZambonie]

You need to do a cylinder leakage test. If it's leaking into the crankcase it's stuck or broken rings or a hole/crack in the piston

[Captkaos]

I agree, put the piston on TDC and run a leakdown test on it and find where the air is going.