gearheads78

So I am making plans to take the money I got out of the 66 to build a new shop. After talking to a few contractors I am a little short on what I need. I've got a 69 Firebird project that I have been trying to sell but its needs body work and only barely runs so I decided to see what it would take to get it running good to help sell it.

So this motor and engine compartment look pretty ratty. Other than some rusty chrome valve covers there is not really any signs its anything other than a stock motor. It has the right heads for the 69 but the block is a 73-74 400 block.

So I start out with a simple compression test 150,150,152,153,148,151,150,0 hmmm that has to be a mistake lets try again 0 can't be right, 0 again rut row

Pull valve covers it got new looking roller tip rockers and screw in studs and guide plates nice supprise.

Pull the intake. Motor is fresh and super clean looking. Look in the intake ports ...heads have mild port job and nice work on the bowls ...really nice supprise

Pull the head expecting to see a vent valve. See fresh looking forged pistons ...someone really spent some money on this motor. No bent valve . No hole in the piston No gasket, piston or block damage. Pushrods and springs all good. No tight valve hanging up in a guide.

It stumped me for a while but I did figure it out. I have never seen this happen before and cause no compression.

Since I have you vested in the story now I'm going to leave you hanging and see if anyone guesses what it is

mike's88

wild guess, on everything you've mentioned, except sparkplugs. The center section of the plug (insulator, electrode) blew out, thus letting all comp. blow out through the plug?

Oldsguy

A bad lobe on the cam????

BIGJERR

No rings! lol

Coltonis

Hmm, that sparkplug idea sounds good too, but I'll go with piston rings on that cylinder are fubar-ed?

**Doh - BIGJERR clicks faster than me...

lshlsh2

No piston at all

gearheads78

DING DING DING. # 2 I and E were ground down so bad the lifters are 1/4" short. The intake valve was never opening to let in any air in to compress. I've seen flat cams before but never so bad the valves did not open at all.

That was quick. Everyone give the old(s) guy a hand

Rickman48

Both not opening would give you compression!
Pull the head and I'll bet you'll find bent/broke valves or a broken piston.
[just another 'old guy'!!]

svnt442

Just an FYI that's not a possibility because you have to pull the spark plug out to check the compression.

D'OH!!

gearheads78

Head is off. The only thing I can find wrong is the flat cam. My thought is since the intake valve never opens when the piston is going down it creates a vacuum holding the gage to 0. When it comes back up all it does compress the vacuum never bringing the gage up.

citcapp

That's a new one on me. Good guess Dan.

Sounds like a new cam will make it a strong runner Richard

Oldsguy

Wow! I are a smart feller now.

citcapp

My hearing is bad Dan, did I hear you say I are a fart smeller

Rickman48

I'd still check for a bent valve - somethings not closing!
Compression testers have a one - way valve!

coltsneckbob

OK.......either:

1) A blown head gasket
2) stuck valve
3) cracked head
4) broken connecting rod
5) Cam was sheared off and not turning for that last cylinder
6) something caught in the intake to that cylinder
7) You have a 7 cylinder engine
8) Broken (sheared off) crank shaft and not pumping that last cylinder
9) bullet hole in the cylinder
10) Missing piston
11) burnt, twisted, warped valve
12) Broken rocker
13) Broken Flux Capacitor
14) Cracked cylinder wall
15) You were listening to Doors on iPod and got stoned

!!!!!!

gearheads78

OK how can a broken rocker be any different than a completly flat cam and ground down lifters so bad that they are 1/4" short? I am pulling it all the way apart soon to tripple check everything but the flat cam is the only issue I can find.

coltsneckbob

Well, I am surprised u didn't question #13, but then again perhaps time travel is not of interest to you. A broken rocker could keep the valve open. Yea same affect as many of the other problems folks cited.....but that doesn't mean it aint the case.

Whoa.

Incidentally, one lobe on the cam is ground down and the rest OK???? Possible, but not likely.....unless something else on that cylinder went wrong....er like broken rocker.

If a single push rod is bent, or lobe on cam is flat, then u really have to determine why that happened. It could be the lifter was imperfect, or metal chips got in there, but I wouldn't just replace the cam till I pretty well determined the cause. E.g. could there be a reason oil didn't get to it?