Low cylinder pressure = bad news

[DoubleV]

My engine has always run a bit rough. Not really rough mind you, just enough for the engine to shake a little at idle but not enough to make a big deal about, but I finally wanted to get my engine purring like a kitten, so I decided to delve into it today. I figureed new plugs and wires was a good place to start;

Most of the plugs looked pretty good, but one looked a bit rougher than the others. Hmmm. So I did a cylinder pressure check on all the cyliders and they were all over the place;

1 175
2 130
3 80
4 40
5 160
6 180
7 160
8 Couldn't reach the damn thing but I already found out what I needed to know.....

Those things are all over the place!

I squirted a little oil in #3 to see if it was a rings and it made no difference. I pulled the valve cover and all the rockers were moving good so I figured it wasn't a wiped cam ( and there was never any ticking either ).

So the only thing I can come up with then is something with the valves not sealing properly. Whether that's the case or not, I'm really not happy with having to deal with major engine work like this in a PRO build mild engine that never saw higher than 5500 RPM's ( and rarely even that high ), proper oil changes with proper oil additives, under 7000 miles, and generally well taken care off engine/car that isn't abused or beated on.

😢 :x

 

[Clone TIE Pilot]

It seems old that the two lowest cylinders are right across from each other.

 

[online170]

Not to sound stupid or make you sound stupid but just want to make sure were all on the same page....

1) was the engine warmed up?
2) did you do multiple cranks until the psi would not go any higher?
3) did you have the throttle wide open while cranking?

 

[DoubleV]

Not to sound stupid or make you sound stupid but just want to make sure were all on the same page....

1) was the engine warmed up?
2) did you do multiple cranks until the psi would not go any higher?
3) did you have the throttle wide open while cranking?

No, yes, and yes. I even did the 2 real bad ones multiple times to make sure the readings were accurate and got the same numbers every time.

It seems old that the two lowest cylinders are right across from each other.

I noticed that too, but I think it's just a coincidence and doesn't mean anything AFAIK. If they were adjacent and all the other cylinders were good, I would suspect a head gasket. The only thing I can think off is the valves not sealing good enough. I guess a leak down test should verify that, but I never did one before.

 

[pontiacgp]

So the only thing I can come up with then is something with the valves not sealing properly. Whether that's the case or not, I'm really not happy with having to deal with major engine work like this in a PRO build mild engine that never saw higher than 5500 RPM's ( and rarely even that high ), proper oil changes with proper oil additives, under 7000 miles, and generally well taken care off engine/car that isn't abused or beated on.

😢 :x

You're taking this alot better then I would be. 7,000 miles on a rebuilt is barely breaking it in. I'd see if the builder would help out on it cause something wasn't done right in the rebuild.

 

[online170]

The wot makes a big difference but the warming up thing not so much in my experience.

Sounds like its time for a leakdown test. Does the engine feel like a pig? Ive had the odd cylinder go down to 80 or 90 and it felt very gutless.

To check the cam might be a better idea to measure lift with a dial indicator.

That sucks big time.

 

[foxtrot]

A few years back I had a similar issue on one of my rebuilt SBO engines. The thing was that I didn't do the rebuild myself and was very disappointed because I paid someone else to do the work. I did the install and on the maiden voyage, had some popping out of the carb. When I started checking a few things, found out that cyl#1 was way low (around 85 psi). Turned out to be a bad intake valve that wasn't seating properly. I don't know how this happens on a brand new rebuild with reworked heads. Anywho, my guess is on bad valve seats...

 

[DRIVEN]

I think you're on the right track. Do the leak-down test and let us know what you found. Definitely sounds like a valve issue to me by your description. Sounds like you've had this problem since day one. They are across from each other. Do they share a runner that might have a vacuum leak? If so, the lean condition could have caused you to burn valves. I wouldn't necessarily expect any help from the builder if any significant time has gone by, even if the miles are low. Can't hurt to ask though. You'll need to do the leak-down first so you have all the info before you talk to him. A polite customer with a specific, legitimate complaint that's done some homework will get a better response than kicking in his door and grunting, "Car broken". Keep us posted.

 

[olds307 and 403]

Rocket Racing did your motor, correct? Your times are awesome, considering those awful numbers. 2,3 and 4 are not good at all. My $500 rebuild, the lowest cylinder is 130 psi. Your luck stinks, hopefully just needs a valve job. A good excuss to up the compression a bit, while they are getting ground anyways. Doesn't sound like rings, hopefully.

 

[DoubleV]

You're taking this alot better then I would be.

I'm not taking it as well as I may be letting on! I think the only thing that makes my situation even remotely tolerable is the fact I was planning on pulling the engine this fall to pack a bit more power into it anyway. I'm still pissed this happened and when I find out exactly what the issue is, then Rocket Racing ( the builder ) will be informed about it too. If RR stands by their work, they should hook me up with what I'm going to need to get this fixed CORRECTLY. I will not be happy if I get the 'YOU must've did something wrong' routine like what many places do, because I know for a fact this problem isn't my fault and could only be from shoddy parts, machine work, and/or assembly AFAIC.

If a pro engine builder that specializes in building Olds can't build a sub 300 HP Olds properly, you've got to question their commitment to quality but I will reserve judgment until I get more info since I don't want to bad-mouth RR without having all the facts, but things ain't looking so good....