Hi guys,
I ran a compression test yesterday and it wasn't as good as I had hoped.
'71 Cutlass Supreme, stock 350. Either 52k miles or 152k.

#1 = 155
#2 = 140
#3 = 145
#4 = 140
#5 = 140
#6 = 126 - wet test = 128
#7 = 120 - wet test = 122
#8 = 135

I have the motor stripped so I couldn't warm it up so these are cold readings. I also don't have the carb on the intake and the bores taped over to keep out crud. But I did uncover the front (small) bores. All spark plugs removed and the same with the coil.
I've been piecing together the story of this car from notes in the glove compartment, parking stickers, and the obit I found online of the PO. and it seems the car sat for a good 6 or 7 years. Could the low cylinders have weak springs? Is it a coincidence that the two low cylinders are sequential in the firing order? They're on opposite banks so it's not a head gasket.
Lastly, I might at least retest the #7 cylinder since it was the last one I tested and the battery might have been lower in charge.
I have the #7 heads if that helps at all. I don't see the letter "a" anywhere. Just 7.
As always, thanks.
-Mac

 

Do you not like all the numbers or just the low two. I would say you need to open up intake and retest all You will get different numbers due to every tester is different so consistence is the key looks like you are not far off

 

The engine should be warmed up for a test and the manifold needs to be open. I think your engine is a bit tired but not worn out. All cylinders need to be with in 10% of each other. #6 and 7 are on opposite sides so no relation for a problem there. What did the other cylinders do wet?

 

You might have a little carbon on the valves, I'd get it back together & running. Once its warmed up use a spray bottle & mist some water into the carb, or you can try seafoam.

 

The car's 40 years old. Don't sweat it.

- Eric

 

I should have mentioned I'm going to pull the motor anyway. I don't think I want to put it all together just to take it all apart and pull the engine. I'd rather just yank off the heads and see what's going on. What might it cost to have the heads cleaned up? I don't need anything fancy. Stock would be just fine, other than the heavier springs I'm getting with the new cam.
However, that doesn't help the piston heads if they're covered in carbon. I don't suppose those can be cleaned with the heads off. I'm picturing lots of crud getting down in the cylinder.
So the Seafoam trick really works? I read it's possible to use a vacuum line to slowly pull the liquid in while running the motor at 2k rpm.
Oldcutlass, I didn't oil all the cylinders, just the two that were low. But I can. Out of curiosity, what would a new engine read on a compression test?
Lastly, I'm guessing a warm engine would give lower numbers. Is that true?

 

Eric, not sweating, just want to do it right....without a second mortgage :-)
I'm going to pull the motor and see where it takes me. My brother in law has been a mechanic for 30+ years and might be willing to help with a rebuild if I decide to go that route. I'm just not sure I'm there yet.

 

Certainly it's good to fix up your car, and nice to modify the engine for more power, but if you have a good-running engine, you don't have an major rebuild or modification plans, and you don't want to incur any major expenses, I would strongly recommend that you let sleeping dogs lie.

Once you get that motor apart, there will be at thousand things that need to be done, and a thousand parts that could probably work fine if you put them back, but that really should be replaced, even if you're not doing a rebuild, but, then again, while it's all apart, you might as well do a little machine work...

Mark my words, once you've turned the first head bolt counterclockwise, you will hear the sound of $4,000 rushing out of your bank account.

- Eric

 

If it was still together I would say change the oil and instead of 5 qts of oil use 4 qts with a qt of either kerosene or mineral spirits. That would have cleaned out the rings a bit for a more realistic reading. Warming it up helps too, as mentioned.
As far as head work goes you can do as little or as much as you want. Just removing them, cleaning them yourself and changing the springs won't cost that much. But it's easy to get in much deeper from there.

 

An inexpensive jobber valve job will probably run around $300ish. A compression test with a warm engine may bring the numbers higher. I agree with adding something to the engine but I prefer 4 qts oil and 1 qt transmission fluid or rislone. Pouring 8 oz of water very slowly (very slowly) into an warmed engine running at about 1500-2000 rpm works well at cleaning carbon deposites in the combustion chamber.

 

Ha..I'm with you.

My old motor has numbers like yours Macadoo, and its run out just fine. Sure high miles, but beware of the "might as wells". They'll add up pretty quick.

I've done the these things the guys are suggesting. Nothing wrong with that. I'm a user of sea foam too.

 

After much thought and budget discussions with the wife, I've decided on a plan. At least one for the time being.
1. Pull the motor (just picked up my 2 ton stand) This is a must. She's leaking from pretty much everywhere.
2. Clean and degrease while all the holes are still plugged.
3. Replace all the gaskets and seals.
4. Pull the heads and clean them up.
5. Replace the timing set, water pump, put in new cam and springs.
6. Paint the block, heads, and exhaust manifolds (I'm keeping the manifolds stock)
7. Put on the Edel 3711
8. Detail under the hood.
9. Re-install the motor, add the rebuilt Q-jet with electric choke, distributor, etc. etc.
10. Replace the hood (this one makes me nervous, I may drill for a couple of alignment pins) Fire it up and use the oil/trans fluid trick. Maybe Seafoam or water (yes, very slowly) down the carb.
11. Brakes, all around
12. Dual exhaust (with flowmasters?)
13. Wheels and tires.
*Of course pulling the heads is still in the "debatable" column. Eric, I drove it about 100 miles on the interstate when I bought it and before the sticky float changed the get-it-home plan, she ran smooth as silk. Acceleration wasn't good but she was flooding herself out at the time.
This is what I want to have done by next summer. Thanks for all the input everyone!

 

I have a shortblock here with appx 20k on it .030. 7 cc cast pistons .040 in the cylinders. Needs to be freshedned up at the minimum. Skirts to have some scuffs but nothing that would worry me. 200

 

What's a shortblock? And where are you located?

 

Oh Elgin, just saw that. Not too far. But really, I think this motor has some miles left on it. Thanks anyway Copper.

 

The shortblock is the whole rotating assembly and block ., pistons rods etc. everything under the heads and intake. Just thought I would mention it. I got a few shortblocks here that need very little work to be out into service.

 

Oh, gotcha. I really think my shortblock is in good shape. Otherwise I would take you up on that. But I really think it's the valves that are causing the issues. Too bad too, I have a brother in law in Elk Grove that the wife and I like to visit.
So your avatar, is that in Rockford then?

 

That's at union grove wisc. I thought I would throw the short block out there if the might as wells kicked in and you had a budget. I no longer runat the grove 45 for a test n tune byron is 40 miles from my house they move the lanes fast and its 25 for a test n tune.

 

didn't think your numbers were that bad

here is what I found on my new 71 and I thought it ran pretty good

these were my dry numbers

#1 -75
#2 -60
#3 -60
#4 -85
#5 -25
#6 -70
#7 -45
#8 -65

 

Daddy, one more argument for leaving the heads as-is. Thanks man! I'm gonna' go with what I know for now. I can always pull the heads with the motor in the car if need be.
Copper, that sounds fun but I'm guessing addictive. And at $25 a pop....which actually didn't sound like a lot until I envisioned myself wanting to run three or four times in a day. yeah, that could add up.

 

It's 25 all day to test n tune. So you run as much as you can.

 

Definitely sounds fun. But I'd need something other than my 2.56 gears

 

If you decide not to take the heads off. Water down the carb is the way to go. You'd be amazed at how well it can clear carbon under presure. If you are worried about 6 & 7 a leak down tester will give you a better idea of whats going on.

 

It really works that well eh? I've seen it on youtube but it always seemed sketchy to me. How do you meter the flow of water into the carb? I read somewhere that dipping a manifold vacuum hose into the liquid will pull it in slowly enough.

 

A spray bottle. It could be any old spray bottle left over...the primary effect is steam to break up the carbon. A little at a time, just like using solvents in a can.

Same but different.

 

I always used a stryofoam cup half full with a hole poked in the bottom with a pen to get nice round drops. My thinking always was/is I don't want it to evaporate in the intake on the way in so make it nice big with a slow but steady bb gun sized drip drip drip, not a solid line of water. and keep it reved to keep in running. A ball of water that size thats trying to get compressed has to make a big bang in the cylinder. just leep it reved up. you dont want it to stall and accidently keep feeding water down the intake, just be ready to move your hand away if it does.

 

All you do is get a glass of water, hold the throttle open, and pour it in.

You'll need to hold the throttle open a bit above idle, and if you pour it in too fast, the engine will start to bog down.

The last time I did this was with a '61 Mercedes, many years ago, and I seem to recall I gave it an 8oz glass of water over about a minute.

Remember, the thing you want to avoid is adding so much liquid that you bend a rod on compression, but since the engine won't run with more than a very small amount of any liquid entering the cylinders (too much gasoline will stall it, too), it's hard to give it that much, unless you just pour the glass in like you're pouring it down the sink.

- Eric

 

I was watching videos tonight of jokers pouring seafoam into the carburetor or brake booster hose WAY TOO FAST. One engine started knocking loudly and the video stopped short. Geez. But it got me to thinking, what's the best way to get a mist of water into the cylinders? Right, a spray bottle. But it seemed there could be a better way so i did a little research and found this article:
http://journeytoforever.org/biofuel_...earth/me3.html
Then I learned racers have been using this method for years. If nothing else, it's interesting.

 

Going by your figures in the original post I'd say the bottom end is in fair shape, but a couple of valves aren't sealing too well.
If I was in your shoes I'd pull the heads and check out the valves and seats. I doubt you'd find much wrong, but a few hours lapping the valves in will probably pay dividends for the price of a gasket set and a little elbow grease.

Roger.

 

Yeah my 72 350 checks in w similar comp numbers. AFAIK it's all original. It starts and runs good but isn't all that fast. But it runs good and uses maybe 1/2 qt of oil in 1500 miles so I pulled it regasketed it and put a t chain in and put it back in.

If on a budget I would run yours as is w new gaskets and chain. I spent about $300 on gaskets, chain mt mounts, belts, hoses and few other little things

 

Yeah fellas, if I pull the heads I'll definitely lap the valves. It's been a few years but it's not too difficult. As you said roger, a few hours elbow grease.