I have low compression (~80 psi) in my #2 cylinder and I think I've traced it down to a stripped intake manifold bolt I pulled the valve cover on the passenger side and the valve doesn't seem stuck.

All of the other cylinders are over 160 psi. Based on the detailed receipts I have from this car, the engine was completely rebuilt about 16,000 miles ago, though the rebuild happened in 1990

Anyhow - I'm planning on pulling the manifold and inserting a Helicoil. I've never done this before. Does anyone know the correct manifold bolt size is so that I can determine which Helicoil kit to buy?

(the stripped threads are one of the two I circled in the img attached - can't remember which and I'm at work right now)

Do we think this could be the culprit?

Thanks,

Justin

 

I very much doubt that is the problem, if you were loosing cylinder pressure there there would be a obvious noise of escaping gas and the head gasket would also have to be blown at that point. I suspect a bad valve, bent pushrod or bad lifter(probably a bad valve).... Just my thoughts....Tedd

 

I also cannot imagine the stripped intake manifold bolt hole being the source of your problem. The lack of a seal at that point should indeed cause performance problems, but not a loss of compression.

 

X3, did you perform your compression test both dry and wet? Also if you do a leak down test it may point to the culprit.

 

Was dry and cold.

So I just squirt some oil in the spark plug hole of cylinder #2 and do another compression test?

What am I looking for?

 

The two bolt marked 7 and 8 are clamping the intake at the cross over on the cooling system so if they were leaking then antifreeze would either be leaking outward or burning when running, can you smell burning antifreeze from the exhaust? Checking for a cooling leak won't work as the leak is ahead of the compression chamber, otherwise I would pull the galley cover and check all of the lifters, a small amount of dirt can clog one enough to not open intake valve enough but move it enough to not make a tappet noise ( had one go bad while driving to a cruise, ended up replacing them all)
Steve

 

I haven't managed to get this engine running long enough to get it hot, since I installed it (seemed to run fine before, 2 yrs ago).

Would you all suggest I get it running for a while before tearing into it? Maybe something will unstick?

Sorry guys - I'm new to this, just learning as I go.

 

Agree with several previous posters, an intake leak is not the current reason for low compression; although, it could lead to a burned valve if it was causing a lean condition due to a vacuum leak. Do a leak down test to see where air escapes from, the carburetor (leaking intake valve), exhaust pipe (leaking exhaust valve) and/or out of the crankcase through a breather or oil fill hole (ring and/or piston problem).

If it was mine I would run it for a while to see if something is sticking as it has only been driven 16K miles in 24 years. The problem could be a weak valve spring if the motor sat for an extended period without being rotated. The springs that are compressed during the long term storage can become weak and will not close the valve tight enough to make a good seal. Replacing a valve spring does not require removing the cylinder head.

The only potential problem I see is if it is a ring problem, there is a chance that running it might score a cylinder wall.

 

Yes a few squirts of oil into the cylinder and redo the test. The leak down test can pinpoint to where your losing compression. As others have said, there are many reasons why this happens and some are not requiring a complete rebuild.

 

Absolutely. Add some Marvel Mystery Oil to the fuel and take it on a nice long drive more than once. Nothing is worse for mechanicals than leaving them sit unused. When you do your compression test the motor should be warmed up, all plugs out, coil disconnected, and the carb wired fully open.

 

Another issue could be if your using the old gas tank is varnish. If the tank hasn't been cleaned there is a layer in there that will mix with the new gas and coat the intake valves and cause them to stick. I've had this happen many times when reviving these old girls.

 

Until a couple of weeks ago I had a line going to a jerry can to provide fuel. I just connected the tank.

But yeah, I'm sure there could be lots of gunk of all sorts sticking things, though I did pull the valve cover and watched the valves bounce up and down as I cranked.

So here's my plan based on input:

1. Try and get engine running til warm
2. Pull the plugs and squirt oil in cyl #2 and re-check compression
3. If compression increases, assume it's the rings (?)
4. If not, fab up something to put air in the cyl and listen for where it comes out (with plugs back in)
5. Report back here

Makes sense? Is this the right approach?

 

I would not worry about anything until it gets running and everything heats up and works back into place. It really does need to be run for a while.

 

From what you have described, I would not think the intake manifold is your problem. If it were me, I would do a leak down test first. Most compression gauges have a hose that utilizes a standard air line quick disconnect. Remove the Schrader valve from the end that screws into the head. You can use a valve core remover tool. Don't loose the valve. It is different than the valve core used for tires, but looks similar. Remove the coil wire. Screw the hose in. Stick your finger over the end and bring the piston up to TDC with a friend bumping the ignition. You can unscrew the hose and put the eraser end of a pencil into the spark plug hole. Now turn the engine very slowly back and forth from the crank balancer bolt with a breaker bar. The reason it needs to be exactly at TDC is, when you put compressed air into the cylinder it will try to push the piston down, unless you have a serious leak. A leak down tester is basically just a hose with two gauges hooked up and an air pressure regulator. One shows how much air is going in and the other shows rate of leakage. You should hook up an air pressure regulator at your compressor. Set it for 50-75 PSI. Now hook up the air and see if you have a leak. Listen at the carb (intake valve), listen at the tail pipe (exhaust valve), and listen at the oil fill tube (rings or piston problem). It's really not necessary to know how much leakage you have unless you're trying to do a comparison between cylinders. The important thing is to pinpoint the leak source. I believe you have a burnt valve. You said you can see them moving up and down so that pretty much rules out a bent valve. Usually if the rings are not sealing well you would not drop that much compression and it would come up by oiling the cylinder for your compression test. Very often when there is a burnt valve you may have back firing. The other reason I would not try running it too long is, you could create more problems, and damage other internal components if you have a bad valve or rings. Good luck, and please keep us posted on what you find.

 

Was really cold out last night so I didn't get to the garage. Today it's around freezing, so I'm going to spend some time troubleshooting with the propane heater going. (Damn, propane prices are double what they were in the fall!)

I'll report back later today.

 

So... waited for the weather to warm up a bit to to get the car running. The plug wires were totally useless, most of the wires were bad, replaced those (and the plugs) and managed to get the car started for a few seconds at a time by pouring a little bit of fuel in the carb. Then it dies.

I replaced the old fuel pump with a rebuilt unit I found on eBay a while back. Removing the line from the fuel pump to the fuel filter results in no fuel exiting the pump when cranking the engine. I checked that the lines were ok with a giant veterinary syringe, no blockages in the line.

Maybe a vacuum issue? Do I go to an electric fuel pump?

 

So, you have fuel to the pump from the tank? Check the rubber lines from the tank to the pump for cracks, it may be sucking air.

 

I was able to prime it with a big syringe - got it to flow to the fuel pump. The rubber lines are new, the main steel line is old. I'll check again to make sure nothing is leaking.

 

Maybe the clog/restriction is in the tank itself, not the line?

 

It's possible the metal line can have pin holes and not leak. I know other members have had that happen. Did you try blow air all the way into the tank?

 

Ah I am glad someone else has a very similar prob! I haven't had the time to do the leakdown test myself... I have figured that I have a bad intake gasket. BUT, I do have antifreeze leaking from at least one of the bolts that are circled in the diagram at the start of this thread. I guess that is what that strong smell is when the engine is running...burning antifreeze I did do the spray carb cleaner around the gasket and I have a bad gasket for sure. I just haven't gotten around to working on the car yet, esp since winter in Ohio has been super bad. I hope your situation is resolved!

 

I'm going to go out there now and blow air thru the system, just to make sure there's no blockages etc.

 

You could test your fuel pump by hooking a vacuum gauge to it. Have a friend crank it over and watch to see if the needle moves.

 

Pulled the fuel pump and re-installed it, making sure the rotor was pointing to the cowl per the instructions in the service manual, and put a bunch of grease on the rocker arm. Pumps fuel now, but no idea how much pressure. I'm able to get some squirting in the carb. So that's good.

Now I need to get the car warmed up at least, but it's now super cold in the garage, close to freezing again. Will run the heater in the garage again and head out tonight for a bit.

 

Can't start it. It starts for a second then dies. Carb seems to be leaking a bit at the base when I pump it lots or pour a few drops of gas in it.

 

If you look down into the carb and operate the throttle by hand, do you get 2 solid streams of fuel spraying out the nozzles?

 

More like 2 streams of mist.

 

Anyone think I should pull the carb and inspect? I've got a carb kit from a few years ago sitting on the shelf...

 

If it were mine I would spend my energy on the things you know are a problem, get a good fuel supply to the engine and a good spark. Other wise you will be installing unnecessary parts only to find out later that they weren't needed or created a new problem you didn't have before that will make it even more difficult to diagnose.

Even with a poor fuel delivery system(carburetor) you should be able to at least keep the car going till warm by adding fuel down the carb, admittedly it will run like crap but it will run long enough that maybe you can diagnose you real problem.

If you take the fuel line loose from the carb and put a coke bottle on the line in about 15 seconds of cranking you will fill it up, if not look for a obstruction in the line could be the screen in the tank is partially clogged that lets some but not enough gas to run the engine or you have a defective fuel pump.One must eliminate one thing at a time or you will get lost in the corn flakes.....Just a few thoughts ...Tedd

 

As mentioned above, most vacuum gauges are also fuel pressure gauges. Hook it up to your fuel line and see what kind of fuel pressure you have. You can T it in with clamps and check both cranking and running pressure.

 

Sensible advice. Thanks... It's always tempting to pull everything apart and replace stuff, learning that lesson...

 

Found this in my tool chest. Had no idea I had this - it must have belonged to my Great Uncle who used to own an automotive test equipment company in Kalamazoo, MI. I was given a box of his old tools a while back.


I'll test at the carb and I guess pre filter?

obzgvru.jpg

 

Ok, I've tried measuring the fuel pressure at the fuel filter and the pump outlet. I'm getting max 2 PSI, and it's not holding steady, the needle is bouncing up and down. I'm assuming this may indicate some kind of blockage? Or a leak?

Should I work my way back from the pump and blow air through the hoses?

 

First of all, 2 PSI is not enough. I believe you should have 5-6 PSI. Here's what I would do. Have a catch pan ready, and disconnect the feed line to the fuel pump. If fuel drains out, try to remove the gas cap. If it continues to drain, cap the end with a hose and a bolt, or a correct size rubber vacuum cap. Now install another fuel line going into a five gallon gas can. Crank it over and check your fuel pressure. If your fuel pressure is good now, your problem is in the fuel line, strainer or gas tank. If you don't have good pressure, you should replace the pump. If you do have good pressure, there's a couple things you could try. Remove the cap from the line and blow compressed air back toward the tank. Don't use full blasted air pressure. Try to listen and feel for a restriction while blowing back to the fuel tank. You should hear bubbling in the tank. If you do feel a restriction, there's a good chance the strainer is clogged in the tank. I'm betting you have a fuel pump issue. If the strainer is clogged you may want to have the tank cleaned or boiled out. Usually radiator shops can help with that. Some of these older cars didn't even have strainers. You could also try blowing compressed air with a rag at the filler neck to seal it up. You should get a nice stream of fuel out of the line into the catch pan. The other thing you should do is inspect the fuel line very carefully from front to back. If you see any signs of dampness, you probably have a rusted pin hole. You could disconnect the fuel line at the tank, plug it, and use a hand held vacuum pump at the other end. Pump it up and see if it holds vacuum. If you're trying to start the car by pouring fuel down the carb, be very careful. I got burned pretty bad a few years back. You should fill the float bowl through the vent hole. Now, I always use an oil can, filled with gas, with a long flex tip. I can't stress enough, to be careful when you have gas fumes or open containers. It happens so fast. I was using a spray paint can cap filled with gas when I had my disaster. When I was pouring down the carb we had a backfire. I jumped back and the fuel spilled on my chest, arm and leg. I stopped dropped and rolled twice. My arm wouldn't go out until I got my jacket off. Please don't be stupid like me. Have a fire extinguisher handy, and it's always good to have a friend near by.

 

I'm trying to be real careful - what I'm doing is pouring a very small amount of gas into the carb prior to cranking. Have got a fire extinguisher handy. Of course, with the small amount of gas I'm pouring in the carb it's just starting for a few seconds.

 

The plot thickens.

Somehow I'm letting the smoke out of the positive battery wire to the starter when I'm cranking the engine to check the fuel pressure.

Cranking seems a bit 'weak.' It also seems to wear the battery down quicker than it should. Starter / Solenoid issue?

This is making me nuts.

 

Do not pour fuel down the throat of the carb. Fill the float bowl through the vent hole on the top as I described. It sounds like you have bad cables or connections. Clean the battery terminals and cable ends. Check the ground on the block and check for corrosion at the starter. This does not sound like a solenoid problem. Charge your battery up and have it tested.

 

Ok. I'll check the terminals etc.

I've tested the battery at the part store recently and it's fine.

 

Was getting frustrated with the fuel pump - had it connected to a jerry can and it still wouldn't pump fuel into an empty vodka bottle. So I pulled it, put the old Delco unit back in (likely the original) and now it's pumping great.

It's late now, so this weekend, I'll connect the carb and fuel line to tank and try again... Very happy to at least get fuel to the carb line...