Inliners International Forums General Discussion Engines Low compression on cyl # 1

Hello eveyone. I have been trying to track down this problem that I thought was just a manifold gasket that was leaking really bad. I discovered that the manifold was missing the next to last hold down bolt, and the very last one was working itself loose. I would tighten it and the faltering on the freeway would go away and I could flog it all the way to 4,000 RPM... until the bolt works itself loose again.

The other day on the freeway, in the midst of a 70-75+ MPH flogging, she started to falter and I backed off immediately. It didnt surge like it usually does when its the loose bolts. It started running really rough, sounding strange, and I could feel a distinct loss in power when trying to accelerate.

I came home and checked my compression, #1 was at ~20-ish PSI dry, and wet only got about another 5-ish PSI. The rubber grommet that seals the compression gauge against the cylinder head had broken, and I was able to use the washer off a spare spark plug to get it to seal. Not the best means to seal, but it worked better than nothing at all. CYL #2 was 125, #3 130, #4 110, #5 120, and 6 was 135. I was able to gain about 5-10 additional PSI when I attained a decent seal. Compression was always on the low side, but never really below around 110-115, and never higher than 135.

My radiator does leak, but I dont see coolant in the oil or vice versa. I thought maybe number one burnt through the cylinder head itself, but im not burning coolant. just lots of oil. all 6 plugs had a lot of ash and buildup on them.

What do you folks think? I hope it's just a burnt exhaust valve. Head gasket would be ok too, just a real P.I.T.A.

Sounds like it ate a ring or two in that #1 hole.

Sounds like it's time for a rebuild.

Bad compression is almost always caused by one of three things. 1. Burned valve or bad valve seat 2. Broken or worn piston rings 3. Blown head gasket, scored or cracked cylinder wall or cracked cylinder head.

You seem to have eliminated a blown head gasket, cracks in the block or head, so that leaves problems with either valves or rings. Either of those means taking the engine apart to fix it. If it's burning a lot of oil, that sounds more like rings than valves. The good news is that since you need to take the radiator out to pull the engine, you can get the radiator leak fixed at the same time.

Thanks for the replies everyone. This was my daily driver, so from the sound of it I should cancel my insurance, as its looking like I wont be driving it any time soon. I googled pics of a burnt exhaust valve to see what it looks like, daaayyyyuuuummm.

Im still hoping and praying its just a valve.

If it turns out to be rings, that's pretty much a rebuild, right? would it be possible just to hone and re-ring it? or will I need to bore it and replace the pistons too?

im just wondering about the price of the parts and what parts I should be looking for. Tlowe has an awesome selection of parts, but im not making enough power or money to justify, but man, do I want em! Im thinking inexpensive, but not stock. like the shallow dish propane pistons, and a nice cam just to get her back on the road. thats about the 6-800 range for parts and about the same for labor and assembly.

I work as a cashier at a kroger and my checks basically cover the cost of school and gas to get there and back, so doing a full rebuild would take a lot of money and probably a couple of months, but its not totally off the table.

I do have a spare engine thats been sitting in the 67 for a few years. It ran fine when I bought it, compression test was ok, thats the only reason I bought it. I had taken the head off it and its been sitting outside and although its been covered by the hood, so it's not totally exposed to the elements, I expect some surface rust.

I am heavily debating cost/benefit ratio of pulling the engine from the 67 and making it ready for duty. I've no clue how to handle an engine that's been sitting for a long time except to use lots of oil on everything before doing anything. What are the things I should do, or shouldn't I do to the engine that's been sitting for like 6 years?

thanks again for taking the time to read this.

If it's a 230/250 and it's toast, I've got most of a short block (230 crank, 250 pistons) that you could piece together cheap. Its just a long drive over the mountains away.

Noblesix, what size engine are you talking about, and what car is it in now?

It's a 292 in a 69 C10 longbed.


Its funny too cause I was actually planning on going over to the other side of the state to see my mom. good thing this happened here in town and not on the pass.

292's are easy to rebuild and parts are readily available. Pending on mileage...and how worn out the engine is will tell you if you can hone and re-ring or get to some fresh metal. .030 over stock type pistons are pretty cheap from summit racing. They even have propane pistons there to. But they are cast and not forged.

It might surprise you on how easy it could be to fix.
Engines can have low compression for a # of reasons as pointed out earlier.
I say, take it apart and figure it out. It may be a bad valve spring allowing a valve to hang open. Replace spring and you are done.
All older engines have varying amounts of compression per cylinder. I would just tell you to fix what is needed and get back to driving it.

I agree, just tear into it and see. It's also possible that it is something that hasn't been mentioned yet. Just start turning bolts and take a look inside.

You might try backing off the valves and putting air pressure through the spark plug hole (there are adapters for this)
This would tell if you have a bad valve or piston

Will Willis

Thanks everyone. As soon as i can buy a basin to catch the coolant, ill take the head off and see what happened. Really dont want that stuff getting into the street. Shes sitting i n the driveway waiting patiently for open heart surgery. Friend of mine drove me home and remarked about how my tires looked so new... told him yeah, saved up for 3 months to get 2 tires and an alignment, and she eats a piston. He laughed and asked when that happened, i replied, on my way home from the alignmemt shop. Ha!

Pulled the head and I cant see anything wrong with the valves. theres a lot of buildup from burning oil, but no cracks or chunks missing or anything. there is some discoloration, and some of the intakes have a lot of buildup on the face, but I expected that. #1 piston has ash built up in the dish and the others look similar. cylinder walls look smooth and not gouged or otherwise damaged, other than the ridge at the top, everything looks nominal. head gasket looked great.

Ill try to get pictures posted

so...I know now its not the head gasket, but I cant determine if I have a bad valve in the head or bad piston rings, although signs are strongly suggesting the rings are non-existent. I dont have access to an air compressor to try that method. if I had the ability to disassemble the head, I would pull the valves and check the seat. I have a cylinder head shop down the road that could take a look at it. they have done work for me in the past.

Now I think its time to try to pull the engine from the other truck. it had good compression before it sat, and its been sitting for about 5 or 6 years, without a head. thanks again everyone for your time.

Before you disassemble the head prop it up and fill all the ports with a solvent such as mineral spirits / degreaser. If they are seating properly there should be little or no seepage past the valves. After several minutes if the level of solvent has not appreciably gone down then the head is serviceable as is. But as long as you have gone this far I would disassemble and at least clean up the valve pockets and lap the valves back in. Of course a complete valve job would be preferable if you can afford it.

thanks for the tip Flyer. ill do just that.