Compression numbers PSI on 301

[Rusty Muffler]

My engine was supposedly rebuild when I bought it out of the car. It is perfectly clean inside and out, has new freeze plugs, gaskets,etc. I adjusted the valves cold and added a couple thousands clearance to be sure they wouldn't be too tight (FSM says to adjust when warm.) It doesn't look to have any new parts except maybe valves (hard to see). The pistons are not new nor is the cam.
Keeping in mind that the engine has NOT been started at all I did a compression test. The numbers run between 39 and 81 psi. After the test I got it running but seems too lean and would run best at full choke when warm so I'll be looking further into the carb. Vacuum gauge hooked to the base of the carb shows in the green and about 1500 rpm. No blue or black smoke. Checked for vacuum leaks with carb cleaner and found one, but didn't seem big enough to cause the lean condition. I'm hoping the rings were replaced and they just need to be run in? After I get it running better I'll check compression again and recheck the valves while warm. Will keep you posted.

 

[Davea Lux]

My engine was supposedly rebuild when I bought it out of the car. It is perfectly clean inside and out, has new freeze plugs, gaskets,etc. I adjusted the valves cold and added a couple thousands clearance to be sure they wouldn't be too tight (FSM says to adjust when warm.) It doesn't look to have any new parts except maybe valves (hard to see). The pistons are not new nor is the cam.
Keeping in mind that the engine has NOT been started at all I did a compression test. The numbers run between 39 and 81 psi. After the test I got it running but seems too lean and would run best at full choke when warm so I'll be looking further into the carb. Vacuum gauge hooked to the base of the carb shows in the green and about 1500 rpm. No blue or black smoke. Checked for vacuum leaks with carb cleaner and found one, but didn't seem big enough to cause the lean condition. I'm hoping the rings were replaced and they just need to be run in? After I get it running better I'll check compression again and recheck the valves while warm. Will keep you posted.

Compression should be about 140psi. Recheck the compression now that the engine has been run. An intake valve that is adjusted too tight will mimic a too lean condition, so will valve timing that is off due to a worn timing chain. A flat lobe on the cam will also cause low compression on its related cylinder. A vacuum leak at the mating surfaces for the intake manifold will also cause a too lean condition as will a bad power brake booster. What year 301 is this?

Dave

 

[Rusty Muffler]

1957. Intake manifold was just dealt with. Got an original rebuilt carb recently from a member here. I pinched off the booster hose. Strange why anyone would go to all the trouble of taking the motor completely apart and boiling it out and not doing the proper service to it. I was told the original complaint was low compression. After the engine was rebuilt, it sat for 9 years in his garage before I bought it and installed it. Anyway, I'll know more tomorrow.

 

[413]

So has this been started and run by the other owner since the rebuild? Or is it fresh and zero run time?

 

[Jakter]

Don't jump into tearing it apart.
Get it running and driving and put a few thousand miles on it at all speeds and then see where it's at.

 

[halifaxhops]

Also did you do the test with oil in the cylenders?

 

[CBODY67]

In prior times, before anywhere near "current times" happened, a "rebuilt engine" could be an engine which was pulled out, cleaned (maybe), with new rings and bearings installed, with a valve job. NO cyl boring, just new rings and maybe a crankshaft journal polish. Before that, with an inline 6-cyl, the hood was removed, the head removed, and the boring bar sat on top of the block's deck surface to do its job, with possibly the back cyl not getting bored, so that one just got new rings, which could cause some piston noise at times. But as long as everybody knew what was going on, that was fine. Of course, a V-8 would have to have been pulled from the chassis. Back in a time BEFORE lots of money was floating around and boring bars were "an expensive tool" that only bigger machine shops had (and could justify the expense of).

IF you don't have one, investing in a HD Borescope that can be used by itself (an integral viewing screen) or attached to your camera might be able to determine if the cyl walls have any fresh hone marks on it. And possibly if a valve on the affected cylinder might not be closing fully.

Give the engine more run-time, with a few more hot/cold cycles to see if the possibly-sticking rings might be loosened up to seal better and for the valve guides to get more lube into them. Then you can also do some more "hot" compression checks and monitor the hot valve lash, too. Hoping things improve.

Happy Holidays!
CBODY67

 

[57fury440]

The above info is all good. I agree that you should run the engine for a while before you change anything. I bought an LA 318 and tranny from a wrecking yard about 25 years ago. I put it in a 57 Belvedere that I used as a daily driver for around town. It started right up but was a little noisy, ran a little rough and blew a little smoke. It was a high mileage engine. I changed the oil and filter again after about 150 miles and a few days later the smoke stopped, and it ran smooth and quiet. Yours may just need to be run for a while like stated above.

 

[Rusty Muffler]

So has this been started and run by the other owner since the rebuild? Or is it fresh and zero run time?

ZERO

 

[Rusty Muffler]

Also did you do the test with oil in the cylenders?

Not yet....

 

[Jakter]

In prior times, before anywhere near "current times" happened, a "rebuilt engine" could be an engine which was pulled out, cleaned (maybe), with new rings and bearings installed, with a valve job. NO cyl boring, just new rings and maybe a crankshaft journal polish. Before that, with an inline 6-cyl, the hood was removed, the head removed, and the boring bar sat on top of the block's deck surface to do its job, with possibly the back cyl not getting bored, so that one just got new rings, which could cause some piston noise at times. But as long as everybody knew what was going on, that was fine. Of course, a V-8 would have to have been pulled from the chassis. Back in a time BEFORE lots of money was floating around and boring bars were "an expensive tool" that only bigger machine shops had (and could justify the expense of).



Happy Holidays!
CBODY67

In car crankshaft grinding

 

[Big_John]

After the engine was rebuilt, it sat for 9 years in his garage before I bought it and installed it.

If it's sat that long, it's hard to tell what the condition the cylinders are in. I would be surprised if it's not rusty. As @CBODY67 mentioned, it might be worth investing in a borescope and checking it. You can find an inexpensive one that works with a smart phone. I have one and it works great... Also very handy for finding things under the couch. The alternative is to pull the heads.

So has this been started and run by the other owner since the rebuild? Or is it fresh and zero run time?

ZERO

IMHO, you compression readings don't mean much until the engine is run and broke in. Then if the compression readings are down, you know you have a problem.

Of course, if you are having second thoughts about the engine build, it might be worth a gasket set to tear the motor down and inspect everything.

 

[413]

Where was it sitting? Was it humid and non heated? Your compression numbers are very low. What was the number from,the vacuum gauge? Of course the timing chain could be on wrong, or the valve grind done wrong, or valves not closing all the way, but you have adjusted those.

I would look in the cylinders with a scope or remove the heads/pan Amd see what is going on.

yes it needs to be driven and broken in.

 

[Toolmanmike]

Run it. Change the oil after a few hundred miles and again after a 1000. Then pull the plugs and take a compression test.

 

[Rusty Muffler]

I've got to take a break today from this. Good news is after running it up to temperature at about 1500 RPM and checking compression again, they are in the range of 88-110psi. My gauge is old so I'm looking into getting a new one. Weird thing is that it will only run with the choke closed (too lean) but only 2 of the plugs are clean and the rest are black? Go figure. I remember when I had an old Harley the plugs could "foul" and not fire any more. I won

der if that's involved and I think this rebuilt Carter WCFB 2302SA carb needs looking into. While it was running about 1500RPM I screwed the idle mi

xture screws all the way in and it made no difference. Maybe that's normal at that RPM? I tried putting my hand over the primary on the top of the carb and about lost my

hand from the suction!

 

[Rusty Muffler]

I've got to take a break today from this. Good news is after running it up to temperature at about 1500 RPM and checking compression again, they are in the range of 88-110psi. My gauge is old so I'm looking into getting a new one. Weird thing is that it will only run with the choke closed (too lean) but only 2 of the plugs are clean and the rest are black? Go figure. I remember when I had an old Harley the plugs could "foul" and not fire any more. I wonder if that's involved and I think this rebuilt Carter WCFB 2302SA carb needs looking into. While it was running about 1500RPM I screwed the idle mixture screws all the way in and it made no difference. Maybe that's normal at that RPM? I tried putting my hand over the primary on the top of the carb and about lost my hand from the suction!

 

[CBODY67]

The idle system ONLY works up to about 1000rpm or so, which is when the main system takes over for higher engine speeds. So what you found is probably not unusual.

If the bulk of the plugs are sooty after running with the choke pretty much closed, look to see if the ones which are clean are on the same air flow route and which side of the carb they are fed by. Seeing the differences in the plug ceramics, I suspect there is a big crack somewhere in the carb or the intake manifold. Seeing which runners those cyls are fed from might yield the key?

I'm glad the compression is looking better. Don't worry about the specific numbers, but more about how uniform they are all together. Especially with a lower compression motor.

In the back of your mind, you might be considering what it would take to make a new AFB or AVS2 of about 500cfm work on that intake. Just a "for future reference" situation. A while back, in a Buick forum, there was one guy who put a new AFB on his '55 Buick VB-8 and it all worked out pretty well. Better than his old Rochester 4bbl that came on the car.

Happy Holidays!
CBODY67

 

[413]

The clean plugs have the vacuum leak or no fuel from the carb. Good advise above, look at the intake and see where the air fuel comes from.

could just be intake gasket leaking also.

 

[Toolmanmike]

Get on Rockauto or wherever and double check your spark plug numbers. Just to be sure.

 

[Rusty Muffler]

Get on Rockauto or wherever and double check your spark plug numbers. Just to be sure.

Those appear to be correct, thanks.