Compression Standard for 1948 Pontiac Streamliner

[Johnny Jackets]

2 cylinders are at 110, 5 are at 120, and 1 is at 95 & 100 wet.  Is that indicative of an issue?

[Bloo]

It depends. Has it been running much lately? 95-120 is more variation than we want to see, but 95 isn't really low enough to indicate a burned valve.

 

if it hasn't been running daily (or even occasionally) for a long time, its probably just some rust or crud on a valve seat, and most likely there isn't anything wrong. If that is the case, drive it. It will probably improve.

 

You might want to check the valve clearances on the low cylinder, and make sure they aren't too tight.

[Rusty_OToole]

How many miles? What's the oil pressure like? Sounds like your engine will soon be due for an overhaul or rebuild. But, if you don't use it much it might go on for years the way it is.

[Johnny Jackets]

Just turned 52,000 which I know are original since my father bought it in 1950.  Also, the engine was rebuilt in 2014 at 49,399 miles.  Oil pressure is good.

[Guest]

Six hundred miles in five years on a newly rebuilt engine is not very many.  In fact not nearly enough.  If the valves were/are set right it needs to be run and run and run to break in the engine.  Don't drive it at a constant speed for a long time.  Drive it at 50 or 60 for a few hours, taking your foot off the gas and let the car push the engine down to about 30 and the accelerate again every 20 minutes or half hour.

[Johnny Jackets]

2 hours ago, Tinindian said:

Six hundred miles in five years on a newly rebuilt engine is not very many.  In fact not nearly enough.  If the valves were/are set right it needs to be run and run and run to break in the engine.  Don't drive it at a constant speed for a long time.  Drive it at 50 or 60 for a few hours, taking your foot off the gas and let the car push the engine down to about 30 and the accelerate again every 20 minutes or half hour.

Thanks

[Pfeil]

11 hours ago, Johnny Jackets said:

2 cylinders are at 110, 5 are at 120, and 1 is at 95 & 100 wet.  Is that indicative of an issue?

Specification  for 1949-51 at operating temp. 120 PSI and no more than 10 PSI variation

[Rusty_OToole]

Tinindian has a good point. I would add some Redex, Marvel Mystery Oil, Bardahl or your favorite lubricant to the oil and gas then go on a few long trips. Start with about a 50 mile trip and work up to 100 or 200 miles at a time. Be alert for overheating, oil or water leaks, etc because a few weak points may show up when you start driving longer distances. But once you clear up these troubles you should be good for a lot of reliable miles.

[Johnny Jackets]

Thanks

[Johnny Jackets]

12 hours ago, Pfeil said:

Specification  for 1949-51 at operating temp. 120 PSI and no more than 10 PSI variation

Thanks

[Robert G. Smits]

On 10/4/2019 at 6:42 AM, Bloo said:

 

You might want to check the valve clearances on the low cylinder, and make sure they aren't too tight.

Agree with Tinindian but would check the valve clearance first before I drove it several hundred miles

[Bloo]

I agree, but was hesitant to suggest setting them to spec unless they are too tight.

 

Too tight is always bad and could cause valves to burn. Too loose might just mean some crud or rust on the valves from sitting, and those valves would tighten up from driving.

 

I would make sure none are too tight and then break the engine in. Then, I would recheck all of them and set to factory spec.

[Johnny Jackets]

52 minutes ago, Robert G. Smits said:

Agree with Tinindian but would check the valve clearance first before I drove it several hundred miles

Thanks

[Johnny Jackets]

45 minutes ago, Bloo said:

I agree, but was hesitant to suggest setting them to spec unless they are too tight.

 

Too tight is always bad and could cause valves to burn. Too loose might just mean some crud or rust on the valves from sitting, and those valves would tighten up from driving.

 

I would make sure none are too tight and then break the engine in. Then, I would recheck all of them and set to factory spec.

Thanks, again