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Compression Standard for 1948 Pontiac Streamliner


Johnny Jackets
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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.

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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.

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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.

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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.

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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

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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.

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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

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