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Hi everyone, I need some help figuring out what's going on with my engine.
1951 Packard 200, 288ci. 97,000 miles. I've had the car 5 years, with no engine repairs under my watch. A month ago the only difference in the running car engine and a swiss watch is the car is bigger. A month ago after starting the car there was a noticeable roughness to the idle. Additionally, while my head is under the hood there was a faint "tonk" tonk" "tonk" as the engine was idling, more visible blow by up the add oil tube and the down draft tube......from no blow by to visible blow by. The car has not burned any oil historically, and the oil is changed annually. I thought I'd round up the usual suspects (spark plugs) and take a look see. All eight plugs clean, evenly colored, no oil or deposits. Reinstalled plugs (original) and pulled a single wire one at a time from the running engine, with mild to moderate engine stumbling while running on 7 plugs. The engine starts easily, does not over heat and at higher speeds the engine runs well with a return to missing at Idle. I ran a wet/dry compression check. Oil pressure is hot: 35/45#'s pressure.
Cyl dry wet
1 90 95
2 110 120
3 95 110
4 55 70
5 100 110
6 110 135
7 65 80
8 50 100
Firing Order: 16258374
Cyl Compression
1 90
6 110
2 110
5 100
8 50
3 95
7 65
4 55

I would like to run a cyl leak down test but am not sure of the procedure. I do have a leak down test kit borrowed, but alas, no instructions. Any ideas? Thanks.

If memory serves, a 10-15% difference in compression between highest and lowest cylinders is acceptable. That would be roughly 11-16 lbs. difference.

As I recall 110 -120 lbs is real good for one of these engines. 55-65 is pretty low....If you have ranges from 55 to 110, there may be an issue with valves, lifter adjustments or gasket issues. Cylinders 4, 7 &8 are suspect. I would imagine the compression would be low across the board if the rings were worn evenly. Have you adjusted the valves to specs? My first guess is poorly adjusted/perhaps burned valves?

my 2 cents...

Thank you Mark for your input. I've never adjusted the valves because I work on the idea: "if it ain't broken, don't mess with it". The engine always ran Sooooooo Good that I never figured there was a pending problem from not adjusting them.

Is the gas reasonably fresh? There were a few reports earlier this year on engines being started, running OK for a period of time and then not being able to start them again. Apparently problem was traced to something in old deteriorated gas and valves reacting to it. Some reported valves sticking to the point of almost being glued in the guides. Perhaps you have a mild case.

My guess - addressing the low compression - yes, it could very easily be valve adjustment but at that kind of mileage if it hasn't already had a valve grind it's way overdue for one.

I sometimes hear the tonk tonk sound in my car 47 Packard-I usually attribute it to lower than normal oil. Put some more oil in and it goes away.

Mine started with a faint knock like that and low compression.

https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?topic_id=9231&forum=2&post_id=106673#forumpost106673

Thank you everyone for your thoughts and suggestions. I've decided that it's "that time" to remove the valve covers then the head to further investigate the problem(s).

I was going to do a leak down test on the bad cyls, at this point is this procedure worthwhile?

HH56.....The gas is good...

Owen_Dyneto.....IF.. I need a valve job, would you also be thinking that since the engine is out for the valves I might as well finish the job and have it rebuilt too?

Owen_Dyneto.....IF.. I need a valve job, would you also be thinking that since the engine is out for the valves I might as well finish the job and have it rebuilt too?

Depends on many other factors. Does it burn oil excessively, is the oil pressure low? How about knocks and other internal noises? Just needing a valve job is not alone indicative of needs for a rebuild but if the engine truly has 97,000 miles on it without prior work you might give it strong consideration.

Thank you for your thoughts O-D.
Best Regards,
Steve Fisher.....packardguy53