Compression test today

[mrbobs48]

1948 Plymouth 218 compression test today not good. Its been backfiring real bad. So here is what I got starting with #1 cylinder.  90-30-0-80-60-70  not happy with #2 and # 3 cylinder readings. I did the oil test too. No change on 2 or 3. Called about a engine rebuild parts are $1450 and labor $1000.  I am looking for a donor engine now.  

[Sniper]

I think I would pull the head and inspect the headgasket, it's probably blown between 2 and 3 cylinder and is a relatively easy and cheap fix. 

[keithb7]

While you are in there, check valve seat seal0ability. Lap the valves. No change in compression numbers  when oil is used, leads me to valve seats.

[greg g]

The casting between the siamesed cylinders is quite thin. A breach in the gasket in those areas is pretty common.  There is usually no fluids involved in this type of failure. When on cylinder is on its compression stroke, much of it is being pushed through the gap instead of building up in the effected cylinder.  Oil won't change it cuz it's not to do with the rings.

[keithb7]

I should have been clearer to specify that aside from the concerns over 2&3 cylinders, 5&6 are down considerably as well. If they did not climb after oil was put in the cylinder, I start thinking about valve seat seal-ability. 

[DJ194950]

These old flathead Mopars will actually run quite well on 60-80 psi if none are to low as stated above.

 

I agree with pull head and check head gasket and valves closely.

 

How many miles have you put running this motor on the road?

 

Been parked a lot or forever?

 

DJ

[Sniper]

My 51 218 runs at about 50 psi per cylinder, they are all even.  I suspect my compression gauge s iffy, I had to take out the schrader valve and clean it up to even get those readings.  But it runs fine, so who knows.  

[Tooljunkie]

Valve adjustment as well. 
occasionally i get one sticky valve,i have run it off and on since october,and its less frequent now than before. I can hear the lifters chatter, as long as they are clicking im happy. 

[Booger]

Priceless information. Thank you gentlemen 

[mrbobs48]

Thanks for the advice everyone. I love this forum. 

[MarkAubuchon]

I agree, pull the head, new gasket, valve job, even cut the head. Thats what i did to my 49, I have two cylinders in the 50-60 range.  Drive it everywhere even it took it Detroit twice.  if that works you can even pull the head, pan put in new rod bearings and rings.   Whats a little smoke

[Plymouthy Adams]

27 minutes ago, MarkAubuchon said:

 Whats a little smoke

 

to the man stuck behind you....a most disgusting car to be following behind and a nuisance to society at large...

[MarkAubuchon]

Mr Adams, I said a little smoke, not a fogger.  I guarantee you every old plymouth on the road today smokes and burns oil.  Just saying

[Sam Buchanan]

1 hour ago, MarkAubuchon said:

Mr Adams, I said a little smoke, not a fogger.  I guarantee you every old plymouth on the road today smokes and burns oil.  Just saying

 

Not every old Plymouth.....  ?

[Sniper]

29 minutes ago, Sam Buchanan said:

 

Not every old Plymouth.....  ?

 

Same here, leaks though, that's another story.

[greg g]

My car doesn't smoke.  It even has no vapors from the oil filler tube after shut down.