Lost Compression on #3 and #4 Cylinders

[dwest999]

Hello all.  I wanted to get some thoughts on what might be going on with my engine.  I got my '40 Plymouth (201 CID) out of storage last week.  Started it and let it run for a couple of minutes.  Drove it from the storage facility to my home which required me to take a state highway.  I got the car up to about 50 / 55 MPH during the trip.  Car ran fine.  So, went out to take the car for a ride yesterday and the car ran really rough.  After some investigation I learned that I have no compression on my #3 and #4 cylinder.  

 

I've done some searching on the forum and think it might be a stuck valve or maybe a head gasket... Just not sure where to start so I figured I'd ask.

 

Thank you in advance for your wisdom and insights

[Doug&Deb]

Could be either. I’m in the same boat but mine is a fresh rebuild with 500 miles on it. Pull the valve cover and rotate the engine by hand to see if the valves are moving. With two low cylinders I suspect the head gasket more than stuck valves. Have you checked the oil? A blown gasket will cause the oil to be milky looking. Good luck and keep us posted.

[DJ194950]

1 hour ago, Doug&Deb said:

A blown gasket will cause the oil to be milky looking. Good luck and keep us posted.

  Not always, sometimes the gasket is only blown out just between the the two cylinders nd has not at least yet into a water passage.

 

A compression test between the # 3 and #4 will say for sure will  in my opinion.

 

Pull the head. Not to hard or time consuming to do.

 

DJ

 

 

 

[Bryan G]

I had this happen with an off-topic flathead six; not much space between those cylinders and the gasket was breeched right there. No coolant issue, just compression leaking between 3 & 4. A new gasket and I was in business. They sure don't have much power that way!

[keithb7]

The small space discussed between 3 & 4 can be seen here. 
 

 

 

[dwest999]

Thanks all.  I pull the valve covers last night and rotated the engine.  Valve all see to be moving so I am figuring that it is indeed a head gasket.  Luckily for me I watched Keith's video (again) last night when he replaced is cracked head (thanks Keith).  I think it's a job I can handle.   Dave 

[slatgrille]

I'm betting on head gasket...exact thing happened between #'s 5 & 6 after running it at 55mph then stopping for gas. Checked compression....nothing. Just finished fixing last night. I'll take it for a ride today!

 

Craig

[keithb7]

1 hour ago, dwest999 said:

  I think it's a job I can handle.   Dave 

Sure you can! Its not hard. You may need a few tools though. Not sure what you have. Nothing too specialized for tools for just a head gasket replacement. It would be a really great time to check for valve leakage and dress them up. Guaranteed a few could use a touch up. Valve seat erosion is kinda like toenail maintenance. It never stops. Just a matter of time when you have to do it.  The good news is your wife isn’t bugging you to do your valve seat maintenance. 

[dwest999]

Thanks again everyone.  I love this forum.  I'll report back for those interested in (as Paul Harvey used to say) "the rest of the story"... Good day.

[kencombs]

Easiest way to prove this is to use air.  Doesn't take a lot of volume or pressure,  Remove both spark plugs,  Make an adapter from and old plug shell and a quick connect male half.   Some can be tapped with a 1/4"FPT, but most will need a little silver solder, weld or brazing, depending on your tools.  Hook your air source to either of the plug holes.  It'll be obvious when the air into one hole comes out the other!

 

This fitting will be useful for leakdown tests also.

 

[dwest999]

Hello Forum Friends, 

 

Well, it looks like I figured out the issue with lost compression... I am thinking I might need a new head gasket.  Thank you to all who responded.  #blow_out.  

 

Dave

 

[Hickory]

There is black between all cylinders, I would check the straightness of block and head. Then make sure the retorque procedure is done after assembly and heat cycles. It looks like it wasn't retorque to me. See it wasn't to hard.

[dwest999]

Hickory, you're right about that... several of the head bolts were not very tight.  My guess is the PO who rebuilt this engine back in the 90s did check for head bolt torque after assembly.  I am going to get the head and then check the block for straightness using a straight edge.  We'll see.

[Dodgeb4ya]

Check the head for flatness...if the block needs decking you're in serious trouble.

[Los_Control]

43 minutes ago, dwest999 said:

My guess is the PO who rebuilt this engine back in the 90s did check for head bolt torque after assembly.

I bet you are right, they did not re-torque the head as needed.

Because the bolts will loosen, compression will lesson .... the gasket will be damaged but nothing serious like warping the head .... I could be wrong.

I'm betting slapping a new gasket on it will cure it ..... if in doubt use two gaskets    

 

Years ago I bought the wife a Toyota Tercel 4x4 station wagon .... fun car & we lived in snow country.

It blew a head gasket and there was actually a recall on these engines for the head gasket issue.

Problem is the block is so small there is no room for head bolts between the cylinders. .... Only had head bolts around the perimeter of the head.

With no support the heads always warped in the middle.

The recall they pulled the head & added a thick cushy shim along with the head gasket.

 

When mine blew it was on me ... past recall dates. Nobody in town stocked the shim so I slapped 2 head gaskets on it & drove it for years after that.

I forget why we stopped driving it .... was not because of the head gasket .... thinking it was carburetor issues.

[dwest999]

Had the head check and it was 14 mills off... had it resurfaced and hope to get the engine back together soon.