Low compression on #1

zorin · 05-02-2009, 04:52 PM

I have been trying to find the cause of white smoke from my '79 3.0L engine with Solex carbs. I did a compression test on the engine today. However I neglected to do it with engine hot. I got about 91 psi on all cylinders except for number one which had 60 psi. I know 91 psi is very low but my concern now is cylinder number one which had 30 percent less compression. The compression increased to about 70 psi when I put some oil through the spark plug hole. I guess this means bad/stuck piston rings. Spark plug on cylinder one builds up hard carbon so after a while it does not fire and it has oil in its thread. See photo below. The other plugs look normal, no soot or carbon buildup.

The car was perfect when I stored it for winter. No smoke and great acceleration.
When I started the car few weeks ago after sitting in the garage for few months, there was a lot of white smoke for about 15 minutes. After couple of oil change and using Seafoam, the engine now smokes after starting from idle at traffic light for few seconds.

I put about 9 L of oil (Castrol 20W50) . The mark is at the middle of two marks when engine very hot, measured at idle.

Yesterday I drove at 5000 rpm on the 3rd gear for few minutes. Oil pressure did not go above 4 and the engine temp gauge went a little above the middle.

Any suggestions?

Thanks.

unclebilly · unclebilly's Garage

I would probably change that spark plug if I were you. Looks like mice got in there...

Larry_Ratcliff · 05-02-2009, 06:25 PM

hmmm... with a spark plug looking like that it would seem that you have some pretty serious problems with that cylinder. Since you have bad compression and an oily plug my guess would be bad rings.

zorin · 05-03-2009, 06:35 AM

Thanks for the replies.
I am just surprised why only on one cylinder would have bad rings. The car was OK before I stored it for the winter. Is it possible that some build up is preventing the rings from expanding against the cylinder walls and forming a proper seal?

zorin · 05-03-2009, 07:49 PM

BTW, Bosch recommends WR 8 for this engine on their web site. Is that the right heat range ?

Larry_Ratcliff · 05-03-2009, 07:56 PM

did you start the engine periodically during the winter? It is very bad for rings to sit for long periods of time in the same spot...

zorin · 05-03-2009, 08:01 PM

I did not start the engine periodically during the winter. Does this mean the rings on that one piston need to be replaced?

Larry_Ratcliff · 05-03-2009, 08:10 PM

Quote:

Originally Posted by zorin

I did not start the engine periodically during the winter. Does this mean the rings on that one piston need to be replaced?

based on the symptoms I think it is fair to say that the rings on that piston probably need to be replaced. The low compression reading in that cylinder would be from one of two things ....

1) the rings are shot
2) you have a valve not seating properly

If you had a valve not seating properly you would get horrible idle, all kinds of spitting and popping on acceleration and It would be very noticeable.

My vote is for bad rings since you have an oil fouled plug, low compression, and white smoke (oil burning smoke) ... bad valve guides can cause the oil burning problem but valve guides tend to wear pretty evenly....

It would seem to me that the time has come for a tear down and inspect....

zorin · 05-04-2009, 09:49 AM

Thanks Larry. I guess I would have to plan a tear down for next summer.

Elombard · 05-04-2009, 10:17 AM

Might want to get a cheap leak tester and leak that cylinder to see where you hear the air?

I wonder if you drive it some more if it might un stick?

Is it possible that carb is really rich or that plug is not firing?

David E. Clark · 11:30 AM

Your picture shows a serious carbon fouling problem. Since it is only appearing in one cylinder I think you should begin by examining causes that only effect one cylinder such as a weak or damaged spark plug wire on that cylinder, cracked distributor cap or sticking valves. While it is true that bad compression could cause the symptoms you are describing it is also possible that your carbon fouling issues could cause you to appear to have bad compression (when you really might not) because of carbon on the valves which is not allowing them to completely close.

You should always eliminate the easy to assess and less costly options before jumping to the conclusion that you need an engine rebuild. These engines are mighty expensive to rebuild!

tharbert · tharbert's Garage

Is it possible an oil ring is stuck? I'm surprised no one has mentioned the ever popular Italian tune-up. Would it be unwise to run it spiritedly though the full range of operating temperatures several times combined with a double dose of SeaFoam?