L24 compression question

[Montana Z]

Hello all,

My engine was running good, but developed an intermittent metallic sound in the head.  I removed the valve cover and discover that the cam oiler had failed.  I replaced that with high hopes all would be well only to discover the mystery sound remained.  So I did a compression test and got the following numbers:

#1=123 PSI  

#2=115 PSI  

#3=123 PSI

#4=40 PSI

#5=138 PSI

#6= 145 PSI

Now obviously there is a problem with my #4 cylinder.  My question is why are the first 3 cylinders all consistently lower than the back 3?  I have dual SU's and thought it may be that the front carburetor was partially restricted.  However, I fully opened the dash pots and throttle and got the same results.  For the record the engine was cold with all spark plugs removed and I did not put any oil in the cylinders.  My car is and early 72 (11/71 build) and the engine and head are original.  Thank you for any feed back.

Cheers,

Scot

[grannyknot]

A cold engine compression check is not going to give you accurate numbers, a hot compression test will still show a problem with #4 but the other cylinders could be very different. Regardless it looks like your engine is in need of a rebuild but people have driven engines in worst condition for many more miles. But driving an engine that doesn't have balanced compression is a good way to wear it out much faster.

Did the cam oiler break off or just crack?

[sweatybetty]

sounds like maybe a slightly warped valve, or maybe something embedded in the seat. is the rocker too tight not letting the valve close all the way?

Edited September 26, 2017 by sweatybetty

[Montana Z]

Thank you both for getting back to me.  The rear section of the Cam oiler came off and fell out when I removed the valve cover.  This all started after a 300 mile interstate trip at a consistently high speed (80-90 mph).  The other issue that I failed to mention before was smoke coming from the valve cover breather. I'm not sure if the issues are related.  The engine stable at the same time as the sound in the head so I'm leaning towards a valve issue of some kind.  The sound is pretty intermittent/ almost non existent at idle.  If it was a tight rocker wouldn't it be more consistent?  This is all a little frustrating because in the 19 years I've owned it it was running the best I can recall

 

Edited September 26, 2017 by Montana Z

[Mark Maras]

15 hours ago, Montana Z said:

Hello all,

My engine was running good, but developed an intermittent metallic sound in the head.  I removed the valve cover and discover that the cam oiler had failed.  I replaced that with high hopes all would be well only to discover the mystery sound remained.  So I did a compression test and got the following numbers:

#1=123 PSI  

#2=115 PSI  

#3=123 PSI

#4=40 PSI

#5=138 PSI

#6= 145 PSI

Now obviously there is a problem with my #4 cylinder.  My question is why are the first 3 cylinders all consistently lower than the back 3?  I have dual SU's and thought it may be that the front carburetor was partially restricted.  However, I fully opened the dash pots and throttle and got the same results.  For the record the engine was cold with all spark plugs removed and I did not put any oil in the cylinders.  My car is and early 72 (11/71 build) and the engine and head are original.  Thank you for any feed back.

Cheers,

Scot

 The lower compression on the first three may be from lack of oil in the cylinders. If you started the test with a dry number one cyl. , by the time you got to number six, oil was circulating and you likely had some oil pressure. 

[Zed Head]

The oil from the oiler also oils the valve stems and their seals, and some slips past for the guides.  Oil draining and flying everywhere when it works right.  When a piece of the system fell off the rest of the holes didn't get any pressure.  The front cylinders might have got some timing chain sprocket and chain splash, while the back was drier.  I'm just conjecturing.

I'd guess things got dry, some valve stems and guides and cam lobes and rocker arms got very hot, and this affected the seals and the valves themselves.  Basically most of the valve train overheated.  Might also be that there was some lobe wear and the valves aren't opening at the correct time.  #4 might be dying.  Did you check valve lash when you replaced the oiler section?

Just one possibility.

[Montana Z]

I did not check the valve lash when I replaced the oiler because I thought I had found an easy solution (silly me).  My plan is to pull the head, have the car towed over to storage (winters here in Montana are not Z car friendly), and spend the next couple of months rebuilding the head.  Once the head is off I figure I'll be able to do a visual check of the pistons which might give me a little more information.  I also plan to install a new timing chain and a more aggressive cam in the process.  Thank you again for all the feedback.  It's nice to have a community of knowledgeable people. 

[grannyknot]

Try doing hot a valve adjustment see if that helps with the noise then do a hot compression test,        dry first then wet, that will give you a much better idea where the problem lies. The smoke coming from the valve cover breather would be the blowby from #4 either pass the rings or maybe up the valve guides. Take lots of pics when you tear it down and post them here, it will be a long winter

[siteunseen]

A picture of the cam lobes where the spray bar fell off is what I want to see.  80-90 mph runs without oil, whoof!

[Montana Z]

I'll post some pictures of the cam lobes later today, but I'm not sure they will show much.  To my untrained eye everything looks pretty normal.

[Montana Z]

As requested here are some pictures of the cam.  At this point I think I will button everything up and tackle repairs in the spring.  My storage unit is not climate controlled and I don't want to leave any critical parts exposed to the elements.

[Patcon]

It may just be the picture but the last three lobes on the cam look a little rough. They should be shiny like the #5 exhaust lobe (4th from the back)...