[Slash]

So, I was driving to work last Thursday when a loud knocking noise started coming from the engine. It sounded like a valve noise due to its speed and tone. It didn't sound quite like a rod bearing, so I slowed down and limped into work. I let the car sit at work all day and when I started it that evening, the noise wasn't there. After I drove the car about ten miles (almost home), the knocking started up again. I parked the car until I could do some diagnostic work on it.

Today, I did a compression check and checked the valve clearances. For the compression check, I removed the spark plugs, propped the choke open, and took the reading after four pulses. The results:

Cylinders 1, 2, 3, 4

Dry: 135, 125, 125, 60
Wet: 155, 160, 150, 65

Intake: .016, .016, .018, .016

Exhaust: .021, .021, .021, .018

Of course, it looks like something is going on with #4's compression. The #4 exhaust valve clearance has tightened up by a couple of thousandths since I last adjusted valves, too. The wet check also makes it look like the rings are worn.

My questions include: What causes low, but not zero, compression? Is #4 exhaust valve burning or burnt? Why does the knocking only occur after the car has been driven awhile? Why did the knocking come on suddenly? What do you all think?

Oh yes - at Eric: I will try to perform a leak down test as soon as I can!

Thanks!

 

[John M]

The knocking and the low compression may not be related.

I would check first for a leak at the header/head connection. Knocking might be just that. The low compression on cyl four and not coming up on oil usually suggests something wrong with the valve or head gasket. That is low...are you sure you did the test correctly? From the other values...it appears you did.

Burnt valve would come to mind if the clearances were very tight. But yours are loose. But knowing these cars...first thing I would think of would be a bad head gasket.

Best Regards,
John M

 

[Erik]

The low dry and good wet presure on 1-3 cyl indicate wear in cyl and/or rings, no. 4 indicate burnt valve, broken valve spring, broken rings or head gasket blown. The knoking may or may not be related.
Probably no thing to do but at head off for inspection.

Erik

 

[Capt Don]

I had a similar knock and rebuilt the engine and it was still there only when the car was warm and rev above 2000 .turned out tome a totally pluged muffler the knock was caused by the exhast gasses not being able to excape don

 

[Slash]

Thank you all for the replies.

The exhaust system is in good shape and all connections are tight. On the compression check technique, I stoppped after four pulses on each cylinder though many people like to do more. I'm more interested in the differences between cylinders and the changes between dry and wet than in the absolute pressure readings. My concern with the valve clearance on No. 4 Exhaust isn't so much with the clearance itself, but with the reduction in clearance since the last valve adjustment - especially since the other three show a slight loosening.

Anyway, as Erik suggests, it looks like (at least) I'll have to pull the head. Thanks again!

 

[ghnl]

But what about the leak down test?!? That'll give you a whole lot more info. (OK, you still might end up removing the cylinder head for repairs but it'd be good to know exactly what you are looking for & what to fix...)

 

[Slash]

Oh, I'll do the leak-down test! I won't be able to do any major work on the Spider until this weekend, so I should have the results by then.

 

[Geezer]

The knocking that you describe can also be caused by a scored piston/cylinder. A leak down will find that. Did you overheat the engine?

 

[Slash]

I haven't overheated it, but the previous owner did about 10,000 miles ago.

 

[Zunige]

I don't think I can offer any other diagnostic suggestions beyond what others have mentioned, but just take your time to ensure that you get to the bottom of this, and then formulate a good solution. Anytime there is some "unexpected maintenance", it's also an opportunity to do so nice performance upgrades...

Best regards,

 

[Slash]

Anytime there is some "unexpected maintenance", it's also an opportunity to do some nice performance upgrades...

I was thinking the same thing. The challenge would be to find the upgrades that would be "invisible" to the California smog inspection and test.

Of course, the inspector would not see mods to the head or higher compression pistons or hi-po camshafts and he probably would not detect an aftermarket exhaust header. The big problem would be choosing the modifications that would not increase emissions beyond what the catalytic converter could scrub out of the exhaust.

 

[Zunige]

I can assure you that the head porting and polishing, even if taken to ultimate level (I did a Sperry Stage V), and without changing any other stock components, will actually improve efficiency to a noticeable degree and you will pass emissions without any problems. The L-Jet is a challenge, since better fuel management is required with increased cam lift, etc., to avoid increasing harmful emissions beyond an unacceptable level. My latest (current) project is fitting a programmable fuel system to replace the L-Jet. I already have a Megasquirt built inside a stock Bosch L-Jet ECU box, so that I can use the same stock harness. It's going to take me a long time however, to come up with the proper maps, and tune everything to an 100% streetable level, but I'm hoping that I can find the time to start this in the Spring and complete it by next Fall...

Best regards,

 

[Slash]

Enrique,


I always thought that the modifications to the engine in your ’84 were about what I’d like to do with mine if I didn’t have to worry about passing an emissions test. I read your posts here and here and really got a lot out of them! Murray’s Spider is fantastic, but way beyond what I am looking for in cost and performance.

If I choose to modify my engine, my goal would be to have enough power to make my heavy, L-Jet inducted Series 3 Spider perform on par with a 1969 Series 1 or a 1974 Series 2 Spider. I’m thinking that I could have work done to the head equivalent to a Sperry Stage III, install 10:1 pistons/liners, install a 10.6mm intake cam, and a free-flow exhaust system.

What d’ya think?

BTW, what is an engine cooling plate and what do trap doors in the oil pan do for you?

 

[Zunige]

Ron,

With the Sperry Stage V head, the 10.6 mm cam, headers, free flow cat and exhaust my '84 never failed emissions in both NJ and OH. Since it now has collector plates, it doesn't have to be tested for emissions compliance, but with the current L-Jet ECU, 12 mm cams and 10:1 pistons, I don't think it would pass. Once I get the fuel management upgrade, I don't see why it wouldn't. (It is a personal goal of mine to keep my '84 fully compliant with emission standards of the period, so I will work on this until I get there.)

With a Sperry Stage III, a 10.6 mm intake cam, stock pistons, and a free flowing exhaust you will achieve very nice power, and should not have any emissions issues. What's also nice is that you don't have to do all of this at once. If you have to pull the head, this would be a good time to have it worked on. You can wait to install the cam later on. I would take a close look at your exhaust levels before changing the pistons (and do this upgrade last), since you don't want to risk going over the limit, and if so, you'd have to move on to a programmable fuel management system, which is a much larger $$ commitment. Also, it will probably be a while before you need to change pistons. New rings, on the other hand, is something you could do if you pull the head, and you'll be surprise to see how much of a difference this will make.

The engine cooling plate is something that Jim Steck (engine builder for "Bonnie") uses in modified Spider engines, to better direct water in the exhaust side of the head. The exhaust side is the side that gets very hot, and a modified engine produces a lot more heat than a stock one. On top of that, the Alfa head is aluminum, and it's easy to warp. (I've also read here on the BB that it can also be straightened, without cutting it, so that's nice to know.) It's not that there is improper cooling or that the water passages are inadequate, but the plate creates a better flow.

Oil trap doors are used to keep the oil around the pump, so that the pump can disperse it properly. This is only an issue on the track, where extremely hard cornering swishes fluids away from the pump, causing the oil level around the pump to go down. (Trust me, on the street, no matter how hard you take a corner, this is just not an issue.) This upgrade is a bit of overkill, but it was one of those enhancements that I had done while the whole engine was out of the car.

Best regards,

 

[gprocket]

Ron:

What is your oil pressure doing? I had a situation where cold the pressure was good with a bit of tapping. As it warmed up oil pressure went to zero and the tapping became really loud. It sounded like valves to me but turned out to be really worn mains and rods. Cold the oil could span the gap and push up to the valves. But warm, the viscosity went south, oil wasn't getting pumped to the cams and the noise intensified.

I agree that the low compression would likely be a separate issue.

 

[Slash]

Rich,

Oil pressure has been fine. I haven't driven the car since the compression check, but the guage has always read low at idle and up past the midpoint at mid-throttle and above - even at full operating temp.

 

[Slash]

A Bit of an Update

I read the procedure for checking compression in the Alfa Romeo Owner's Bible and realized that I had run the previously reported test while the engine was dead cold - and Pat Braden said to test compression on a warm engine. So, I warmed up the engine and ran another compression check with the following results:

Cylinders 1, 2, 3, 4

Dry: 155, 160, 130, 70

Wet:155, 160, 130, 70

I also did a rudimentary leak-down test by bringing each piston to TDC with its valves closed and then pressurizing the cylinder with my compressor. I did #4 first and got air rushing out of #1's open spark plug hole!! I noticed that cylinder #1's exhaust valve was open a bit and thought that the air was getting past #4's exhaust valve and running to cylinder #1. So, I put a spark plug in #1 and re-pressurized #4. I heard air running out of the exhaust manifold runner for #4, but no noise from the tailpipe.

The other three cylinders, when pressurized, passed air to the crankcase (noise from the oil fill hole), but nowhere else.

Now, I guess that my rings may not be as bad as I previously thought, but I still have a problem with cylinder #4 and now I have a problem with #3.

Yes?

 

[ghnl]

I'm puzzling over how you got air squirting out of #1 when #4 was pressurized. Maybe if #4's intake was leaking badly (or not closed) then air would go out to the intake plenum and back in through #1's open intake valve. It would seem that if #4's exhaust valve was leaking (or not closed) then air would (should) just exit out the exhaust pipe. I can't see how it would back pressurize out an open #1 exhaust valve unless the exhaust pipe was plugged (faulty catalytic converter?) But if were plugged that badly it should have never been able to run.

Well, with the change in exhaust valve clearance mentioned on page one and these new tests, it does sound like the head needs to come off.

Next is a case of the while-I'm-at-its. You know, while I'm at it, I might as well re-ring it. And replace the bearings. And how about some hi-performace cams. And if I'm gonna remove the pistons, how about some high compression replacements....

 

[Slash]

If I'm not mistaken, when #4 is at TDC with both valves closed, #1 is at TDC with the exhaust valve still open a bit and the intake valve still closed but getting ready to open. As for why the air came out #1 instead of the tail pipe, I don't know. The car was running too good for the cat to be plugged, but with the cat, the muffler, and the resonator, maybe the path back to #1 offered the least resistance.

As for the what-ifs, I'll have to stick mostly with reliability upgrades. Performance upgrades will have to be limited so that I can comply with California's emissions standards and the constraints of my budget. Porting and polishing (Sperry Stage II) will definitely be a consideration. Fortunately, there is an Alfa cylinder head specialist local to me who agreed to meet with me and discuss my situation.

I'm going to pull the head tomorrow and see what it looks like.

 

[ghnl]

I think you are right about the position of the valves on #1 when #4 is at TDC. I just couldn't figure out why air would exit out of the #1 cylinder and not the tail pipe.

Post some photos of what ever you find when you tear it down. We likes pictures!