Head Removal Due to Power Loss

[Bruce A]

Hi Everyone,

I have an Islander 34 with late model A4. The previous owner replaced the exhaust manifold and head gasket about 5 years ago. Since then the engine has accrued about 100 hours (maybe less). Currently the compression is as follows:

#1= 100 psi
#2= 75 psi
#3= 75 psi
#4= 100 psi

Note that cylinders 2 and 3 always would have the same reading on any given compression test run whereas cyl 1 and 4 would vary somewhat.

I fabricated a leak down test setup and did a leak down test. From this I determined that cylinders 1 and 4 were OK but when the leak down was performed on cylinders 2 or 3 the pressure gauge dropped immediately and I could hear air rushing out the complementary cylinder, i.e. when attempting to pressurize cylinder 2 air could be heard blowing out the spark hole of cylinder 3 or visa versa. I have had power loss problems for the past few years but never enough to really affect our sailing experience (could never get above 1500 RPM). However, it seems that the wind has been less cooperative lately and we need to rely on the old iron jenny, so I would like to solve this power loss problem.

The immediate conclusion is that there is a blown head gasket that allows the exchange of air between cylinders 2 and 3. The leak down test I think concludes this fact. So today I removed the cylinder head and CANNOT find any evidence of blow-by via the gasket--it looks perfectly intact between cyl 2 and 3. As noted above, the PO replaced the head gasket and he used a graphite version which is Westerbeke's latest gasket style released in 1996. The PO only installed one per the Westerbeke bulletin on the subject. Apparently, per internet buzz, Victor makes this gasket and recommends two gaskets whereas Westerbeke recommended only one gasket. The gasket is made of very thin graphite material and appears rather flimsy.

Since I do not see any evidence of a cracked or scorched gasket is there any other way (besides a warped head) that the two cylinders could be shorted together as indicated by the leak down test?

I have not completely examined the valves but I don't see any way they could cause the observed problems unless I just can't see the forest for the trees.

Should I conclude that the head is warped and have it milled? Any suggestions?

Also, if I use the head gasket set on Don's web catalog when replacing the head, it is suggested to use two gaskets. I am afraid that with this thicker two gasket setup (as compared to the single gasket that was previously installed) the compression would go down in all cylinders because with one head gasket cylinders 1 and 4 barely maintained 100 psi. Another thing that comes to mind is if a copper head gasket set is used with a salt water cooled engine (as mine is) do I have to worry about electrolysis? Westerbeke, in their bulletin about the single graphite head gasket, states that it was introduced because of poor service life when using two of there standard head gaskets (presumable copper).

Any and all suggestions would be greatly appreciated.

Thanks,

Bruce

[ILikeRust]

Did you take a good look at the valves? Any possibility that the valves are not seating fully and the compression is leaking out that way?

Since you've got the head off, now would be a good time to consider replacing the valve springs and lapping the seats.

[Bruce A]

Hi Bill,

I have not completely investigated the valves--will do so today or tomorrow. I was hoping not to have to pull the manifold but I will if it necessary. I don't see how leaky valves could cause the exchange of air between cylinders 2 and 3. I seems that the air would just leak out through the intake and exhaust ports and not directly between the two cylinders.

My quick inspection of the valves indicated the usual fouling of the intake valves---exhaust look pretty clean. Also, the seats did not have much angle, is this typical of the A4? All-in-all the condition of the valves looked better than most of the pictures I have seen posted on the forum.

Another reason I am reluctant to take the valves apart is that I cannot get to the first three valves without cutting up a bulkhead, at least that is the way it appears.

Last thought, is there any way to clean up the valve surfaces without a complete disassembly?

Thanks

[ILikeRust]

Here is a picture of the block with the manifold removed:



You will note that even though there are four cylinders, there are six holes.

Well, that's because some cylinders share intake/exhaust passages in the block and manifold.

Now, I don't specifically recall which cylinders share which passages, but if it might be the case that 2 and 3 share an intake passage, if you've got stuck intake valves, that could explain how air from 2 would leak into 3 and vice-versa.

[Bruce A]

Thanks Bill,

Very good point about the communication through the shared ports--I did not know that they were shared in the A4. I guess if the throttle butterfly was closed, which it was when I did the leak down test, that air could have been diverted from one cylinder to the other through the shared port. I need to find out which ports are shared.

Is there any way to test for a leaky valve now that the head is off?

Bruce

[edwardc]

I believe the term is "sistered" for the shared passages.
Only the intakes are sistered. The exhausts all have their own ports.

In Bill's picture, from left to right, the openings are
#1 exhaust
#1 & #2 intake
#2 exhaust
#3 exhaust
#3 & #4 intake
#4 exhaust

As you can see, #2 & #3 don't share a passage.

The only two ways to observe the behavior you're describing is either a blown head gasket between 2 & 3, or a cracked block. I'd say the gasket is far more likely. A crack would have to span the area between the #2 & #3 exhaust valves.

Are you sure the air was only coming out of the one other cylinder? Badly seating exhaust valves on 2 & 3 would allow air to leak into the manifold as well. This should be easy to check with the manifold off.

[jpian0923]

IMHO, I would have re torqued all the head nuts...or at least checked them. Air could have been rushing between the two cylinders because of loosely torqued nuts, without head gasket failure or cracked block.
Then rechecked compression. Too late now though.

Now that the head is off I would clean off the carbon build up with "elbow grease" (chisel, razor blade, dental tools, etc...and acetone) Power loss can be the result of all that carbon build up. Carbon absorbs gas which means you are not getting the right fuel air mixture, hence power loss.

By the way, use 2 head gaskets. I'm sure everyone here will agree.

Also, I've never seen or heard of head warpage on this forum. Thererfore, I'm guessing it's highly unlikely.

About the valves, after cleaning, re-gap them. Exhaust is .12" and Intake is .10". Even the slightest turn of the adjustable part of the tappet makes a big difference. A wider gap is better than not wide enough. No gap or "short" gap means valves won't seat all the way, resulting in compression loss.

[Bruce A]

I appreciate the info on the sistering of the ports from Edward. I removed the manifold and valve train inspection plate today so that I could get a better look at things. As Edward pointed out, the Intakes are "sistered" and the exhausts have individual ports. So for my "problem" cylinders 2 and 3 could not directly exchange air through a sistered port since the sistering of intake ports occurs between cylinder 1 and 2 on one port and 3 and 4 on a separate port--no communication between 2 and 3. This afternoon had the head cleaned, magni-fluxed and checked for flatness. There are no cracks and the head is perfectly flat. So as Edward pointed it looks like a gasket problem. The engine re-builder that did the head work (who also rebuilds A4's on a regular basis) says it must be valves or rings or a combination of both that are causing my problem. I still don't see how valves could allow the obvious flow of air between cylinder 2 and 3 as it should just exit to atmospheric pressure if it leaked through a valve and would not be so obviously present in the adjacent cylinder.

Anyway, a detailed inspection of the valves indicate that cyl 2 exhaust may have a minor blemish in the area where the angled valve surface contacts the seat. Also, there are no stuck valves and no broken springs.

I have only 5 inches of clearance to bulkheads on the side of the engine where the valve access is so I find it hard to imagine using a spring compressor in that confined space. So I was wondering if any one has tried to lap the valves to remove minor surface pitting by applying valve grinding compound to the seat and the beveled valve surface, lowering the valve onto the seat and rotating the valve with the spring in place. I know this sounds strange but I tried it on a couple of valves and it is possible to rotate the valves by hand if you fine tune the pressure that the spring exerts i.e. rotate crank/cam very slowly while lower the valve onto the seat until you can still rotate the valve by pressing at the top of the valve for friction with one hand and spinning the bottom of the spring with the other (I can do this with the space limitations that I have to deal with). This way you can rotate valve and spring as an assembly and there is still substantial engagement of the valve face and the seat. After doing this to two valves with valve grinding compound I can see a noticeable improvement in the smoothness of the valve beveled surface (not sure how effective this on the valve seat as it is so hard to see in there). It is somewhat hard on the fingers but it can be done. Does anyone have any suggestions as to how effective this might be OR can it be detrimental to the valve train?

Thanks to all for this great forum.

Bruce

[Bruce A]

I posted the above reply before reading Jim's comments. To clarify, I did re-torqued the head when doing the compression checks several months ago and it did not change the compression readings. And (as indicated in my new post) the head is flat as pancake as Jim suggested it probably would be.

Thanks,

Bruce

[ILikeRust]

Hey, if that works for you and you can get the valves lapped, go for it.

My sole concern would be getting all the grit cleaned out of there.

[Bruce A]

Bill and Ed,

I have a compressor, shop vac and every cleaning agent known to man onboard so i think i can get the grit out. So I guess I will proceed.

To answer Ed's question I do believe that their was some air flowing into the intake manifold because when I put my ear to the carb inlet I could hear a slight hiss. I could not hear or otherwise specifically detect exhaust valve leakage while doing the leak down test but I would not doubt that their was some leakage based on my observation of the condition of #2 exhaust valve. But definitely the bulk of the air was flowing cylinder to cylinder--I could put my cold wet finger above the spark plug hole of the complementary cylinder and feel the air rushing by. Maybe the head gasket did not seal properly because the PO only used one instead of two gaskets?

Also, for Ed, you said in your previous post that it would be easy to determine if there was an exhaust valve leak in #'s 2 and 3 now that the manifold was off? Is this just by observation of the valve surface or is there some test I am not aware of?

Jim suggested very carefully adjusting the valves which i will do when finished. I have not done this in an A4 and I don't see any lock nut on the adjuster. Is there a lock nut or do you just crank the adjuster to the specified gap and hope it stays there?

Thanks again,

Bruce

[sastanley]

Hi Bruce...regarding your valve adjustment questions...you need to read the thread below!

No locknut.

http://www.moyermarine.com/forums/showthread.php?t=2927

[edwardc]

Also, for Ed, you said in your previous post that it would be easy to determine if there was an exhaust valve leak in #'s 2 and 3 now that the manifold was off? Is this just by observation of the valve surface or is there some test I am not aware of?

What I was refering to, unfortunately, requires the head to be still on. You rotate the engine until both valves are closed (TDC on the compression) and listen or feel for air on the associated exhaust port. It may also be possible to to replace the spark plug with a fitting and use an air source instead.

[Bruce A]

Thanks Ed,

That clarifies it.

I have another question for the forum:

My head came off very easily (took about 20 minutes) and only one stud came out in the process. All studs are in good shape (including the one that came out) with no evidence of rust or corrosion. It would be easier to clean the block with all studs removed but with my luck I would probably break one (or five) of them. Is it OK to leave the studs in as I proceed to clean things up and reinstall the head or is it really necessary to remove all the studs?

Note that the gasket came off as single piece and any residue on the block surface seems easy to remove.

Bruce

[edwardc]

It is definitely possible to do the job without removing the studs. I've done it twice that way. The head is a little fussier to get off and on that way but it does work.

One secret for cleaning this way is to get a good sharp 1/4 inch wood chisel to clean up the thin strip of block outside of the studs on the manifold side. This tool works really well for that purpose. Just be sure to keep it at a very shallow angle so you don't gouge the block surface.