The compression results are in, not good. (3GM30)

[westwinds]

Get the head off and measure the wear in the cylinder. If you have a bad injector that gave too much diesel, this can cause severe wear. Most wear occurs at the top of the cylinder if it is too much diesel. Did you get black smoke after warmup? The blow by needs to be checked and will tell you whether it's the piston or something else. A burned valve you would see. It could be a cracked head or cylinder, but that would show at the coolant tank with a carbon dioxide tester. If it were a loose injector, you would have noise and exhaust in the engine area. Use a micrometer for cylinder wear, check blow by, head to machine shop to check for cracks then if nothing, pull the engine to check for broken rings or broken piston where the rings are (piston ring lands). I would not use the engine until the problem has been determined as you could cause more damage or because of reliability problems. Is there water in the oil caused by a blown head gasket or crack?

[mackrobertson]

Can anybody help me with what the normal/average/acceptable compression pressure should be per cylinder on a Westerbeke 40? The mechanic gave me values on each of the 4 cylinders but no reference value.

[a64pilot]

Ref compression
Any Diesel, if it starts easily and doesn't smoke visably, who cares what the compression and or the oil consumption is. Now this may sound like I'm being flippant, but i've seen and currently have a Diesel that burns quite a bit of oil and is down in compression, but as it doesn't yet look like I'm fogging for mosquitos, who cares?
Now if it is a bear to get going and or leaves a blue fog where ever you go, then maybe you need to do something about it.

Now if your a perfectionist this won't play of course, but if you don't use it a lot, a worn Diesel may have years of service left

Meant for Mack, not the rest of this thread


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[travellerw]

A little Google Foo and I think I found what you are looking for.. Here is the Technical Service manual for that engine.. Direct from Westerbeke

http://www.westerbeke.com/technical%...%20ed.%208.pdf

[dtlx11]

Op back again with the latest. Suspicious of the Yanmar professionals results of 0 compression on cylinder 3 (as well as the €300 euro price tag) I bought my own compression tester and did my own test.

I couldn't get it to fit properly but jury rigged something together which allowed me to read at least a little pressure over all cylinders, so I know his results are less than trustworthy. Had a conversation with the guy but unless there is any interest I won't go into details.

Anyway, I also rebuilt my injection pump as another job worth doing whilst I was adjusting the injection timing, now everything is back together and running again. I did the blow-by test (thanks for the tip SailorChic!) and saw no smoke, got it all on film too. Can someone have a listen and tell me whether I need to replace my rings/lands as suggested or should I just say job done at this point.

[westwinds]

Unless an engine is not running on all cylinders, it is hard for me to make a diagnosis unless it is main bearing noise, rod bearing, rocker arm (valve), king pin, and piston slap. But anyway seems OK. What I am more interested in is the fact there is no blow by at the breather. That means you have a good piston ring seal on all cylinders, no cylinder with excessive wear, (taper at the top of the bore) from a bad injector that destroyed the cylinder with excessive wear or just a worn out engine. This wear occurs at the very top of the cylinder right where the piston goes to top dead center and then reverses direction, where the rings are. With no blow by, that really means something very good. Also, I am guessing there is no “white” smoke which means unburned diesel as in one cylinder has so little compression that combustion is not taking place and you are getting unburned diesel out the exhaust. There will also be a very strong diesel odor.

Did the compression test you tried to accomplish show about the same compression across all cylinders? If it is about the same, even if you had enough extra hardware to reduce the pressure reading, the fact that all pressures are even means all cylinders are the same, not one cylinder with zero pressure. This assumes you got a good seal on each cylinder while using your testing apparatus. Unless you are doing a leak down type of compression test, valve lash, speed of cranking and other factors influence the test so you are likely to see variation from one cylinder to another. I am thinking the engine is all right, but keep an eye and ear on it. What was the original problem before overhaul?

[dtlx11]

Thanks for your reply Westwinds. In answer to your questions, The original problem was difficult starting and a desire to familiarize myself with the engine so I can fix it if we are stranded. I will try and run the engine on one cylinder at a time rather than 2 at a time as I did here, that will help to isolate problems. I was also very surprised at no blow by, not even a bit. I checked 2 or 3 times to be sure. The exhaust looked pretty clear, lots of unburned diesel directly after start up (I had to crank a lot with only one cylinder compressed to get it to fire) but it cleared up after, perhaps a little white smoke in this cold weather but no sheen on the water.

As for my own compression test, at the time the starter wasn't connected so I had to try and crank it by hand, I managed to get each cylinder to show around 100psi before I went up to the guy at Yanmar and asked how he managed to find zero on cylinder 3 and I found something. His reply was that the results he gave me were for a leak down test. (in the interests of honesty, I had also re-adjusted my valves in-between his leak down test and my compression test) He pulled out a knackered old Yanmar he is breaking and showed me 3 pistons in different states of repair, one had broken rings (like the top ring here), he told me this was what he suspected was the problem on piston 3. I think that perhaps now I have adjusted the valves the problem of compression has gone away. (as well as my cash that could have gone on other parts )

If anybody is interested I documented the whole process and made a long video. I don't claim to be a mechanic or an expert but maybe it will help others attempting Yanmar overhauls.

video

[Cherp]

What a woman.

[HappyMdRSailor]

Quote:
Originally Posted by a64pilot
Reading your post again, you have had the head off and re-built?
If so make sure valves are adjusted correctly, one isn't too tight

Most likely scenario with zero compression...

Quote:
Originally Posted by Cheechako
I was lucky and my cylinder was fine... no groove. Only my bottom piston land was cracked.

Maybe you get lucky like cheech if it is a piston land...

Quote:
Originally Posted by Zai
A quick way to test the rings is to inject a little oil into the cylinder and re do the compression test, if it is considerably higher then most probably the rings.

You might ask the mechanic if he can do a leak down test, as that would tell exactly where the problem lies.

Search both of these with google.... these are standard evaluation techniques

Quote:
Originally Posted by a64pilot
O compression isn't wear, something's broken, or a stuck or bent valve
At TDC compression the rocker arms on that cylinders valves should be a little loose
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+1


As stated early on.... tight valves most likely.... Mechanic giving "0" compression definitely should have told you this.... If she looked OK in the #3 hole, and it runs like it sounds.... Button her up and go...

[westwinds]

Originally Posted by dtlx11

... I think that perhaps now I have adjusted the valves the problem of compression has gone away....

Lets check this out some more and DO NOT RUN THE ENGINE. Did the valve clearance (lash) become less? As a engine wears, the valve lash becomes greater, you can get a thicker feeler gauge in there. If the lash became less, or even enough to hold the valve slightly open with no compression, then the valve stem is stretching. This means the valve will soon break with the head of the valve getting caught between the piston and the top of the combustion chamber. A hole gets smashed through the top of the piston and maybe the head is also damaged. If the valve lash did become less then pull the head and have the valve replaced.

[leftbrainstuff]

Cranking by hand is not a reliable compression test. You need to have a firm pressure tight connection. Get the correct fittings.

Even at cranking speed you are only looking for consistency.

A leak down test without cranking for each cylinder at top dead centre is also a good test of valve seat seal and piston ring sealing. This is the test i'd run on competition engines throughout their life. You can diagnose valve seat leakage easily using this approach. You can also detect blowby from venting through the crankcase.

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[a64pilot]

Originally Posted by westwinds

Lets check this out some more and DO NOT RUN THE ENGINE. Did the valve clearance (lash) become less? As a engine wears, the valve lash becomes greater, you can get a thicker feeler gauge in there. If the lash became less, or even enough to hold the valve slightly open with no compression, then the valve stem is stretching. This means the valve will soon break with the head of the valve getting caught between the piston and the top of the combustion chamber. A hole gets smashed through the top of the piston and maybe the head is also damaged. If the valve lash did become less then pull the head and have the valve replaced.

Usually, valve clearance get's tighter as an engine ages, this is not due to valve stems stretching, it's due to the valve and the valve seat wearing and the valve sitting further in the head. Eventually if you do not adjust the valves, they will leak and "burn" which of course is just a bad leak, but you do lose compression.

"loose" valves other than being noisy usually do not cause any harm, tight valves on the other hand, do

[dtlx11]

Originally Posted by a64pilot

"loose" valves other than being noisy usually do not cause any harm, tight valves on the other hand, do

This is where I'm thinking, when I re-adjusted my valves I found the intake valve on 3 to be too tight so at TDC the valve was probably a little open.

[capt jgw]

Originally Posted by dtlx11

So I'll add 'measure injector housing size' to the list of jobs when I'm next down the boat.

I've read of people making their own compression testers from old injector parts. Anybody have any success with this?

Did that with an old Albin AD2. Took apart an old injector and threaded he tester into the fuel port. Worked pretty well.
Current Universal engine has glow plugs and the adapters thread into those holes. Easier to remove than the nozzles.