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Old 14-01-2015, 16:34   #16
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Re: The compression results are in, not good. (3GM30)

Ah blowby, yes. With the engine idling, remove the oil fill cap. If you get a cloud of smoke, then odds are its rings. Good rings = no smoke. Also check your valve lash first. A tight valve could cause a zero reading.

A zero reading, to me, assuming the valves are adjusted right and the head gasket is good, pretty much points to rings and broken rings at that. It's not the end of the world. I rebuild my 3gm, myself, in the cockpit with very few tools.

I recommend a come-a-long/cable hoist to lift the engine. you'll need a 36mm socket, cut in half and welded to a 7" (18cm) long pipe to remove the nut holding the governer weights off. A big breaker bar and a cheater pipe is handy for breaking that and the pully nuts loose. everything else is easy..
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Old 14-01-2015, 17:57   #17
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Re: The compression results are in, not good. (3GM30)

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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Old 14-01-2015, 18:23   #18
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by a64pilot View Post
It may be a stuck valve or something, I've had that on aircraft engines pretty often.
Your parachuting is good then?
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Old 15-01-2015, 02:21   #19
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Re: The compression results are in, not good. (3GM30)

All great replies.

I certainly want to try the smaller and easier repairs first to see if that improves compression but I don't want to keep paying the mechanic for a compression test so I will have to fashion my own compression tester.

I was hoping all would be good after I managed to get it running again, looks like I'll be taking it to bits again and spending more $

Can I at least re-use my Head gasket? it has less than 1 hour on it
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Old 15-01-2015, 04:56   #20
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Re: The compression results are in, not good. (3GM30)

Greetings and welcome aboard the CF, Paul.
About time you contributed.
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Old 15-01-2015, 05:29   #21
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by a64pilot View Post
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 View Post
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 View Post
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 View Post
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

Quote:
Originally Posted by sailorchic34 View Post
I'm going to bet that when the OP pulls the engine apart, he'll find #3 with broken rings and lands. That's exactly what I found on mine. Yanmar has a tiny problem with piston lands breaking in some model years of the GM series.

Luckily parts to repair are about $700 and machining, I had the block milled and a sleeve installed on my #3 was $300. Be advised that pulling the inner crack nut off requires a special tool, which you will need to make or have a welder make.

Oversized pistions are available. Stock size was $95 with rings two years ago. 10 over was $150 each. Whe I machined the one bore as the other two measured as new.

You can read my sage here: I was Bored so Pulled the Head on my Yanmar
I "almost" let this go.... I must be getting soft....
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Old 15-01-2015, 07:39   #22
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by dtlx11 View Post



Can I at least re-use my Head gasket? it has less than 1 hour on it
No.....
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Old 15-01-2015, 07:53   #23
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Re: The compression results are in, not good. (3GM30)

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Originally Posted by MarkJ View Post
Your parachuting is good then?
A parachute goes along with my job, sometimes I wear it, have never ridden one though, good friend has ridden one successfully, twice
Almost always a sticking valve on an airplane engine means it just runs a little rough and of course is down on power just a little, the Lycoming engine is more susceptible to it, if you are curious
Dealing with Stuck Valves - AVweb Features Article

Thing is on some engines, it comes and goes, making people think it's some other minor problem that goes away.

If he can get air pressure to the cylinder like how you do a leak down test, that will tell the problem, if it's an intake vale, the air leaks out the intake, same for exhaust, cylinder, of course you hear the air leak in the crankcase vent. Real advantage on a leak down test over a regular compression test is it tells you exactly where the leak is.

Oh Mark, kind of airplanes I test, I can't imagine jumping out from an engine failure, jumping is sort of reserved for when it's coming apart around you, I have not checked that block
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Old 15-01-2015, 08:30   #24
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by dtlx11 View Post
Can I at least re-use my Head gasket? it has less than 1 hour on it

Not a chance, it's already been crushed.....it can only be crushed once.


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Old 15-01-2015, 22:34   #25
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by sailorchic34 View Post
Ah blowby, yes. With the engine idling, remove the oil fill cap. If you get a cloud of smoke, then odds are its rings. Good rings = no smoke. Also check your valve lash first. A tight valve could cause a zero reading.

A zero reading, to me, assuming the valves are adjusted right and the head gasket is good, pretty much points to rings and broken rings at that. It's not the end of the world. I rebuild my 3gm, myself, in the cockpit with very few tools.

I recommend a come-a-long/cable hoist to lift the engine. you'll need a 36mm socket, cut in half and welded to a 7" (18cm) long pipe to remove the nut holding the governer weights off. A big breaker bar and a cheater pipe is handy for breaking that and the pully nuts loose. everything else is easy..
Quote:
Originally Posted by sailorchic34 View Post
I'm going to bet that when the OP pulls the engine apart, he'll find #3 with broken rings and lands. That's exactly what I found on mine. Yanmar has a tiny problem with piston lands breaking in some model years of the GM series.

Luckily parts to repair are about $700 and machining, I had the block milled and a sleeve installed on my #3 was $300. Be advised that pulling the inner crack nut off requires a special tool, which you will need to make or have a welder make.

Oversized pistions are available. Stock size was $95 with rings two years ago. 10 over was $150 each. Whe I machined the one bore as the other two measured as new.

You can read my sage here: I was Bored so Pulled the Head on my Yanmar
Hey Sailorchic

I wouldn't mind sailing with U

Considering this engine has issues since October last year I think the way things go we could sail around the world before its fixed.
What do U think ?
Im shure it would be a lot more exciting
than hanging around on a dock, marina or what ever and waiting for something to happen and paying my butt off....what a nightmare.

If we just anchor in places with cheap booze ......with that budget
we might even have some money left over for the next round
and for the rest we set up a Yanmar Online customer service.

Since You did this job allready once.... imagine this very serious situation
Our Yanmar baby quits in the middle of the night.....no moon shine...dark as hell.
I can only help You with a romantic candle
Can You do it ?
Ahhh ..how can I ...all most forgot....shure I also would fix U a nice drink

Just a choke
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Old 21-01-2015, 13:34   #26
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Re: The compression results are in, not good. (3GM30)

So after replying to the mechanic asking if he suggested a leak test he replied saying he already did one (thanks for letting me know mate!)

He says it all indicates leaky rings on my third cylinder, provided I can believe him, (he does stand to benefit being the local Yanmar parts dealer) the current shopping list is:

My own compression tester
New rings (around 50 I've seen online)
ANOTHER head gasket

But tbh my engine runs, and with the top end rebuild it fires up better than before. I also have reason to believe piston 3 does get compression once everything is warmed up and lubricated so I think ill have this rebuild planned for next winters project.
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Old 21-01-2015, 15:39   #27
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Re: The compression results are in, not good. (3GM30)

I've never seen rings wear out in one cylinder and only rings I've ever seen broken were very well worn.
Seeing as how your engine has a history of broken pistons, that seems likely.
Myself I'd take a broken piston over worn out cylinder bores, hoping no scored cylinder of course.
It's certainly fixable, really not that bad a job. Getting it in and out would be the hardest for me.
You know SC did it.
I hope you get lucky and it's a head gasket or cracked head


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Old 21-01-2015, 15:45   #28
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Re: The compression results are in, not good. (3GM30)

Quote:
Originally Posted by dtlx11 View Post
So after replying to the mechanic asking if he suggested a leak test he replied saying he already did one (thanks for letting me know mate!)

He says it all indicates leaky rings on my third cylinder, provided I can believe him, (he does stand to benefit being the local Yanmar parts dealer) the current shopping list is:

My own compression tester
New rings (around 50 I've seen online)
ANOTHER head gasket

But tbh my engine runs, and with the top end rebuild it fires up better than before. I also have reason to believe piston 3 does get compression once everything is warmed up and lubricated so I think ill have this rebuild planned for next winters project.
My cracked lower piston land was the #3 cylinder also. Cant remember about Sailor Chics.
My mechanic insisted on replacing the piston and rod. I think they come as an assembly from yanmar.
if you continue to run it until next year, you may score the cylinder. Your turn to roll the dice....
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Old 21-01-2015, 16:40   #29
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Re: The compression results are in, not good. (3GM30)

The other thing too, is w/o compression that cylinder it going to load up with fuel (no ignition) and it has to go somewhere. Either out the exhaust polluting the waters or in the crankcase polluting your motor oil. Even if it started firing on low compression, it would carbon up the cylinder and start the wear (scratching) process. But it's your nickel.
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Old 21-01-2015, 16:49   #30
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Re: The compression results are in, not good. (3GM30)

I beleave that cylinder is loaded with fuel allready and the glow plug is wet
Conclusion this cylinder is not getting proper lubrication anymore

I would fix that engine while I can get away with some rings
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