3GM30F Service Issue
- Thread starter skunther
- Start date
I don't really know the answer to this question - but it could well work. Ether does not provide lubrication. Oil would be better. But if you've gotten it running, that may suffice. Diesel fuel is a lubricant. You don't want to keep using ether....
The use of ether to start diesels is commonly done on old engines with poor compression. So if you engine starts and runs using ether, then all the other systems are working - no fuel line problems, no significant air leaks - this leads me to believe there is no question as to if you have a compression problem - you have a compression problem.
With the number of hours on that engine, the fact you have consistent compression currently says to me that just replacing the rings would most likely work - if they don't begin seating well from running the engine. I'd give that engine a good run though. "Occasionally" does not sound right. You need to run that engine so it get fully heated up and then some. I'd say run that engine at close to WOT for several hours - like 4 hours or more - of course under full load. So go take a a nice half day motor sail and see what happens.
dj
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The manual indicates continuous rating of 24 HP/3400 RPM, while the one-hour max output is 27 HP/3600 RPM. @dLj are you recommending I run it at 3400 for 4 hours? Or go for broke with 3600?
Nevermind. I’m only getting 3200 at WOT under load. However, I was able to get 3400 WOT before work was performed. Not sure how relevant that may be.
I will run it hot and see what happens.
Nevermind. I’m only getting 3200 at WOT under load. However, I was able to get 3400 WOT before work was performed. Not sure how relevant that may be.
I will run it hot and see what happens.
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3400 is more than adequate to heat it up properly. There is no need to max it out for long periods. I'd be surprised if you can even achieve 3,600 under load. If you can run 3,000 to 3,400, that will give it a good workout for sure.
What RPM are you typically running your engine at? How often and how close do you get to these upper RPM numbers posted below in your normal usage?
Note the comment by Mark - an excellent comment.
Let me know how you normally run that engine.
I doubt you can get to 3600 rpm with the compression you currently have. But hey, truth is stranger than fiction...
Let's start here: Describe how you normally run your engine? What is a normal max RPM you typically run at? Where are you sailing your boat?
dj
Note the comment by Mark - an excellent comment.
Let me know how you normally run that engine.
I doubt you can get to 3600 rpm with the compression you currently have. But hey, truth is stranger than fiction...
Let's start here: Describe how you normally run your engine? What is a normal max RPM you typically run at? Where are you sailing your boat?
dj
My engine manual says I should run the RPM's up to 3000 rpm for 30 seconds, drop slowly down to idle, then repeat this another 2 times when shutting down. We don't have the same engine, I have a late model Yanmar. But the 5 to 10 seconds sounds pretty short to me. Also repeating it a couple times seems like a good idea. Warming up for 20 minutes or so sounds too long. Does it say to do that in your engines manual? Does your engine manual have recommendations for shutting down? Mine does.
Diesel engines like to be worked hard. they don't like to be babied...
What's your cruise speed at 2700?
As far as seeing if you can get your rings to seat properly, I'd probably run up to 3200. Like Mark said, you want to run up and down a number of times. You need to watch your exhaust. You need to listen to your engine. I'd run up to 3400 a couple times if everything is sounding and looking OK once the engine is fully warmed up. Run it up there for half an hour or thereabouts. If the engine is rated for continuos operation at that RPM, you aren't going to do anything bad to it. It's designed to run there. Watch your exhaust and see if you get any black soot coming out at any point. It's hard to give advice without being on your boat and listening and seeing how the engine is responding. Read your manual.
dj
Diesel engines like to be worked hard. they don't like to be babied...
What's your cruise speed at 2700?
As far as seeing if you can get your rings to seat properly, I'd probably run up to 3200. Like Mark said, you want to run up and down a number of times. You need to watch your exhaust. You need to listen to your engine. I'd run up to 3400 a couple times if everything is sounding and looking OK once the engine is fully warmed up. Run it up there for half an hour or thereabouts. If the engine is rated for continuos operation at that RPM, you aren't going to do anything bad to it. It's designed to run there. Watch your exhaust and see if you get any black soot coming out at any point. It's hard to give advice without being on your boat and listening and seeing how the engine is responding. Read your manual.
dj
I guess the real question is not what you cruise at ... when WOT under load, what is the highest RPM your engine achieves? I regularly run my engine above 3,000 rpm when motoring along and it reaches about 3.400 under load at WOT.
If you have very low compression, I doubt you would achieve even 3,000. If you can achieve over 3,000 rpm under load, I think your compression can't be too bad ... but I'm no expert by any means - not even close.
I’m currently able to get 3250 rpm at WOR under load. Formerly I could get 3400.
I would think you should have been able to get higher RPM's towards the end if indeed your rings were able to seat well. I suspect you need to pull the head and fix the problem.
Depends where the oil smell is coming from. With bad rings you may well be burning crankcase oil.
Depends where the oil smell is coming from. With bad rings you may well be burning crankcase oil.
I tried starting the engine again yesterday and no difference. It still doesn’t catch, and I stopped cranking after 10 seconds.
Would more cranking amps make a difference in starting compression? I currently have a new Costco battery that’s rated at 550CCA, but it’s not holding a charge and I need to return it. I’m thinking of possibly picking up a different 24DP that has 840 CCA, but it costs roughly twice as much and I don’t know if it will make any difference. If it would help with starting it seems worth it.
www.westmarine.com
Would more cranking amps make a difference in starting compression? I currently have a new Costco battery that’s rated at 550CCA, but it’s not holding a charge and I need to return it. I’m thinking of possibly picking up a different 24DP that has 840 CCA, but it costs roughly twice as much and I don’t know if it will make any difference. If it would help with starting it seems worth it.
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I’m going to bring a 1000 CCA jump starter down to test if more cranking amps makes any difference.
The engine cranked over stronger and started up within 10 seconds. Not as good as it was before, but a huge improvement on what it’s been.
Does anyone know of a good high CCA size 24 DP battery? Or does that AGM I linked in my above post look like a good bet?
Interestingly, after this start, rpm under load at WOT maxed at 3500, while it had previously maxed at 3250 (prior to the work in question was done to the engine last fall, I could get roughly 3500). I’m not sure if the ring seals set while I was working the engine at WOT those 4 hours, but it seems an improvement, and I plan to pick up that battery with 840CCA/1000MCA and see if the trend will continue.
Does anyone know of a good high CCA size 24 DP battery? Or does that AGM I linked in my above post look like a good bet?
Interestingly, after this start, rpm under load at WOT maxed at 3500, while it had previously maxed at 3250 (prior to the work in question was done to the engine last fall, I could get roughly 3500). I’m not sure if the ring seals set while I was working the engine at WOT those 4 hours, but it seems an improvement, and I plan to pick up that battery with 840CCA/1000MCA and see if the trend will continue.
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No doubt you were able to affect a positive change! I'm not sure I understand how your mechanic arrived at the low-compression argument. I think that if you really had low compression, you never would have achieved the rpm's that appear to be normal for you. I couldn't explain the reason why you maxed out at 3250 during your test run and then later achieved above 3400 but it sounds like a victory to me and it would put my mind at rest in regard to "low-compression" (if not yours 
).
A small battery should start these small engines, but I would also go along with your assessment to get the 840 CCA battery. The 550 CCA battery just sounds too small to me. I wouldn't hesitate to use a dedicated start battery with high CCA and not bother with a "dual purpose" battery.
If you have any lingering questions about the rpm, I would measure it with a pulse meter to get a truly accurate reading. You never know how accurate the instrument gauge may be without an independent reading.
).A small battery should start these small engines, but I would also go along with your assessment to get the 840 CCA battery. The 550 CCA battery just sounds too small to me. I wouldn't hesitate to use a dedicated start battery with high CCA and not bother with a "dual purpose" battery.
If you have any lingering questions about the rpm, I would measure it with a pulse meter to get a truly accurate reading. You never know how accurate the instrument gauge may be without an independent reading.
With all due respect @Scott T-Bird - everything @skunther is describing about how his engine is running can easily be due to low compression. It can't be as low as his original numbers quoted or his engine wouldn't run - at least I've never heard of a diesel that could run at those compression levels.
Hard to start, spinning the engine faster to start, not achieving stated rpm's, are all indicators of low compression. His RPM indicator may not be overly accurate, but it's the same one he has used previously so it's unlikely to be a measurement error.
Bear in mind, with poor compression, you are also contaminating your engine oil notably more than with proper compression. This means that the longer you run your engine this way, the more wear you will inflict on your bottom end. Rebuilding the top end is easy. Rebuilding the bottom end is not.
I would do a ring job on this engine. All indicators point to that solving your problem.
dj
Hard to start, spinning the engine faster to start, not achieving stated rpm's, are all indicators of low compression. His RPM indicator may not be overly accurate, but it's the same one he has used previously so it's unlikely to be a measurement error.
Bear in mind, with poor compression, you are also contaminating your engine oil notably more than with proper compression. This means that the longer you run your engine this way, the more wear you will inflict on your bottom end. Rebuilding the top end is easy. Rebuilding the bottom end is not.
I would do a ring job on this engine. All indicators point to that solving your problem.
dj
If the rings aren’t sealing, wouldn’t the resultant blow by produce smoke/fumes in the oil system? I have removed the oil cap and dip stick immediately after running the engine to check for this, and there are no fumes or smoke present.
Another compression test seems necessary. I’ll get a kit at the end of the season and check it.
Another compression test seems necessary. I’ll get a kit at the end of the season and check it.
Not that you should be able to detect. If you had that much blow by, your engine wouldn't run. Gasoline engines are not the same.
But you will be contaminating you crankcase oil. I'd suggest, if you wish to not fix your compression issue, change your oil frequently.
dj