I rebuilt my 2GM20F two years ago. There is no way to easily do a proper compression test on any Yanmar GM because of the following: 1. They don't have glow plugs 2. They use injectors that are oddly sized and compression fit, not threaded in. No off the shelf compression test kit would fit those holes and assembly. 3. I've seen compression test adapters from questionable sources for hundreds of dollars. I personally didn't bother. 4. Removing injectors from a GM engine is a multi-hour job, especially the first time you do it, because of how tight all the spaces are and the need to remove hard fuel lines. I would suggest the following in this order. 1. Take off the valve train cover. Adjust the valves. Then identify intake and exhaust valves, turn the engine looking at the valves to see if the engine is nearly impossible to turn when both valves are closed on a cylinder. It's not accurate but will show you glaring issues. 2. Take out your injectors. Test them if you can, if not, open and clean them if you suspect clogging or rebuild them yourself, or give them to a diesel shop to rebuild. Sailboat diesel mechanics are nearly impossible to find, but if you take out your injectors you can take them to almost any diesel truck repair shop. 3. While the injectors are out, inspect the cylinders and valves with a boroscope. If you see a lot of deposits you may need to take the head off. Similarly but separately if you see oil in your coolant or vice versa, or if you see an oil leak at the head gasket you may need to take off the head. This is pretty rare with these engines though, as they are very durable. I posted this in a reply to one of the comments but its probably worth it to put it at the top level.
Very good ! Excellent explanations. Additional notes. After a compression test pour one spoon of oil through the injector port and re-test. If the value improves the problem is the piston rings, if it does not improve is the valves . White smoke also comes through low diesel mixture ( a clogged diesel filter)
Very well explained Tim - people assume a compression test is very complicated, until they do one! An outboard is great to try on. _It'll get interesting when [firstly] the "luxury" builders start putting modern' CRDi turbos in to sell us a 'carbon neutral luxury e-lifestyle'. We don't want unfixable boats, like 2024 cars, but I'd say it's coming._
I've seen more than one cruising channel where there was engine trouble and they didn't have one of these on board, so they had to wait until reaching land to get the bad news. I would think it's a good idea to have one. It can let you know whether it's a serious problem, in which case you can stop fiddling with filters or whatever. Or if compression is fine, then continue to fiddle with fixable things. What do you think? Required equipment for cruisers?
Great video but you forgot a VERY important step in doing a compression test. You absolutely need to hold the throttle wide open so there is no restriction for the air entering the cylinder or your reading will be lower. Also I’ve never heard an atomic 4 referred to as “tried and true” 😂 and lastly it’s funny that Canada still uses PSI. I would’ve assumed KPA or BAR like the rest of Europe uses with the metric system.
Thanks Tim. Great informative video, no waffle, no labourious footage of things already shown. Clearly explained. Keep them coming. I always watch and look forward to your stuff.
Ignition systems should get a ground path or arcing will occur inside the coil or after it, and do hidden damage. My nearly new diesel is prone to ring rotation, and will periodically lose some compression and smoke for a spell, when the ring gaps line up. Some engines develop occasional ailments that go away. I try to get an engine healthy, then button it up.
Very good informative advice. It may be worth noting that it's not just what compression results you get on a multi-cylinder engine, but also how _quickly_ you get those individual results. If you're getting a total of results across cylinders that are about right, but one/two of the cylinders are taking many more spins of the crankshaft to get there, you need to investigate that. As an example, if you're getting ~150psi across 3 cylinders, but cylinder no.3 took noticeably more crankshaft rotations as the other two to get up to 150psi...you have a problem. It's normal to expect a little deviation between cylinders, say an extra rotation or maybe two, but if it's excessive then it's a red flag and you may need to seek further advice about it.
Thanks again going to set up a compression test on my Universal Diesel . Noticed it started to give a little smoke . Will let you know what the numbers are soon
I rebuilt my 2GM20F two years ago. There is no way to easily do a proper compression test on any Yanmar GM because of the following: 1. They don't have glow plugs 2. They use injectors that are oddly sized and compression fit, not threaded in. No off the shelf compression test kit would fit those holes and assembly. 3. I've seen compression test adapters from questionable sources for hundreds of dollars. I personally didn't bother. 4. Removing injectors from a GM engine is a multi-hour job, especially the first time you do it, because of how tight all the spaces are and the need to remove hard fuel lines. I would suggest the following in this order. 1. Take off the valve train cover. Adjust the valves. Then identify intake and exhaust valves, turn the engine looking at the valves to see if the engine is nearly impossible to turn when both valves are closed on a cylinder. It's not accurate but will show you glaring issues. 2. Take out your injectors. Test them if you can, if not, open and clean them if you suspect clogging or rebuild them yourself, or give them to a diesel shop to rebuild. Sailboat diesel mechanics are nearly impossible to find, but if you take out your injectors you can take them to almost any diesel truck repair shop. 3. While the injectors are out, inspect the cylinders and valves with a boroscope. If you see a lot of deposits you may need to take the head off. Similarly but separately if you see oil in your coolant or vice versa, or if you see an oil leak at the head gasket you may need to take off the head. This is pretty rare with these engines though, as they are very durable. Hopefully this helps. I'll post this comment to the top also.
Going to view a boat for sale, how easy is to persuade the selling owner to allow you to make a compression test on the engine? Is it a rule of thumb that if he doesn't let you than the engine has a problem or is it normal for him not to let a stranger messing with the engine??? 🤔🤔🤔
You could just get a regular mechanical inspection, as you would a car., by an authorised mechanic. _No, I wouldn't let possibly crazy buyers dismantle my engine, but an inspection is fine. Cheers._
Most, if not all, marine surveyors will not dismantle anything for liability reasons. You break it, you pay for it. If a diesel engine starts right up, doesn't smoke and runs smoothly, you probably don't need a compression test even if the owner would allow it.
Do a sea trial. Insist the engine is checked in all regimes. No load idle and max RPM as well as idle and max RPM under way. Insist on running the engine at max power in forward. Check the max RPM against the engine manual. Check for smoke, irregular noises, overheating, etc
Having this whole kit connected and judging engine is nothing special. What special is to sayl about engine condition WITHOUT any kit. Just basing on fumes and noises. Any stupid can cay abt compression having this kit in hand.
I assume you would just crank the starter, but I'm no marine diesel mechanic, just a guy with a neglected old boat and a neglected old diesel that I've neglected to do anything with yet
I love both channels you represent.Im That being said,how about a video of someone actually sailing. Or would that be impractical? I apologize three channels.
An added diagnostic test if a cylinder has low pressure is the wet test. After getting a low reading on one or more cylinders, add about a teaspoon of motor oil through the hole. The idea is to coat the cylinder walls to help a failed compression ring seal. A significant increase in the pressure indicates a failed compression ring. A slight or no increase indicates a valve issue. This works best on vertical pistons but on horizontal pistons a sprayer can be used for the oil.
Not with the spark plugs removed from both the ignition leads n engine. Only get a spark from the plugs. N he moved the leads out of the way. Very little to zero fuel atomization outside of the internal cylinders.
I rebuilt my 2GM20F two years ago. There is no way to easily do a proper compression test on any Yanmar GM because of the following:
1. They don't have glow plugs
2. They use injectors that are oddly sized and compression fit, not threaded in. No off the shelf compression test kit would fit those holes and assembly.
3. I've seen compression test adapters from questionable sources for hundreds of dollars. I personally didn't bother.
4. Removing injectors from a GM engine is a multi-hour job, especially the first time you do it, because of how tight all the spaces are and the need to remove hard fuel lines.
I would suggest the following in this order.
1. Take off the valve train cover. Adjust the valves. Then identify intake and exhaust valves, turn the engine looking at the valves to see if the engine is nearly impossible to turn when both valves are closed on a cylinder. It's not accurate but will show you glaring issues.
2. Take out your injectors. Test them if you can, if not, open and clean them if you suspect clogging or rebuild them yourself, or give them to a diesel shop to rebuild. Sailboat diesel mechanics are nearly impossible to find, but if you take out your injectors you can take them to almost any diesel truck repair shop.
3. While the injectors are out, inspect the cylinders and valves with a boroscope. If you see a lot of deposits you may need to take the head off.
Similarly but separately if you see oil in your coolant or vice versa, or if you see an oil leak at the head gasket you may need to take off the head. This is pretty rare with these engines though, as they are very durable.
I posted this in a reply to one of the comments but its probably worth it to put it at the top level.
Very good ! Excellent explanations. Additional notes. After a compression test pour one spoon of oil through the injector port and re-test. If the value improves the problem is the piston rings, if it does not improve is the valves .
White smoke also comes through low diesel mixture ( a clogged diesel filter)
Very well explained Tim - people assume a compression test is very complicated, until they do one! An outboard is great to try on. _It'll get interesting when [firstly] the "luxury" builders start putting modern' CRDi turbos in to sell us a 'carbon neutral luxury e-lifestyle'. We don't want unfixable boats, like 2024 cars, but I'd say it's coming._
Great job, Tim. You're getting better and better at this UA-cam thing, and I hope you're making piles of green. Please keep it up.
I've seen more than one cruising channel where there was engine trouble and they didn't have one of these on board, so they had to wait until reaching land to get the bad news. I would think it's a good idea to have one. It can let you know whether it's a serious problem, in which case you can stop fiddling with filters or whatever. Or if compression is fine, then continue to fiddle with fixable things.
What do you think? Required equipment for cruisers?
Not a topic I might have asked for, but I'm happy you taught me something new! Good video
Great video but you forgot a VERY important step in doing a compression test. You absolutely need to hold the throttle wide open so there is no restriction for the air entering the cylinder or your reading will be lower. Also I’ve never heard an atomic 4 referred to as “tried and true” 😂 and lastly it’s funny that Canada still uses PSI. I would’ve assumed KPA or BAR like the rest of Europe uses with the metric system.
Thanks Tim. Great informative video, no waffle, no labourious footage of things already shown. Clearly explained. Keep them coming. I always watch and look forward to your stuff.
You forgot to tell everyone to hold the throttle wide open to allow maximum airflow into the engine while performing the compression test.
Ignition systems should get a ground path or arcing will occur inside the coil or after it, and do hidden damage. My nearly new diesel is prone to ring rotation, and will periodically lose some compression and smoke for a spell, when the ring gaps line up. Some engines develop occasional ailments that go away. I try to get an engine healthy, then button it up.
Very good informative advice. It may be worth noting that it's not just what compression results you get on a multi-cylinder engine, but also how _quickly_ you get those individual results.
If you're getting a total of results across cylinders that are about right, but one/two of the cylinders are taking many more spins of the crankshaft to get there, you need to investigate that.
As an example, if you're getting ~150psi across 3 cylinders, but cylinder no.3 took noticeably more crankshaft rotations as the other two to get up to 150psi...you have a problem.
It's normal to expect a little deviation between cylinders, say an extra rotation or maybe two, but if it's excessive then it's a red flag and you may need to seek further advice about it.
Good explanation Tim
I've only worn out 3 orb4 of those gadgets 😊
Thanks again going to set up a compression test on my Universal Diesel . Noticed it started to give a little smoke . Will let you know what the numbers are soon
Thanx Tim. Great educational episode
My thumb stays up for each episode of yours. Happy Sailing ⛵
nice bit of knowhow for troubleshooting. do you have to have the throttle wide open when doing a compression test?
All of a sudden grade 9 shop class came flooding back 😂
I have a Yanmar 3GM diesel that does not have glo plugs. Is there a way to do a compression test on this engine?
Search youtube I think ⚓
Yes, good question. You would remove the fuel injectors and attach the hose there.
I rebuilt my 2GM20F two years ago. There is no way to easily do a proper compression test on any Yanmar GM because of the following:
1. They don't have glow plugs
2. They use injectors that are oddly sized and compression fit, not threaded in. No off the shelf compression test kit would fit those holes and assembly.
3. I've seen compression test adapters from questionable sources for hundreds of dollars. I personally didn't bother.
4. Removing injectors from a GM engine is a multi-hour job, especially the first time you do it, because of how tight all the spaces are and the need to remove hard fuel lines.
I would suggest the following in this order.
1. Take off the valve train cover. Adjust the valves. Then identify intake and exhaust valves, turn the engine looking at the valves to see if the engine is nearly impossible to turn when both valves are closed on a cylinder. It's not accurate but will show you glaring issues.
2. Take out your injectors. Test them if you can, if not, open and clean them if you suspect clogging or rebuild them yourself, or give them to a diesel shop to rebuild. Sailboat diesel mechanics are nearly impossible to find, but if you take out your injectors you can take them to almost any diesel truck repair shop.
3. While the injectors are out, inspect the cylinders and valves with a boroscope. If you see a lot of deposits you may need to take the head off.
Similarly but separately if you see oil in your coolant or vice versa, or if you see an oil leak at the head gasket you may need to take off the head. This is pretty rare with these engines though, as they are very durable.
Hopefully this helps. I'll post this comment to the top also.
I love these videos. Keep them coming.
Great info. Thanks!
Going to view a boat for sale, how easy is to persuade the selling owner to allow you to make a compression test on the engine?
Is it a rule of thumb that if he doesn't let you than the engine has a problem or is it normal for him not to let a stranger messing with the engine??? 🤔🤔🤔
You could just get a regular mechanical inspection, as you would a car., by an authorised mechanic.
_No, I wouldn't let possibly crazy buyers dismantle my engine, but an inspection is fine. Cheers._
Most, if not all, marine surveyors will not dismantle anything for liability reasons. You break it, you pay for it. If a diesel engine starts right up, doesn't smoke and runs smoothly, you probably don't need a compression test even if the owner would allow it.
Do a sea trial. Insist the engine is checked in all regimes. No load idle and max RPM as well as idle and max RPM under way. Insist on running the engine at max power in forward. Check the max RPM against the engine manual. Check for smoke, irregular noises, overheating, etc
Having this whole kit connected and judging engine is nothing special. What special is to sayl about engine condition WITHOUT any kit. Just basing on fumes and noises. Any stupid can cay abt compression having this kit in hand.
How do you "cycle" an inboard diesel engine for such a test?
I assume you would just crank the starter, but I'm no marine diesel mechanic, just a guy with a neglected old boat and a neglected old diesel that I've neglected to do anything with yet
Liked!
I love both channels you represent.Im That being said,how about a video of someone actually sailing. Or would that be impractical? I apologize three channels.
An added diagnostic test if a cylinder has low pressure is the wet test.
After getting a low reading on one or more cylinders, add about a teaspoon of motor oil through the hole. The idea is to coat the cylinder walls to help a failed compression ring seal. A significant increase in the pressure indicates a failed compression ring. A slight or no increase indicates a valve issue.
This works best on vertical pistons but on horizontal pistons a sprayer can be used for the oil.
Excellent Tim ! I actually understood all that !
Shouldn't you disable the ignition? Doesn't pulling the cord generate a spark from ignition cables that could ignite fuel?
Not with the spark plugs removed from both the ignition leads n engine. Only get a spark from the plugs. N he moved the leads out of the way. Very little to zero fuel atomization outside of the internal cylinders.