very low compression, non starter

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niallw

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Having tried and failed to get my 1GM10 to start after winter layup, I think my options now are OVERHAUL / REPLACEMENT.

I carried out a wet compression test, as per my Yanmar manual, the difference in compression (as opposed to cranking in dry test, without gear oil added into cylinder) was night and day.

In the dry test I can hand crank engine no problem with very little resistance on the compression stroke. In the wet test, large kick from my crankhandle on the compression stroke, but it will eventually go through the compression stroke. It seems as though if i give it enough time the gear oil will seep through whatever leak there is in piston/cylinder wall.

WHAT TO DO? Removing the exhaust elbow to check for corrosion, i found elbow was fine but a significant buildup of soot/carbon inside exhaust port. Ive not had time to remove this yet but dreding what I might find.

Having only recently purchased this Nic26 with 14 year old Yanmar 1gm10, I am now considering if a replacement of engine is the best option to get trouble free sailing.

Alternatively can anyone recommend a good machining workshop to get an overhaul/rebore if nessesary of my 1gm10. I live Dundee, the boat at MRC (near Oban) so anywhere in Central/eastern Scotland is worth considering. The cost of overhaul as opposed to replacement is obviously the main consideration. Does anyone have idea of costs;

A) of overhaul

Im guessing if cylinder needs rebore then probably as well to replace.

B) replacement. How much to supply and fit a new 1gm10 or equiv. Ive heard good things about Chinese manufacturers producing cheap, reliable marine engines, also consider Kubota Beta or similar.
 
The difference between the dry and wet tests is telling you the rings are not sealing. This could be due to their fracture but it could simply be that they are stuck in their grooves due to some corrosion or gum over winter. Have you tried starting the engine since putting oil down the bore? This might be all it needs to get it going. The bore is not lubricated at starter motor speeds, so once it has started all may be well.
 
Highly unlikely the bores are worn. As Vyv says, more likely to be sticky rings. Other causes of low compression are bent rod (usually from water getting in) and poor;y seating valves. The black gunge is probably caused by the engine not being run long enough and hard enough.

The 1GM is a very robust engine, and if you can get it to go and run it hard under load, the rings will probably clear.

For replacement a Nanni or Beta 14 is the best (I replaced mine with a Nanni). They have virtually the same footprint as the Yanmar, but a bit bulkier high up and the exhaust is on the other side. You will need to adapt the exhaust hose as the Beta is 40mm, Nanni 50mm and Yanmar 45mm, plus a 3/4 water inlet rather than 1/2". However budget around £4k with all the bits. If you can get the Yanmar going you should be able to get up to £1k for it - I got £1200 for mine (still running in the boat) and could have sold it many times over.

If you are happy with the performance of the Yanmar it is probably better and cheaper to sort it rather than fit a new engine. It is light enough to lift out by hand and take home to fix in your garage if needs be.

Hope this helps
 
OK, thanks for comments, Tranona and vyv-cox...

I will try starting engine again.

What do you mean when talking about "bent rod" please explain Tranona.

I agree about the likely cause of black gunge buildup, in my ignorance last year i was not running the engine under full load in mistaken belief i was 'taking care of it'. In future if i do manage to get this thing running I will give it a good blast of full throttle before stopping.

Secondly, please give advice about how to clean the valve seats/valves without dropping gunge into cylinder.
 
niallw said:
Secondly, please give advice about how to clean the valve seats/valves without dropping gunge into cylinder.
Click to expand...

Clean the port and manifold mechanically, with a scraper. Once the engine is running, take it for a flat-out run for about 15 minutes. Any carbon on the exhaust valve will be burnt off. Make sure the rest of the engine is OK before doing this, if the bearings are knocking, oil pressure low, old and contaminated oil, it would not be the best thing to do.
 
As others have said if it was running when you put it away it is likely just gummed up rings.

Get is started and give it the 'italien tuneup' full power full rpm under load for 5 to 10 minutes.

As a last resort to get it started, introduce some burning newspaper soaked in fuel into the inlet manifold while cranking the engine over. Remove any air filter first though.
 
niallw said:
I will try starting engine again.

What do you mean when talking about "bent rod" please explain Tranona.

I agree about the likely cause of black gunge buildup, in my ignorance last year i was not running the engine under full load in mistaken belief i was 'taking care of it'. In future if i do manage to get this thing running I will give it a good blast of full throttle before stopping.

Secondly, please give advice about how to clean the valve seats/valves without dropping gunge into cylinder.
Click to expand...

One of the endearing features of the 1GM is that it can run backwards for a couple of revolutions when you shut it down. This can suck water back through the exhaust and cause what is known as hydraulicing (spelling?) - that is the cylinder works as a pump, and water does not compress so the connecting rod distorts. That means the piston is lower in the cylinder so reducing compression. It can also happen if you do not have an anti syphon valve in the water pipe from the outlet in the head to the injection point. Water coming in also does no good to valves. However if your elbow is not corroded away internally then you probably don't have a water fedback problem. The workshop manual has all the details on dealing with a bent rod - but it is a a major strip down job. There is however a process for measuring whether it is bent without taking the head off.

As Vyv says, if you can get it going run it hard under load the valves will probably sort themselves out, but getting the head off and reseating valves is not a major exercise. You may also want to check that the exhaust system is clear as a collapsed hose can cause excess back pressure. Heating incoming air is a good idea - but maybe not burning paper as TQA suggests. A hair dryer is very effective. The motor does not have glow plugs so warm air, good compression (maybe turning it over with the compression lever up and dropping it) will all help, as will openng the "throttle".

Good luck with the beast - I have fond memories of mine, great little engine.
 
sounds much more likley to be the valve seats leaking due to pitting, when the oil is added it creates a better seal. they are renown for getting pitted and i have many scrap valves from gm engines. Yanmar sell more valves than any other rebuild part for the gm engines.

As the exhaust port is corroded up with carbon the head has to come off to remove it, do the valves at the same time, the engine recon company can put new valve seats in which will reset the valve height back to factory level thus resoring any loss of compression due to any previous valve grinding.
The rings are far less likley to be a problem unless they have been damaged, the bore however does also glaze up badly when the engine is run at slow speed with little load for long periods.

Hope this is helpfull.

Steve
 
niallw said:
Having tried and failed to get my 1GM10 to start after winter layup, I think my options now are OVERHAUL / REPLACEMENT.

I carried out a wet compression test, as per my Yanmar manual, the difference in compression (as opposed to cranking in dry test, without gear oil added into cylinder) was night and day.

In the dry test I can hand crank engine no problem with very little resistance on the compression stroke. In the wet test, large kick from my crankhandle on the compression stroke, but it will eventually go through the compression stroke. It seems as though if i give it enough time the gear oil will seep through whatever leak there is in piston/cylinder wall.

WHAT TO DO? Removing the exhaust elbow to check for corrosion, i found elbow was fine but a significant buildup of soot/carbon inside exhaust port. Ive not had time to remove this yet but dreding what I might find.

Having only recently purchased this Nic26 with 14 year old Yanmar 1gm10, I am now considering if a replacement of engine is the best option to get trouble free sailing.

Alternatively can anyone recommend a good machining workshop to get an overhaul/rebore if nessesary of my 1gm10. I live Dundee, the boat at MRC (near Oban) so anywhere in Central/eastern Scotland is worth considering. The cost of overhaul as opposed to replacement is obviously the main consideration. Does anyone have idea of costs;

A) of overhaul

Im guessing if cylinder needs rebore then probably as well to replace.

B) replacement. How much to supply and fit a new 1gm10 or equiv. Ive heard good things about Chinese manufacturers producing cheap, reliable marine engines, also consider Kubota Beta or similar.
Click to expand...



Speak to these folk.....They are on your doorstep and used by many boat mechanics.

http://www.agraengineering.co.uk/index.php
 
Another way to test for rings sticking is to take the oil filler cap off and turn the engine over dry with the starting handle again, when it comes to the compression stroke listen to the filler hole for the hissing.

I still think its valves and you will hear it coming from either the inlet or the exhaust ports.


Steve
 
I hate to say this and I dont like it but...........

If you really are having problems getting it to fire........ easy start. :eek:

Not many people like it and I'm in that group, but, it will get the engine to run then you can as has been suggested give it a good hard run.

The biggest problem with most marine engines is they never really reach the correct temperature. that has noting to do with water temperature it is the internal cylinder temperature. You said that you had carbon build up in the exhaust, I would suggest running the engine a little harder to clear the products, and making sure that your thermostat it working correctly.

Dont strip it down just yet !

Tom
 
steve28 said:
Another way to test for rings sticking is to take the oil filler cap off and turn the engine over dry with the starting handle again, when it comes to the compression stroke listen to the filler hole for the hissing.

I still think its valves and you will hear it coming from either the inlet or the exhaust ports.


Steve
Click to expand...
Oil in cylinder, compression improves, RINGS!!!!!!!!!
Stu
 
"
LittleShip said:
I hate to say this and I dont like it but...........

If you really are having problems getting it to fire........ easy start. :eek:

Not many people like it and I'm in that group, but, it will get the engine to run then you can as has been suggested give it a good hard run."

Pragmatically-

I wouldn't use Easy Start routinely but the tales of it damaging engines are very mixed/apocryphal.

In truth, it's only ever used on sick/dead/dying engines which sometimes expire soon after. It's easy to say it's the ether, QED, wot dun it.

I have a diesel book from the sixties, mainly lorry engines. In the section on cold starting there are described builder fitted cold start mechanisms for applying ether to the manifold. So ether per se is not death to engines?

Nick
Click to expand...
 
Last edited:
Yep. It's a coffin-dodging method of keeping a crappy old motor going a bit longer. We had a little breakdown truck that didn't like starting from cold and was way past it's sell-by date. A little hit of easy start would see it going for the day.

If the motor is in good nick it's not a habit to start, but as a diagnostic tool it is fine. It'll get the motor going and enable some load running to free off the rings.

Bit of lighter fluid would do it if you have some handy.
 
NickRobinson said:
"
LittleShip said:
I hate to say this and I dont like it but...........

If you really are having problems getting it to fire........ easy start. :eek:

Not many people like it and I'm in that group, but, it will get the engine to run then you can as has been suggested give it a good hard run."

Pragmatically-

I wouldn't use Easy Start routinely but the tales of it damaging engines are very mixed/apocryphal.

In truth, it's only ever used on sick/dead/dying engines which sometimes expire soon after. It's easy to say it's the ether, QED, wot dun it.

I have a diesel book from the sixties, mainly lorry engines. In the section on cold starting there are described builder fitted cold start mechanisms for applying ether to the manifold. So ether per se is not death to engines?

Nick
Click to expand...
Easy start is made from predominantly ether, it "explodes" rather than "burns" It gives the effect of detonation or "pinking" in a petrol engine. The uncontrolled explosion has the same effect on the diesel piston, it squashes the ring lands in the piston and causes them to break. This is why they get "addicted" The prob mostly is that peeps dont do as they are told in the instructions, use a little bit on a rag or similar, they squirt loads in to the the intake and BANG!!
If you have to use a start aid, WD40 is better, it contains a propellant ( I think its a propane type gas) and an atomised white spirit, they appear to "burn" slower and do the job just as well without causing more damage
Stu
Click to expand...
 
Many years ago a Mini-owning friend had the bright idea of mounting a can of Easi-start on the dashboard with the tube pushed through to the carburettor inlet. When he needed a bit more power for overtaking he could press the button for a few seconds to give him a quick burst. It worked about five or six times, then the engine blew up in an extremely dramatic way.
 
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