Assessing a used Yanmar 8HP diesel engine

[MicHughV]

True, I've met some old time mechanics that could rub their thumb and forefinger over a shaft and tell you " this is out of alignment by 0.001".
Not many of those around anymore.

But, a surprising number of technical savvy folk on this forum.

[HorseshoeBay]

A mechanic shared some of his expert knowledge, which I haven't seen from any amateurs online.


He really knew how to look at different parts in fine detail and identify and eliminate what were the issues with the engine stop running.


In his work, for example, he hones cylinder liners.


Pity is, he's gone on a 3-month work trip.

[Wotname]

Originally Posted by HorseshoeBay

"What can go wrong?" from now seems an important question to consider.


Need:
- compression
- fuel injection
- air
- timing.


Right?



Other service matters include filters, fan belts, impeller servicing and reconnecting the electrics.



Ideas appreciated

In the spirit of what can go wrong, here are some ideas...

Compression - with a new liner / piston / rings and valves that seal, then not much can go wrong BUT make sure the rings are in the correct order and the right way up. Set the ring gap BEFORE fitting them to the piston. Make sure the liner protrudes from the block by 0.06 to 0.14 mm. Too much or too little will cause compression problems. Set tappet clearance after torquing down the head.

Fuel Injection - if the injection pump has not been touched, then not much to go wrong. Confirm the injector is not leaking after it pops (this is a DIY item with injector removed but connected to the injection pump). It is quite likely the pop pressure will be a bit low (say <20%) but it will still start and run.The only way to check the pop pressure is to take it to an fuel injection shop. If the pump has been removed but not otherwise not touched, make sure the shims are refitted as removed. If the pump has been serviced, then the timing will need to be checked and shimmed as required.

Air - not much to check except to check the exhaust and mixing point are not blocked.

Timing (valve timing) - if crank and cam shafts have not been removed, nothing to check except tappet clearance as noted above. If either shaft has been removed, then refit noting the alignment marks as per service manual.

Timing (injection timing) - as noted above.


Other items -

Thermostat - check it starts to open at 42C and is fully open at 52C.
Fit new anode.
Oil feed - check the external oil feed line from the top of the block to under the head. This steel line does rust out, especially as it goes under the head.
Oil Filter - remove, clean and refit.
Oil pressure - good idea to check it when warm at idle as the book value for the low pressure switch is an amazingly low 1.4 psi (0.1bar).

Hope the reassembly goes well.

[MicHughV]

There is some satisfaction in getting an old diesel engine up and running again.

Many years ago, I was tasked to bring a vintage Volvo back to life.
I did all the usual things, replaced everything I could, but it simply would not start.
Begging and pleading the engine did little good.

The engine was fitted wit a monstrous flywheel and could be handcranked if so chosen.

After depleting the battery, in desperation, I lifted the decompression levers and put my last ounce of strength on the crank handle.
Sumbitch, iffen dat thing didn't rumble to life in cloud of smoke, surprising the hell out of me.
Ran fine after that.

[Wotname]

^^ it was testing you...
Never mind the begging and pleading, as you found out, it needed a firm hand crank...

[HorseshoeBay]

MicHughV great story. Back in 1993 in Gothenburg, old Volvo station/ranch wagons were proudly shown off along the main avenue, with some having a large sound system in the back.


Love built to last and serviceable products.


Built-in redundancy products, for example light globes and tubes, are an abomination!


Back to my YSM 8; the groove around the top of the cylinder that holds the liner isn't rusted at all. An old toothbrush cleaned it up.


I haven't checked the fuel injection yet.


While first examing the engine, I clumsily broke the glass bowl under the fuel filter.


Does the head need to be on to check the high-pressure fuel pump?


Flesh well away from it!

[MicHughV]

As a youngster, with little to no money, I had my head stuck under the hood (or bonnet if yer English) of many a car that myself and friends had as our transport back in the day. Invariably, these were hand me downs from our parents. These cars were old relics of the day, many dating back to the 40's.

Not far from where I lived, was a big scrapyard, filled to the brim with these relics. I knew every each inch of the place as I was often to be seen there trying to scrounge some or other part.

Most everything we did was makeshift of one type or another. Getting a car to run for another day was considered a major achievement.

In this same way, I'd approach your Yanmar rebuild. Fix and repair what you can with what you have and concoct the rest of the parts.

[Wotname]

Originally Posted by HorseshoeBay

.........
Does the head need to be on to check the high-pressure fuel pump?


Flesh well away from it!

No.

Of course you can only do a go/no go test at home but providing you can rotate the camshaft, you can actuate the high-pressure fuel pump.

[HorseshoeBay]

Hi Wotname,

May I please ask about “BUT make sure the rings are in the correct order and the right way up. Set the ring gap BEFORE fitting them to the piston”?

Correct order?

Right way up?

Ring gap? (Orientation?)

[HorseshoeBay]

Placed conrod in piston and inserted piston rings according to the Yanmar manual.

Compared with the original gummed up rings, the new rings stand out much more.

[Wotname]

Originally Posted by HorseshoeBay

Hi Wotname,

May I please ask about “BUT make sure the rings are in the correct order and the right way up. Set the ring gap BEFORE fitting them to the piston”?

Correct order?

Right way up?

Ring gap? (Orientation?)

Sounds like you have already fitted the rings to the piston as per the manual so I guess you also checked the ring gap as per the manual before fitting them to the piston.

[HorseshoeBay]

Yanmar Manual

[HorseshoeBay]

The rings were taken from the package and flexed just enough to get around the piston and into the recesses.

Was that approach wrong?

Can the gaps be adjusted once the rings are on the piston?

[HorseshoeBay]

I applied waterproof grease to the cylinder liner in accordance with the manual.

I tried to insert the cylinder liner with the o-rings around it in the grooves. However, it was a very tight fit getting the liner in with them on, so I inserted the liner WITHOUT them.

There was some resistance in the last 5cm, due to a tight fit on the end inside the engine. The inside edge next to the top of the cylinder (A) was free of rust and had been scrapped, brushed and dusted.

The piston conrod is ready to be attached to the big end of the crank.

I will us a feeler gauge to check the projection of the cylinder line from the cylinder block.

Please share your thoughts on not having the o-rings and having some resistance at the inside end when inserting the liner.

[Wotname]

The O'rings MUST be in place. They are the ONLY thing that keeps the oil in the crankcase away from the cooling water in the water jacket.

Without them, the oil and water will migrate!