Yanmar YSB12 partial rebuild

[stav]

Hi All,

I am having a go at rebuilding a friend's Yanmar YSB12. He was going to buy an old outboard from me but the challenge of getting the engine going is too much to resit and if I get it going he said he would donate beer tokens towards my boat if I am successful and take me fishing! Anyhow I tried bleeding the fuel and checked for clear air in and a clear exhaust, breather on the fuel tank and all looked correct. The head/block has a dark mark that looks like someone has heated it with a blow lamp. So I have removed the head and found the inlet quite rusty but no obvious marks where the head gasket might have failed. It all came apart very easily. I wondered if this might be to do with the heating of the head and differential expansion? I put puddles of diesel on the valves and it drained away almost immediately so have reground the valves, pop tested the injector which opened at the right pressure but the spray pattern wasn't; just a squirt.

The situation I am puzzling over is whether to take out the cylinder to check the rings. There is a little corrosion at the top of the cylinder liner but otherwise it is smooth with no signs of a ridge at the top. Therefore I was contemplating putting the head back on with the old gasket to see if it shows signs of starting and if it did disassemble and put back with new injector nozzle and new head gasket. If it didn't then take out the cylinder and progress from there.

The engine is in the boat and taking the cylinder out requires I remove the alternator and may be starter but this would also give access to TDC mark and therefore I could check the timing of the injector pump. I am keen to get my friend's engine going but it is old and being done more as favour than for profit. So some ideas about where to draw the line would be useful.

Thanks in advance.

 

[theoldsalt]

I think I would refit the head and do a compression test. As you have lapped the valves and the bores look good you may be lucky and have good compression. If the injector pump has not been disturbed it may not need retiming. So have the injectors reconditioned then try to start the engine.

 

[30boat]

I would take the cylinder out as a matter of course and have it honed and then fit a new set of rings making sure they're correctly gapped.
If you've gone to the trouble of taking the head off then go the whole way.The injectors also need to be reconditioned by a specialist.It wouldn't cost much more to take the pump along for him to have a look as well.These are very simple engines and there's very little to go wrong .

 

[davidbfox]

The liner pulls out with determination. I did it on the boat in situ with YSM12. New liner, piston rings, big end shell, injector, reground valve seats, new valves and gaskets added up to around £500 in parts. The engine has run really well since with no smoke and no oil consumption.

Removing the alternator etc is easy enough. A few bolts removes the crank case cover on the right and gives access to the big end bolts. The workshop manual describes a puller that you can get made up. I think it is the same on YSB as YSM.

The right hand cover on a YSM has an internal oil deflector plate which sticks off at an angle. There is nothing in the manual or on the part or the fitting to show which way up this goes, so take careful note when disassembling.

Good luck!

 

[vyv_cox]

When I had one of these engines many years ago it failed totally just a few minutes from my mooring at the end of a three week cruise. Investigation found that the nuts on the cylinder head bolts, which have a fairly coarse thread, had backed off. The head was slightly damaged, sorted with a new gasket, and a water passage was completely blocked by a mixture of salt and carbon. No idea whether the two were connected but it ran fine afterwards.

 

[rotrax]

I have had a VERY high hours one which was fitted to a 40 foot steel narrowboat-underpowered or what!

Apart from that, the only troubles ever experienced were with the externally contracting band in the transmission and the raw water pump. This would get the valves stuck with debris from the canal. Raw water cooling was not ideal!

I lifted it out-by hand-took it home and stripped the top end.

The injector was serviced, the valves ground and the engine was turned so the cylinder was vertical.

I turned the crank so the piston was an inch or so down the bore, filled the space with TQF Auto Trans Fluid-which is very light, and left it with a damp cloth covering it.

24 hours later the level had only dropped a tad so it went back together and AFAIK is still working in the same boat.

This was in 1983, so it proves what a tough old donk they are.

The band was lined with brake lining material, the raw water pump just had a spanner on a string hanging off it.

With the engine running, slacking off the plunger nuts bled it and got rid of the debris from under the valves.

The engine never overheated as you would hear the change in exhaust note without the water in the system, and you would deal with it at once.

Try the TQF trick-it could save time and money.

Good Luck.

 

[stav]

Thanks for all the replies and certainly makes me fell hopeful the little old beast can be resurrected. So this morning popped to the boat with the intention of popping out the cylinder but gave in to curiosity and popped the head back on with old gasket: negligible compression. So will order all the parts needed on Monday including piston rings and will take it to that next level.

Thanks again for the advice and comments. Parts will take a week to ten days so will leave it alone until then!

 

[superheat6k]

I installed a YSB 8 on my last sailing boat. Good engine for me until it started running on its own oil and oversped blowing the head gasket - this was on the test sail as I was selling the boat.

Definitely change the rings. I could only stop the bloody thing by covering the air intake, and at that time i would have preferred not to be that close to it.

This might be of use to you ...

https://www.dropbox.com/s/08mt0prkzjk7mvw/Yanmar YSB.pdf?dl=0