Yanmar yse8

[Stevemattingly]

So all of my checks on the fuel side have been fruitless. I had convinced myself it had to be fuel due to it petering out under load. Although compression feels good I am going to try a test. Due to the cylinder head being on its side it is very inaccessible unless I remove the engine bay side wall. (Or remove engine).Would valve adjustment cause a running engine to suddenly loose compression. Apparently it was on full throttle and depositing black soot at the time of the demise. Yet she had been starting without easy start in about 5 seconds prior to the failure. Sorry Wotname!

[Stevemattingly]

Sorry it's another update. So, confident the fuel is right I have just checked the tappets and they have a nice gap. Managed to then borrow a compression tester. Ran the engine and compression is running just below 300psi. I think this is just a little low but maybe the reason she only starts with a sniff of easy start. Any comments welcome as usual!

[Wotname]

Oh...that's bad news. Compression should 400 to 450 psi.
300 would account for very hard cold starting and even a warm/hot start might takes extended cranking.

[Stevemattingly]

Many thanks Wotname, still don't understand how she was starting fine on a nice day one minute. Now won't start without easy start. It somehow must have lost compression quickly. Assume rings is primary cause or would regrinding valves be enough thus saving engine removal.
Cheers again Steve

[glenn.225]

You need to do a leak-down test. Basically, air out the crankcase indicates rings, air out the exhaust or intake indicates valves.
Just google leak-down tester. Cheap ones are available. The better ones are not inexpensive, but you may be able to rent one.

Sent from my SM-A536W using Cruisers Sailing Forum mobile app

[gap6126]

Hi, did you run the engine with a clean fresh fuel supply we had customers fill up with gasoline or got water in the diesel.

[Wotname]

Originally Posted by Stevemattingly

Many thanks Wotname, still don't understand how she was starting fine on a nice day one minute. Now won't start without easy start. It somehow must have lost compression quickly. Assume rings is primary cause or would regrinding valves be enough thus saving engine removal.
Cheers again Steve

Start with the easiest things.

Being a horizontal cylinder, the lower part head gasket is prone to failure as moisture / condensation collects and lies in the head/cylinder interface.

The exhaust valve does pit etc.

It is easy enough (if you have access) to remove the head and have a look if you don't want to arrange for a leak down test. It would be good time to inspect the mixing elbow for obstruction.

If there is access port and starboard, the rings (and piston / liner) can be changed in situ without removing the engine.

[Stevemattingly]

Thanks for the input guys. Wotname, I followed your advice as access was available both sides. Took the head off and the waterways were blocked at the bottom and restricted everywhere which probably accounts for overheating and loss of compression. Bore and piston look ok but will remove piston from opposite end and put in new rings and hopefully regain compression. Valves look good as well but again a regrind can only help. While the piston is out I hope I can reach in and retrieve a push rod which I am certain dropped into the sump as the head came off! Cheers again! Steve

[Stevemattingly]

Another update (wotname). Not a bad job removing the piston once the starter is off. Got the piston out and apart from a very rough piston top the rest looked ok. Took off the top ring and a piece of piston between the first and second ring fell off. It was black so an old break. Probably where compression was being lost. Ordering piston, rings, crank bearings and gaskets then rebuild and fingers crossed!

[Mr. Kevin]

Thanks for the update, sir. I look forward to hearing how the rebuild goes.

[Wotname]

Yes, thanks for the update Stevemattingly. It is always good to hear how the original report gets resolved.

[mcpusc]

thanks for the updates! watching as well

[Stevemattingly]

Just ordered all of the parts. Some from UK but some from sunity Taiwan. Prices and service have been excellent and the parts I have had in the past have been very good. Delivery via DHL around 4 days which will possibly beat UK parts.

[Adelie]

Welcome to CruisersForum!

I would suggest updating your profile with your general location and your boat make & model or “Looking” in the "Boat" category. This info shows up under your UserName in every post in the web view. Many questions are boat and/or location dependent and having these tidbits under your UserName saves answering those questions repeatedly. If you need help setting up your profile then click on this link: https://www.cruisersforum.com/forums...ml#post3308797

I would happily help more if the link above is not enough.

[Stevemattingly]

Hi all, happy update! UK parts turned up 3 days after Taiwan (sunity, excellent service/parts and price) and bearings from Singapore. All rebuilt and compression is now excellent. Didn't start immediately so changed back to the yse12 pump
and after a little adjustment she fired up and ran beautifully with no smoke. Customer went straight out to play and I am a happy received boy.
Now working on a Nanni 14 so will send a new thread as I have a question! Cheers all for help and support, we will get there!