New project - Seahunter 520

[sonny1]

hi @ChrisParish never too late to treat yourself to a new engine

[IanH 72]

The next chapter:

We plugged in the computer and read the data from the engine. It has done 2000 hours, 80% of which was done below 2000 rpm which holds with the backstory we were given of it being used for training. The temperature warning has gone off 130+ times!

The Suzuki has two temperature sensors: a block sensor and an exhaust manifold temperature. The alarm can go off for block over temperature or exhaust manifold temperature rising too fast (they call this the gradient alarm). It is the gradient alarm which has been going off.

We ran the engine in a bucket and using a thermometer we monitored the temperature across the engine and found an anomaly:
The engine has three cylinders. At the moment that the alarm went off, the exhaust manifold temperature on the lowest cylinder was around 45 degrees C, the middle cylinder was at 60 degrees and the top cylinder was at 96 degrees. This leads us to believe that either: a) there is a blockage in the water jacket or; b) there is a crack in the manifold and exhaust gasses are entering the water passages.

The next job will be to remove the power head and split the cylinder block. This will allow us to inspect the water passages and with any luck effect a repair.

I am going to video the process and post some pics when we do it, which will probably be late October - COVID allowing.

[9-R]

You're most likely correct about the blocked passages. After you described it though, I did immediately think of a possible lean condition on the higher-temp cylinder which could cause the difference. Wondering if the jet/injector may be malfunctioning or clogged as well? Quick check of the spark plug should be able to tell you though.

[ChrisParish]

Good call there, @9-R. I’ll check it next time I get out to the garage.

[Limecc]

Good call there, @9-R. I’ll check it next time I get out to the garage.

Could swop a couple of injectors around and see if the problem moves?

[ChrisParish]

@Limecc and @9-R - I swapped two of the injectors today and unfortunately it made no difference at all.

So we have started stripping the engine down - picture to follow!

[Limecc]

You have the same engine as me, my DF50 is a couple of years newer. The seller ran it up on muffs but first covered the water intake under the cavitation plate with gaffer tape. Said it is essential on these, I never heard of it before, have you?

Is the tell-tale stream any good? Mine's not, I'm going to flush with some salt-away. You flushed yours with acid, but you might have been better going caustic with some TFR or sugar soap? Might release any internal grease that was sucked in?

P.S. I've a PDF copy of the workshop manual if you've not got it already.

[ChrisParish]

Hi @Limecc.
I hadn’t heard about covering the area under the AV plate, but we always run in a bin so it’s not been a problem.

The tell-tail is rubbish on these; it is on the low pressure side of the system.

The idea behind the acid rinse is that sea water has a ph of around 8, and vinegar brought the ph of the tap water to around 5.
Assuming that the deposits remain around ph8 the acid solution should dissolve them. In reality I don’t know how much difference it actually makes, but it is cheap so I gave it a go. Salt Away’s active ingredient is sulfamic acid.

By TFR do you mean traffic film remover? I hadn’t looked at that, but I will.

Thanks for the offer of the manual, but I have the PDFs already; they came with my software for the ecu connection.

We have started stripping the engine down. So far we have removed the flywheel cover and the inlet manifold. Next up is the electrics and ancillaries on the front of the engine and then we can remove the power head and split the head.

[Oldman]

On my little Suzuki 8hp DT8 if you use a flush hose adaptor then the manual says you should tape over the water intake, so he wasnt telling porkies, thats the way you are supposed to do it.
Like you I dunk the leg in a drum of water anyway

[ChrisParish]

During lockdown mk2 my Dad has been working on the seats for the boat.

Webbing for the hinge

Nice EVA foam top

He’s not going to catch much there

We have also been doing some more work on the engine, prior to the start of the lockdown. We have found why it was overheating. Full post on that to come once we have run it again, but here’s a hint: do not lubricate the impeller with silicone grease.