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BF8d - no tell tale after changing impeller

J

jaziniho

Member
I've been working through a bunch of servicing tasks on my BF8D - firstly, thanks to everyone who replied on all the other threads i've asked!

So far this is what I've done:
  • new impeller and gasket (not housing)
  • pressure test lower case
  • new gear oil in lower case
  • new oil filter
  • new engine oil
  • new thermostat
  • new carb
  • new fuel filter
  • new fuel hose
  • fresh fuel
  • steering (work in progress!)

I'm on an longshaft with remote + electric start.


Drained off tank, put fresh fuel in and successfully started first time after putting everything back together - so pretty happy with that to start with.

However... there's no water coming through the tell tale.

My initial setup was with muffs atttached to the bottom, ran it for 30seconds - 1minute or so a couple of times, but still no tell tale.


I switched over and attached hose directly to the flush port, up by the thermostat. You can see when rigged like this, water cleanly flows out through the tell tale. So it seems like there isn't any kind of blockage in the engine block or the tell tale pipe?


Also tried putting in gear briefly - it turned ok (prop was removed), so seems like drive is connected fine.


Any suggestions of what to look for? I assume i'm going to have to take lower case off again, and have a look at the impeller housing etc, but wondering why might have gone wrong here? I was pretty careful putting woodruff key etc back in.



Side note:
This is the first i've run it since putting new carb, oil etc - there's was very little smoke, seemed really clean - but appreciate feedback on how it's idling, fast/slow.. not really got an 'ear' for that yet.

Cheers
 
Yes - exactly, thanks!

dropped the lowercase, checked a couple of bits then refitted - being careful to line up the feed pipe with the pump this time.

Wasn't able to run long enough to get engine fully warmed up (some noise restrictions in the yard on Sundays), but this is starting from cold - best flow out the tell tale i've seen on this engine since i got it with the boat.



Seems to me that's quite fast idle, but maybe that's because it's not warmed up yet...
Will try and run it properly for longer in the week and see how it ticks over hen
 
So I got back down to the boat yard, and ran the engine up at idle on muffs with hose properly.

Initially, the engine seems to run OK, with a decent stream of water out the tell tale.
I think this is when it’s running in an initial faster idle whilst warming up?

After a few mins, the engine starts to idle slower. The tell tale stream gets quite a bit slower. The water out of the tale is then quite warm.

A later (couple of mins?) the temp alarm went off, so I immediately turned off the engine.

Ran it on idle again after some time to cool off - couple of videos below.
Pretty sure i had a stronger tell tale stream initially again, then weaker.

A few thoughts I had...

I’m guessing the thermostat is opening at the point the tell tale stream gets weaker - so at that point the water is being redirected from bypass, to instead round the block. The weaker stream might be a sign that the water channels round the engine are silted up / lime scale etc ?

I was also wondering what the relationship between idle speed and impeller speed / pump power is. It’s a new carb on an oldish engine, still set as per factory. I was thinking that after initial warm up, the idle speed might be a little slow - so maybe not enough for impeller to really push water through? But on the other hand - trying to get it to idle faster so it doesn’t over heat seems sort of opposite...?

My plans to try next were:
- use some kind of descaled like citric acid or a vinegar pumped in through the flush port by the thermostat housing, then flush with water after
- adjust idle speed up slightly to see if it helps

Any ideas or thoughts on other possible causes and suggestions...

Cheers
 
Initial faster idle, with stronger stream:

Later, slower idle, with weaker stream (before over heating.. but heading towards it again i think)
 
You have probably got internal blockages. First place to look is inside the water jacket behind the plate the thermostat mounts in, down around the internal anode. There is a slotted hole below the anode that tends to get blocked with salt.
 
I have a 20d and gave up completely on the muffs, just not enough real-estate to get a good seal. Throw her in a trashcan and fill about 3-4 inches about cavitation plate and run again. I bet she'll do just fine.
 
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