"Thanks Nuku for a terrific explanation of these wee beasties. I’d be very interested in your full explanation. My DV20 is about 35yo now and is proving very reliable, but does tend to blow steam, which I guess indicates hot spots in the block."
You're very welcome. Here's the full descale method and after that some notes on my Bukh DV20:
First: If you haven't done a full descale before, it is a good idea to remove the water injection device from the front of the block and give it a good clean in an acid bath, then re-install with a new gasket
. If the tube that sticks into the block is full of crud and partly blocked, the acid flush may not actually get all the crud out of it. For subsequent descaliing, after I remove the hoses from the water injection device, I have a thin flexible flat wire about 400mm long that I poke into both tubes. This wire will go all the way through the tube inside the block and ream out any salt deposits. I do this to avoid taking off the water injection device each time I descale.
Preparation: to descale you will need an acid-proof small centrifugal pump. I got mine, a magnetic drive with no seals
to leak, from a craft beer/wine making supply place here in Nelson.
Then you need a hose from the input side of the pump to a 10L plastic bucket that will hold the water/acid mix. Try to keep this hose as short as possible.
The output side of the pump is connected to a single hose with a "Y" fitting at the end. The "Y" fitting has two short hoses which will connect to the 2 tubes of water injection device on the front of the block after you remove the hose going to the water pump
and the bypass hose to the thermostat housing. You can use a single hose clamp on each hose.
You will need to remove the thermostat from the thermostat housing on the exhaust manifold and replace the cover of the housing. Then block off the bypass hose with a wooden tapered plug
. Remove the outlet hose from the thermostat housing (the one that goes to your wet exhaust elbow) and connect a hose from that outlet fitting to the bucket.
Fill the bucket with fresh water. Now you have a loop: water will be sucked out of the bucket into the pump, then pushed into the block, through the exhaust manifold, into the thermostat housing and back into the bucket.
Secure both hoses in the bucket so they can't come out of the water!
Flush the salt water
out of the engine with dock
hose (see below step 8). I put a on-off valve on the end of the dock hose so I can control the water without having to turn it off and on at the hose spigot on the dock.
Turn on your pump (you may have to help the pump get a circulation going by sticking the end of a slowly running hose from your dock spigot into the pump intake hose briefly while that hose is under water in the bucket.
Now here's more of the process:
Descaling: Do it once a year if engine used regularly, more if not used much.
Procedure using the desalting kit described above and 30% hydrochloric acid:
1) Remove the bypass hose from flange on the water injection device on the block, block off the hose with a small tapered wooden plug
2) Remove hose from salt water pump where it connects to the water injection device (make sure your salt water seacock is closed!)
3) Connect “Y” hose to both tubes (use 1 hose clamp on each hose)
4) Remove zinc anode from the block and screw in a blind plug (you don't want to cook the anode with acid!).
5) Remove the thermostat housing, cover and theromostat. Clean all in dilute acid. Put the housing and cover, minus the thermostat, back on the manifold with a gasket. (I make my own gaskets out of sheet gasket material from an auto parts
6) Remove hose on outlet side of the thermostat housing and connect a new hose which goes to the bucket (secure hose in the bucket with a cord!).
7) Connect output of centrifugal pump to free single end of “Y” hose. Connect extra hose to input side of the pump and secure that in the bucket.
8) Connect fresh water hose from dock to centrifugal pump inlet hose and flush salt water in the engine into the bucket. You can just hold the ends of the hoses together by hand to do this. Empty bucket and repeat. Empty bucket and fill Ĺ with fresh water. This is done so that all the salt water is out of the engine before you do the acid flush.
9) Fill bucket with freash water. Put inlet hose from centrifugal pump into bucket. Turn on the pump. Get circulation going using the fresh water hose (you must keep both hose ends held together under the water in the bucket for a bit, then remove the fresh water hose).
10) Once you are sure youu have circulation, add Ĺ to 1 litre of acid to the bucket. Circulate for 30-60 minutes.
11) Stop pump. Remove the inlet hose from the bucket and connect to the dock hose again. Flush acid/water solution into bucket with dock hose twice.
12) Install zinc. Disconnect “Y” hoses from water injection device. Re-install the thermostat in the housing. Reconnect all engine hoses. Open up the salt water sea cock and run engine and check for leaks
10. Flush centrifugal pump and hoses with fresh water.
If you have any questions, just ask and I'll try to reply soon.
Some details of my Bukh. Note that my Cavalier 32 has the engine mounted backwards with a "V" drive connected to the propshaft. That's why there is a thrust bearing.
Bukh DV20 serial
Injectors rebuilt: new nozzles, 19-07-2019, 1,812 hrs
pressure with hot engine: 0.8kg/cm2
Running temp: 70˚C
Transmissions: on engine ZF-BW6 reduction ratios: 2.5 forward 2.75 reverse,
spare ZF-BW7 reduction ratios: 2.5 forward 2.75 reverse
R&D split coupling 202-153, flexible coupling 910-001
PSS seal: Saft seal model# 07-100-200R 2” shaft log X 1” graphite plug
Shaft thrust bearing: SA205-16G spherical self aligning, single row, eccentric lock 1”
Johnson pumps, (one on engine the other is a spare):
Johnson #353-9/16-35118-1, Shaft OD at impeller ⅜” Shaft OD at drive end Ĺ” with slot drive
Impeller #808 B-1 V286, 6 blades 40mmOD X 19mm width X 9.5mm/3/8” ID
*Install pump with cam down
VDO Water Temperature Sender: #323803/001/006, 96C +/- 3C, 3W, 2 spade terminals: small is warning, large is gauge
Pump: AC Delco 7971291, alternative part number is 461-199
1) Paris-Rhone D9E51 K3 8, overhauled with new brushes
2) Bosch 829 D001315004 12V solenoid 0331 302060 − 560 12V 020 828, overhauled 1/2021
2 X Bosch 85A #9 120 060 009 K1-14V 14/85A, 92032637, Internal Regulator
: EP 14V4 9 190 067 020, Sterling external regulator
belt: 7435mm X 10mm, Alternator
pulley dia 75mm, flywheel pulley dia 160mm. ratio: 2:13, Engine rpm 2,000= alternator rpm 4,267