Thursday, August 26, 2010

Suzuki DT 20

Today I spent some of my time in the shop scraping the head for a Suzuki DT 20 outboard motor. It had a blown head gasket, a bad water pump, a cracked tiller arm, and a was in need of a general clean up/ tune up.

The water pump impeller is an easy fix, just take four bolts out and replace the impeller. I found another old motor to take the tiller arm off, just two bolts and the two throttle cables. But, the old gaskets on the head and water jacket are very stubborn. I think when the motor over heated (from the frozen water pump) the gaskets got cooked into a rock hard state. I may end up flat filing it and then sanding the gasket surface on a large flat plate?



  1. I have an old (1995) DT20 on my own boat and it just stopped working. Since I have a long, dark winter in front of me I was planning to fix it myself..
    Do you have any idea of where I could find some schematics or at least the tightening torque specs? Thanks

  2. There are lots of places on the net that have old service manuals to download. Some of them are free and others only cost a few dollars. Search for "service manual", you do not want "owners" manual. One that I found right away is

    The DT 20 is a very simple motor. Almost all problems can be figured out without needing any factory specs.

    Start with the basics: does it have a good spark, is it getting fuel, is there compression?
    Most of the problems on these old motors are related to fuel and spark.

    Pull the spark plugs out, hold them against the block and have a helper pull the rope, look for a spark. If there is no spark I'd start by disconnecting the kill switch. I have seen the kill switch short out on a few of these old Suzukis

    If the spark tests out ok then look at the fuel. Pull the supply line off the carb and pull the rope a few times. The pump should squirt a bit of fuel with each pull of the rope, if not check the diagrphram in the pump. They can wear out and get holes in them.

    I hope this helps you get started.


  3. Thanks for your kind reply C.O.!

    The motor had a few minor issues that I thought were related to the fuel line and spark.
    I checked filters, spark plugs, fuel intake while on the water and for a short test run the motor seemed just fine. But then wouldn't start anymore on the next day.

    I spent about 150$ at a local mechanic to have it checked troughout. He said that there is a clogging of the cooling system (weird, motor had been squirting just fine and the water pump is still working anyways) that caused overheating and a slight expansion of the piston head.
    The motor came back as it was, practically untouched, and the cost for even opening the head and checking it properly would exceed the value of the motor (quote was 1500$).

    So I thought that since it's quite a simple thing and I will have lots of time on my hands I could open it up myself in my basement and see what can be really done. I couldn't find anywhere the 1995 DT20 (only up to 1988) schematics but I guess the '88 ones are pretty much fine.
    If you know or remember the torque specs for the motor head I guess I'd be fine, most of the other torques are not so vital..

    Oh I miss so much my spaces and my resources at home. Everything has been 2 times more difficult since I relocated here. Wish I had a workshop like yours!

    If you ever could need any information about my field (fish biology) don't hesitate to ask. I owe you one.

  4. I don't trust the mechanic's story. Is the paint discolored on the head? When you overheat one of those Suzuki's the paint gets noticably darker. Even after overheating the motor will normally still run. The best test to determine piston or cylinder damage is to do a compression test. You should see around 120 psi in each cyl.

    If the engine was damaged from overheating it should still be easy to fix. That motor has traditional cast iron bores that can be honed to remove any damage. A basic three stone hone that you spin with a drill will work fine. The pistons may still be useable but if not they should be around $60 each, a head gasket is about $30, and rings are probably $15 for each set. Don't worry about the torque specs, just crank them down tight.

    All of this talk assumes that it was an overheating problem. Make sure it is not spark or fuel related first. There is no point pulling the head off only to find that everything is ok in there. Check the spark, if the kill switch is shorting or you have a loose conection in the wiring you could have no spark (or even worse a weak spark). Has the motor been used in salt water? The salt it hard on electrical connections.


  5. Thanks for the advice.

    My uneducated guess is that the mechanic wasn't a really good one..the paint is not darkened at all and if there is anything wrong it might be enough to change the rings.

    I don't know if you're familiar but here the sea is quite weird. It's not freshwater but the salinity is rather low (5 ppm as opposed to over 30 ppm in normal saltwater). Still the salt might work tricks on engines and reels.

    I cannot thank you enough for your advices, writing with you has been of great motivation for me. I'll promise I'll take some pics of the works and send them over. I owe you two now.

  6. As promised, today I finally was able to start looking at the engine.

    Anyhow, I checked the fuel line and all looks good. There is compression and the piston is moving normally, everything spins right. As I thought the motor is far from being burned/overheated as the mechanic said.

    The problem seems to be in the spark plugs. There is no spark at all. S-plugs were clean and heated so I figure it's something in the wiring.
    Wiring seems alright from what I can see, all connectors are rubber insulated and no one shows corrosion.

    I didn't have a tester with me but I will get one and check again whether there is an interruption (rather where it is). I guess I should also have a look at the stator, just in case.

    I feel quite ripped off already since that mechanic clearly sold me an overpriced story.

  7. The first place to check if there is a spark problem is the kill switch. The kill switch on these motors (like most small engines) is a open circuit when running and is connected to ground to stop. To test for a bad switch you can simple unplug it. The motor will run with the switch disconnected.

    The next thing to check out is the connection between the plug wire and the cap. The caps screw onto the wires. Inside the cap is a piece that looks like a wood screw, this is simply screwed into the end of the wire. Sometimes on old engines the wires break off inside where they touch the screw. The solution is to cut 1/2" inch off the wire and put the cap back on.

    Good luck, let me know how it goes.

  8. Alright, we're currently checking the engine with my friend.

    We checked the fuel line and there is no problem. Gas gets to the carb regularly.

    We were finally able to check the electric part with a tester.
    We tested connectors before what looks like the ignition coil/CDI unit. We got a voltage peak that decreases gradually to 0 after recoil start, like it discharges to ground.
    On the other hand we got no voltage at the spark plug caps level.
    We re-tested the spark plugs on the engine body and we got a very weak spark.
    Is it possible that the problem is in the CDI unit and the weak spark?

    What do you think?

  9. Milo,
    It is very unlikely that the CDI is bad, they rarely fail. The voltage peak decreasing to zero sounds like the correct result for the output from the stator.

    You cannot test for voltage at the spark plug cap. You can test the resistance of the coil. Check the resistance between the plug wires, it should be around 2k ohms.

    I just looked at my motor tonight and I realized that the spark plug caps are not the screw on type, the rubber part pulls off and there is a spring hooked into the wire inside. Take a look at them and see if the hook is making contact with the wire inside.

    The most likely problem is the kill switch. There should be two wires coming from the tiller handle, one goes to a ground screw and the other (blue with red) has a plug that connects it to the CDI. Unplug that wire. This will remove the kill switch from the system.

    When working on my motor this fall it would not run, it looked like it had a weak spark, I unplugged the switch and it ran great. The switch was partially shorting to ground and limiting the spark that the CDI could produce.


  10. Hi C.O., yeah, I figured we wouldn't be able to really measure it right :)
    I'll try to measure it again as you suggested.

    Spark plugs caps are pretty fine and they seem to be doing contact.

    My DT20 came with an electric start and wheel drive therefore the wiring is a bit different.
    There is a rectifier in between the ground connection and the ignition coil (with a ground wire) and two ground connections before the CDI.
    Overall the wiring is much more messy than with normal start (and wiring colors are..well, original so to say..).

    I oughta take a better picture and show it to you.
    Damn, I should take much more pics so that you can make a new post on "tele-repairs"! :)

    Thanks, as always

    here it is, the best picture I could take in the middle of a work symposium. You can see one ground wire on the top of the rectifier (black cable) and there are two more in the down right corner (just under the CDI).
    All the wiring looks pretty new and connections are sealed and not rusted.

  12. Milo,
    you need to figure out which wire goes from the CDI to the kill switch. On my motor I think it was blue and white. The kill switch connects that wire to the ground. Disconnect the that wire and test for spark. Are you testing the motor with the remote controls connected? If there is a key switch it will be tied into the same circuit, when you turn the key off it connects a wire to ground to disable the spark.

  13. Thanks C.O. but I gave up.

    I got the contact of a trustworthy mech near my place and took the motor there 2 days ago.

    It was delivered today in working condition after a minimal check (and a minimal fee).

    In the very end it was mostly a carb issue (plus other minor things), the other mechanic charged me for cleaning it but it wasn't clean at all. I shouldn't have assumed he actually did any job on my motor.

    After all this I would really like to take a course in a mech shop on fixing engines. I'll see if I can find any.