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Converting A St2 Engine To Aircooled.

Discussion in 'Builds & Projects' started by CAT3, Aug 1, 2020.

  1. I have a question for those who might be knowledgeable in such things.

    Is it possible, by that I mean just swopping barrels & heads & L/H crankcase cover, to convert a ST2 944 water cooled engine to a 900SS/Monster type air cooled engine ?
    The reason for the question is the project we have in mind is based on an air cooled engine & although in fairness the air cooled & water cooled engines look almost identical, espicially from the right-hand side, we don't want radiators on the finished bike.
    We would also be junking the injection system & using carbs, maybe flat-slides.

    On the face of it, the two engines look to be basically the same so we were thinking conversion could be quite straight forward, (forgetting about any cost implications at the moment too).

    I know some may think this is a bit like reverse engineering, but we have aquired a very cheap ST engine (came with a frame for a project) & although in was a non-runner, (reason unknown at the moment) & quite grubby it does look quite clean internally from what we have seen so far. The water pump is very clean internally & the intakes look quite clean, (we've had a borescope down them). We'll take the plugs out too & have a look at the bores too today.
    Obviously before using this engine we would strip it down, but providing nothing is beyond economic saving & it can be converted to air cooled we could return it to use.
  2. Why would you? There are plenty of aircooled Ducati engines, they still use them in Scramblers.
  3. Yes, it is possible to convert ST2 heads and barrels to oil cooling.
    See Andy’s motorcycle obsessions on youtube. He starts with a 900ss bottom end.
    With some lateral thinking, converting the whole ST2 engine should be possible.
    #3 Jon Wright, Aug 1, 2020
    Last edited: Aug 1, 2020
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  4. Maybe because a very cheap ST engine has come their way? A bargain you could not say no to
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  5. A little/lot like some folks did with the 906 Paso engine, fill the water jacket with oil? Is that your thinking?
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  6. Like Jon Wright says, in the Youtube channel he mentions a water cooled top end is plugged and converted to air cooling.
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  7. Exactly as Michael Couque says, we aquired the engine very cheap, a bargin we could not say no to.

    To be honest, no. We were thinking if we removed the water cooled barrels & heads & replaced them with air cooled barrels & heads & then replaced the water pump equipped L/H engine cover & replaced that with the air cooled side cover we would be left with an aircooled engine.

    We know the ST2 engine is 944cc, or thereabouts & an air cooled 900 engine is a different displacement so that in itself would require a piston change at the very least.
    Both my mate & I have lathes, my mate also has a Bridgeport miller & we have access to CNC machining, 3D printing, etc facilities & both have backgrounds in engineering so would be quite capable of carry out most work that might be required.

    It's really the basics at the moment we were interested in. For example if the air cooled barrel stud positions are different & other more involved differences like head shape/stud positions are different although it is always possible to modify something, the actual work involved in carry out such changes would not make it worth continuing with this conversion we thought might easily be possible.

    We'd never though of converting a water cooled engine to oil cooled, so we'll have to have a look at the YouTube video that have been mentioned by Jonwright, Ducatiscud & Dan600SS. Thanks guys, that's another interesting option.
  8. Don’t forget that the 904cc two valve engine is designed to have the barrels oil cooled.
    The Oil and water galleries are similar on the 904 and 944 engines, but not identical. They can be modified to suit though. You would also have to clean the water gallery of all limescale and other deposits before connecting it to the engines lubrication circuit, otherwise it may not last long till new bearings etc. become necessary!
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  9. There are two types of barrel on 904cc two valve engines.
    Early ones had external lines to/from the barrels, whereas later ones had internal galleries.
    This is the early ‘93 type (Thanks for the image @Nasher !)

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  10. Looks like another cracking thread developing, what this website is so brilliant at, an amazing resource that brings together amazing talents of DIY opportunities and the vast base of Ducati knowledge to be found here. Keep us posted with photos.

    if I am lucky I can just about change a plug according to SWMBO.
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  11. Just a thought: Do you really need an oil cooler?
    If not, could you mount a small water radiator instead and still keep a nice clean engine?
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  12. It's not just the radiator, there is also the plumbing.
  13. No, you don't really need an oil cooler on a 900ss for road riding
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  14. Spark Plug, Mains plug or a bath plug?
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  15. I can’t say from experience that you definitively need an oil cooler on a road SS but I would not run an SS without one.
    My reasons:
    - Poor airflow to rear cyl from L twin engine config
    - Generally restricted airflow from fairing shape
    - a road SS with an Oil cooler and oil temp gauge runs at correct temp normally, certainly not overcooled
    - a track SS with single oil cooler runs over temp within 15 mins on track
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  16. I have to be perfectly honest & say although I'veowned my '94 750SS from new I never realised that they had oil cooling around the barrels in addition to being air cooled as are the 900SS/Monster engines. You just never stop learning !!

    As you say Jon, knowing what I know now from you helpful souls on here I too wouldn't run one of these engines without the oil cooler, if for no other reason than the cooling of the rear cylinder.

    I've had a quick watch of the "Andy's Ducati Obsession" YouTube video that some suggested on here, where he is dealing with converting the water/air cooled barrels to oil/air cooled. That looks quite simple to do & well within our ability.
    I have to say he looked a bit rough counterboring the barrel with a 18mm cone cutter in his pillar drill to fit the core plug, but it obviously worked. Just need to check out what head work might be required now.

    Many thanks to everyone so far, it's been interesting & enlightening thus far. We're certainly not going to bin the idea of using the ST engine now.
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  17. All valid reasons without firsthand experience, however, I can say from experience that thrashing one for all it's worth, with no oil cooler on the road, has never troubled it. Another carbed 900ss I know very well, doesn't have an oil cooler either, it belongs to a Ducati engineer, it is out in all weathers, in town, or getting absolutely leathered around North Wales and has been for many years, without any complaints. The question was "Do you really need an oil cooler?" The answer is no.

    Would you run your bike without one? That's a different question and why would you? Tens of thousands of owners don't either.

    Oil cooler eliminator..

    Oil cooler eliminator.JPG
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  18. Is it a single phase or 3 phase motor? If you are not going for injection there could be difficulties in triggering an ignition system. I think the single phase might accept the flywheel and pick ups from a Monster or SS but the 3 phase definitely won't,
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  19. In our UK climate an air cooled Ducati twin even when used in anger on the road rarely needs an oil cooler.
    I find myself often blanking off the cooler on my 950cc highly tuned air cooled twin.
    I made up a little alloy plate to cover the oil cooler that sits under the seat with a few spare cable ties for the job.

    Oddly so my seriously tuned 140 rwbhp 851/955cc Desmoquatro also suffers from over cooling, (it's fitted with a Corse 888/926 rad') on anything other than really hot days. Most of the time I tape off a 1/3rd of the rad.

    Steve R
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  20. Or you can get the M600 pipes to connect to the carb heaters when there isn’t an oil cooler fitted?
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