Bad design ?

We all know that the Parallel Twin suffered from the cost cutting down regime in the mid seventies. Some might even suggest that parts of the engine where designed by apprentices but I wouldn’t go that far. In the design of the engine you can find some elements that suffered from that regime. As we are planning to race a pair of Parallel-twins at the DCR in may we thought of some improvements  like straight cut primary gears, a dry clutch to keep as much heat out of the oil as possible, fitting an oil cooler and better lubrication to the camshafts. Unfortunately we can’t do everything at once so we started with the clutch.

The oily stuff

What Mototrans developed from the original Ducati engine was a smart move. They new that the oil level and temperature was a problem with the Parallel twins. The roof of the oil sump in these engine cases is quite low as you can see.

So with little oil you will bound to have trouble especially if the level drops due to leakage or usage. So in my opinion it’s always best to get your level as high as possible and even “overfill” your engine to get as much oil as possible  in there. Mototrans recognized the problem and started in the early 80-ies with fitting an oil cooler to the engine. There are some small modifications needed for fitting the cooler so the plugged the oil feed to the head and used the oil supply from the main channel running through the cases. The hole where the pressure switch sits was used as the feed to the cylinder head via an oil cooler. In a way it is a very simple modification and the Mototrans engines lasted a lot longer and suffer Les beating than the Ducati engines. Come to think why Ducati never did this . . . . ?


Modifying the oil feed

With nearly all “modern” motorcycle engines the oil feed to the head, or heads, is through the cylinders upwards in a separate channel or alongside the studs that fix the head to the casings. With the Ducati Parallel-twin the oil finds it’s way to the head travelling upwards along the studs. In these cases the oil heats up significant and could lose some of it’s lubrication and with a tuned engine or extreme temperature surroundings, the oil gets so hot it nearly burns and loses all of it’s lubrication when it reaches the cam’s and rockers.

On the Parallel-twin there is also a possability  that the main- and conrod bearings are starting to get bad and you will lose oil pressure. You can lose so mutch oilpressure that the oil doesn’t reach your cilinderhead and your cam’s and rockers will seize !

So the best way is to get the oil to travel outside of your engine. Heat pickup will be minimal and you are sure that the oil will get where it is needed. This is not a plug-and-play setup and you will need to do significant work on your engine. We started with drilling holes in the cylinder head and try to fit an oil connection to the oil journals situated in the head. Unfortunately there was not very much aluminium to get a nice fit in there so we just welding some plugs in place to fix an oil connection. As you can seen in the picture we did some mayor welding to get the plugs fixed. The space to weld is minimal so it’s hard to get your nozzle from your welding machine in there but when you do it nicely it will look something like this. Don’t over do it otherwise your camshaft bearings will not be circular anymore and you can’t fit the cams either and the heads needs a re-work !  Drill holes in the plugs according to connectors you will use, you can use banjo’s or angular fitments as we did.

When you are finished with the head it might look something like in the next picture. Take any kind of fitments you can find. We took air pressure equipment because we could get a hold of it and as you can see they are nicely situated in a way that your oil lines are as straight as possible. What ever you do, avoid narrow angles so your lines will break, damage or fold together with no oil flow as a result. Make sure that the lines you use can take the heat of the oil. Don’t forget to seal off the original oilfeed at the bottem of the head. It meight safe you some leakage.

When this is finished there is still another part that need to be taken cared off, you will have to seal off the original oil feed in the bottom end of the engine so all oil flow will go through the outside lines. You can do this in many ways I guess but I just made some thread in the crankcases and closed the holes with a plug. You just have enough space to do the job, I used a sealant to be sure it is tight and the plug won’t come out by vibrations.

If you think you are done …… think again !

By now your engine is build together with the necessary precautions to allow external oil feed but you will need to connect the oil coming from the pump to the cylinder head. You can do it directly from the oil feed where the oil pressure switch is situated or you can fit an oil cooler between the feed and the cylinder head. The oil get’s hot as hell anyway so it might be a wise discussion to find a small oil cooler you can place in front of the frame above the front wheel.  







As you can read and see it is not something you can do in half an hour, you will have to take your engine apart and put it back again.  Remember you are modifying the oil feed so if you leave debris in the oil ways you will be in trouble eventually. Killing your engine is the last thing you want to do. Good luck with the modification !!


An other way forward for your oil modification is the way my dear friend Arthur van Til did it. Still the oil feed inside the engine has to be blocked but the welding activities to the head are way less and the chance of the head being deformed are reduced to zero. Olie aansluiting kop PTYou will have to use the camshaft bearing cover to weld a piece of aluminium to fit a standard banjo and use it as the oil feed to the head. But ……… the paralleltwin has two separate cams which are connected in the middle so you’ll have to make sure that the oil also reaches the other side of the engine. Arthur did it by fabricating a connection piece with O-rings so the oil reaches the other camshaft. For the oil feed he’s using brake lines to keep oil pressure up.
Koppelstuk nokkenas PT






Another mod is weight reduction. The hardest one is yourself!
The others are done by machining, like the oil pump shaft and sprocket.

19 thoughts on “Mods

    • Hi Chris,
      You can contact us (André or me) via email or ask us here.
      Which parts are you looking for in particular?


  1. 2x ducati clubrace with my 500 and worn gearbox, but no problems with shifting or jumping out of gear so far; only some spitting during the last 2 rounds, not got round to finding out what it is.
    currently i’m rebuilding (long term!) a 500SD which will have newly made shaft and 5th gear sprocket and a different mainshaft bearing; looking into alternative bearings, will post here when i find out.
    cheers and happy holidays!

  2. Hi I have owned from new a 1978 500SD and have done 40,000 km. I have studied your excellent website with great interest. I realise you guys are into racing but I note the lack of gearbox issues like broken selector forks and worn gear dogs. Back in 1984 the gearbox layshaft had so much side load on it it destroyed the bearing. I got whole bottom end and gearbox from the late Mick Walker (factory sealed) this one now is starting to jump out of gear like the first one did before the bearing catastrophe. I used to have an engine overhaul manual which includes the gearbox which is now lost. do you have any documentation which may help? – thanks very much, sorry about the long dialogue!! Regards,

    Barry Porteous (UK)

  3. Hi,
    how cool, a website about the weirdest bike ever. I also like them for a few reasons, and have got one myself. It’s a 1979 SD500, it’s a goer and has had much obvious love lavished on it in the years before I acquired it. It’s got two major problems which I will fix before riding it too far. One is a leaky petrol tank (I can put a liner in it), the other one is a leaky head gasket.
    I can fix that myself with a lot of care, and also do the valve seats and desmo clearances while I’m at it. I heard (hasn’t everyone)that there are several grenade like design features with the engine and want to do what is necessary to neutralize them while the engine is out. The main dramas I have read about is oil pressure problems to the cams and a weak starter motor (and weak spark, bad camchain tensioner, etc).
    I have read on here some great info on oil feed modifications, the thing I really want to know that I haven’t been able to find out is if the SD models can be fitted with a kick start. I have gotten hold of a kick start shaft and gear etc off a GTL500 and can get a kickstarter arm, just need to know if there’s any reason itcan’t be installed. There is a plug on the engine where a kickstart shaft would have been (like on my Darmah), I am assuming it’s possible to retro-fit a kickstart shaft to an SD500 but I would love some more info or confimation before I split the cases. Apart from wanting to fit the kick start there would be no reason to otherwise, and a shame to do unnecessarily.
    Any feedback on this would be much appreciated,
    cheers, Brett

    • Hi Brett,
      just checked with some cases GTL and SD: the GTL/GTV have all the necessary bushes for the kickstart assy, however, the SD does not have the bushes in the case nor in the cover, nor does it have the longer special bolt to disengaged the starting mechanism when the kicker is up.
      so if you want to place a kickstarter in the SD, you’ll have to split the cases! mind you, i also thouht the kicker doesnt clear the foot pillion or brake pedal, so you’d have to place foldable pillion/brake pedal, too!

  4. I need a couple of small parts for my GTL 500 engine. I need the chain tensioner complete and the actuation rods and bearings for the clutch. Can’t seem to find anyone who wants to sell them to me. Small parts are really hard for me to get. Thanks, Dewey Greear (77′ GTL Cafe Racer)

    • Hi Dewey,
      Where are you situated ?
      I might be able to help you with those parts, new or used.
      I will have to check the parts manual to see exactely what you mean and will come back to you with more info.
      Please give me some time.
      If you have pictures regarding the parts please send them to me so I can have a look at them.
      Contact me on
      regards, Andre

  5. Hello PT friends,

    just found this very interesting site – great!

    I own a nice 500 SD (76, red) plus a “rolling chasis” (350 SD, yellow) once meant to become a racer. Until now I haven’t found time/courage to really start into engine revision (lacking experience and good advice if needed).

    The red one suffers from heavy oil loss between head and cylinder. It may be a crack problem, but the former owner had also removed the sleeves bridging the gasket. After carb/ignition readjustment the terrible starter now fires at the first touch of the button but has an (ignition?) problem above 4500 rpm. After solving the oil problem I think about replacing the ignition by a Sachse electronic one.

    In case someone intends to initiate a reproduction of main bearings: I do own a set of NOS. I can also supply quite a number of reproduced intake rubber sleeves (500 SD carbs).

    The 500er is parked now since 4 years but I eagerly want to put it in operation again.

    Greetings to everyone from Germany

    • Dear Michael,

      How are the bikes coming ?
      Have you found the ingnition problem ?
      Please let me know if you find what was wrong with the engine.

      Regards, André

    • Michael,

      Would you be able to supply a set of intake rubbers for the GTL500? Im thinking 44m – 38mm?

      Best regards


  6. update on the mainbearing story:
    do NOT use Aluminium-bronze (CuAl10Ni)! the engine seized once it revved higher than 4000rpm (yes the engine was warm!). turns out Aluminium-bronze is good for low speeds and high loads (is strong and keeps its geometry well under high loads).
    the experiment gave 2 conclusions:
    1-design of the mainbearings is good
    2-wrong material.

    now i have to make new bearings from a different material (copper-tin or copper-lead alloy) and try again 🙂

  7. Andre i have a parallel twin that was raced years ago. Do you know if you can still get the main crankshaft bearings? And if so where? Also my understanding is they take pantah big-end bearings as well? Is this correct. Thanks Chris Boucher.

    • Hi Chris,
      Unfortunately the main bearings for the cranck are all out !! I can’t find them anywhere anymore.
      If I would find a new one there would be a possability for reproducing them but until than I can’t help you on that point.
      The big-end bearings however is a different story. The ones you buy at your local Ducati dealer will fit your Parallel Twin. Ask for Monster 600 ones from the 90-ies for example. It is my believe that big-end bearings for all modern 2-valve Ducati’s will fit.
      Good luck !

    • Hi Chris,
      i also had this problem, even when i managed to get the last new mainbearing available in Holland.
      So i did some research and made my own mainbearings. i have them in my racing PT now awaiting trials.
      material is Aluminium-bronze (CuAl10Ni), and with extra groves for the oilfilm to build up and not scraped away like in the original bearings.

  8. this is all very interesting .. as i looked in detail at the oiling on my motor when i had it in bitz ,, my engine had a fair amount of oil climbing the outer of the bore and spraying out of the head gasket .. on closer inspection i decided to alter the wafer thin liner as it was distorting and nipping the piston ,, have you seen this before ??

    • No, I haven’t seen that before Toby.
      But have you had a good look at the small aluminium bridge between the two combustion chambers. The heads is famous of cracking at that point. The crack will run from front to back and many oil leakages occour from that crack.

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