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Crash Dummy's Aprilia RS125 (Full rebuild)

Discussion in 'Modifications and Projects' at netrider.net.au started by Crash Dummy, Jun 5, 2010.

  1. Continuing from here..

    The previous owners thread was getting a bit cluttered so I thought I'd make a new one and fill it with my own poo.

    What I'm about to post has been posted on another forum so there's going to be some copy and pasting happening. Each post pretty well represents a day.
  2. 10th May 2010

    The time has come that on my last ride the engine has started to develop some new noises including more clatter and develops some hellish vibration like it's trying to impersonate a jack hammer when you load the engine up. I'm guessing the cheap arse piston has worn out and it's time for a rebuild. With the number of k's travelled the engine is now due for it's bottom end to be rebuilt so that's on the to do list now. I'll be dropping the engine out in the next few days and doing an inspection so I can order parts.
  3. 13th May 2010

    Today I pulled the top end off and here's what I found. I'm not rocket surgeon but I think this piston is rooted.


    Isn't this beautiful ?








  4. IMG_6617Medium.

    15th May 2010

  5. IMG_6635Medium.

    Phew. It took all day. I needed to chill out after having a melt down because I couldn't get the work done. I had no way to sling the bike up was stressing and going nuts. I eventually got something sorted out and was able to drop the engine out and begin the dissassembly process. Of course a flywheel puller had to be fabricated. Oh how I wish I could just have the right Aprilia / Rotax engine tools to do this job.

    Anyway that's all the progress i've made today and might get back into it on Monday. Tomorrow I'm off to Wakefield Park, NSW to photograph the stroker's racing. That should be insperation enough for me to get my engine back together and humming again.

    I'm at the point however that I have to ask myself. What have I gotten myself into and boy do I wish I could just hand it over to someone with the new parts and say make it work please. :D
  6. 25th May 2010

    This is pretty much where the work has stalled while I wait for parts.
    I did make some progress today. I've successfully removed the crankshaft and the gearbox but didn't have the camera with me to snap some photos. I'll get some photos of the carnage tomorrow.
    At first I thought I was pulling the engine down for nothing. The crank felt good and everything seemed fine until I got to the part where I tried to remove the crankshaft that was stuck in the right hand side crankcase. Then I noticed the bugger was wobbling all over the place thanks to a well and truly flogged out bearing. I don't feel bad about tearing it down anymore. Things are looking up. :)

    What you would see now is a bench with rags everywhere, bags with bolts and a gearbox, selector forks and many confusing things in the order they came out. A crankshaft sitting in a rag and 2 crankcase halves looking very happy with themselves. Tomorrow I plan on attempting to remove the gearbox bearings from the crankcase by heating them until they fall out. 75.C is the magic temp where the release. 100.C should have them falling out on their own. I'll see how I go. Once they're out I'll give the crankcases a real good wash and prep for the overhaul.

    I'm planning on if I feel keen doing some minor porting work while I'm in there. Crankcase to cylinder port matching and smoothing the crankcase and cylinder of any dags and nasties from casting. Basic stuff that nets minor gains for not a whole lot of effort. It just helps things along. If I can't see that it needs any work I'll just leave it alone but I've never seen a cylinder and crankcase that didn't have room for improvement.

    Before anyone tells me. NOTHING is getting a polish. Port and polishing is for hotrods who want to look good going slow.

    The major operation being the big end crankshaft pin, bearing and conrod replacement I'll have to outsource. I don't have the skills or tools to perform that procedure.

    This engine rebuild process has really taught me a lot and explains the mentality of your average Aprilia RS125 seller. Look on bikesales and ebay. They nearly always have 15,000km on them and have just been "rebuilt" 16,000km is the max service life of the piston top end components. It's an easy rebuild but it still costs a lot to have a mechanic done. Aprilia Australia charge around $400 for the piston and I've no doubt most people don't have a clue that they can get aftermarket goodies for 1/3rd the price but the stealership still hurts to have install the top end kits.
    Bottom end is due at 30,000km. Mine's done 31960km and i'm very confident by the time I'm done rebuilding her it'll be as damn near good as a new one as I'll ever experience.

    This rebuild is worth it. The piston and rings were totally worn out beyond tolerances. Crankshaft main bearings are worn out also and require replacement. Servicing at this correct interval has saved a catastrophic engine failure that could have resulted in the end of my life.
  7. 26th May 2010
    Here is the photos I couldn't take yesterday.

    Empty crankcase
    I later removed these bearings by heating the crankcase halves in an oven set at 150.C I'd leave them for 15 minutes, pull them out sit the crankcase half on the bench and start wacking with a peice of wood and some of the bearings were kind enough to just fall out. The stuburn ones had to be cohersed with a makeshift slide hammer.

    Exploded gearbox
    The confused look that is on my face behind the camera isn't for show.

    The crankshaft removed. The bearing still attached is knackered and needs to be replaced. At the same time the crank will be split, big end pin, bearing and conrod will be replaced at the same time.

    And the parts arrived!

    I went back out to the shed and started work. One thing I wanted to do before I begun the reassembly was to correct these issues. There was a few of these around the engine but this is an example of one mismatching port / duct.
    Porting mismatch

    Ports corrected
  8. IMG_6689Medium.

    After that I gave everything a good clean and wanted it clean enough to eat off ready for the rebuild. I'd heard it was good to throw the engine bits in the dish washer so that's what I did.
    This is where my day turned really bad as I was unaware of how nasty dish washing powder and aluminium would react.

    There was a layer of powder everywhere on the engine and it had changed colour. :shock: I knew I was in trouble.

    A few hours of work scrubbing and removing all the old aluminum oxide layer and we have some win again.

    Tomorrow. Work begins on giving this girl a heart transplant. Freshened up internals and the road to recovery begins.

    Here have a look at the inside of the cylinder where the reeds would normally sit :)
  9. June 1st 2010

    Small update.
    All of my gearbox bearings have arrived. Koyo C3's. I've now had the crank split and new pin, bearing and conrod installed so that's ready to rock. I've had the cylinder honed lightly as well as all of the factory crosshatching was gone.

    I've tried to take a measurement of the piston to wall clearance. I can't. The thinnest feeler gauge I have is 0.04mm it very nearly fits but not quite. So I'm in the ball park of 0.02 - 0.035mm of clearance. Down from 0.11mm with the old piston. LOL.
  10. #10 Crash Dummy, Jun 5, 2010
    Last edited by a moderator: Jul 13, 2015
    2nd June 2010

    The cylinder has been honed with a diamond hone or some fangdangled thing like that. At any rate it's hard enough to actually hone a nikasil coated cylinder.

    Some photos in sequence of events tonight.

    Bearings installed into the crankcase. The cases were heated in the oven at 150.C for about 10 minutes. Then I was able to just drop the bearings straight into their spots.

    The gearbox is laid out on the bench. I'm scratching my head trying to figure it out. I've tried reading the manual. I'm confused. I tried reading the Haynes manual. This just raises further questions. I give up on RTFM and just bang the thing together my way. I found the best way was to install the output shaft side of the gearbox first. Pull the last 2 gears off the input shaft and then sit them on top of the the end bearing on the crankcase in the correct order. This allows you to just slide the input shaft in, line up with the gears you'd pulled off then slide into the bearing. Otherwise if you try stick in the gearbox in as a whole unit shit clashes and it is needlessly painful

    I've just installed the input and output shafts. Then quickly realised I would need to pull the shift drum back out and change the order in which i'm doing things.

    Now it's a complete gearbox again. All of the thrust washers and bits and pieces are where they should be now. I can select gears. Gotta be careful trying to downchange though because the rods the selection forks slide along will try explode themselves out of the housing.


    Complete with balance shaft.

    That's it for tonight.
    *edit* Later my friend Dewy recorded on request of a member of another forum how to assemble the gearbox so here it is.

    I just wanted to say. I've thrown a lot of pictures on here because I know most people don't have a clue what is inside the gearbox on a bike or how they work. This hopefully will confuse you all further. I feel smarter for managing to reassemble this without assistance and feel like I could do it again with my eyes closed now. I really feel like i've learnt a lot from this step in the build process and have found it very rewarding.

    Attached Files:

  11. 2nd June 2010

    Today has been a total downer. Nothing wanted to go right. It took me about 4 hours to even get to the point where I could join the two crankcase halves. Then when I did get them together I tore the left hand side crankshaft seal. :cry:

    Good news at least is Dewy was with me today and recorded some 1080P video of me assembling the gearbox which I'll edit and put up online at a later date.

  12. 3th June 2010


    Today was a toughie.
    I've fitted the right hand side main crank bearing to the crank as per the instructions. It wasn't easy by any stretch of the imagination.

    Right hand side main crank seal installed prior to the bearing.

    My weapon of choice. Heat the crankcase while installing the crank for best results.



    Being a home builder I'm equipped with only the finest quality tools money can't buy.
    yes that is a home made crank puller made of plexiglass. :LOL:

    Stop laughing

    Crank is pulled up nicely into the case. Time for a hot chocolate to celebrate
  13. IMG_6743.
    The right hand side crankcase is laid on it's side and the gearbox internals refitted. This is now ready to accept the left hand side crankcase.

    Fit the gasket

    I'll trim that gasket later


    The crankcase halves ready to be mated. The left hand case needs to be preheated before installing or else you're going to have a hard time getting it to slide over the shafts.

    Easy goes it.

    Done. Except the oil seal I had preinstalled has been torn apart by the lip on the crankshaft. The seal looks as if it were turned inside out. I disassembled the 2 halves and removed the seal then reassembled them and called it a night.

    Tomorrow I'll get a replacement seal and see about fitting it.
  14. 4th June 2010

    Stator and starter gear installed.

    Flywheel fitted and nut torqued to 70nm

    Hmm something is missing here.

    I've stuffed rags into the crankcase opening to prevent and nasties from falling inside such as flying gudgeon pin clips.

    Fitting the piston

    Fitting the rings
  15. IMG_6879.
    Hot chocolate isn't cutting it anymore. I need a pick me up. 10cc's 2 stroke oil stat.

    My assistant and I have gone mad

    After fitting the piston select the thinnest cylinder base gasket and fit the cylinder followed by the combustion chamber dome which I am torquing the bolts up to 20nm in a cross pattern. Surprisingly all that seals this is a simple little O ring of the rubber variety.

    Seen here I am measuring the volume of the combustion chamber with the piston at top dead centre. From here I can work out my static compression ratio. I have 12.1:1 compression. Not as high as I would have liked but I can't get more unless I'm prepared to run without any base gasket at all or start getting things machined to bring the squish zone down. Ideal this engine would run 1.5mm of squish. I've got somewhere around 1.7mm. for max performance i'd be looking at 1mm squish.

    What you are seeing is only wrong if you have a dirty mind. 2 fingers stuffing a rag up a greasy exhaust port. :eek:

    Nearly there!!!
    Bolting on the water jacket. Don't forget the O rings Crash…. Before doing this I tested the thermostat function. That's working perfectly.

    This is the reed block. This mounts directly between the cylinder head and the intake manifold.

  16. IMG_6911.
    The engine is complete. All covers are on. Ohh wait a second..


    Now it's done.
    Power valve housing, exhaust manifold flange and 17 tooth front sprocket are all now fitted.
    The build is complete. I've stuffed rags in the intake manifold and exhaust housing for the night. Tomorrow I'll begin refitting the engine to the bike.
  17. 5th June 2010

    Today was spent installing the engine.

    Here is a picture of me doing something

    The bike is slung from the ceiling to support it's mid section. This bolt I am removing is both the swing arm pivot bolt and engine mount. When the gear is installed the frame, swing arm and engine all squash each other and form a rigid structure.

    High tech equipment is required to raise the engine carefully into the frame.

    I am doing more things. Installing the front bottom engine mount bolt here.

    The engine is being supported in the frame now. I've just got to install the top engine mount that bolts on to the head.

    Shown here is the incorrect tool used for adjusting the top engine mount.
  18. IMG_6967.
    The top engine mount is now bashed and bolted into place. Carburetor and oil pump have been fitted. Power valve connected to actuation cable. The engine install is complete

    Fitting the cooling system

    In goes the air box

    Play the digidingdingdoo

    Hook up the battery and wonder why the bike has no power. Look in amazement.
    Connect these earth wires to the crank case then proceed to this next step
  19. #19 Crash Dummy, Jun 5, 2010
    Last edited by a moderator: Jul 13, 2015
    Fit the fuel tank and check all hoses are connected and clamped up. Cooling system if filled and bled of all air.

    Ready to start!

    BTW the back wheel isn't fitted at the moment. I changed the wheel bearing seals and removed the chain in preperation to replace it. I didn't get around to refitted them both tonight.

  20. 5th June 2010

    The run in period has gone well so far. I spent the first 70km or so trying to keep my revs at 7000rpm and under but constantly loading up the engine by slowing then rolling on the throttle. After that I started using some more revs up to 9000 and very quickly the engine begun to free up so I just rode fairly normally after that. Somewhere between sedate and hard with a mix without trying to do my best impression of a MotoGP rider going for the win.

    The engine is most definitely smoother and in the spurts I gave it inside of the power band I believe it's make more power then before. I'm sure the run in will be finished after tomorrows ride.