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  1. #1
    Airfield Ops Thebreeze's Avatar
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    Rotax 582 Decoke

    Im attempting my first Decoke of a 582 on the bench as im in the early stages of a full flexwing teardown/rebuild. Im yet to do any measurements on the rings/pistons etc however on inspection, the pistons have suffered a very small amount of blow by, the rings were sticky in one spot and there was a lot of carbon. On cleaning, the ID marks on the piston crown are no longer visible (pistons have been removed and on the bench) . Im guessing that this means the pistons are worn beyond OK on the crowns. Anyone else had this and if so do you recommend a new set of pistons? I plan to change the bearings, pins etc as the pins are marked with signs of slight wear. The sides of the pistons have no marks or damage (apart from slight discoloration due to blow by) and the cylinders look excellent with all hatching still present. I'll be measuring the units as per the rotax repair manual in due course. just looking for opinions. Any advice greatly appreciated. Many thanks
    Dave "breeze" Brennan

    North Northumberland


  2. #2
    Co-Pilot Randombloke's Avatar
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    Quote Originally Posted by Thebreeze View Post
    Im attempting my first Decoke of a 582 on the bench as im in the early stages of a full flexwing teardown/rebuild.
    Did you measure conrod bearing wear before taking the heads off? It's worth knowing how much life there is left in the crank before doing a decoke then having to pull it apart again. Our X-Air had a gasket blow end of last year, the planned decoke was binned after the rear conrod bearing wear was close to end of life, we got a new crank as part of a refurb kit, and asked Simon Worthington at Eccleston Aviation to sort it out. We'd have done a decoke ourselves, but the crank replacement and gearbox service was worth delegating.
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"


  3. #3
    Airfield Ops Thebreeze's Avatar
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    Hi Steve. Yes that was my first job. I measured both cylinders and got a reading of 0.035 at both which is pretty good. I did look at the repair kit you mentioned. Well worth the money if you need a crank at the same time especially as you get the pistons etc with it. The reasons that i havent just sent the engine off to someone like Simon are two fold. First and foremost, Im very much enjoying the learning process and the "hobby" of doing this myself. If im stuck then i have no issue seeking professional help. Secondly, its an old blade. The wing and trike are going to cost way more than the finished product is worth. Again its about learning the aircraft and all of its parts that interests me on this. I will be sending the wing off as im not experienced enough on that side of things and with going SSDR i feel its even more important to get that right. Many thanks. Dave
    Dave "breeze" Brennan

    North Northumberland

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    Randombloke (28-10-18)


  5. #4
    Captain MadamBreakneck's Avatar
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    "Worth" is an interesting concept (philosophically, at least). I'm sure an aircraft that you know intimately and have checked out yourself is worth far more to you than anybody else would pay you for it. After all, you could sell them the airframe and paperwork but not that personal knowledge and the confidence it inspires.

    Also as you say "First and foremost, Im very much enjoying the learning process..." that has worth too.

    Enjoy


    Back to just bimbling

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    Arielarts (29-10-18), Martin Watson (28-10-18), Thebreeze (29-10-18)


  7. #5
    Co-Pilot Arielarts's Avatar
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    I don't think loss of piston top markings is any measure of 'worn' pistons. Check for any wear in the piston ring slots (up and down movement or notching where the rings end) and any evidence of cracking (skirt and gudgeon pin bosses), and you're good to go. If you check out Rotax piston prices, you'll be well motivated on this...

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  9. #6
    Airfield Ops Thebreeze's Avatar
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    Couldnt agree more Madambreakneck! Thanks for the reassurance
    Also thanks Arielarts. Having had time to weigh it all up, i plan to measure both pistons and cylinders as per the repair manual and see where im at regarding "life left" in all units. My view at present is if the pistons are anywhere near the limit then it pays to change now while everything is on the bench. I totally get what you mean about prices. A set of standard size pistons, new bearings and pins etc is well over 400. I suppose compared to a new engine its cheap and will give better peace of mind. Ill see how they measure up as soon as i can beg borrow or steal an external and internal micrometer. I have calipers but dont trust their accuracy and are not the correct tool for the job. Its a good learning curve and most enjoyable process (apart from the cost lol). Many thanks.
    Dave "breeze" Brennan

    North Northumberland


  10. #7
    Co-Pilot Arielarts's Avatar
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    If there's no appreciable lip at the top of the cylinder, and the piston skirts show little wear (you can compare areas of the skirts that are obviously unworn (tooling marks, etc) with areas that look worn), you can just about forget measuring cylinder wear. (Another accurate way of checking cylinder wear is to slide a ring into the bore and measure and compare the gaps (feeler gauge) at the top and middle of the cylinder. The diameter wear will be around a third of the gap difference.)


  11. #8
    Airfield Ops Thebreeze's Avatar
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    Thanks for all of the help folks but on closer inspection the pistons were worn but the cylinders had signs of vertical scoring. I have obtained new 1st oversize pistons, cageless bearings etc and the cylinders are with the machine shop (along with the pistons to assist them in getting wall to piston clearance right) for a re bore. It will instill a bit more confidence and should provide a much better oil seal etc. Ill have to run it in though which takes an hour. Just need to find something to strap the trike down to first as part of the run in is at full power. Its proved a bit more expensive than i would have liked but it should run like a dream for a good 50 hours with the usual maintenance before the cylinders need to come off again. With the weather up here thats about 6 years haha.
    Dave "breeze" Brennan

    North Northumberland

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  13. #9
    Co-Pilot BobH's Avatar
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    Dave,

    Why do you say 50 hrs? A 2 stroke engine probably won't need even looking at till it's done at least 200 hrs. Just use your bearing tester and a compression tester on a regular basis, and as long as the readings stay consistent there's no need to dismantle the engine at all. After 50 hrs, assuming you've been using cheap 2 stroke oil, like chainsaw oil for instance, if you want you can take the heads off and give the piston tops a gentle rubbing over with something softer than the aluminium the pistons are made of in order to remove carbon build up. You could use paraffin or 2 stroke oil to soften the carbon, and one of those plastic pan scrubbing things you can buy for your kitchen to rub on the piston tops, or if you can get hold of it, use an upper cylinder cleaner. Kev Armstrong used to use a spray that was meant for Yamaha motorcycle engines, but I don't know if you can still get it nowadays, or where to get it if you can.

    Something people get all worked up about is piston rings sticking in their grooves. The upper one, the L shaped Dykes ring, normally never gets stuck, but the lower one often will. However, it's worth knowing that this normally only happens while the engine is cold. As it warms up the ring will become loose in the groove, and do the job it's supposed to, i.e. keep up the compression. The reason why the bottom ring sticks in the groove when cold is because the ring is a very tight fit in its groove when new. As carbon builds up on the top of the piston, so a small amount will build up in the ring groove as well. This means that when you switch the engine off, the aluminium ring groove will contract around the steel ring and trap it there. However, the next time the engine is started, as it warms up the aluminium groove will expand and the steel ring will become loose once more. So panicking over a sticking ring is probably an unfounded worry.

    The reason I know all this is because I've worked on 2 strokes since I was a Lambretta riding mod back in 1966, and I spent the first five years of my working life (1966 - 1971) working in an engine reconditioning company in Bristol, where my main job was boring and honing engine cylinders.

    By the way, I have my own boring and honing machines, along with the necessary inside and outside micrometers for accurate measuring of all components.


  14. #10
    Co-Pilot Randombloke's Avatar
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    Quote Originally Posted by BobH View Post
    Why do you say 50 hrs? A 2 stroke engine probably won't need even looking at till it's done at least 200 hrs. Just use your bearing tester and a compression tester on a regular basis, and as long as the readings stay consistent there's no need to dismantle the engine at all.
    Agreed, if you feel the need to have a look then I suggest you get a cheap (10) endoscope type camera which will plug into a phone or tablet to look inside the combustion chamber with one spark plug out. Make sure you get one with a ring light around the lens.
    Steve U.
    PG, HG & microlights
    "Weekend bimbler, day to day car driver & genuinely undeserving Southern oik who has never done anything of any worth"


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