Top End Rebuild! (2 Stroke)

protip whenever or wherever you have a dial indicator setup especially if a tense indicator make sure to tap everything go tap crazy make pretend you're trying to make a younger sibling cry everyone will assume you're a professional [Music] I was broke my hip coming through that doorway how about you and I get comfortable wait I messed that up how about you and I get out of our comfort zones this thing is a beta Evo Evo Evo it's a 125cc not a big engine but a fun bike attentive viewers may have noticed I didn't wheelie into that intro for two reasons second this engine has lost some power cut to the chase we're gonna have to crack her open and take a look at the piston cylinder and piston rings I'm almost positive it's a compression issue I really wanted it to not be I went through and I removed the carburetor clean that fuel filter air filter look at and clean those little Reedy valve things none of that really helped the whole time in the back of my head I knew it was the compression I mean I don't want to speak too soon that's the point of this exercise we're gonna open it up and just check everything if nothing else we'll get a good look at how this thing's been treated before we all rush down into the comments I've already changed both brake rotors that didn't fix it my first clue was just how easy this thing is to kick over I mean I could do this by hand I can sort of do it by hands but again I'm not a hundred percent maybe you can kick over all 125 s with your hand personally mine is a 300 cc engine and that takes four simultaneous grown men to kick over the smart thing to do would be to run a compression test on that cylinder but I don't have a compression tester that I trust well I do I've got one of these craftsman I guess it's a Sears brand compression tester for small engines well I guess for any engine technically 300 psi but I can't easily get this into that spark plug position you'd press this into the spark plug hole this cone creates a seal kick it over do that a million times and see how much compression you build I did think about making an adapter for this just making some plumbing to get into that space that I do have but again that might have been a lot of work for naught I have one of these things from Amazon I think eBay less than 30 bucks problem is I don't trust it a good compression tester probably costs in the two to three hundred dollar range used this a handful of times and always got weird numbers initially I tried to debug it these connectors are pretty chintzy I figured it was leaking somewhere but no avail I did try this on this engine it was telling me about 60 psi I think and I could just tell even by hand it's more than 60 this was measuring my bike at 90 and my bike's got to be like 4,000 buyer beware I suppose it's too good to be true it probably is actually it dawned on me that after I do whatever I do inside this engine you the viewer will have no idea if things got better things got worse so despite not necessarily trusting this gauge you might help to give you a reference see what we get and then we'll do this again after I've taken the spark plug out and installed the compression tester in its place now I'm gonna kick this thing like it owes me money holding the throttle all the way open and the kill switch is on can't get that past I don't know maybe 70 psi about 5 bar an engine like this should probably be around 150 give or take yes you're right I really should have washed this first I hope it goes without saying that this isn't a how-to video I don't really consider myself an engines guy but there's no way I'm paying someone else to do something I'm fully qualified to do after reading that one magazine article 15 years ago I was expecting a little more coolant it helps if you take the radiator cap off I moved away some of the junk in this area just to make some space so I can work fan and radiator some brackets now I think I can open her up taking the top off first think it's technically called the lid my end game is to get the piston and the cylinder out and on the bench or we can take an intimate look at it and take some measurements I guess it's more like the intermediate game end game is to get this thing fixed look at that there are no score marks in the cylinder wall that I can feel it's an awful lot of junk in there though I wonder if it's just worn piston rings is that wishful thinking let's get it out of there so that's definitely blow-by I think anyway the piston shouldn't be black below these piston rings or maybe as black what do I know those rings seized no top ones okay no bottom ones good too you're still springy I'm checking for twists I'm trying to get a sense for how the bearings are doing in this thing I see a little bit of scoring on the intake side let me get this out and I'll meet you back at the bench Pistons the tarot cards of the engine world ask ten mechanics about this and you'll get 15 different answers can you make out the carbon buildup near the edges is shinier than that in the middle that means the front tire pressure is low and/or we're in for a wet summer all right I'm sorry I'm being a little cheeky there are some really good mechanics out there I'm not one of those but this is a textbook case of blow-by how do I know well I have a textbook with pictures and there's enough where in these rings and or the cylinder bore that combustion gases are getting past them and maybe gearbox oil is getting up to the top all of which results in a loss of power very little engine compression this is why the Kickstarter felt so light I see some long very fine scratching - these don't look like seizure marks to me but again I'm no expert I'm willing to bet the air box is full of dirt and this engine is sucking some of that in see what I did there snuck in a generalization to build your confidence in my predictive powers all dirt bike air boxes are full I can't really know anything here unless I start to take some measurements in order to do that I need to get these parts cleaned up give me a minute I'm just gonna head over to the bench grinder I don't know why still bothered with that ultrasonic cleaner it maybe softened some of this up but I still had to scrub it by hand time to break down and buy the right detergent for that thing this the pin and the cylinder cleaned enough to take measurements well I do that I just wanted to share this thing with you this was a seized piston from a neighbor's weed eater 30 year 35 CC and here you can really see the scoring in the gouging this was run I think without or with very little lubrication still two-stroke theater ran it with straight gas or did their math wrong and didn't put enough oil in there hopefully you can make that out but that is pretty severe I can more than feel those ridges in comparison it might look like this ones still doing pretty darn good but let's take a closer look and see what the numbers say if you squint your eyes hopefully you can make out on your right-hand side you can still see the grooves from manufacturing and here it becomes smooth and shiny where the wear has occurred I'm wearing my op divisors and I'm gonna try to strike a line where I see the turning marks disappear so maybe somewhere in here if I work my way around and do the same thing here just super shiny area up here down here is a little bit cooked that's the exhaust side I think yeah if you can't tell which side is which once you get this out of a bike or an engine they're usually marked with an arrow see if that's still in frame there's the arrow that's the front or the exhaust side if you can't find your arrow if you accidentally took it off at the bench grinder or your engine is having some detonation issues and you have a gigantic hole on the top of your piston you can check where the pins are in the piston grooves I do this there's a pin there for the piston ring and another pin there these always go towards the back towards the intake side where your carburetor and the air box are technically none of that was important but we're gonna be taking a measurement across the piston skirt front to back from about here to here that's where the piston is wearing the most it's attached to the crankshaft via the connecting rod at this pin and it has sort of this degree of freedom I mean it can shuffle left and right a bit the piston rings keep it centered but the forces from combustion and the return force from the connecting rod tend to push this skirt into your cylinder wall fortunately the bike manufacturer is kind enough to provide like a basic service manual they tell you an accessible wear limit I hear they're showing us a very specific area to measure on the piston skirt some distance up from the bottom across the front in the back you can see that's where the pin comes through and in my case for the 125cc model this bike I want to measure eleven and a half millimeters up from the bottom and I have an a piston in there it's labeled it's stamped on the piston and the cylinder my wear limit is fifty three point nine three five millimeters anything less than that and the piston needs to be replaced I've struck some small lines where that eleven and a half millimeter mark is from the bottom I don't have a metric micrometer so I converted the 53.9 three five millimeters to inches which comes out to two point one two three four not making that up to point one two three four this piston is toast now it's only about 2,000 or so arguably is this thing still good technically no could you get away with reinstalling it but just replacing the piston rings maybe I won't know until we check the cylinder bore or the prices for new Pistons the engine cylinder these things always scare me first we're measuring an internal bore which is never fun and second anything out of spec here is usually pretty expensive to fix similar story there specking a depth at which take a measurement in this case for the 125 I'm going down 10 millimeters and for the a cylinder my wear limit is 54 0.005 I've already taken the liberty to convert that in our target is two point one six oops two point one two six one two point one two six one that's the wear limit anything bigger than that number is bad news bears I don't have a dial bore gauge but I have a telescopic gauge and a micrometer telescopic gauges have always been quite finicky you do need to develop a bit of a to get these things to work properly to get a real dimension rather when I first started out I used to keep things like bearings or just other junk with precision bores in them of different sizes and take repeated measurements on a known dimension with the snap gauge and a micrometer to develop the feel for that particular range maybe you know it's different if you're holding a one inch micrometer or a six inch micrometer again I'm measuring front to back I'm also at the limit between snap gauge sizes let me go into the bore I like to Snug it up a bit right now I'm targeting that 10 millimeter depth on one side I'm just gonna pull it through and I'm like how that felt I'm gonna do that again if you don't think I haven't taken this measurement already like 400 times before the camera started rolling over 10 or so measurements I'm getting to point 1 2 6 4 so technically out of spec but only 3 tenths some have been below that some above that trying to measure tenths with a snap gauge that dimension probably changes if you missed that 10 millimeter mark but I've been beating myself up about this and I'm gonna call this cylinder good good enough those curious two people out there there's a look at the inside there's the exhaust side doesn't look like the end of the world to me now I'm just shooting from the hip here a new one of these probably set you back 4 or 500 clams 550 and the shipping of course a new piston maybe a hundred bucks 120 bucks if you get a fancy one all in if you're swapping both which one you'd probably change out you know bearings piston rings of course maybe the pin I don't know you can get expensive fast it used to be you could bore these things out throw this in the mill Center it up bore out the wear and install an oversized piston technically you still can do that but for better for worse these things have fancy coatings on the inside this thing has like a Clearasil or something in there to get it recoded you might be spending 150 bucks sure it's cheaper than buying a whole new cylinder but of course will take some time you got to ship it out they'll coat it ship it back given what I'm saying and the fact that this isn't my bike I'm gonna go with new piston and rings by the way I should mention just for integrity sake that it's not smart to mix and match old and new parts like putting a new piston in an old cylinder although technically might work you're not gonna get the bang for your buck out of your new piston no way you're sort of throwing money away trying to save money your new piston and a new part or whatever will wear faster and in a funny way not haha funny just see this through and because I have a spec for it I removed the piston rings piston rings if I haven't said this already are essentially like the seals in the engine make the seal between the piston and the cylinder wall without these you would have no compression and no power younger me got a little bit excited that it could have just been worn rings and I think if you stay on top of your bike maintenance you can probably change these out a few times before you get to this point before you get to a worn piston but whoo-wee kid anyway these are like snap rings there's a special tool piston ring pliers they just have these old like wedge ends that you can come in up against the side of the piston and they'll pick up on the piston rings and you can remove them off the top sort of like that sorry I didn't show you taking them off but to measure the easier remove them from the piston and you install them in the cylinder you just sort of push them in there it's important that it goes in there nice and square let's use the piston put it in from the bottom and use that to sort of square up the ring that gap there is what we're trying to measure we bring it closer according to the service manual the wear limit is 0.6 millimeters the more that ring wears the larger that gap would become come in here with a feeler gauge this is 0.6 millimeter and you can see that piston ring is shot that wear is more like 2 millimeters just fun and because I'm curious I thought we'd take some more serious measurements of this cylinder although the service manual only provides one pass/fail dimension front to back 10 millimeters down and best I can tell the cylinder still appears to be pretty good I mean bumping up against that wear limit but still technically good let's see if it's gone oval or tapered or who knows what I'm set up on the mill table I stoned and cleaned it on some one two three blocks and after two hours of pulling my hair out finally centered in the bore I'm using a tense indicator and although that might be fine if you're looking at a more worn cylinder maybe one of those older cast-iron cylinders at this point I'm looking for changes in tenths of an inch so ideally I'd want a millionths indicator as crazy as that sounds fortunately I don't own one of those just to preface what you're about to see an increase in material will cause that indicator to move counterclockwise an increase in material in this case means a tighter bore so if I push this needle back it goes counterclockwise let me try to zero this out again but these things are impossible good enough for me we're a tenth high I can try to rotate the face but it's gonna make things worse Oh would you look at that this is in a holder the middle is out of gear and I can turn the spindle by hand sweeping the indicator around the bore I've already centered this front to back so it's set on zero at the front if we swing it 180 degrees it'll read zero at the back now I'm just gonna rotate it 90 degrees and you're not gonna be able to read this but if I get you in there close enough you'll see that we picked up one tenth maybe a smidge more one and a half that's two and a half thousands of a millimeter in the back we should still be at zero if we swing over another 90 degrees we pick up another 10th 10th and a half though maybe that's two tenths so one and a half on the left one and a half or two on the right that's probably three years three and a half total across the left right direction now remember that's tenths of a thousandth of an inch which is like points oh seven millimeters what does that mean I have no idea this thing has either worn remarkably cylindrical or it has very little to nowhere the handbook doesn't tell me right from the factory what this dimension should be to continue the antics I'm gonna drop the indicator down as far as I can probably right before I hit the exhaust port it won't tell you so in the manual but swinging a tense indicator across an exhaust port is bad for the indicator if that indicator now looks a little bit higher than it did in the previous shot where I was whining the table up it's because I won the table up swung the indicator and ran into the exhaust port so I had to back it out a bit I picked up a little bit of taper on the right hand side I'd take that with a grain of salt that's probably more due to the fact that I'm trying to use my milling machine as a CMM but more interestingly when I swing this it goes from more or less zero picks up a sow or drops off a sow and heads back to zero in the back there's also a sow had you not skipped ahead during the cylinder where measurement you'll notice that that's the same place that the piston has worn again those Torquay forces at the skirt we've been throwing around a lot of numbers let's take a moment step back and consider the big picture numbers our mathematical concept used to represent a call forget about engines what we have here are two parts that need to move relative to each other this piston needs to go up and down to do its thing that means we need clearance between the two we need some space in there the manufacturer who designed and built this engine tells us the upper limit to that clearance that space between the two parts for this size engine is two and a half thousand metres will the engine stop working when it wears that far no no it won't you could likely double that wear number and still have a great time on your bike of course you'll gradually lose engine performance and if it wears too far and you end up with too much space in there well the bike might still run fine I mean it likely won't have any power but it'll start and move you around maybe but if it wears too far and it gets too much space this piston could start to wiggle so much that it could break itself to pieces it'll slap around in there so much these parts could crack you might get a piece of your engine skirt down inside the crankcase which would be catastrophic then instead of just a new piston or new rings you're looking at a new engine I have no idea where we left off but it's now 15 years later my kids have moved out I'm on my third wife and the engine parts just showed up great now I've got the hit to get this thing together so I'm just going to do everything I did till now only in Reverse but with a lot less talking or maybe reverse talking here and that's it any extra money thing when we know this was a kid it actually came with a new wrist pin and snap ring so throw those in too before I do that though there are three things I want to tell you you thought you were gonna get off easy first I love you second I'm going to double check the new piston ring gap just like we did before install them in the cylinder and use a feeler gauge though in this case it's more of a sanity check that the ends don't collide but if the rings are too tight I'll just file the gap open a little bit with a small file enter I'm going to compare the new piston with the old piston very carefully this is not om part I couldn't find OEM but I know the diameter is right because that's what I base the order on it should fit the bike but I want to double-check overall piston height and the location of the wrist pin with respect to the top surface if this new piston is just a little bit taller than the old one or the wrist pin isn't exactly in the same position I could risk driving this poor thing right up into the cylinder head where the spark plug hopefully it goes without saying that's not a good thing in the off chance that it is a little too long that's exaggerated I'd likely take the piston to the bench grinder I may have to add an additional gasket underneath the cylinder to move it up dang it by whatever amount it takes to have clearance at the top to check that I just put a straight edge across the top and use a feeler gauge I should have a spec for that and again I just shim the cylinder up effectively lowering the piston until I get the clearance that I want may or may not have to do that but something to look out for well I'm just back from a test-drive I'm happy with how the thing feels now no leaks except I use the wrong goop on the tailpipe on the exhaust you see that junk all the way back in there just sprayed everywhere all over my bullets and everything so if nothing else I gonna get this muffler and exhaust off clean that up and put the right junk in there I just pulled the spark plug and although this is an old plug and I haven't been able to write it out much I thought I'd show you what it looked like I'm looking at the electrode in the center and I'm happy to see that it's dry and there's some carbon on here probably time for a new plug to be honest but given that I was driving around pretty slow and for not very long I am okay with how that looks all right it's the moment of truth Judgment Day is upon us every day in the United States alone approximately 893 people have something to say about your cylinder honing decisions some of you may have noticed I did not hone this cylinder bore I didn't touch it no ball hone no flex hone no nothing I just scrubbed it clean with some hot soapy water I ain't know the first thing about cylinder honing but I know one or two things about coatings let's just back up a sec when you have a worn cylinder and you're installing a new piston and rings traditionally you'd hone the board classic cylinder hones look like this though you can get flex or ball hones that look like this you'd run one of those quickly up and down the bore with a drill perhaps both do approximately the same job recut the old service a bit reconditioning the bore if you will honing the bore scuffs up the inside surface knocks off any glaze that may have developed gives the oil something to hang on to and the Rings something to work against however this thing has a nickel coating nikka SIL is a trade name for a nickel silicon carbide a very thin layer of that stuff is deposited on the inside it's what keeps the steel piston rings from just eating the aluminum wall for breakfast silicon carbide is extremely hard a standard cylinder hone will do absolutely nothing to it well except maybe chip and breaking it right off the aluminum substrate which is very easy to do in a two-stroke engine with all the ports and harbors in there so unless you own something like Sun and diamond hone the only thing you and I at home might be able to do is make a bad situation even worse if the coating is worn you have to send it out to someone that knows what they're doing which is why I didn't touch it that and the fact that it looked like it had a little more life in it Oh ain't that something and I should have tried this first this is the other accessory in the kit or one of the other accessories my compressor is at 90 psi I'm reading about 45 oh let me try this with this year's one my foolin myself here alright why isn't that holding pressure now peak reading I'm seeing about a 100 105 the gauge on the compressor says 90 I think I have my answer what has this world come to when you can't even trust a tool that you bought for less than what it costs you to walk to the mailbox to pick it up let me know down in the comments if I'm mistaken but I don't even think an engine like this would start with 50 60 70 psi of compression minimum viable has got to be at least 85 90 95 psi but fact of the matter bike starts on the first kick okay maybe the second and it's got a lot more get up and go than it used to which was the whole point of this exercise let me wash my hands and we'll wrap this up something to keep in mind after rebuild like this the engine does need a little time to break back in the piston rings haven't yet worn into the new position the new piston rings in the old bore probably only touching off on a handful of spots it's not really getting the seal that it needs this thing probably needs to be ridden a good I don't know 20 minutes half hour I only did a quick 10 minute run around the block I didn't want to be that one knucklehead run around making noise while everybody's locked up inside not to mention it's still kind of early I wrote it till the engine came up to temp till the fan came on again maybe you can see in this shot the exhaust got hot enough to melt whatever that goop was that I put in there by accident first impressions are good though I mean it's still a 125 but in first gear do you wait the suspension pull the throttle all the way open on a slight incline the front tire will come up before the new rings it required a bit of a clutch dump to do the same thing so for a hundred bucks I think I've made some progress here again it still needs a little bit more break-in I expected to get a little bit better and I wish I'd done this sooner I hope you like that thanks for watching this interruption it's me old Tony from the future I just finished editing this video and I can't believe I wrapped it up without ever starting the bike back up for you I wouldn't blame you for thinking I was raised by savages the bike is stone-cold it's been sin here a couple of days let's see how many kicks it takes to get to the center of a she's doing good maybe once this whole thing it's doing great feels like a new bike maybe one of these days once this whole thing blows over I'll take you out for a ride with me I know that was long for those of you stuck around thanks for watching

Channel: This Old Tony

Views: 693,546

Rating: 4.9687004 out of 5

Keywords: 125cc, trials motorcycle, trials, piston rings, 2 stroke, 2 cycle, compression tester, cylinder testing

Id: 2t4vnJA4KyI

Length: 27min 46sec (1666 seconds)

Published: Sat Apr 25 2020

Reddit Comments

[u/davidmlewisjr]

On different(s)subject So I discovered This Old Tony recently and have been binging the content...😀 🏆 So the Grinder Rebuild seems to be missing part 4... Has this been lost or is it just hidden somewhere😟

On one episode, Old Tony talks about old electricity books for boys... found one & Have PDF... how to send it?