Yamaha RD250 Disaster part 3

[@-DC-]

The only disaster is not experiencing a Two Stroke 👊

[@RepairandRideout]

That's so true. Watched Neevseysbikes the other day and his face lit up recalling his two stroke days

[@MX-fo2nu]

Very right, and after it runs again the fun will be yours

[@martinowl]

Good luck with the strip down. Hope it all went smoothly & not too much damage found. Looking forward to the rebuild. It’s a nice looking bike you have.

[@RepairandRideout]

Thanks so much, I'm sure there will be hiccups along the way

[@yvonnetaylor6274]

I have not had much experience with a 250 but lots with a RD 400 including oil pump failure which I found does not cause piston holing. An air leak , over advanced timing , to much compression or lean carburation caused problems for me. If my memory serves me correctly early RD250 were plagued with holing pistons due to a batch of head gaskets which were too thin.

[@RepairandRideout]

Hi Yvonne thanks for your advice. I will definitely be looking at all these things with the rebuild

[@julesvern-u4e]

Hi from Canada. I rebuilt an RD400C from scratch. Something I bought was a leakdown tester kit.. it was around $50 USD. Im glad I did because no matter how much care I took putting the engine together I discovered a few leaks. Around the head gaskets and also the intake and reed ages sandwich areas. Only way I could stop them was using high temp silicone, an exhaust type gasket sealant (orange stuff) on each side of the head gaskets and on each surface of the intake read valve areas. I had all new parts as well.. even the intake boots that sit against reed cages were new yet there were still leaks. Once I did all this and it would hold 5 psi back in the bike it went and Ive had to wonderful seasons on it so far.

[@RepairandRideout]

Hi @user, thanks for sharing your experience, much appreciated. I will be doing leak down tests on the rebuild as I naively thought that all new parts (used before) would cure all ills

[@Scott-ph2yk]

Greetings from the USA. Great bike you have there. A couple of suggestions for you. 1. Track down a shop manual, or at least a Haynes manual. Your best friend in the garage. 2. Buy or build a leak down tester. Find and eliminate all air leaks. 3. Check your heads for flatness, deck them if necessary. Owning a two stroke is great fun, but they can be confounding at times. Keep at it, you are learning as you go. enjoy the adventure.

[@RepairandRideout]

Hi @Scott, thanks for your very sound advice. I will certainly be doing all three things

[@Scott-ph2yk]

@@RepairandRideout almost forgot. Be sure to have fun in the garage!😉

[@RepairandRideout]

my new home! @@Scott-ph2yk

[@Scott-ph2yk]

@@RepairandRideout That's the spirit!😅 I suspect you are looking at air leak issues, based on the huge piston hole, and the "blow by" mark on your cylinder head. When you open up the cases, you are going to find aluminum bits everywhere. They will have done a number on your bearings and seals. Engine rebuilds are expensive parts wise, but if you can do most of your own labor, they are not too bad. Yamaha still sells most of the parts, and it sounds like you are clued into Webike and Yambits too. You will have to have a shop bore your cylinders, hone them, and chamfer the port edges. The crank rebuild will need to be done by the shop too. In the garage you can do things to save you money. 1. Using some plumbing plastic pipe fittings, hose clamps, and pipe plugs you can cobble up a leak down tester, very inexpensively. 2. Find a dead flat surface in your garage, or buy a piece of float glass(cheap!), which is dead flat. You can use the flat surface to gauge the flatness of your cylinder heads with feeler gauges. If needed, you can attach fine grit sandpaper to your flat surface with spray adhesive, and lightly sand your heads until they are flat. This process is detailed in most shop manuals. If not, the RD500 forum has a post that demonstrates the process. 3. Track down a tube of 3 Bond 1211 or Moto Seal fuel resistant sealant. You will use this the re seal your engine cases and intakes. The Yamaha Banshee ATV (350 YPVS powered) guys use sealant on the intakes, cylinder base gaskets, and crank seals as well. Fire up a pot of tea, or some strong French coffee, and dive into it. The Yamaha two stroke twins are easy to work on. You can do it.😊

[@RepairandRideout]

Thanks for your encouragement. There's more to come on the strip down and some things you have suggested. @@Scott-ph2yk

[@the_forbinproject2777]

another great video . I hope these thoughts will help in getting to the bottom of the issue ;- 1, timing : - the GT185 I rebuilt had timing differences as follows for an example , then I looked up the RD250 pitmans K and L 20* or 1.83 + 0.58 ( range 1.83 - 2.41, 20-26* ) M 2.62 ( 28.63 A 2.64 ( 28.85* ) haynes K and L 1.83 M and A 2.63 (28.74 * ) For Yamahs RD250 seems its 1.8 or 2.0 ; others may chime in on what to set it to 2, whilst researching how to set up my engine timing (thats been in many parts for years) I found this ;- "Timing advance means that the spark plugs are firing earlier in the compression stroke, farther from TDC. The air and fuel mixture in the combustion chamber doesn’t burn right away. Ignition timing advancing might be needed to allow time to get everything ignited. The major benefit to advancing the timing of a vehicle’s ignition is increasing the horsepower of an engine. Advancing the ignition timing helps raise the high-end power while reducing the low end. It also helps get the spark past the ignition delay and run at peak power. Retard Timing causes the spark plug to fire later in the compression stroke. The effects of retarding ignition timing include reducing engine detonation, which is combustion inside the cylinders after the spark plug fires. This is also known as engine knocking." So perhaps its not detonation thats the cause. Again other posters can chime in with their knowledge. Looking forwards to te next episode ;-)

[@sidecarbod1441]

"So perhaps its not detonation that's the cause. Again other posters can chime in with their knowledge"....I've said all along its not detonation that holed the piston! The hole in the piston is just plain wrong for it to be detonation, it has been smashed thorough and has rough edges, a hole caused by detonation looks like it has been made with a sandblaster. I'll explain why you have to run ignition advance and why the curve is actually a retard curve which is the exact opposite of a four strokes advance curve. Firstly a couple of 'golden rules' 1. An engine (any piston engine) requires the peak cylinder pressure to occur at around 14-20 degrees after top dead centre on the power stroke, the likes of Ricardo Engineering worked this out many years ago, its all to do with crank and con-rod angles. (Peak cylinder pressure is the maximum pressure above the piston, it will occur sometime after the plug has fired, initial cylinder pressure is the pressure in the cylinder just before the plug fires). 2. It takes time for the pressure to build up in the combustion chamber once the spark plug has ignited the mixture, the speed of the flame front is determined by several things but two of them are the initial cylinder pressure, i.e. the pressure just before the plug fires and the quality of the mixture (i.e. how much exhaust gas is still present from the previous combustion event and how well the air and fuel have been mixed together). On the face of it in order to get peak cylinder pressure at the right crank angle at say 2000 RPM the point in time when the plug fires will differ than at 4000 RPM as we only have half the time at 4k to get the mixture burnt, so on the face of it the solution would be to fire the mixture earlier in the compression stroke at 4k RPM. in other words we need to run an advance curve, firing the plug earlier and earlier in the compression stroke as the RPM rises. It is more or less what goes on in a four stroke engine (there are other factors that I won't bore you with!) Bear in mind that we are igniting the mixture several degrees BEFORE TDC in order to get that peak pressure at around 14-20 degrees ATDC. So why does a two stroke run a retard curve (or maybe a curve that initially advances but then at a certain RPM starts to retard very rapidly), well its down to rule number two, when a two stroke is out of its powerband (the exhaust and intake not 'resonating' in time with the engine) the initial cylinder pressure is low, this is because there is no harmonic supercharging of the engine taking place, also there is plenty of time for the exhaust to reverse flow and dump exhaust gases back into the cylinder, or never full leave in the first place. So we have a poor quality, low pressure mixture just before the plug fires, this mixture burns slowly, this means we need a load of ignition advance in order to get any useful work out of the engine, i.e. peak pressure at 14-20 degrees ATDC. Now when the engine comes on the pipe things change, yes the RPM is going up which makes you think we need more advance BUT the engine is now in resonance, the volumetric efficiency (VE) can go past 100% (for a 250cc engine it pulls in more than 250cc of fresh charge on the induction cycles), this pushes the initial cylinder pressure up much higher, there is less exhaust gas contamination in the cylinder, also the whole mixture is, well mixed better due to turbulence so the flame speed goes up much higher, to get the peak cylinder pressure at the right angle in the power stroke we need to retard the timing, i.e. fire the plug later. This also explains why skimming the head and/or getting the squishband working properly will require the timing to be retarded from standard, the higher CR creates a higher initial cylinder pressure and a working squish band creates more turbulence in the combustion chamber (amongst other things) Now some people will argue that the timing is retarded on a 'stroker' engine in order to heat up the exhaust, this increases the resistant frequency of the exhaust, I could agree with them but if I did we would both be wrong! (The temperature of the exhaust will go up anyway as more and more hot gas goes through it as the RPM goes up). Note that even stock exhausts will still have pressure waves bouncing around inside them, they do resonate to a degree but clearly not as strongly as a 'proper' expansion chamber. I believe this bike is running AllSpeeds.

[@RepairandRideout]

I've read both that the timing is 1.8mm or 2.0mm BTDC. I went for 2.0mm thinking that, a slightly tuned engine running expansion pipes & jetted carbs on premium fuel, would be the best option

[@sidecarbod1441]

@@RepairandRideout Nope, you need to retard the timing on a 2 stroke if you do anything that increases the air flow through the engine per induction cycle, i.e. increasing its 'VE' Having said that I don't think you're engine is anywhere nearly 'tuned' highly enough to be happy on 1.8mm and yet blow up on 2mm! One thing I forget to mention in my long rambling post is that many ignitions systems don't run any retard curve at all, they run 'fixed' timing, in other words the timing is set to the correct value for high RPM and everywhere else it is way too retarded. basically its a 'cheap-ish, that will do' system! It could be that you set your system up at say 2mm by doing it 'statically' but if you run the engine and pointed a strobe light at the timing marks you would see that at low RPM show way more advanced than 2mm but as you rev the engine the timing backs off towards 2mm, if your system does this then that's great, it has a retard curve built in., if the marks remain the same regardless of the rpm its a 'fixed' system. You really need to use a strobe when confirming the timing on an engine, if it runs fixed timing and the marks don't line up then you just need to take this into account when statically setting the system up. (you can scribe a new mark). I'd run your engine at around 1.8, you could try 1.6 and if you don't feel any loss then leave it at that, 1.8 would still be safe enough though. Years ago I ran a TZ350 engine in a F2 sidecar outfit, it had a fixed timing system set at something like 1.6mm, the engine was a pig at low RPM, it could not pull the skin of a rice pudding below 5k, I had to slip the clutch all the time just to get the outfit moving. I swapped the system for one that fired at 3.5mm BTDC at low rpm then backed off to 1.6mm at high rpm, the engine left like a huge V8, it would pull from nothing with no clutch slipping at all!

[@RepairandRideout]

I just about kept up with you on all the technical info about the timing. I will try a strobe light when I rebuild & re-time the engine. My guess is that it will be a fixed system. umm maybe I'll look at the Vape website.... @@sidecarbod1441

[@the_forbinproject2777]

@@sidecarbod1441 older machine like mine have fixed timing - all the 2 strokes I had were fixed , the 4 strokes like CB250 G5 and GSX550 had advance/retard even if was mechanical . These days you can get electronic systems for 2 strokes that do advance and retard .And the reports I 've read show marked improvement in power and response as you said. Havent found one for a Suzuki GT185 yet , worse luck.

[@cbrider726]

@Repair & Rideout . The Insta 360 is what i want for christmas lol . We can only hope . I love to watch other poeple working on bikes because we learne from each other no one knows every thing and i have picked up so many tip by watching people like you . I have been in the trade for over 30 years and i get a kick out of watching you . Thanks for putting the time and effort in on these streams . I know how much time goes into each stream with editing . Thanks mate well done . The last time that i saw damage like this was the wrong spark plug ???? new fuels could be a factor ??? 👍👍👍👍

[@RepairandRideout]

Hi cbrider, thanks for commenting. Not sure how many tips I'm providing, good ones at least? But there has been terrific advice from those who do know what they're doing. I'm looking forward to getting some new filming equipment. It is time consuming but I'm enjoying it.

[@philipkenyoncarbon1291]

Hi. In 1976 i had the orange rd 200cc

[@deepakmenon1579]

Do a leak test, other than timing or air leak .. the left crank oil seal can be a culprit

[@RepairandRideout]

Thanks for your comment, I have made a contraption to do a leak test. I will certainly use it when the rebuild the engine

[@rodneyperkins1057]

Hi their am enjoying the blogs, bringing back memories from the 70s when I owned many rd250s and 400s. Plus lucky enough to own Suzuki gt380 and 550, plus Kawasaki 250 and 350 as you can see a two stroke nut. Reason I have contacted you is I am concerned the way you are setting ignition timing. Piston and cylinder head are domed not flat so timing setting may be wrong with inevitable consequences. I would strongly recommend use of dial gauge with head torqued to correct setting to ensure timing is correct. Squish band is important too. I used a mitutoyo dial gauge with appropriately shortened bicycle spoke to perfect timing. Sorry if someone mentioned this to you before just thought you should be aware. Also you can shim up pump for extra oil, but make sure marks on pump and carburetors line up at correct point. Some people also do not understand that long periods of coasting downhill with light or no throttle on a two stroke starves crank and pistons of oil so a blip every hundred yards or so will help. I speak from many years of experience with two stroke engines. Thanks again for blog .😇

[@RepairandRideout]

Hi Rodney, thanks so much for getting in touch. I have a dial gauge and will be using it to set the timing while the engine is out of the frame. I found it too difficult to use while the engine was in position. I may also mark it up for strobe light setting as well? You've had a fantastic selection of bikes over the years. I would love a Kawasaki 2 stroke triple, in fact any of the bikes you've owned. There are just so many classics to enjoy and not enough time or money to try them all these days

[@shanelottering5090]

I had a 350 ypvs , blew the motor twice . Both times right cylinder failure. What I did thereafter was to put a 250ml two stroke oil in the tank every time I filled the fuel tank .

[@RepairandRideout]

Thanks for your comment. I do need to look at the oiling system for sure

[@bananabrooks3836]

That masks the problem not solves it.

[@madeljacky]

Late timing wont blow a hole in a piston, an air leak somewhere or a lean mixture will rise the cylinder temperature enough to almost melt the aluminium piston crown and the compression will help blow the hole in it, ive worked at two Rotax 503 Microlight engines that were running perfectly fine but when the head was taken off for the 50 hour decoke the rear cylinder piston had a depression in the crown where it had got that hot for some reason the aluminium went cheesy and it almost had blown through,

[@MX-fo2nu]

To late fire will not kill piston with hole, this is to early fire to lean , air leak is also to lean, hard gasket ok but not a big nok look, so all need to be leak free with Break Cleaner to test during running. You need bigger main jet with full power kit :-) and may be needle one higher means clip lower ;-). 2stroke like late fire and even more at higher RPM .

[@RepairandRideout]

Hi MX thanks for the info. Will do a leak down test on the rebuild

[@MX-fo2nu]

@@RepairandRideout i would start with 23 degree at idel if you have ignition with Curve to go later at 5000 an 6000 to about 18 or less. Later you can go earlier at idel if not Pre Detonation noice, if fix fire i would go as late as possable at idle 20 or even 18 degree , Depending your switch gab, smaler= less ealier fire

[@MX-fo2nu]

And via try later or earlier step by step 2 degree, anf then fine via 1 degree changes

[@RepairandRideout]

Thanks for the extra info. I'll go for 1.8mm BTDC to start with @@MX-fo2nu

[@MX-fo2nu]

@@RepairandRideout let it run ;-)

[@gk73man51]

The vape doesn’t fire exactly where the manual claims. I would make a timing mark and strobe it once the engine is running again. Quick one, was the other cylinder showing any signs of overheating? My 350 melted a piston earlier this year after 2/3 years of hard use without a problem. However the giveaway was the other piston showed signs of the same thing in progress so it wasn’t an air leak or blocked jet. My vape is keyed and the woodruff key was fine, I run an Ignitech box so that was a possibility, but on testing once the engine was rebuilt all was fine. I’m 99% certain it was down to fuel, it blew up just after filling the tank and several 2 stroke tuners have reported bikes doing the same or bikes with a proven set up coming in on the dyno and suddenly needing upjetting after several years running due to the AFR ratio falling lean. Something is changing with fuel beyond just the E5 and E10 issue. In the meantime I’ve gone conservative on the squish and lifted the needles for running in and will check the jetting on the dyno in the new year. On your bike which is relatively standard I would be concentrating on timing, air leaks and blocked jets, I assume the jetting has been fine for the pipes up to this point ?

[@RepairandRideout]

Hi @gk73, Thanks so much for your comments, really useful advice. My Vape isn't keyed so maybe once I'm sure the timing is correct I'll put a little paint line on the crank and rotor and check for slippage. I'll strobe it for sure. The other piston was in perfect condition. It was work in progress getting the jets & needle position to the point where there was no bogging down in the mid-throttle range (off the pilot and on to the main) but I was riding thinking that it was sorted - right up until the moment it wasn't

[@gk73man51]

@@RepairandRideout you’re welcome, I’ve battled this a few times and it can be frustrating to get to the bottom of. First time was detonation due to insufficient head volume (coupled with a lack of experience of how detonation sounds / feels).

[@RepairandRideout]

I'll try to make a better job of it this time@@gk73man51

[@Keith-rk4td]

My friend had a RD250. He ported the heads and added Factory Pipe Products chambers ad sum flat slide carbs. He pissed off lots of people on track day. He was out classing much bigger bikes. It was a go cart track in N EAST TEXAS. Very tight corse. Guy on a Ducati race prepped 999 got his bum really hurt,that the 250 was getting better lap times🤭 🤘🤠🤘

[@stephengunrunnerhanson3550]

Hole in a piston caused by a seal going and running a very weak and it blow a hole in piston

[@RepairandRideout]

Could have been. Seals were new but who's to say there wasn't a problem there

[@jabbalechat7910]

Were the carbs rejetted on the mains when the stinger pipes were fitted?

[@RepairandRideout]

Hi thanks for asking, yes they were. Can’t recall off the top of my head if they are 140 or 150

[@colinculverwell325]

That doesn't look like lubrication failure. The scoring on the piston and alloy stuck to the cylinder wall has most likely been caused by excessive heat on the piston crown. I would be looking at incorrect timing and jetting/air leaks. Most likely timing. Things to consider. How was the timing set? Needs to be done static with dti and double checked with strobe dynamically. What plugs did you have fitted? Should be B8ES or for real hard running B9ES. If you have B7s they will run far too hot. Head gaskets. Standard on the non German models was 1mm for C and D models , 0.5 for E/F. Standard timing on the C/D is 2mm btdc. E/F 1.6mm. Either way you apprx 1mm is not right and the most likely cause. You can use the 0,5 mm gaskets on the C/Ds just need to make sure it's timed right. The heads and cylinders are all the same for c/d German or not. Its only the gaskets that are different.

[@RepairandRideout]

Hi colin, thanks for your advice. It's running .5mm gaskets with B8's. I've read that the timing is either 1.8mm or 2mm BTDC and I was aiming for 2mm. So far the comments section is suggesting lean mixture (carb set up or air leak) and/or timing are the culprits

[@colinculverwell325]

@@RepairandRideout I'm running 1.8mm on my 250c with 0.5mm gaskets.

[@ThomasCaldwell-k6y]

Years ago I had a holed piston on a 2 stroke twin it was a loose spark plug. Drawing air I would think that it is a head gasket problem

[@paulb1034]

Does using the thinner head gasket mean that the spark plug is too close to the piston crown and causing an overheat?

[@RepairandRideout]

I honestly don’t know but a go of thought. Most comments suggest lean mixture or poor timing

[@teej710]

Putting a hole into a piston, basically comes down to having too high cylinder temperature and pressure. This happens because the fuel mixture expands during burning. The faster it expands and the hotter it gets BTDC, is what determines the power characteristics of the engine. Unfortunately, there is an optimum point, before detonation comes into play and damage occurs. In a 2 stoke engine, many factors influence the burning of the fuel mixture, timing, compression, squish, spark plug value, air/fuel ratio, exhaust design etc. Therefore, changing any one or more of these from the original design can be detrimental to the reliability of the engine, unless they are compensated for. After watching this latest video, I would question the method of setting the engine timing. A 2 stoke engine is very sensitive to ignition timing settings, which if set wrong, it will hole a piston, in the blink of an eye. The video implies that the timing could have been set to 1mm BTDC. If this was correct, then the timing would be extremely retarded, compared to standard. This would pretty much negate any chance of detonation, as the late ignition of the fuel mixture, would prevent any high cylinder pressure being created and the burning mixture would probably be already exiting into the expansion chambers, before optimum pressure was reached. A noticeable lack of power would have been evident. The only way to safely ensure that the ignition timing is set correctly, is by fitted the heads and using a dial gauge indicator through the plug hole, onto the piston crown. This will measure at 0.01mm accuracy. Using it you can then determine the exact TDC position and subsequent desired BTDC advance value. If the cylinder head compression has been increased, due to a thinner head gasket, then retarding the ignition timing from 2mm to 1.8mm BTDC may be a safer bet, as the increased compression will increase burn speed. Obviously, as already suggested, there are many factors, which can cause the holed piston, so my comment hopefully will help eliminate a potential timing issue. I have created a KZbin video about how to set ignition timing. Although this is a different engine, the principle of using a dial gauge is no different kzbin.info/www/bejne/sIXOq5aDbd-nf5ofeature=shared .BTW please forgive me for the cheesy background music, it's one of my early video attempts ... Lol 😂

[@RepairandRideout]

Thanks for your comment, so much useful information in there. Dial indicator on its way me thinks

[@cbrider726]

Where did you get the expansion pipes ? Just a tip i always Take videos of the wiring and pictures . It helps .

[@the_forbinproject2777]

Chris said they're Allspeeds and I beleive 2nd hand

[@RepairandRideout]

Hi cbrider, From someone on the aircooled RD owners club. It was a few years ago

[@agee8322]

Think you / someone mentioned deto/pre ignition ....... on a 2t, you get a really audible rattle/tinkling when running ..... did you hear any? Also, dont assume new rubber/plastic parts are good ..... new manifold boots might be less than flat and let air in. Permatex is your friend here.

[@RepairandRideout]

Hi agee, no warning at all, it just let go

[@stephengunrunnerhanson3550]

Very interesting

[@buckpotter3184]

😂😂 Buck Potter KZbin channel we say that's too much work too complicated we stick with the Predator engines😮

[@johnsmith-sm6mh]

Subscribed 😊👍🏻

[@rainbowboa100]

so here's the secret shhh, use german main bearings instead of the japanese ones. you'll have a smoother running bike that will go well past the normal redline. also use a .020 base gasket instead of the .030 one, good luck!

[@WoBlink1961]

You may already have found the reason (I realise this video is more than a week out of date) but in my experience, the primary cause of holing a piston is overadvanced timing. In the days of contact breaker points ignition, too large a points gap meant the points opened early thereby giving overadvanced timing, high cyl temps and pressures, and , a holed piston (as I found out one dark and wet winter's night on the M2 on my GT250 in 1979!!!) Your RD is presumably electronic ignition? Is the timing adjustable - I presume so, given you said you had set it. I'm just trying to figure out whether the German head gaskets being 1mm thicker, means the ignition timing was originally set differently - ie 1mm later in relation to the piston position. Mind you, if you had set the ignition timing 1mm late then it is retarded which I wouldn't expect to cause a holed piston.... EDIT - Actually I think the timing should be the same DE/UK as the BTDC point is set so that the bonfire in the cylinder peaks just after TDC - this should be about the same whatever distance the head is away from the piston crown). Final thought - are the German specified plugs different to the UK specified plugs? If the German version took hotter plugs because of the lower compression ratio, and you are using them in what is effectively a higher compression UK engine, that could easily cause a holed piston.

[@RepairandRideout]

Hi Buster thanks for your comments. The cylinders & crank are now at the shop so it will be a while before I get them back. I shall set the timing on the bench and check with a strobe once running. It's running BS8's with a .5mm head gasket

[@roythearcher]

If there was a leak of gasses past the head gasket you would hear it as a high pitched hiss not unlike an exhaust leak and there would be a lot of oil deposited around the head to cylinder joint.

[@RepairandRideout]

Hi Roy, thanks for your comment. I remember back in my moped days having a leaking head gasket, it sounded it it was blowing a raspberry

[@torevenheim9607]

Remember back in 80-82 this happened on my Suzuki gt 100

[@MrWiskin]

Its clear it was running lean, on the right!