Welcome to part 2 of Yamaha RD250 Disaster. In this video I strip down the top end of the engine for cleaning and a temporarily rebuild it again using old parts so that I can better understand what is broken. It’s all a bit sketchy
Listen to good advice. Take the engine out and rebuild it totally. Never ever try to rebuild the top end and just run it. No matter what you do there eill be metal fillings left in the casing and these will start to wear your gears and bearings etc. The only way to be sure it's going to be OK is a total clean out and rebuild.
Really don't want to tell you what to do, but I would say there is a major chance that melted piston crown and bits of aluminium will be in the crank case somewhere, if it was me doing this engine, I would strip it down and have a good clean out , maybe check crank beaing and seal as well, for what it is worth in the long run , at least you will then have peice of mind, and know all is as well as it can be . It would really be a shame if this happened again due to debri in the crank case. Just a thought ... I typed all above then heared you say the engine is coming out, Realy GOOD to Hear ... I hope it all goes well either way you choose .
It’s worth doing all the repairs for such a historical bike like the RD. I hope you can still find all the parts for it. I had a Mach III 500 triple back then. We used to race the 2 strokes hard and really abuse them. Chains and sprockets I had to change often, because they wear out quick. Now in 2023 you enjoy the faces of people that had all these two stroke bikes too in the 70s. They approach you, talk to you and ask questions. All the good memories come back. Speed of these bikes is not important anymore today. Just the fact that you still have 1 of these bikes today is a blast. Drive safe, drive careful sir. And most of all, enjoy and have fun in public. Wish I still had my 500 triple widowmaker. On the other hand, I’m still very glad that I’m alive.!! LOL.
Hi benny, thanks for for sharing your memories. These bikes do bring people together, even kids today on their tuned 50cc bikes like to tear it up with you from the lights. Mach III 500 is a legend - check out harrys garage on RU-vid he took his out for a run a few weeks ago. I have all the parts now but I'm unlikely to start the rebuild until the new year
The hole in the piston would seem to indicate detonation and hot temperatures, be sure of the ignition timing and the jets and air leaks in the manifold, plus confirm oil delivery.
Hello, not sure if just flushing the crankcase out with oil would remove all the tiny particals from the crankcase, would be a shame to damage all the work youve already done .
Hi David, thanks for your comment. At the time I think that I knew in my heart that I would have to split the crankcase in the end. Possibly wishful thinking that I could get away with a top end rebuild
Bollocks dropped me mobe me part 3 i was sending you disapeared. My engine had gone bang same as yours. Id just had me crank rebuilt by stan stephens back in early 1990s. All new bearings rods taper at left side where rotor fits on. Id only just ran it in new crank and topend rebuild. 1000mile then started using her propper. Poxy unleaded we didnt know back then. Tuned motor 130 mph when she let go. Engine stripped all me new crank bearings full of bits alloy plenty alloy dust. Bollocks. And its now a welded up unit like race prepped. I sprayed out bearings with wd40 then put kitchen oven on at 120 degress the missys was out at this time. Bearings still grouchy. Got me hose pipe with jet spray nozzel used that to flush bearings clean. Now nice n smooth. You can see bearings starting to rust sheen over seconds after hosepipe applied. Yikes. More wd40 then engine oil and crank went in oven to dry. She survived hosepipe ordeal. All bearings smooth. In light she'd blown up at 130mph i wonderd if crank was true. I phoned stan the man told he what happend and could i send crank back to check all ok. £50 i guess for stan check it over she was fine good to go. Crank sent to me to fit me bottom end together whilst he rebored me barrels and suplied piston kits. Tis 2023 now and me crank still sweet. Happy days. When ya motor rebuilt check compression if its higher than standard then you deffo need higher octane fuel and that pro boost silkolene in with it. My lc 350 motor makes 170 psi each barrel. She's had 2.5 mm raised exhaust ports. Head skimmed by 0.8 mm. Lose bit comp by raising ex ports then gain comp by skim head. Squish clearance check. If you got higher comp ratio check ya ign timing. With them tweeks my motor has. A standard 350 lc plug sparks at 2 mm before tdc. With skimmed head raised comp and gives engine easier time. Ign is advanced to 1.8 mm before tdc instead of 2 mm. Any less than 1.8 mm say 1.6 or 1.7 you will have engine startjng problems. So yes check ya ign timing any air leaks carb setting. Use new crankseals at engine rebuild either end of crank dont forget new gearbox seals too. Ok tis late im goin bobies. Ansome lil bike ya got git that motor rebuilt go get can pro boost 1 full measure to gallon e5 v power. If you go out a ride and only fuel you can get is standard unleaded shite. Then same again use a full measure per gallon then another half measure to compensate the standard unleaded. Tis what i do with me 350 and since last blow up in 1990s ive never had an issue. I keep a set of b8es ngk standard plugs under me seat but allways now use b9es plugs in motor. They run at a cooler temp. All this you will have a great heathy engine. Crack on with they spanners. Phil the dood
We used to replace the stock pistons with the early YZ 125 pistons when the cylinders had to be bored. If you check, the wristpin location to the top of the piston, the dimensions are the same. But the YZ piston is much lighter, and the skirt design optimizes the induction for much more horsepower, and quicker revving. YMMV, good luck, and cheers.
Hi @thebegrrsshow, thanks for your comments. Sadly the new pistons have already arrived but I will compare them to the stock ones as they look a little different
back in the day when I had a 76 RD 400, I ran Wisco forged pistons, Bassani expansion chambers, Boyesen dual stage reeds with 32mm Mikuni flat slide carburetors. Plus, a little port work and shaved heads what a fun little bike that was. Lookes like you had a leak and ran a little to lean. I had problems with cracks in the intake boots but not bad enough to put a hole in the piston. My biggest problem was with the pin breaking in the oil pump. it runs really strong for about a minute till it locks up. after two broken pumps and a few pistons I started to premix. Anyway, I would split the case and clean and inspect the bearings an replace if needed and a good time to replace the crank seals which could be possible source of the leak. You can run a little lean or without oil for a short time, but the bearings will not survive chucks of piston in them. Love the two strokes I owned RD 250, 350, 400 and a RZ 350 over the years. sometimes I wish I still had them all. So good luck they are some fun little bikes.
Hi Micheal, your RD400 must have been great fun. Thanks for your advice, there will be more videos on my progress as I inch forward. Like you I love 2 strokes and I may get another next year
Good decision to strip it, even if it took the noisy engine to convince you. It's a pity I can't post pictures in the comments section as I'd show you what my crankcase looked like even after I'd swilled it out. There was still a handful of essentially sand caught in everything. Oh, and I'm sure you will but any insight into why it happened would be great. I'm still trying to work that out
Hi Stuart, thanks for your comment. It had to be stripped in the end. The bottom end bearing seemed fine but that noise was a concern. Looks like one or both mains. Lean mixture seems to be the consensus in the comments section
I had a highly tuned gt250 back in the early 80's, it would blow a hole in the righthand piston every 3 months, (bottom end never suffered once eveything cleaned out) as someone else has already said.. ignition timing is the cause. The noise you heard on start up sounds like a broken ring to me. Possibly snagged when refitting barrel? Just a thought before you remove and dismantle whole engine.
I love two strokes . take me back to the 70s and early 80s . Owned a Suzuki GT250 rode like a dog but the noise was just addictive . There was an oil that had strawberry smell when you ran the engine. I crashed a DT125 when it decided to completely lock up . The two stroke tank was empty but had oil in the little window . Wouldnt have been to bad but it happend out side the cop shop LOL .
Oh no! Back in my youthful FS1E days I made the mistake of running Castrol R, just dumping it into the tank rather than properly mixing it. I was chasing the aroma (!) but seized the engine!
As someone already stated, the only way to remove all the aluminium debri from the big end and main bearings, is to completely strip and rebuild the bottomn end !! If not you will have BIG problems literally.... down the road.
Painful. We have 2 RD400's 1 RD350, and an RZ350 in the shop at the moment. 3 of the 4 have met similar deaths. We have 16 motors in the shop waiting for restoration. We service and restore vintage and classic motorcycles up to 1979. Good luck on this project. You will succeed.
Red line job, when I did this several times, a mechanic told me that the plug turned into a mini blow lamp when you red lined it which burned through the piston. Never did find out if that was true or not but the plug was buggered as well. Most people say it’s a timing issue.
From the barrel 'damage' that I can see in the vid personally I would not be re-boring the cylinders, a blunt knife (like a knife and fork knife) can be used to scrape the barrel, it seems to be a shame to me to rebore that barrel just to get rid of a few smudges of ali that are stuck to it. Each time you rebore a barrel it is one step closer to be worn out and therefore scrap. You can even hand hone it with a bit of wet and dry.
That's a very good point and to be honest was a direction I was going in. Getting the new pistons in the same size was the issue. Wemoto France didn't have them in stock but said they did have the +.050 but it turned out after I had ordered them they were on back order! So the .050 arrive tomorrow
Your problems with the piston debris might be worse than you think. It would be better if you stripped the motor down, that debis could cause a fatal blow to the motor if it is still in the crank case.
My 76 rd 250 dx as it was called. That holed a piston while on the motorway luckily the mess shot straight out the exhaust . All done under warranty. Copper head gaskets where too thin should have been 1 mm
I kept Yamaha in profits during the 80's with the number of pistons I had to replace on my 400. And despite my best efforts I never got to the bottom of why the bike would melt pistons. I feel your pain but I'm interested to see what you find out. Clearly the mixture on the rh cylinder was running lean at higher rpm, maybe a leaking crank seal contributed to the failure? No doubt you'll descover something on the strip down.
Thanks Steve. In the next video I look for more input from those with more knowledge/experience as I propose the potential reasons why it holed the piston. I'm struggling to work it out too
@@RepairandRideout as a general rule In this scenario there are only three things to focus on. A mechanical fault, (leaking seal/gasket/weak or damaged reed valves or in some cases, the wrong type of spark plug- running too hot. Although theres no evidence on the lh piston of hot running . Timing ( You've fitted electronic ignition) but still worth double checking. Or carburation (lean mixture).
Need to adjust the carb jets when fitting expansion pipes. Otherwise engine runs too lean and it's holed piston time. (bitter experience). Check the inlet rubbers for air leaks too. Looks like a 'D' model so it should have electronic ignition. Timing shouldn't be an issue then.
Phil the dood back again. All that alloy dust will be into the main bearings and big end bearings they'll be grouchy the balls and tracks they run in will be coated with a layer of alloy. Piece piss to strip and rebuild that motor. Only special tool you require is a rotor puller and a torque wrench. Oike it out do job right. Send crank to a 2 stroke engineer specialist. They fit new bearings all gotta come apart to replace big ends labrinth seal between etc. Then trimmed and trued on lathe jig for tolerance run out. You order complete gasket set whilst crank gits sorted. Washout crankcases etc new crankseals and gearbox seals too. My god i strip rebuild that motor blindfolded. Bin that honeing tool. When motor built and back in bike and running id give it 500 miles upto 4ish 1000 rpm then onto 5 to 6 thou for next 500 miles. Vary speeds not fixed speed mile after mile. Critical miles first 300 whilst port edges polish into rings. Use V power or same sort and git that bleddy proboost into fueltank too. Let me know how you get on. Mr phil the dood
I noticed the z650 in the background the rocker cover is chromed , did you restore the Z , I had a B1 it was black with a sports seat and the rocker cover was chromed , a great bike bomb proof .
Hi thanks for your comment. The rocker cover is just polished. I brought it much as you see it, just had to do a few mechanical things including an electronic ignition a couple of years ago. It's a nice bike to have and I really enjoy riding it
this was just brutal, unnecessary torture. here comes the fun of finding a shop that will split a twin crank... try marine guys. yes, the entire crank needs splitting. center bearings, seals, big end rod bearings, thrust washers, pins if scored beyond use... look into "brinelling"... anything into those bearings has destroyed them. there is no way around it. the whole crank comes apart. no ifs, no buts. its now what thirty years ago was considered "stuffed beyond repair" and would go to a wrecker for $50. face it, you do it from nostalgia and hope to recover lost money, or make it feel worthwhile. now its dead and its going to take a lot of determination to see it through. it all needs repressing, lining up, getting rid of runout. twins are not easy, but boat guys can deal with up to four... there are v8 twosmokers out there. its possible to do at home but hell, its not for the faint hearted. practise on some singles maybe. at least then you know the inner seals are good as well ;)
Hi Paradise, I hadn't thought of a marine engineering company - great idea. All of the above parts have been ordered and I'm waiting for them to arrive. I have a automotive engineering company I have used before in mind but I haven't asked them about this job yet
@@RepairandRideout not many auto places press cranks apart... its a two stroke thing. pulling it apart is the easy bit. but yeah, watch a few vids on people doing it, worst comes to worst... its just a decent press, delicate pressure control, and a lot of beating with a hammer to pull it into line again? hence, marine guys. outboards and jetskis. maybe hunt down some racers and find a shop with a good reputation... therell always be "that one place"... lot easier when you do it all day every day and are set up for it.
I see others have covered engine removal and cleaning out the crank, air leaks and timing ( hurrah electronic !) . I'm not sure anyone has covered low octane petrol , ie regular . I holed a piston in my 250LC , not as bad as to melt the spark plug and piston though, I used 97 octane from then on and had no issue . Sorry to ask but did you stray from the recommended air screw setting as modern fuels leave the combustion chambers black ( not grey pink , I'm old enough to remember leaded petrol !!) , always run 2 strokes on the rich side . great video , look forward to the next episode
Hi Forbinproject, thanks for your comment. I use 98 premium fuel as it's 0-5% methanol, I use it on everything I have petrol powered. I wondered if the slight pink hew to the good spark plug was indicating a high octane content and thereby a potential problem?
@@RepairandRideout be careful of shell V power as I beleive thats still high methanol content (!) . I tried to take another look at the top crown of the good piston from the video but looks a little too light for me ( air screw settings are standard ?) , I would have expected more soot - have they been recently decoked / cleaned? The plug pinkish can mean its ok but I cant tell if theres signs of "blisters" so more light chocolate better ( always err on the slightly richer ;-) ) ( sorry havent looked through all the videos - just two for this machine ? ) PS: I ran Hytec reed valves on my LC as they made the ride smoother and the advantage is if they do break plastic doees less damage than metal? maybe, yamaha club thinks not - never had an issue myself ( Boyesen Dual Stage Reeds are not cheap ! )
replying to my own comment - found the vid on using a plug device for mixture . I have never used one on my two strokes - ok on the 4 strokes I had but I suspect maybe the carbs set to lean/weak, did you get a slight hesitation on pulling away ? I'd set the mixture screw back to manufactures setting myself then do plug checks .
Pulling away was fine, I had been working on mid throttle stuttering and had been changing the position of the needles. On this ride out mid throttle had improved and wide open was great @@the_forbinproject2777
@@RepairandRideout okey doke , I've been doing catch up on your vids btw as your channel only appeared to me today ( got to love yt - NOT) . A standard tuned RD should run quite well on std setting for needled jets , etc. . You have expansions but normallt there wouldnt be changes ( unless they're race and they are very noisey ) . btw did you have the carbs cleaned ? . as you say raising the needles richenen the mixture but you shouldnt need to . Compression all ok ? peakyness is expected for good spannys and removing the air box normally removes any low end grunt ( 5K or less ) . When uncertain for history best to check everything as we have no idea what anyone has done .
If your runnimg no cylinder gaskets head & barrel your creating higher compretion therfore advancing the timing so would hole pistons ? I used to retard timimg by 1degree and fit 9 heat rated plugs instead off 8's or you may have a blockage in the main jet on thay cylinder or inductio air leak but normaly it would run ruff and rev high on idle, you cant beat the sound of allspeeds on an RD" good luck
Hi @fastboy, thanks for your comment. I'll probably brush on 2 stroke oil on the bearings as I reassemble and then run on pre-mix in the tank while I test the oil pump to see if it is set correctly and distributing evenly
Ok so I hope you read this post ....so the reason the piston has a hole in it is from early detenation, the timing is firing to early on the right side....if u replace the top end without fixing the problem it will blow another hole in the next set ...
Hi Jamie, thanks for your advice. I'm wondering how to set the ignition timing for individual cylinders as there is only a single trigger point on the ignition system? Am I missing something - wouldn't be surprised?!
