Engine Tear Down Yamaha RD250 Disaster

[@russellharvey8590]

Having owned my '75 rd 350 since new, I say: Cleanliness is paramount especially with two strokes.

[@the_forbinproject2777]

ah the bad old "forbidden glitter" in the crankcase - spot on job !

[@RepairandRideout]

Thanks for your comment. More glitter than a Poundland Christmas card. I think the easy bit is taking it apart......

[@sidecarbod1441]

9:39 The lateral movement of the bearings is pretty normal for a crank that has done a few thousand miles, a brand new bearing won't have any movement that you can feel by hand. The main bearings on the 'blown up' side of the engine won't really have any more movement than the 'good side', the problem is that they are full of crap and it is very hard to get it out, some of it will have been hammered into the inner or outer races of the bearings, it basically welds its self to the races so you can never get it out. When you refit the crank make absolutely sure that the roll pins or little 'pips' on each bearing go into the recesses in the cases before you fit the top case!

[@RepairandRideout]

Thanks sidecarbod. I did see those little pins and figured they were for locating the bearings. The good side bearings were a lot smoother rolling than the blown side, but I thought I'd better replace them all

[@davidbrayshaw3529]

@@RepairandRideout The specifications for those tolerances are in the book. But those bearings don't sound great to me. While your there...

[@RepairandRideout]

Thanks for your comment. To be honest I went by the sound they made rather than checking the in the book. So as you say, while I was there...@@davidbrayshaw3529

[@malcolmbrady1958]

You did a Great job splitting the engine !! It can be a bit daunting when your doing it alone and not done this type of thing before, like you said take plenty of pictures, You will be fine, Your doing really well !!

[@RepairandRideout]

Hi thanks for your support. It was a bit verve wracking, I had visions of bits of gearbox springing out never to be seen again

[@Pokemongold88]

Definitely the right decision to rebuild peace of mind is the main thing nice job have a great Xmas if you're not back posting before cheers

[@RepairandRideout]

I didn't have a choice really.The mains have quite a rumble about them. Hopefully something before Christmas but unlikely to be the rebuild

[@dogshome7110]

I had an "event" on my RD nn years ago. It was getting to the blue light on the clock without any trouble. With a couple extra teeth on the front sprocket. The problem was a lean mixture, hole in piston, full on seize. I rebored and fitted new pistons and flushed the crankcase out with a hose then petrol, then WD40. I can't say how long it lasted, but it was many months more of thrashing to work 30 miles away and back.

[@RepairandRideout]

Great story. I’m probably a bit too chunky these days to add teeth on the front sprocket 😂

[@richardsouthey430]

Definitely need a crank rebuild, god luck with the rebuild 👍

[@RepairandRideout]

The crank is done just waiting for the cylinders to come back

[@RodgerMoore-m3r]

Same thing happened to my Suzuki AP50 piston blow out I just changed the piston turned out to be wrong spark plug gap , your main bearings are knackered , but you can take the bearing sizes and buy them anywhere I use KOYO , I currently have my KMX125 engine in bits on the coffee table main bearings are knackered and has worn the bearing housing on the mag side so I'm going to glue the bearing in place , it's been on the table for 6 months just lost interest but luckily my friend has a off roader so I borrowed his engine for last summer ⛱️ lol 😎 ps: don't forget to oil the bearings.

[@RepairandRideout]

Thanks for the advice, AP50 the nemesis of the fizzy, that brings back memories

[@Scott-ph2yk]

Great job splitting the cases. I see your shop mate, Mr. Haynes Manual is keeping you company.😅 Regarding the crank primary gear, the safe way to break it loose is to wedge a cloth rag in the gears before you remove the clutch basket. The rag will not damage the gears or put stress on the crank. The primary gear nut is torqued to 47 foot pounds, so it is a bugger to break free. The gold glitter you found comes from the thrust washers between the crank webs and the connecting rods. This is a tell tale sign your crank needs a rebuild. As long as you are in there, plan on replacing all of the crank bearings and seals. Pay particular attention to the clutch side crank seal. The castellations on the seal should face in, towards the connecting rod. Silly detail the catches everyone out, the first time they do a tear down and rebuild. A good KZbin resource for engine reassembly is South Texas Banshee. He has some good how to videos on how a home mechanic can do a good build with ordinary garage tools. If you ignore the water pump, a Banshee engine will look very familiar to you. Most definitely in the same design family. Lot of good tips in his videos. I learned a lot from them. He also discusses leak down testing and how to do it. Key take away is low air pressure! 6-8 psi or 1/2 a bar. Hang in there, you are doing great!

[@RepairandRideout]

Hi Scott, thanks so much for all that great advice. It's up to the engineering shop to get that primary drive off. I knew of some 'unorthodox' methods of getting it off but the thought of having to replace any collateral damage led me down the leave it alone route

[@Scott-ph2yk]

@@RepairandRideout Smart man! Just be sure to get your primary gear back with the crank. The primary gear and the clutch hub gear are a matched set. Yamaha matched them at the factory to optimize minimal gear lash. Trying to find a 40 plus year old, matched, primary gear and clutch would be a daunting task. Do not lose that gear! Ok, Sermon over. I started watching some of your ride videos. Great stuff from a part of France I am not familiar with. Very nice. Makes me miss strong French coffee and genuine croissants. Thank goodness we have a bakery owned by an ex-pat Frenchman in the area. His croissants are very good. I try to visit a few times a year. All that butter is bad for your health, but a an occasional treat makes life worthwhile. 😉 Ride safe.

[@RepairandRideout]

I didn't know they were a matched pair, thank goodness I didn't get hammer happy with it. The insta 360 with bike kit has arrived from santa, so I'll do my best to make some better quality ride out videos in the spring. Fantastic rides around here, well worth a visit@@Scott-ph2yk

[@Scott-ph2yk]

@@RepairandRideout The gentle approach is always better, when it comes to mechanical stuff. Looking forward to future ride videos. Thank you, Santa.🎅 Adding another part of France to my travel bucket list. 😊

[@agee8322]

Langcourts! Best for doing crank rebuild/balance and cylinder work. ...... anyway, make sure you super clean everything when you get it back.

[@RepairandRideout]

Thanks agree. I have found somewhere for both the crank and cylinders. Not sure when they'll be ready though

[@iantaylor5579]

Digitron in the U.K. would turn your crank recondition and rebores around in 10 days usually,

[@RepairandRideout]

Hi Ian, thanks for the info. It’s with an engineering shop now but if they can’t do it I may well take it to the UK for rebuilding

[@WoBlink1961]

....Yup, those bearings are shot! Spinning a decent bearing, it should be practically silent......

[@RepairandRideout]

I could use them for maracas ?

[@howhistory5877]

A copper coin (2p) is ideal for locking the clutch basket so you can undo the primary drive on the crank.

[@RepairandRideout]

Thanks for your advice, good to know

[@BillyWillicker]

@@RepairandRideout NEVER wedge the gears, even with soft metals. Use a proper clutch tool or lock the crank with a soft wedge at the rod's big end. Even soft metal wedges in gear teeth can and will cause gear teeth to crack and then break when run after reassembly.

[@crozwayne]

no coin is made from copper in the uk, so that's your advice trashed, as would the primary gears if a tuppence piece was used, these things are elecro plated mild steel pressings

[@howhistory5877]

@@crozwayne Well smart arse, up until 1992 they were a copper/bronze alloy, hence the 'copper' in my reply. Can you also explain how a 'copper coated mild steel coin' post 1992 could actually harm a pair of hardened steel gears? Perhaps i have been doing this longer than you sonny?

[@BillyWillicker]

@@crozwayne Never wedge gears and apply any torque while wedged. Gear failure from wedging can occur immediately or at a later time, but wedging gears will cause a tooth failure eventually.

[@bigears4014]

They ran a high clearance bearing in these . I fitted standard clearance bearings on mine fine

[@paulcasey5204]

Never mind Xmas, be thankful its not August........

[@julesvern-u4e]

Do you have a leakdown tester kit? Its a very good idea.. I rebuilt my rd400 and was meticulous about it and it still had leaks. All brand new gaskets everywhere but it leaked. Around where the reed cages are sandwiched and boots attach.. I had to use sealant to get them to stop. I also could not get the new copper head gasket to seal 100%. Had to use high temp sealant on that as well. I never would have known about these issues if I didnt buy that kit and could have fried my new engine. If I didnt kill it, it never would have run properly and Id be chasing jetting non-stop.

[@RepairandRideout]

Hi, Thanks for your advice. I'm going to put one together as this seems to be a very hot topic for the RD motor

[@deepakmenon1579]

You can use a BP manual machine and some Delrin stoppers for intake blocking and some rubber strip for exhaust and you would be sorted..

[@RepairandRideout]

Hi deepakmenon, thanks for your advice. I think I may have something in the garage I can use, not as professional as your idea though@@deepakmenon1579

[@sidecarbod1441]

9:20 Yep that bearing is full of crap! 9:48 that one is also full of crap!

[@BillyWillicker]

The rods and rod bearings look fine. The mains on the failed cylinder's side are clearly damaged and noisy. Having them replaced competently can be tough unless you find a GOOD crank person for the job. The main bearings should be 6305's, get quality C3 open types for it.

[@BillyWillicker]

You don't need bearing with the dowels in them, they were removed from later engines(RD350/LC/YFZ350) and are far easier to get and much less costly.

[@nigeldungan6651]

Hi just wondering what brand motorcycle ramp/ lift your using thanks

[@RepairandRideout]

Hi Nigel, here's the link for the bike lift www.torros.fr/fr-fr/pont-moto-hydropneumatique-450-kg-tpsl450?gad_source=1&gclid=Cj0KCQjw6PGxBhCVARIsAIumnWZXYKNz3-_YuZ63q_PG7PNOUgf0yUbKh6pxhTPKrQDk-BQ45szhE4oaAvpvEALw_wcB

[@nigeldungan6651]

Thanks for the reply, the videos are great 👍

[@the_forbinproject2777]

is shipping to the uk prohibative ? mind you the shops I'm thinking off would want to use their parts

[@RepairandRideout]

That would have been my next option. I travel between home & the UK quite a bit so I would have taken the whole lot with me

[@alexmartinmap]

Not your biggest problem but those anti-vibration rubbers on the fins are bugging me - can you drop them down by a fin when you put the engine back in the bike. Don't think I've got OCD but who knows!!!🤣🤣🤣

[@andrewrogers-lk3sn]

Probably Intake sucking air making it to leen

[@RepairandRideout]

I am going to do a leak down test as lots of comments are suggesting a leak somewhere

[@raymondsteele4142]

Hi Chris , glad your getting stuck into it . A tip for undoing the primary drive nut is to wedge a piece of flattened copper pipe between the clutch drum gear and primary gear . Don't use a copper coin , these are mostly steel copper plated in the UK. Those main bearings r/h side are buggered . Get the crank rebuilt and all the crap cleaned out of the crank case . Use proper crank seals and the right sealer between the crank cases .

[@RepairandRideout]

Hi Raymond, thanks for the tip. I am being extra cautious, that nut is on really tight.

[@BillyWillicker]

@@RepairandRideout Yamabond 4 is the best sealer I have used, for all brands of moto engines. The surfaces that it will be used on should be clean and dry as well. I use lacquer thinner to clean and isopropyl to dry, both on a white paper towel, and then once the iso is dry I apply the sealer and assemble the cases.

[@RepairandRideout]

Hi Billy, thank you, great advice. I did get a tube of sealant (Three Bond TB1215 Grey OEM) along with all the bearings. Hope this is OK? Otherwise I can call in at my local Yamaha dealership @@BillyWillicker

[@BillyWillicker]

@@RepairandRideout I have not used that type of sealer so can not make a yes or no recommendation on it. I have had excellent results with the Yamabond 4 consistently though. One to avoid is Permatex Motoseal.

[@RepairandRideout]

Thanks Billy @@BillyWillicker

[@stesmith7040]

New sub here mukka 👍

[@seanmccarthy7760]

RIDE not Drive. oh, and don't ever smack your wrist pins without holding the rods .

[@bananabrooks3836]

Bear in mind the cause is still unknown......

[@crozwayne]

Just rebuild the crank, easy enough to do for any half decent bike shop

[@RepairandRideout]

Going down that route. Hopefully found someone that knows what they're doing