Beginner RD250 project questions

[RDryan]

Crayons work better on steel studs in aluminum than penetrating oil if you are using heat. The wax doesn't evaporate as easily. The oil just burns off. Use several heat cycles on them to let the wax get down as far as possible into the threads. Some people say metallic crayons work better. At least silver is a better match on aluminum.

IR8D8R

Interesting to know. Now is a crayon different than candle wax?...I did watch a video of a stud removal with the wax being used.Seemed to work nicely but as it was demonstrated the heat was put on much longer than I felt comfortable doing myself. I would say a solid 45 seconds then the candle was nudged into it and this was repeated three times on a steel exhaust stud in aluminum.

I got nervous with wiring and gas being so close to the work area, not to mention a bit impatient putting the heat on those studs so I gave up on it. Saying all that even after learning from my mistakes of not covering wires and rubber bits so close to the work area...and like you say it seemed like I was just burning off the PB Blaster I was using. 

That and the fact that m in SC emphasized that I could get away with the shorter studs. For better or worse I proceeded with the install and at present everything except the carbs are reassembled. Not sure if it was a bad idea or not but I dabbed a very little bit of anti seize  on four of the studs I did manage to remove prior to assembly.

[RDryan]

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all excellent info, thank you! it sounds like you can simply put the 350 pistons on the 250 rods with a wider wrist pin and bearing, that seems almost too easy.

the key i've found so far is be sure to make progress every day, even if it is just a little bit. no different than any big project but daily progress adds up quick on a motorcycle as long as you avoid going too deep down the rabbit hole. easier said than done sometimes, it is motorcycles after all.

so i read your thread m in sc on those cylinders, seems like they require quite a bit of prep to be ready or maybe optimal...is there a shop or machinist here that you recommend to prep them the way you did? followup, looks like HVC Cycle in Nebraska is sort of one stop shop for all engine things RD.

and what do you know, ebay has them right now with a coupon you can apply for $30 off so they come in at $161 +tax. https://www.ebay.com/itm/284771396485




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That's the same seller I bought mine from and I thought I got a good deal $181.86 with tax. They arrived super quick from Texas to where I am in Ma. in like four days from ordering. I was impressed, really well packed in a thick styrofoam box inside a carboard box.

I'm definitely not an engine builder/expert as far as what to look for in quality of cylinders and pistons  but from what I could see everything was ready for assembly. Like you I read the topic/thread m in SC started about these cheap cylinders, up to that point I was hesitant to get em. I read all the horror stories. The only thing I did to prep mine was cleaning the protective oil film on the bores also I noticed some small metal chips, just a few left behind from machining processes. I did radius that center middle tab on the intake side of the piston skirt just because m in sc did it,seemed like a good idea...but I don't know if you need to. I left the ports as is regarding smoothing out rough surface castings because admittedly I am not an engine tuner.

Yeah I just bolted it all together this morning. Had the hang up with four of eight cylinder studs not wanting to come out easily so I left em as is being impatient as I am and trusting that there's enough threads to bolt it all down. Now I can attest I omitted using the washers on the cylinder head just to get a little extra tightening the nuts and they fastened down just fine. You do get an extra quarter inch of threads with the longer 350 studs. It's what's recommended and designed by Yamaha but you will have to spring for those longer studs $5 to $9 bucks a pop(shop around), there's 8 of em plus the $20 to
$30 stud removal tool.Still gotta put on the carbs so I haven't fired it up yet but I did cycle the kick start a few times and she turns over quite nicely in the sense that nothing sounds weird of binding up if that makes sense.  I do think there is a certain cheap quality to the pistons but I dunno. It just seemed like  the rings were tedious to keep well seated in the grooves and centering ring gaps in relation to the locating dowel pins of the piston,as I was holding each cylinder seating them to the pistons during assembly. I dunno maybe I just needed a third hand or there is some kinda engine builders secret? So in stating that I can see maybe why some folks splurged on different pistons.

Don't forget you also need the bigger 350 heads. Gotta find em used or maybe get some pricey aftermarket upgraded ones.

[RDryan]

If these cylinder kits get any cheaper.[/url

Not sure how legit this Ebay seller is but they also offer more savings if you buy in bulk.

[m in sc]

not all 'cheap' kits are made the same, just be aware. those pistons def look different that the ones i run in the 72.   

[RDryan]

not all 'cheap' kits are made the same, just be aware. those pistons def look different that the ones i run in the 72.   

You are not kidding! Well I am just getting online now. Fortunately or unfortunately I don't have to go to work till 1pm, late clamming tides so I have to time to mess with the bike. I just got the carbs installed this Morning and literally just fired up the bike for the first time. Doesn't sound good. A lot of rattling on idle speed and quiets down real quick with revs. I think it's coming from the left cylinder/fuel tap side. Just doesn't sound right. I know it sure as hell ain't my crank. Well I think it's those pistons/rings. I hope it didn't mess up the cylinders, ughh. 

[RDryan]

FWIW and I know it's hard to convey what's going on with my bike to all of you. Thank you for being helpful. Anyways I did liberally soak wrist pin bearings,pins and rings in two stroke oil and finger lubed the cylinders with the like. Primed the oil lines.I tried to be carefully seating the piston,rings as I guided the cylinders home but those rings just felt too loose like it was hard for em to stay put but I figures once everything was together nice and tight they would make a home. I just don't know, I'll have to take it back apart. Obviously.

[RDryan]

Ok I probably should wait till after I get the cylinders off to type this but I just took the heads off and still in shock/disgust with myself...this. I hate to say it but it feels like both the  connecting rods have play up and down. You can hear the rattling just kicking it over slowly and I can push on both pistons to feel the play,just gotta move em around on the right stroke. This sucks, well back to pulling it apart.

Maybe the piston skirts met the crank? Maybe some grit got in there in my haste to take it apart?,I don't see how that could mess up both connecting rod bearings.I dunno I was careful to keep it clean and make sure it was prior to reassembly. I will say the cylinder walls look Ok and the pistons don't seem to be binding up like the rings are ok. I don't know we'll see more later. Stay tuned.

[mlakritz]

so the heads on my 250 came off effortlessly, but the cylinders are a different story. any tips on how to free those up from the cases? i gently tapped at a few diff angles with a rubber mallet and also used gentle pressure with a wood pry bar between the cylinders but they are stuck pretty good.

attached pics of the 250 cylinders/heads/pistons, wonder if there is any info that can be gleaned from the condition of them? i still see cross hatching in the cylinders and the surfaces of everything look great. is there anything to look out for when purchasing used 350 heads, other than the obvious...not cracked, surfaces flat, generally clean?

i see some dry rot on the plug seals so i assume replacing all seals is the way to go. any suggestions for seal kits would be great, there are so many out there would like to get a set that people have had good luck with. related, is replacing all the seals a diy job or should i look to lean on somebody who's done it before? i am sure there is a thread here documenting changing seals but just curious how labor intensive it is.

and the cracked plastic trianglular thingy with the lead...that must be a neutral position sensor?

[RDryan]

Assuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders?

I never tried pulling those transmission plugs either side of the  off without splitting cases but I know it can be done. What's on the other side of them is the shafts that hold the gears,if they don't leak then I would leave em. You can get replacement plugs thru either Economy Cycles or HVC Cycles and they are easier to access if you split the cases but like I say if the don't leak just leave em. Yeah you are correct that white plastic triangle is the neutral sensor if the cracking is bad and bothers you then I imagine you may source one in better shape used on Ebay,Not sure if you can get that new? I would just call Economy Cycle or shoot em an Email and ask.

The seals to focus on are the crank seals and that shift shaft seal maybe nice to replace. Another maybe is thek seal where the crancase halves meet as well as the drive sprocket seal while it's apart.

Just my 2 cents.

 

[mlakritz]

Assuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders? 

i got the cylinders freed up this morn. i squirted a bit of penetrant into the stud recesses in the cylinder and 5 min later a gentle tap with the rubber mallet freed them both up. this motor ran tight when it last ran 35 years ago and turns over super smooth, so i have to think everything is in good shape inside but it will get a once over inside as well.

As far as the seals, none of them are leaking so it does fall into the aint broke don't fix it category i suppose but dry rot cracks on seals seem like a red flag that those are going to fail sooner rather than later. and as long as i'm doing all this work, doing the seals feels like the logical thing to do. the seal between the cases looks great and shows no signs of any leaks but if i want to have any idea of the condition of the lower end i'll have to get in there and have somebody who knows what they are doing take a look.

[RDryan]

Assuming your engine isn't seized...I see the kicker still attached,did you try moving the pistons? Ask me how I know things can be stubborn to move Maybe the cylinders are just stuck to the gaskets and you gotta try exerting a bit more effort to pull of the cylinders? 

i got the cylinders freed up this morn. i squirted a bit of penetrant into the stud recesses in the cylinder and 5 min later a gentle tap with the rubber mallet freed them both up. this motor ran tight when it last ran 35 years ago and turns over super smooth, so i have to think everything is in good shape inside but it will get a once over inside as well.

As far as the seals, none of them are leaking so it does fall into the aint broke don't fix it category i suppose but dry rot cracks on seals seem like a red flag that those are going to fail sooner rather than later. and as long as i'm doing all this work, doing the seals feels like the logical thing to do. the seal between the cases looks great and shows no signs of any leaks but if i want to have any idea of the condition of the lower end i'll have to get in there and have somebody who knows what they are doing take a look.

Oh good, yeah you can send out what you need done to Either Economy Cycles(a forum sponsor) or HVC Cycles. I actually just got off the phone with HVC regarding my problem and they were super helpful. Again FWIW those two black plugs either side of the neutral switch are basically metal covered in rubber.

BTW here's a link to the neutral switch, HVC has the replacement part. https://hvccycle.net/neutral-switch-1l9-82540-00-00/?searchid=459451

They also offer a full suite of machine shop/engine build services, I know you mentioned that. I'm sure they don't mind if you wanna take the process as far as you feel comfortable and do a handoff so to speak in regards to rebuilding the bottom end.Or just take your time with it. I make mistakes and folks here on the forum have been helpful with me but I understand there is certain aspects of engine building that I won't venture into alone. So with these RD engines the cases do split really easy and the crank seals are pretty easy to replace. You really don't have to touch the transmission at all to do that just don't go much further with disassembly if that makes sense. You gotta take off the magneto,stator,generator and everything on the clutch side. and the cases are pretty much ready to split. I kinda forget a few special pullers and tools but they are available Thru either HVC or Economy. I will add that when I did take off all the necessary parts to split my cases the bottom end was still in the bike but that's not a requirement, I just didn't know any better way. 

As an aside everything worked ok with my chinese cylinder kit but my problem is that six years ago I replaced the original 250 crank with a Vito's crank. Unbeknownst to me the Vito's has a beefier connecting rod and used a bigger set of wrist pin bearings. Hence the slapping I heard. So the OEM RD350 wrist pin bearing will not work in my case(O.D too small for the connecting rod end), I should have been more observant of this yesterday when I put it together.

I will also say that those Chinese cylinder were messed around with by HVC Cycles and I was told that they do have differences but there is a slight maybe they have gotten better quality wise. Something about softer metals used to make em. Slight variations in dimensions, just better to find the Yamaha ones even though they are rare and most of the time they will need to be bored out. I'm gonna order the bigger wrist pin bearings thru them as I am too far into the build to give up but even I am wondering if it's worth it. It's a chance to take.

[m in sc]

yeah the vutos cranks use bigger diameter caged bearings but they don't contact pistons, or cases, period. I can't speak to 6-7 year old Chinese cyls but the ones I have run, that have been our for a few years are absolutely fine. I'm almost on year 3 on my set and I beat the r5 pretty good. Matt has a set in his 73, and my buddy travis had a set on his, I still have them and they wear just fine but they need to be prepped correctly, chamfer the ports, etc.

[RDryan]

yeah the vutos cranks use bigger diameter caged bearings but they don't contact pistons, or cases, period. I can't speak to 6-7 year old Chinese cyls but the ones I have run, that have been our for a few years are absolutely fine. I'm almost on year 3 on my set and I beat the r5 pretty good. Matt has a set in his 73, and my buddy travis had a set on his, I still have them and they wear just fine but they need to be prepped correctly, chamfer the ports, etc.

OK, I feel so stupid about this.I had the bike running on three or four tries for maybe thirty seconds total. Upon tearing it down I really can't see any noticeable damage or wear. Despite listening to the awful sounds of those pistons slapping.

I just ordered a set of two of them, was going to get em thru HVC but I found em on Ebay direct from Vito's at a much cheaper price between a 15% discount free shipping and buying as a set rather than individual. Sorry HVC if you're out there reading this, you are super helpful but I am just short on cash and tall on mistakes.

Can you expand on the chamfering of the ports? Is it just a bigger edge break than how they come as is?

[mlakritz]

i got the cylinders freed up this morn...

anything of note to comment on with the cylinders freshly removed?

[m in sc]

the poet windows need to be radiused on cul a bit, no sharp edges.  as far as that bottom end, aside from the muck and rust nothing stands out, just check the rod up and down play and side to side.