Beginner RD250 project questions

[mlakritz]

just checked mine. yup there's a difference. also can say, there's never been an issue on my bike so me, i wouldnt sweat it. 0.02

not sure if this is 100% accurate, but some research revealed that the thinner sleeve design was changed maybe starting in the early 80's in the Japan and Euro markets and that's what the current aftermarket cylinders are based off. not sure if it really matters, if it doesn't blow up or disintegrate then it's all good, right? I did order some amazon ones just to compare so we'll see what those look like and go from there.

[m in sc]

mines been pretty abused and they are holding up fine for 2+ years, it gets shifted at 9- 10k a lot, the rev limiter is set to 10.5 on the cdi. it's an interesting point though.  my guess would be more it was based off the Indian radjoot garbage cylinders.  the real early ones had that porting and it was just dismal, so they def adjusted the sleeve layout to match the us spec ones. either way, good observation I didn't bother to make.

[RDryan]

I just got those repo cylinders in my 75' RD250B and it runs good. Ran it approximately three separate occasions and rode about 15 miles between the 2nd and 3rd running in attempts. The first attempt was just running on the center stand for 10 minutes then I let it set and cool down for an hour. Not quite sure if I did that right with the"heat cycles" but it made sense.

Bike is good pretty much all stock except for the Vito's crank, Vape ignition and some Boysen reeds in the stock reed block.

Gotta get the jetting right but it fires right up and runs good.Too bad I had the wrong wrist pin bearings, my goof on that and also just a bit clumsy chamfering the ports. However I took advantage of the discount and ordered a second set of em just in case there's some demons going on with this install. Never hurts to have extra parts,albeit very cheap parts.

[mlakritz]

All great info, super helpful. Next question, anybody have any tricks for removing gaskets that have basically fused with the case? Pretty sure this is the factory clutch cover gasket on here, and I swear in some places it is hard to tell where the metal of the case ends and the gasket starts. How do i get that off of there without damaging the mating surfaces? Penetrant? Solvents? Razor blade? Once off, what is the best way to clean any residue off the case so it is ready for a fresh gasket? And then also just want to confirm that this tiny washer (see pics) that fell out when i pulled the clutch cover is from the kickstarter shaft? Eh, never mind, just found it on a schematic, confirmed it is the washer plate that slides on the kickstarter (the pic file name says shift shaft but it is the kickstarter shaft).

[m in sc]

1st off, correct on the washer. that gets frequently lost. as far as removing the gasket material.. heat helps, scraping, cursing, etc IF you have air tools a die grinder or angle grinder w a green wheel with rubber fingers makes quick work of it. but, it also makes a mess. (rolock bristle pad)

[mlakritz]

1st off, correct on the washer. that gets frequently lost. as far as removing the gasket material.. heat helps, scraping, cursing, etc IF you have air tools a die grinder or angle grinder w a green wheel with rubber fingers makes quick work of it. but, it also makes a mess. (rolock bristle pad)

softened the gasket with some adhesive remover and let it sit for an hour and came off pretty cleanly with a razor blade at a super shallow angle so as not to ding up the case. more adhesive remover took the rest of the residue off.

[mlakritz]

Anybody want to chime in on the pros/cons of decking 350 cylinders so you can use a 400 gasket? Some very reputable people (some on this forum) have suggested this as a way to go, and with no disrespect to them, just want to gather more info so I can decide if this is a mod I want to do and if the benefits are worth it and if there are any significant cons. I'm still going for reliability over pure power so curious what people think.

[m in sc]

I have a set like that but tbh, I wouldn't go out of my way to do it

[mlakritz]

Ok, cases successfully split...so now what? It's unexpectedly clean inside and am unsure of what to do next or how to clean everything properly. Got a Vito's crank to install, and once the case is cleaned and ready to reassemble, I'd love to hear any insider tips and tricks to avoid any pitfalls or to make the assembly go smoothly. I've read on the forum about gaskets and seals and additional sealants or waxes to prevent leaks and stuff like that but would love any tips from the experienced so I have a successful reassembly. I have a tube of gray Yamahbond liquid gasket that I plan on using on the case mating surfaces, seems like that (or something very similar) was used at the factory, pretty sure this case had never been split before.

[Jung]

Anybody want to chime in on the pros/cons of decking 350 cylinders so you can use a 400 gasket? Some very reputable people (some on this forum) have suggested this as a way to go, and with no disrespect to them, just want to gather more info so I can decide if this is a mod I want to do and if the benefits are worth it and if there are any significant cons. I'm still going for reliability over pure power so curious what people think.

I've done this on a couple - it's a 5 minute job with a fly cutter on the mill. I like it as you can do it in conjunction with setting the squish. Worth noting that if you want to set the squish tighter than about 0.9mm, you want to pin the heads to the barrels so it stays consistent. I've done this with two bits of drill rod through both heads into the cooling fins on the barrels which is not the most accurate way but works very well. You take them out once you torque the heads on.

I'd buy 250 heads as they are way cheaper and pay someone to recut them - it's not a hard job and you get all the benefit of a real performance head for a fraction of the price. I've done them at 50/45/40% squish area and various CCs. I think 21cc would work on a stock(ish) bike, but I had to go larger on a ported engine and good pipes as it was detonating. Think I ended up at 23cc. Squish somewhere between 0.7mm and 0.9mm has always worked well. Stock is insanely large, like 2mm, so there's loads of room for improvement.

I've had a set of Kveldwulf cylinders up and running for a bit - they work great once cleaned up. Mine came honed quite large for some of the cast pistons but worked perfectly out the box for pro-x. Definitely measure first. I've never run the stock pistons they ship with.

If the main bearings feel silky smooth and are still covered in oil, I'd just change the oil seals (crankshaft and gearbox output shaft) and bung it back together with the yamabond. Give all the dogs in the gearbox a quick once over too.  You could measure the run out on the crank if you feel like. I have had good luck with the new Taiwanese aircooled cranks you can find on ebay - the last one I bought was about 400bucks and insanely true. That said, it's still in the box as the current 250 crank that's in the engine keeps humming along smoothly.

[mlakritz]

Thanks for that info Jung, super helpful. I'm working through pros/cons of different options and think i've got a good plan moving forward. I got a set of performance 350 heads that won't require me to deck the cylinders and have squish and CC's right where they need to be for this project (mild street/midrange porting, CDI ignition, expansion chambers) according to a few tuners i've spoken with. I have a tube of YAMABOND 5, the drying liquid gasket as well as the Hondabond HT silicone liquid semi-dry gasket. I assume the semi-dry that stays more flexible is the better option for the cases? As far as the crank, the OEM one was out of tolerance on lateral play on the large bearing end so I got a Vito's to replace it.