$79 Ebay 350 cylinders spec check

[1976RD400C]

Ran the micrometer on the new cylinders and pistons.
Cylinders were within .0005" of taper and each other. Pistons were exactly the same size. Ring end gap was .009" and 3 of them and .000 on 1 of them. Piston clearance is about .003". Not really any port chamfering done. This is very odd, look at how the small transfer port is lower than the larger one. It's so low it is not open all the way when piston is at BDC. The larger tranfer is at the right stock height but the little ones are too low. The exhaust port seems a bit small, and the top is 31.5mm down, stock is 29.5mm. The wall thickness of the sleeve that sticks out the bottom is 2.75mm, an oem cylinder is 4.50mm. I think you would have trouble if you installed these without checking and adjusting a few things.

[m in sc]

i think these are based on the radjoot low torque cyls 

[2t Fan]

Chinese cylinder exhaust port height between Indian HT and US Spec at 31.5mm 

Stock US exhaust port height 29.5mm (39bhp)
Indian HT exhaust port height 32.00mm (30.5bhp)
Indian LT exhaust port height 36.00mm  (27bhp)

[SoCal250]

I still have to get detailed measurements of mine, but the listing I bought them from specified:
"Us/Uk Specification" and "The Exhaust Port Is 38mm Wide And 29.5mm From The Cylinder Top."   I'll have to see if that is true.

[m in sc]

I was referring to the transfer ports. not saying they were identical but that low of a transfer port.. either way still, def different than the sets I got

[1976RD400C]

The exhaust port width looks ok. I'm just going to raise it 1-2mm, raise the little transfers to the right height, clean up and chamfer. The intake looks good. You couldn't oversize bore these to 2mm because the sleeve is so thin on the bottom.

[RDryan]

This is a very interesting topic as I bought two of these kits. https://www.ebay.com/itm/284771396485

I paid way more than $79 per kit,not sure if I got a more genuine replica of the Yamaha OEM cylinders. This kit just seemed right and I thought the quality and value good enough to stock up on a second kit. However I really have nothing to compare it with as my bike is a 250 model.

I will say the kit currently on the bike is very forgiving. I did a lousy job of chamfering the ports with a Dremel tool then I didn't account for the uniquely sized wrist pin bearings for a Vito's crank that's been in my bike for years now. Anyways it all came back apart and put back together with new bearings. A few tweaks here and there with the jetting and rebuilding the clutch and the bike runs strong.

Now I have to say I like it a lot and although it is a step up in power over the 250 it doesn't feel that much faster and that could just be that I still have 100% 250 gearing. However I was hoping for some power wheelie torque and I dunno maybe it's just the way I ride but I can't seem to lift the front wheel off the ground. I also don't really try too hard to that just spirited riding, I know it sounds silly but I've seen enough videos of others with basically stock 350 that do seem to wanna loft the front wheel in say 1st or 2nd gear. Again I dunno but I just wonder if the powerband is more Rajdoot than say genuine Yamaha RD...it could be just that. Like I said I just went by visuals opening the box of new parts and feel. Everything just seemed new and a good fit. For the most part I feel lucky that she hasn't blown up. I guess it would be interesting to do a more detailed comparison of specs as I feel like there could be more power to be had despite my bike being pretty much a stock tuned engine but I'm not an expert. I look up to all of you for that.

My bike does pull pretty good right up to 7k seems to take a bit longer to rev up to 7.5k from say 6.5k but she does up all way to 7.5k and maybe beyond but usually at that point I get nervous to leave her pinned for long(doesn't feel like she would actually wanna rev another grand anyways) and I am in 6th gear doing about 85mph. All according to the stock gauges. She doesn't smoke (I guess that's nice?),truly barely any smoke but she does burn oil fine with the original oil pump. Jetted with 150 mains, needle in the fourth POS. #30 pilots 3/4 turn out on the air screws. Of course stock carbs K&N air filter in the stock airbox and Vape ignition stock exhaust. So pretty much a stock bike. Like I said I know there are some things to do to tune better like change out the exhaust baffles and may go richer on the main to say 160 jets but I dunno if that produce just that little extra juice to the front wheel up, again I know it sounds silly just say'in. I think it could be anything but my bike does run pretty good and knock on wood I imagine it may even be worthy of a long all day in the saddle adventure and I think that maybe as good as it gets for me for now. 

[m in sc]

might just be some minor tweaking in tuning needed ryan.  that being said,most times w stock 250 primary gearing, you can go up one tooth on the front sprocket and might be better

[RDryan]

Yeah that's what I'm thinking too. I do have a practically new rear sprocket that's one tooth smaller but I know that would be more of a hassle to change and not as much of an effect as going up a tooth in the front.

[RDnuTZ]

you need to get performance pipes if you want the extra power you think you are lacking. You could also get TDR or other reeds that could help power delivery. Going smaller on the rear is the opposite direction of what you are trying to achieve power delivery wise 

[RDnuTZ]

BTW: your eBay link goes to the seller who sells the Kvedwulf supplied kits. I also bought 2 of these a couple years ago and paid about what you paid. The quality seems much better on these than others we've seen pictures of. Check out bottom side of cyl pictures and look at the sleeve match to cyl with no gap for example. I believe the sleeve looks thicker than others I have seen too. YMMV

[m in sc]

did you get the 350 baffles in the pipes or still rocking 250 baffles?

[38special]

BTW: your eBay link goes to the seller who sells the Kvedwulf supplied kits. I also bought 2 of these a couple years ago and paid about what you paid. The quality seems much better on these than others we've seen pictures of. Check out bottom side of cyl pictures and look at the sleeve match to cyl with no gap for example. I believe the sleeve looks thicker than others I have seen too. YMMV

Yes, the Kveldwulf, currently on ebay for $147 for the cylinders only, claim to be "Original US/UK specification" in the listing.

I bought 2 sets and the bores were all dead nuts, but the ports needed more chamfering.  I do not have a pair of true OEM's to compare the port specs to unfortunately.

[1976RD400C]

Being that the lower part of the sleeve on this $79 set is much thinner than oem there isn't much support in this area and if you bore it, it will get worse.

[RDnuTZ]

I don't think anyone is disagreeing with you that your set looks less than top tier reproductions. There absolutely are multiple versions from apparently different Chinese factories and not all of them look like yours. I compared mine side by side with OEM barrels when I got them and there are no visual differences between Keveldwulf and OEM. There are many positive reviews on them over time. Not all are created equal and the old saying about you get what you pay for seems fitting here.