Just joined Forum. Have QT50

Been lurking awhile, posted a bit on Moped Riders Assoc. a while back (2012) Not much activity there.

So...I'm 57, retired, and have a 1981 Yamaha QT 50 since brand new still in GREAT shape. In 2012 I gave it an all Yamaha 60cc top end (no longer available from Yamaha) PW50 gears, orange clutch springs, and IRC 77 tires. Still on stock carb and rear bored out muffler.

I can do 35 mph I think, can't top speed test where I live, my road has big potholes and on a ridge top so I don't like going steep downhill to get to flatter areas. Also bike is not correctly titled. My Dad signed it over to me without a notary before he died and I still have to try to get through the red tape to make it mine.

I've read about doing compression tests on these engines that regular long hose testers give low readings. True?? I'm getting 90 PSI on mine.

So how are the 60CC Niche kits REALLY? I have a YT60 head I'm using for cooling. I'd just use the cylinder, piston, rings, etc.

I also have had a line of motorcycles through the years, currently a 2015 Yamaha FJ-09.

I wish this forum had sections by bike type. Also when you post, always put bike type in it. Shows up in searches that way.

I hope to help here, have wrenched on my own bikes for years and also was an automotive tech. way back.

Re: Just joined Forum. Have QT50

Welcome!

If you are looking for repair help you can post in repair or if you want help getting it faster you can post in performance.

I installed a 35$ niche top end on my son's pw50 last year, it was ok but needed a lot of work to clean it up. The ports needed chamfered and I cleaned up the porting, ring gapped, the piston had razor sharp edges I cleaned up. The gaskets that come with it are trash and I had to cut new ones. I ran double oil (50:1premix plus injector) for break in and it's Got about 2-3 tanks of fuel though it, runs great.

I think if I hadn't done that prep it wouldn't have ran for more than a few minutes.

Re: Just joined Forum. Have QT50

Cross hatch ok in cylinder? Had to chamfer ports in Yamaha cylinder anyway.

I'm laying in a supply of Yamaha 60cc head gaskets since they may go AWOL soon. Base gaskets same for 50 and 60cc. Should be available from Yamaha forever.

Re: Just joined Forum. Have QT50

I bought a used 84 that already had that kit on it. The yamahopper had been knocked over onto its left side at some point in its past. When that happened it broke off the brass oil injection nipple going into the side of carb. Someone half ass rigged it and it was not staying put. I drilled out the broken stub still in the carb and managed to get what's left of nipple to press tightly back into carb. After that I surmised it would be smart to have a look at the cylinder. The kit has been soft seized (with lots of scoring) and still runs good. Hits 30-32 consistently with all else completely stock. Truth be known the broken injection nipple was probably the reason the kit was installed to begin with. Anyway I purchased a second identical kit and have yet to put it on. The kits are hit or miss. Some research found that there are porosity issues within the bore of some castings. All in all worth the money if you get a good one. Like Graham said, they are not bolt on and need cleaned up. (edited)

Re: Just joined Forum. Have QT50

The Malossi kit is more expensive but is much higher quality, IMO. I've seen those Niche kits lose big flakes of nikasil and trash themselves.

Re: Just joined Forum. Have QT50

They're nikasil coated?? Really?

I thought only Suzuki did that.

Re: Just joined Forum. Have QT50

I think he's referring to the porosity issue I described above. Its a cast iron cylinder and nikasil is typically applied to a cylinder liner thats used in aluminum cylinders. Besides, the cost of true nikasil would be cost prohibitive at that price point. (edited)

Re: Just joined Forum. Have QT50

Oh yeah, my mistake, I was thinking of a different cheapo cylinder.

Re: Just joined Forum. Have QT50

Looks like when the time comes I'll try a Niche kit. Currently $60.

2 strokes just don't live long enough to justify $200 or more top ends.

Re: Just joined Forum. Have QT50

It's your money, do what you want, but many folks here have thousands or even tens of thousands of miles on their $200+ top ends.

Re: Just joined Forum. Have QT50

> Brian F wrote:

> -------------------------------------------------------

> It's your money, do what you want, but many folks here have thousands or

> even tens of thousands of miles on their $200+ top ends.

I agree.^^ Better quality can get you the option of replacement rings and over sized pistons when the time comes while reusing most of the parts from the initial kit. Try getting a set of replacement rings or oversized pistons and rings for overboring a worn out cylinder from niche. Try getting any one single part out of that kit for that matter. When something breaks, you just buy another $60 kit. Theres no right or wrong way to do this because everyone has different priorities. Some build to ride and keep forever and others are more casual and maybe have a budget. For what you get, its worth $60. I paid less 3 years ago. (edited)

Re: Just joined Forum. Have QT50

If you have a genuine Yamaha 60cc top end, keep it. New set of rings or at worst bore it and put a new piston as well. The Yamaha pieces are much better quality.

Re: Just joined Forum. Have QT50

Come take the trip to the Burgh sometime

Re: Just joined Forum. Have QT50

Go on one of the Yamaha parts sites the 60cc stuff is drying up. Cylinders, pistons, rings...Gone.

50cc all there of course. PW50 still made in 21, have to see if it comes back for 22.

10k miles out of a 60cc 2 stroke? That would be great!

Any input on compression tests?

Re: Just joined Forum. Have QT50

Uhhh yeah it's a dumb shitty hunk of cast iron. The piston and the fit and finish is slightly better on the OEM Yamaha but not much for like 6x the price. People just have a natural desire to feel like they need to buy the more expensive thing. The Yammy is better but once it's cleaned up, installed, and ripping nobody will ever be able to tell the difference.

They should both get about the same usage. Most cast iron kits last 4-6000 miles if you have them tuned and take care of them. Even OEM service interval is about the same.

I would definitely try to figure out what's going on with the current cylinder since it doesn't sound like you've put a lot of miles on it. You can mess with putting oil in the cylinder or doing a real leak down test but it's usually way faster and easier to just pull it off. The rings could be stuck from carbon (oil injected bikes tend to run too much oil) or maybe it never got a good break in, or wasn't tuned right or soft seized.

If the bore is clean and you can find a stock oem or even knockoff piston that's probably the way to go, but if it needs bored I would just get the niche one and call it a day, maybe sell the old OEM cylinder to one of these guys that think they are magic blessed by the tuning fork fairy.

Re: Just joined Forum. Have QT50

Jack Rutherford /

35 is right in the ballpark if you are running stock exhaust and carb. More compression won’t help your top speed.

Re: Just joined Forum. Have QT50

Thanks for all the replies!

So compression gets me acceleration not top speed?

Re: Just joined Forum. Have QT50

Jack Rutherford /

It will help your low end acceleration and won't do much for top speed, if anything.

As I suspected, there's a little something in the moped wiki on Compression

and a recent thread on compression as well (edited)

Re: Just joined Forum. Have QT50

So I sanded my yt60 head down about 2 mm and got my compression test from under 90 to 110 psi.

low speed pickup did improve.

I think tomorrow I'll drop down into the valley and re-check top speed if the weather holds out.

BTW: On the speedometer when it passes 30 mph just use geometry. Look at the the other end of the needle. When its a straight line pointing at 10 mph your doing 40 mph. Straight down is 45 mph with the other end pointing at 15 mph.

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Re: Just joined Forum. Have QT50

Well took it out my main road, immediately hard downhill then right back uphill. I was reminded why this thing just doesn't work here in PA. On the uphill it just keeps slowing down to nothing. Luckily that was at the crest of the hill. Then back down to a left turn where it's mostly flat for a bit.

There it goes 35 mph on the level.

I'm sanding the head down further.

This thing would be great in the midwest where it's nothing but flat. Ohio, Indiana, Iowa, Wisconsin, etc.

When I got home I jumped on my other Yamaha, the one with about 800 more cc's and loved that all I had to do was move the throttle 2mm to charge up the same hills.

There's no replacement for displacement.

Now about to rain and then cold again. May have been the last day riding till Spring. YUCK! 🥶☹

Re: Just joined Forum. Have QT50

Instead of guessing your speed download a gps application to your smart phone. I start the app and then have it running in background, screen off while my phone is in my pocket before I take a blast.

Re: Just joined Forum. Have QT50

I've already done the GPS app. My speedo is perfect to it. 35 on the app. and my speedo pointing past 30 with the rear of the needle pointing at 5 mph.

Re: Just joined Forum. Have QT50

Replace the rings. Should come up a hill with no problem. I live in NC and I have to go up a hill either way I go to get to my house. My QT has a Yamaha YT60 top end and it has no problem going up hills, not talking about gentle grades either. Not the easiest to keep cool though.

Re: Just joined Forum. Have QT50

What rings should I use? No 60cc rings available from Yamaha anymore.☹

Re: Just joined Forum. Have QT50

I bet you could get a set from weisco.

Re: Just joined Forum. Have QT50

Nope, no Wiseco.

Re: Just joined Forum. Have QT50

They do make custom rings which means you're gonna have to reach out to them for what you need. Its not gonna be listed on thier website. It means you will have to take measurements and know what type of material the rings are made of.

Re: Just joined Forum. Have QT50

JE, Hastings, total seal, precision rings...someone has or can make any size under the sun. Chop chop.

Re: Just joined Forum. Have QT50

I've had good dealings and service from Hastings Piston Rings when I needed rings that were NLA for my Simplex . Email them with measurements . They are pretty easy to deal with .

https://www.hastingspistonrings.com

I've directed others to them and all have had excellent experiences .

Re: Just joined Forum. Have QT50

You can buy one of those cheap Chinese piston kits and use the rings from it. I’ve done that before. Or you could get them from Treats. I think the ones available now are the Chinese rings, not sure though.

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