1984 Yamaha QT50 - smokes a lot and loses power on ride

I have a qt50 that idles fine but under load smokes like crazy and will lose power, after a few seconds will be good to ride a short distance then do same. I’m leaning towards right crank seal at this point but wanted to see if anyone here might have fixed something similar.

Compression = 90psi

Also, it looks like prior owner may have broke an exhaust bolt off in the cylinder so instead of fixing it the right way they jb welded the damn exhaust to the cylinder. Which means to even get to the crank seal I have to fix this first. So to get the muffler off the entire cylinder needs to come off. Since I have to do all this now anyway, are there any good replacement cylinders and piston kits? May just replace that stuff while its off.

Thanks

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Seems like 90psi may be a little low as far as compression, but I'd need to look that up. I was initially thinking the rings could be worn or perhaps your carb could need adjusting (or your oil mix is wrong), but without knowing your setup, that's a little hard to tell.

For the cylinder, there a TON of chinese QT/PW50 knock off cylinders all over the place on the internet. Cheap. Some are 50cc, others are 70cc "big bore" kits. Quality seems to vary and the castings appear to be rough, but I've heard of a few people with pretty good results running them. Jimmy C...are you out there?

With a 70cc kit, you'd probably have to take a closer look at your carb.. upjet for sure if not replace with something slightly larger.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> E BinOH Wrote:

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

> Seems like 90psi may be a little low as far as compression, but I'd need

> to look that up. I was initially thinking the rings could be worn or

> perhaps your carb could need adjusting (or your oil mix is wrong), but

> without knowing your setup, that's a little hard to tell.

>

> For the cylinder, there a TON of chinese QT/PW50 knock off cylinders all

> over the place on the internet. Cheap. Some are 50cc, others are 70cc

> "big bore" kits. Quality seems to vary and the castings appear to be

> rough, but I've heard of a few people with pretty good results running

> them. Jimmy C...are you out there?

>

> With a 70cc kit, you'd probably have to take a closer look at your

> carb.. upjet for sure if not replace with something slightly larger.

Originally thought same that 90psi seemed low but manual says 6:1 which is roughly 88.17 as acceptable spec for compression.

I’ll be checking the oil pump to make sure its not sticking when throttle is off and sending more oil into the carb.

Everything is stock on the bike and prefer to keep it as close to stock as possible knowing cylinders are most likely going to need to be aftermarket.

I’ll have to take the cylinder off to fix the jb weld on the exhaust port and what I suspect is probably a broken exhaust bolt so I’ll check for pitting when its off. Would also be a good time to just swap it out entirely. Amazon has a kit made by Niche but not sure if its any good.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

The Chinese bolt on top ends are all 60cc kits. Malossi makes a 70cc kit for more money. I’ve been running a niche 60cc kit for a few years, soft seized it once, been riding it since and it’s been good to me.

If you’re mechanically inclined with the proper tools, repair the broken exhaust stud. If you’re not up to it or lack tools, just go buy a top end, 50cc or 60cc. You can buy oem Yamaha top end parts if you want to stay true Yamaha, you’ll pay for it though.

I would suggest replacing crank seals either way, although your symptoms sounds suspect of a crank seal.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> S C Wrote:

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

> Amazon has a kit made by Niche but not sure if its any good.

I find Niche products to be of good quality .

I've used their bearings and such with excellent results .

I bought a piston kit for my FA50 . Very nice product .

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> Sparkles 76 Wrote:

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

> The Chinese bolt on top ends are all 60cc kits. Malossi makes a 70cc

> kit for more money. I’ve been running a niche 60cc kit for a few years,

> soft seized it once, been riding it since and it’s been good to me.

>

> If you’re mechanically inclined with the proper tools, repair the broken

> exhaust stud. If you’re not up to it or lack tools, just go buy a top

> end, 50cc or 60cc. You can buy oem Yamaha top end parts if you want to

> stay true Yamaha, you’ll pay for it though.

>

> I would suggest replacing crank seals either way, although your symptoms

> sounds suspect of a crank seal.

So what I’ll try doing is superheating the jbweld and scraping it off with a wire brush then drill and extract that bolt to get it back to normal. I can retap the threads if needed.

Do you know what size bolts go in there? Also where I can pick up an exhaust gasket.

I did find some crank seals and bearing from all balls on amazon. I’ve used their carb rebuild kits for other things and it was good quality. The only part of getting those changed out that concerns me is not having a flywheel puller or something to keep it from moving on me.

If all that fails then niche top end kit will be ordered.

I checked the oil pump and its not sticking so I added some lithium grease to the outer moving parts and covered it back up.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

One of our members bought a $40 Amazon 60cc kit for his FA50, and it didn't even last 20 miles before a huge chunk of the nikasil plating broke off and trashed it.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> P D Wrote:

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

> > S C Wrote:

>

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

>

> > Amazon has a kit made by Niche but not sure if its any good.

>

> I find Niche products to be of good quality .

>

> I've used their bearings and such with excellent results .

>

> I bought a piston kit for my FA50 . Very nice product .

Good to know! They have the 50cc kit on amazon that has everything except the exhaust gasket. If needed I’ll go that route. Hopefully I can get the original one back in shape.

Have you replaced the crank seals on the qt before?

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Whoops, yeah I meant 60cc on the chinese kits.

Just did the crank seals. Pretty easy and there are some youtube vids out there on how to do it. It wasn't any fun taking the ignition side apart (make sure you have an impact screw driver), but overall not too bad. I think on that side you can put a screw into the seal and then use a pliers and yank it out.

I'd really like to find the real Yamaha YT60 top end (60cc) but seems like those are pretty hard to find in reasonable condition these days.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Original equipment bearings and seals are available at your local Yamaha dealer .

Or :

https://www.partspitstop.com/oemparts/a/yam/5004263af8700209bc7884e5/crankshaft-piston

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Here is the exhaust to cylinder situation… looks to me like jb weld. That being said, i doubt I can take the cylinder off with exhaust attached due to the muffler hitting the crank case on right side. Can I hit that with a propane flame long enough to scrape off the jb weld or will it ignite oil/gas?

453D8B5C-050F-4121-883E-6DF67610EC10.png

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Get a flywheel puller. It makes getting the flywheel off so much easier. The screws holding the magneto on can be difficult. Lay the engine on it’s side and use good quality #3 Phillips screwdriver. A couple of good hits with a hammer and the screws should come right out. Run a sheet metal screw into the seal and with pliers, pull it out. Put some grease on the inside lip of the new seal and gently tap it in with your hammer.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

I think I would try grinding away the excess and see if it won’t pop off. Maybe a few light taps with a hammer.

A possibility with the excess smoking is oil being pulled in from the transmission past the crank seal.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

I'd try a sharpened cold chisel between the exhaust flange and whatever that crap is .

Might just pop right off .

Good luck .

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Buy the flywheel puller. I believe there are cheap options on Amazon that work just fine.

If that’s JB weld, just hit it with a chisel. JB weld is strong but like a rock, it’s brittle. If it’s welded on you’ll need to grind, cut, etc to remove it.

Find all the parts you need and then some at treatland.tv

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Well damn its welded together, looks like Im gonna have to get the angle grinder to it… and you can see the broken off bolt as well.

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Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

campeona del mundo /

woof, looks like someone actually welded it to the cyl. i would just pick up a new pipe if you have the cash to spare. if not, im sure you could get a used stock pipe on b/s for like 20 bucks

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

punkrock randy /

¡¡Holy desperation!! What a way to fix an exhaust leak/broken or stripped shit🤦🏼‍♂️ I hate cleaning up previous owners hack work. (edited)

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> campeona del mundo Wrote:

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

> woof, looks like someone actually welded it to the cyl. i would just

> pick up a new pipe if you have the cash to spare. if not, im sure you

> could get a used stock pipe on b/s for like 20 bucks

Yeah its nasty. Started grinding it but looks like a storm is headed this way. Will pick it back up again Sunday.

Ive got a grinding and cutting wheel for the angle grinder and also cutting disks for the dremel once all the major stuff is gone I might cut a line with the dremel and see if it will break loose. Hopefully the weld isn’t between the exhaust and cylinder. If they just did around the front edge that should come off.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> punkrock randy Wrote:

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

> ¡¡Holy desperation!! What a way to fix an exhaust leak/broken or

> stripped shit🤦🏼‍♂️ I hate cleaning up previous owners hack work.

Haha exactly. What a damn mess. Just don’t want to mess up the exhaust flange since it seems like stock ones are kinda hard to come by new.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Used a grinder with grinding wheel to beat back the weld then dremel with cut off wheel to cut a groove/channel above the exhaust. Kept working on the groove and it popped off. May have to double up on an exhaust gasket when I put it back on but otherwise should work.

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Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

A belt sander will even the mating surface nicely .

S would a flat file , with a bit more work . ;)

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> P D Wrote:

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

> A belt sander will even the mating surface nicely .

>

> S would a flat file , with a bit more work . ;)

Heres a close up of the top after cutting it off. Looks like maybe a gasket was there too? I’ll have to see about getting a new gasket for it. Otherwise its got enough meat left to make it work.

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Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

What a nightmare. If I were you I'd throw that cylinder and exhaust in the trash.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> Brian F Wrote:

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

> What a nightmare. If I were you I'd throw that cylinder and exhaust in

> the trash.

Yeah its a damn mess. The cylinder actually doesn’t look all that bad inside but I ordered a new one with new piston and ring set anyway. Along with new exhaust gasket and bolts.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> S C Wrote:

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

> Heres a close up of the top after cutting it off. Looks like maybe a

> gasket was there too? I’ll have to see about getting a new gasket for

> it. Otherwise its got enough meat left to make it work.

Good you have a new gasket coming . The raised section sticking above the flange is the old gasket . You should be able to dig it out and replace it .

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> P D Wrote:

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

> > S C Wrote:

>

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

>

> > Heres a close up of the top after cutting it off. Looks like maybe a

>

> > gasket was there too? I’ll have to see about getting a new gasket for

>

> > it. Otherwise its got enough meat left to make it work.

>

> Good you have a new gasket coming . The raised section sticking above

> the flange is the old gasket . You should be able to dig it out and

> replace it .

Yeah thats the plan for now. Do those old gaskets have metal rings around them? Seems like some sharp thin metal on the edges.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> S C Wrote:

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

> Yeah thats the plan for now. Do those old gaskets have metal rings

> around them? Seems like some sharp thin metal on the edges.

If you look , you'll see that the metal rings are one piece .

It's a 'scroll' type gasket with some kind of material between each 'layer' of metal .

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

> S C Wrote:

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

> > Brian F Wrote:

>

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

>

> > What a nightmare. If I were you I'd throw that cylinder and exhaust

> in

>

> > the trash.

>

> Yeah its a damn mess. The cylinder actually doesn’t look all that bad

> inside but I ordered a new one with new piston and ring set anyway.

> Along with new exhaust gasket and bolts.

Good call. Getting a good seal on that mess of an exhaust interface would be way more trouble than it's worth. That's probably why they welded it on in the first place.

Re: 1984 Yamaha QT50 - smokes a lot and loses power on ride

Ha . They welded it because they were frickin idiots . ;)

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