82Yz80J,also 83,84,85,86 Yz80's

[T-Dub13]

I bet you could fit a KX60 piston into it. If you're a collector, it's a great deal. You could make that back by parting it if you can't get it running.

[PlanetMinis.com]

[thekidd77]

I just bought a 84 yz80 for $50, it is missing all kinds of parts

got some stuff you will sell me Hobbeekid? I need everything on the bars, and a carb. I also think I need some wheel spacers and chain tighteners but wont know which spacers are missing until I get it apart.

[T-Dub13]

I think you can get most of those parts from Yamaha still. Check with your local dealer or online dealer before paying a high price on fleabay for a part everyone thinks is obsolete. I've made that mistake!

[thekidd77]

I took apart the 84 yz80 and even though it looks like it was a new top end the piston has been hitting the head, the Bottom end bearing in the crank has up and down play in it, it needs over 300 in parts plus the bottom end and head so not worth the hassle, thinking about putting my 82 motor in the 84 which will solve my rad problem, does anyone know if the wheels are interchangeable? They are definitely different rims but I have the new bearings in the 82 rims, and the 84 is missing the spacers

[thekidd77]

I took apart the 84 yz80 and even though it looks like it was a new top end the piston has been hitting the head, the Bottom end bearing in the crank has up and down play in it, it needs over 300 in parts plus the bottom end and head so not worth the hassle, thinking about putting my 82 motor in the 84 which will solve my rad problem, does anyone know if the wheels are interchangeable? They are definitely different rims but I have the new bearings in the 82 rims, and the 84 is missing the spacers

I guess I can answer this now
The fork tubes are a different size, bigger on the84, which means the front axle bolts is longer on the 84 but the wheel takes up the same room so the front wheel from the 82 bolted right to the 84 and brake drum fits the stop on the left side.

The rear wheel was wider on the 82, but also had a big spacer on the left so it may have been ableto fit with out the spacer, decided to use the 84 rear wheel though as the sprockets are way more readily available and I wasn't missing any spacers, the 82 chain adjusters fit to complete the rear setup, also stole the shoes from the 82 that were identical and had more pad material.

So I now have an 84 rolling chasis with an 82 front rim, front fender from 82 bolts to 84 but wouldnt work the other way around as the 82 fender has a dip for the bottom hose for the 82 handlebar rad.

My new dilemma is I only have the parts to rebuild the 82 top end so need to use it, but that cylindr has the carb coming straight out the middle the 84 cylinder has a bend so the carb angles off to the left side where the airbox connection is, anyone know if there is enough play in the rubber boot on the airbox to reach a carb in the center and not angled out? If it wont reach any ideas on what to use to plumb the airbox to the carb? I'd answer this myself but don't actually have the original 84 rubber boot that attaches to the carb and airboxo dont want to order one if its a waste of time.

In other news I have my $100 1986 kx80 fully operational, took a few hunded in parts but cant complain about having new sprockets chains levers and cables. As long as I remember to shut the fuel off after each ride it starts first kick. The suspension seems soft and likely could use a fork rebuild but I also weigh 230 and it could just be me.

[T-Dub13]

Looks like most parts (crank, rod, bearings, piston and cylinder) have different part numbers. But I'd still try to fit the '84 top end on the '82 motor to see if it fits. I wouldn't be surprised if it fit. Yamaha may have changed the stroke though. That may be the reason why the piston was contacting the head in the first place. ANyway, don't be afraid to swap parts and see what works. Yamaha's are parts bin bikes and they share tons of parts with other years and models.

If you do ise the '82 top end, then you can plumb the air intake with radiator hose from any auto store. Take a look at the rack of hoses and find a pre-curved one that will work.

[thekidd77]

I dont have a piston or rings, and the cylinder is in rougher shape on the 84, i have everything for the top end and good cylinder for the 82 so that is how i will likely go, I found some rubber sewer pipe couplers that looke good today, the carb is 1.7" and airbox is 2" I seen a 2" to 1.5" coupler that looked like the real 84 joint, i think a combination of two of those rubber couplers should work, I havent seen rad hose yet that changed sizes so i will have to keep looking for that, it will probably be a week or so before I find the ambition to put the engine back together so have a bit of time to snoop around

[hobbeekid]

Hey Kidd, I think I can accomodate ya, it's been a minute since I've been on here, pm me with a list of what you need and I'll see if I have it.....

[hobbeekid]

I guess I can answer this now
The fork tubes are a different size, bigger on the84, which means the front axle bolts is longer on the 84 but the wheel takes up the same room so the front wheel from the 82 bolted right to the 84 and brake drum fits the stop on the left side.

The rear wheel was wider on the 82, but also had a big spacer on the left so it may have been ableto fit with out the spacer, decided to use the 84 rear wheel though as the sprockets are way more readily available and I wasn't missing any spacers, the 82 chain adjusters fit to complete the rear setup, also stole the shoes from the 82 that were identical and had more pad material.

So I now have an 84 rolling chasis with an 82 front rim, front fender from 82 bolts to 84 but wouldnt work the other way around as the 82 fender has a dip for the bottom hose for the 82 handlebar rad.

My new dilemma is I only have the parts to rebuild the 82 top end so need to use it, but that cylindr has the carb coming straight out the middle the 84 cylinder has a bend so the carb angles off to the left side where the airbox connection is, anyone know if there is enough play in the rubber boot on the airbox to reach a carb in the center and not angled out? If it wont reach any ideas on what to use to plumb the airbox to the carb? I'd answer this myself but don't actually have the original 84 rubber boot that attaches to the carb and airboxo dont want to order one if its a waste of time.

In other news I have my $100 1986 kx80 fully operational, took a few hunded in parts but cant complain about having new sprockets chains levers and cables. As long as I remember to shut the fuel off after each ride it starts first kick. The suspension seems soft and likely could use a fork rebuild but I also weigh 230 and it could just be me.

Damn, if you had only hit me up when I parted out my other 83 yz80! it had a airbox but I think I threw it out LOL!!!! it had the angle you are talking about.I'm supposed to be getting a complete 92 yz80 frame with airbox. problem is it's in Las Vagas.tho only other airbox is on my 83 frame which I plan on restoring! sorry! I'll se if I can locate a airbox for you if your still interested....

[hobbeekid]

Well here's a little update,got my so cal yz80 apart and guess what? the crank is burned up on it too!!! :-/ also bought another 82 yz80 engine basket case off Craigslist.Good cylinder& head combo, still has a few bores left.Cases were broken And crank was burned up on it too... @ this point I have four cranks that need rebuilding sooo I'll quit trolling around for used yz's and concentrate on reburbishing the ones I have.I see pro x rod kits coming down the pike right now to rebuild these cranks.Once they're done, I'll have 2 bottom ends ready to go back together.I have one refurbished crank on the way back from this So.Cal. bike shop along with a pair of cylinder heads I had milled so I going to combine the milled head with the ported cylinder & hopefully a procircuit pipe for my So. Cal. 82 rebuild. Next I'll be sending the rear shock out to have it rebuilt also. stay tuned.....

[vintagemx]

Ya know, if I remember right, it was either the RM80 or YZ80 from the early 80's (they were both yellow then) that was notorious for burning up cranks. I seem to recall something about the side clearance being off coming out of the factory.

That said it is a 30 y/o bike and most 80's were thrashed by kids who'd mix in anything from canola oil to used crankcase oil at ratios from 4:1 to 100:1.

[T-Dub13]

Sad but true about the condition of most of these old MXers. They have been thrashed to pieces, rebuilt and thrashed again on who-knows-what kind of premix. Another crank killer is running with a dirty air filter. I'd be willing to bet most of these bikes never got any sort of maintenance and most you will find with no filter installed.

Interesting about the side clearance thing. I don't know of that was SUZ or YAM. Never heard of that, but I don't doubt it's true.

[vintagemx]

I looked at a few older twin shock and non-linkage 80s for my son to race vintage mx. The running ones were out of my price range and the project (non-running) ones were junk. So I decided to go with an XR75, that put a few running projects in my price range.

The crank thing I remember as a buddy of mine worked for a dealership back in '83/'84. They were training him to be a tech. The distributor sent in new bottom ends and he had to swap over the top ends, stick the motor in the bike and stamp the serial number on the case. The sad part is those replacement bottom ends failed too.

I just can't remember if it was Suzuki or Yamaha. An adult video store now sits where the dealership was.

[T-Dub13]

I worked at a Yamaha dealer in 1985 and I don't remember ever hearing about a lower end problem on the small bikes. Not to say it didn't happen, but I'm hoping that it was a Suzuki problem since I don't own any of them heheh.

[vintagemx]

Wish I could remember. I was into muscle cars and girls then. Only knew bikes by their color. Yamahas went from yellow & black to red & white around then. Since getting into vintage bikes I've come across a lot of thrashed bikes, but occasionally you find a gem out there that someone tucked away and forgot about. Good luck with YZ!

[hobbeekid]

From my personal experience with the two strokes, if you fail to let the bike warm up properly before flogging them that in itself will lead to pre mature crank failure.I burned up the lower main rod bearing on both a 78 yz80 and a 81 rm125 by not letting them warm up properly.That 125 taught me a good lesson cause I had to find a job and save up to fix that F up! LOL!!! that taught me a real lesson about these two cycle engines.The yz80 I can't remember how I fixed that one, I think I found another good crank for a good price at the time.That was around 1982.The 125 was about 1983ish.....

[hobbeekid]

Finally got my cylinder heads back from the machinist along with a refurbished crank.The heads have been milled about 30 thou or so, the chamber modified with the squish band flattened, wider,sharper, and more pronounced.This, along with my ported cylinder,boysen reeds,and aftermarket pipe,should make this 80 run like a raped ape! Here's a pic of the stock head vs the reworked one...

[T-Dub13]

Awesome. Yeah, that will make a big difference. Be careful not to detonate though. Did your machinist / engine builder give a recommendation for fuel octane? Also, what's the CR now?

[hobbeekid]

I know stock it's like 9:1 the milling and slightly smaller chamber should bring it up 1 point.And no he did not give a recommendation. Heck it took lots of phone calls just to retrieve my stuff. I plan on running 100 octane fuel through it though....

[T-Dub13]

Seems reasonable. I'm not positive, but I think 100 octane should support up to 11:1 or higher, depending on your ignition timing. Just keep your ears peeled for ping and back off the throttle immediately if it starts to detonate. I'd hate to see you hurt that motor.