YZ85/YZ80 Top End Motor Rebuild

I show how to do a full top-end rebuild on a yz85/yz80 motor.
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If you have any questions, feel free to leave a comment, send me an email, or message me on Instagram @projectdirtbikes
Thanks for watching and have a great day!
Filmed with a GoPro Hero 6 Black
All music is royalty and copyright free

[@Wooley689]

I always would put one circlip in piston before inserting the wrist pin, reduces droppage and makes installation easier.

[@projectdirtbikes]

Thanks, that’s a good idea 👍

[@masonbrossoit4998]

@@projectdirtbikeshey do you drain the radiator before hand?

[@projectdirtbikes]

@@masonbrossoit4998 yeah

[@jmtwilson]

Well done, good to see a young guy putting his work on display. I would suggest leaving the rag wrapped around the con rod for the entire process-safe beats sorry. And maybe you did it off line but it’s good practice to put the ring into the cylinder before installing on the piston, to check end gap. The ring may need a little filing. If the gap is less than minimum specified, in a running engine the ring ends can contact each other and score the cylinder instead of fully seating into the ring groove.

[@projectdirtbikes]

Thank you! And thanks for the tips, I think that I checked the ring gap, but I never actually knew what would happen if the gap was too small. Thanks for letting me know, from now on I'll always make sure it's in spec before installing.

[@Elduck000]

I just bought one, like the maintenance you give to the carburetor.

[@marcuslasey218]

Perfect job, professional quality

[@projectdirtbikes]

Thanks!

[@MrNuggington]

Thanks dude I'm picking up my first bike tomorrow

[@projectdirtbikes]

Awesome bro! Have fun!

[@chris123451233]

Awesome video man! Hey I have to rebuild a 1974 yz80 and was wondering if you had any ideas for a rebuild kit and a carburetor. I can't really find any info on it, thanks

[@projectdirtbikes]

Thanks man! eBay is a treasure trove for bike parts. I found a NOS kit for a ‘74 YZ80 (good deal too). Link below. And my personal opinion on carb rebuild kits is that they are overrated. I would recommend going through your carb and just making sure that all of your jets are clean and still in good shape. Then clean out the bowl, needle and seat, and slide. Might be a good idea to get a float bowl seal. Overall, cleaning and reusing all of the stock parts is cheaper and prevents the chance of getting a knock off junk part from China.

[@projectdirtbikes]

www.ebay.com/itm/NOS-1974-1976-Yamaha-YZ80-Piston-and-Rings-492-11631-00-97-Standard-Size-/183758526406?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

[@ralph9987]

gr8 job, wondering if you ran in the new piston for a few hours before you gave it full throttle does it need to be run in?

[@projectdirtbikes]

Thanks! For some reason I just now saw your comment. KZbin is weird like that sometimes... Yeah I ran it through a few heat cycles, then rode it around a few times before giving it the beans

[@DimitrisTsoykalas]

@@projectdirtbikes from yz manual These parts require about 30 minutes of break-in operation at half-throttle or less. Observe the condition of the engine carefully during operation.

[@DimitrisTsoykalas]

Engine break-in WARNING EWA10321 Failure to properly maintain the ve hicle or performing maintenance ac tivities incorrectly may increase your risk of injury or death during service or while using the vehicle. If you are not familiar with vehicle ser vice, have a Yamaha dealer perform service. 1. Before starting the engine, fill the fuel tank with a break-in oil-fuel mixture as follows.Mixing ratio (gasoline to oil): 15:1 2. Start and warm up the engine. Check the operation of the controls and the engine stop button. (See page 4-1.) 3. Operate the motorcycle in the low er gears at moderate throttle open ings for five to eight minutes. Stop the engine and check the spark plug condition (see page 7-8); it will show a rich condition during break-in. 4. Allow the engine to cool. Restart the engine and operate the motor cycle as in the step above for five minutes. Then, very briefly shift to the higher gears and check the full-throttle response. Stop the en gine and check the spark plug. 5. After again allowing the engine to cool, restart and run the motorcy cle for five more minutes. Full throttle and the higher gears may be used, but sustained full-throttle operation should be avoided. Stop the engine and check the spark plug again. 6. Allow the engine to cool, remove the cylinder head and cylinder, and inspect the piston and cylinder. Remove any high spots on the pis ton with #600-grit wet sandpaper. Clean all components and careful ly reassemble the cylinder head and cylinder. 7. Drain the break-in oil-fuel mixture from the fuel tank and refill with the specified mix. (See page 4-3.) 8. Start the engine and check the op eration of the motorcycle through out its entire operating range. Stop the engine and check the spark plug condition. Restart the motor cycle and ride it for about 10 to 15 more minutes. The motorcycle will now be ready to ride normally. After the engine break-in period, thor oughly check the motorcycle for loose parts, oil leakage and any other prob lems. Be sure to inspect and make ad justments thoroughly, especially cable and drive chain slack and loose spokes. In addition, check all fittings and fasteners for looseness, and tight en if necessary. NOTICE ECA15560 ● When any of the following parts have been replaced, they must be broken in. Cylinder or crankshaft: About one hour of break-in op eration is necessary. Piston, rings or transmission gears These parts require about 30 minutes of break-in operation at half-throttle or less. Observe the condition of the engine carefully during operation. ● If any engine trouble should oc cur during the engine break-in period, immediately have a Yamaha dealer check the vehi cle.

[@mclovin_it8872]

Just did my first top end rebuild. Everything went smoothly watching your video. But i think i might of done something wrong because the day after i couldnt start my yz85. I did notice coolant in my piston port if your looking down through the spark hole. Any idea why or suggest were to start?

[@projectdirtbikes]

Hey man, thanks for the comment. Luckily there are only a few things that can cause this, with the most common being a faulty inside head o-ring, or an improperly torqued head causing a poor seal between the water jacket openings and the combustion chamber. Did you use new o-rings and torque the head to spec? I had this same thing happen on my yz250 with a failed o-ring. Some other things it could be is a cracked head/cylinder or a scored cylinder to head mating surface. Keep me posted and good luck!

[@projectdirtbikes]

The torque spec is 22 ft-lbs for the head nuts

[@mclovin_it8872]

@@projectdirtbikes yup new orings along with new cylinder and piston kit. However maybe its cuz i left my oring in the garage and i live in fl with the heat maybe just maybe it expended my orings because i did notice it wasnt a tight fit placing the ring ontop of the cylinder. Im going to remove my top end anyways to inspect and possibly order another oring/gasket kit.

[@mclovin_it8872]

@@projectdirtbikes when it happend to your yz250 did you have to drain the oil since you were getting coolant in your piston port. Or you just left it like that and make sure everything was spec dry of coolant? Hope my message makes sense lol.

[@projectdirtbikes]

@@mclovin_it8872 Yeah it could be that the inner o-ring didn't sit in the grove right. It should sit nicely in the groove. You can use a small amount of vaseline or grease to make sure the o-ring stays put when installing the head.

[@oscarjaime342]

new to bikes is there any bleeding process for coolant or gas , might be dumb question just want to know before ripping apart bike

[@projectdirtbikes]

Hey, yeah you should drain your coolant before doing anything with the engine. The bottom bolt of the water pump cover is the drain bolt. You can leave the gas in the tank since the petcock valve shuts off the flow. Not a dumb question at all, good luck with your project!

[@lawenforcement9133]

Good job. Can you link where you purchased that rebuild kit?

[@projectdirtbikes]

Here it is. Just a heads up though, you may have to cut the head studs a little bit because I found that they were a little bit too long, or you could use regular nuts instead of the ones they provide. www.ebay.com/itm/Cylinder-Kit-Fits-1993-2001-Yamaha-YZ80-YZ-80-Rings-Piston-Gasket-Top-End-93-01/282437674919?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[@christianlemonade5355]

Did you gap the ring ? I’m confused because the ring on the yz85 are not flat there pointy ? So I’m confused

[@DayZJ]

Do I have to use there studs? Or can I just reuse mine?

[@projectdirtbikes]

If yours are still in good shape then go for it

[@deedadon8683]

I have a question , I rebuilt it but now I have less compression. Is there anyway you could help me diagnose the problem

[@projectdirtbikes]

You could be loosing compression out of a crank seal. If you kick over the bike with the oil fill cap removed, and air comes out, the wet (right) side seal is shot. Let me know if you have questions, and you could email me [e-mail] and I could help you out better.

[@ChopacabraSS]

What’s the link to everything you replaced

[@superhamsterpuppet3022]

how long did this topend kit last? also will it fit a 2001 yz 80

[@projectdirtbikes]

I sold the bike a few years ago, but it still had this top end and still worked great. Yeah it will fit an 01

[@gideoncraig6828]

Good video

[@projectdirtbikes]

Thanks

[@TheGamer-ei5xk]

I got an 2000 yz80 had 30 psi I order an new top end hope it helps 🙏

[@projectdirtbikes]

I hope so too!

[@hasaanrutherford3419]

Think a yz85 rebuild kit can go into a 2001 Yz80 ?

[@projectdirtbikes]

It will fit but, you will have to rejet your carb to account for the extra displacement.

[@drtim9560]

What parts do you need for a top end can you guys list them here plz?

[@mcbluhjo4156]

my yz 80 has no compresion and bogs down when i do get it started and the only way i can start is is to push start it

[@projectdirtbikes]

Have you cleaned the carb yet? It sounds like your pilot jet may be clogged.

[@projectdirtbikes]

Just reread your comment, I read it wrong earlier. It sounds like you need to rebuild your top end to get your compression up. If you still don’t have compression after the rebuild, ten you are probably loosing compression through one of the crank seals.

[@Romeo21Rxw]

What oil do I need to use for lube?

[@projectdirtbikes]

I use 2 stroke premix oil. Any oil or assembly lube will work though

[@treceapparel7323]

Is the chain sprocket and brake hub the same as the yz 85

[@projectdirtbikes]

I believe so

[@foonigan3571]

where did you get this kit?

[@projectdirtbikes]

from ebay

[@gideoncraig6828]

🤘🤘🤘🤘

[@YN-em8zk]

What coolant do you use?

[@projectdirtbikes]

I believe I used Prestone any make/model.

[@tigerishkan2059]

Do you think it will fit a yamaha yz 80 1987?

[@projectdirtbikes]

I think that there is a different top end for an ‘87 but the rebuild process would be the same

[@tigerishkan2059]

@@projectdirtbikes could you please link a cylinder kit that fits my 1987 yz 80

[@projectdirtbikes]

@@tigerishkan2059 www.google.com/aclk?sa=L&ai=DChcSEwjJ8c_b_57wAhULGa0GHRvVDIsYABA0GgJwdg&sig=AOD64_0io943qgGOqrSsTsVzWrVNzqNeIw&ctype=5&q=&ved=0ahUKEwi2_Mnb_57wAhXLHTQIHUSfAToQ2ysIjgE&adurl=

[@projectdirtbikes]

eBay has everything you’ll need

[@danielallison402]

I have a 1990 Yamaha YZ80 and everything seems to work out when I get parts from like craigslist and stuff like I needed a new exhaust header and pipe silencer and so when it got here and I went to the garage to start the process lol I took it out and it had a tag on it saying that it was from a 1986 Yamaha YZ80 so being that the part was already sitting there in front of me and it did say that the part will fit on my 1990 Yamaha YZ80 and it was not going to be a hard task to put on an find out if it would be a problem or not beings I already had the old smashed up exhaust header and pipe silencer off the bike already so I mounted it up and sure enough nothing was wrong

[@DabZ_bongs]

Yo can I put a 85 top end on my 80 ?

[@projectdirtbikes]

Hey, you can, but you won't gain much power and you will have to re-jet your carb for the increased displacement. I did that before and in my opinion, it's not worth it.

[@connorpetersen8392]

I’m having zero compression on my 94 yz80. Back tire locked up when riding. Still kicks, engine is not seized(at least I think)Is it possible it needs a top end? And would this same kit work for my 94 yz80?

[@projectdirtbikes]

You will definitely need a new top end since you don't have any compression. But depending on your rpm when it locked up, you may need to replace your crank as well. The connecting rod could be bent. The kit that I got will fit yours too, but if your connecting rod is bent, here's a complete motor rebuild kit. shorturl.at/jpvE8

[@gabe10222]

The cylinders on these are ceramic you probably melted the piston to the cylinder piston is usually aluminum. Use pool acid on the cylinder where the aluminum is and it should come off

[@isaacflerchinger9928]

What is the link for the rebuild kit

[@projectdirtbikes]

I’m not sure if they make this exact kit anymore, but here’s a similar one. Lots on eBay. www.ebay.com/itm/254437813161?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=YWc0p_pxRxy&sssrc=2349624&ssuid=loy-bm6kq3w&var=&widget_ver=artemis&media=COPY

[@projectdirtbikes]

Just make sure you buy the one specifically for a yz80. Sellers may try to sell you kits for yz85s since they will physically work, but the engine won’t run right without rejetting.

[@gheorgheandrei2255]

can i put a yz 85 top end kit on a yz 80?

[@projectdirtbikes]

Yes, but you will have to re-jet your carb for the increased displacement

[@evasantmier1953]

Put a new top end on my 2000 yz80 and it still has low compression whats wrong does any body no why

[@projectdirtbikes]

You could be loosing compression out of a crank seal. If you kick over the bike with the oil fill cap removed, and air comes out, the wet (right) side seal is shot. Let me know if you have questions, and you could email me [e-mail] and I could help you out better.

[@traceyjolly5187]

Hey my bike revs out in neutral but not gear it's a 2001 YZ80

[@projectdirtbikes]

Hey, have you tried cleaning your carb? You could have a clogged jet

[@junipicassos6377]

Torque specs please!!

[@projectdirtbikes]

www.thumpertalk.com/uploads/monthly_2020_10/2731DFF1-207B-4EBF-92B2-5BEE94A9399B.png.8576402df80cc3d01024c2fe699e7b6c.png

[@projectdirtbikes]

22 ft-lbs for the head nuts and 9.4 ft-lbs for the cylinder and head studs. Let me know if you need anything else!

[@joeconsorte6708]

Foot pounds?

[@projectdirtbikes]

Yes