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Old July 21st, 2013, 07:22 AM   #1
lowdown112
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Honda 80Cc Dirtbike

Didnt know where else to put this. But anyways, my friend just gave me a 80cc Honda Dirtbike. He said one day he put straight gas in it and ran it by accident and now it wont start. Anyone know how to fix this? Apparently it takes Mix Gas. Its a kickstart. It sounds like it has compression but wont turn over. This may be a simple fix but i figured id ask anyways because i know nothing dirtbikes or mix fuel things.
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Old July 21st, 2013, 07:31 AM   #2
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Flush out all of the straight gas and put mixed gas in the tank. Take the spark plug out and clean the electrodes. Before putting the spark plug back in pour a spoonful of motor oil in to lubricate the cylinder. See if this helps it start.
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Old July 21st, 2013, 10:06 AM   #3
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Sounds like the piston seized. The whole job can be done in under an hour but the cylinder is probably damaged so it'll need repair or replacement.

Drain the coolant, pull the exhaust, the radiator and the cylinder head and cylinder. I'd bet you find gouges and melted/welded rings on the piston. You may need a hammer to get it apart too.

Measure the damage to the cylinder, this will dictate whether you need to replace/re-plate or just hone it. Then, you get the piston kit to match the bore size you end up with.

If the piston/cylinder is intact, and it still won't spin, the crank/rod will need a rebuild.
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Old July 21st, 2013, 10:16 AM   #4
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If you want to unseize it without scratching / destroying anything, pour very hot engine oil ontop of the piston in the cylinder, wait a short while then try turn the engine over manually with the head off.
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Old July 21st, 2013, 10:48 AM   #5
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Any updates for us Keith?
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Old July 21st, 2013, 05:18 PM   #6
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Like others have said, sounds like it is seized up. it is probably not even worth the hassle to fix. Bike was probably neglected since day one and maintenance was never kept up on since it is a kids bike. You will most like need complete top end rebuild including cylinder unless you get it bored and sleeved but not even sure how feasible that is on an 80. With any luck the bottom end is salvageable but most likely not because again, it was probably not taken care of right since day one and it is due for a bottom end rebuild even if it survived the seizure. I would try and sell it as is for whatever someone wanted to give me for it. It will cost more to rebuild than to just buy a used one that already works and that is not even factoring in other things that need replaced from standard wear and tear.

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Old July 21st, 2013, 11:09 PM   #7
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Any updates for us Keith?
Tried flushing and replacing gas.
Changed spark plug.

I tried starting fluid still wont go.

Gonna take it apart tomorrow probably is seized which would suck. Idk how to rebuild motors. I mean it was free so ill definately give it a go anyways nothing to lose type deal.
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Old July 21st, 2013, 11:14 PM   #8
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running a motor without oil is usually a bad thing.
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Old July 21st, 2013, 11:16 PM   #9
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Sounds like the piston seized. The whole job can be done in under an hour but the cylinder is probably damaged so it'll need repair or replacement.

Drain the coolant, pull the exhaust, the radiator and the cylinder head and cylinder. I'd bet you find gouges and melted/welded rings on the piston. You may need a hammer to get it apart too.

Measure the damage to the cylinder, this will dictate whether you need to replace/re-plate or just hone it. Then, you get the piston kit to match the bore size you end up with.

If the piston/cylinder is intact, and it still won't spin, the crank/rod will need a rebuild.
How would i measure the damage? Wish u were here to look at it. I have no idea when it comes to the guts of a bike motor.
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Old July 21st, 2013, 11:17 PM   #10
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running a motor without oil is usually a bad thing.
I didnt do it. My friend did by mistake
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Old July 22nd, 2013, 03:50 AM   #11
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Your engine is a two stroke if it takes an oil gasoline mixture. Two stroke engines intake the air fuel mixture differently than four stroke engines in that when the piston goes up in the cylinder the air fuel mixture is sucked into the crank case then when the piston moves down the pressure in the crankcase pushes the mixture through ports up into the cylinder. The oil in the gas lubricates the bearings on the crankshaft and connecting rod as well as the cylinder wall. In order to seal the crankcase so it can suck in the mixture and the pressurize it there are seals on the end of the crank. Due to the lack of oil in the mixture there is a good chance the bearings on the crankshaft are no good. If these bearings get sloppy the end seals won't seal and the crankcase won't suck and blow the air fuel mixture and you will have what you have now. I have come experience with these engines and off the top of my head your looking at about $250 in parts to do the job, labors free if you do it yourself. You will need a special puller to get the flywheel of other than that, standard tool are all you need. Good luck.
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Old July 22nd, 2013, 07:46 AM   #12
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How would i measure the damage? Wish u were here to look at it. I have no idea when it comes to the guts of a bike motor.
Get it apart first, and even though it is simple, organize everything well as it comes apart. IIRC the Honda doesn't have a power valve, which makes it even easier to tear down. When you have the cylinder in your hand, look inside it. Any scratches that you can catch a fingernail on means it needs to be rebuilt. If an iron liner they might be able to bore it oversized. More likely it is nikasil lined, which requires a bore and replate.

Get it apart first. Try the hot oil trick and maybe rock it backwards in top gear too.

With a crank rebuild, You'll be in it about 6-700 bucks. The overall condition of the bike should guide your next move after you see the damage. Running but ratty examples are about that price already.
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Old July 22nd, 2013, 11:03 AM   #13
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Gotta question, if the motor is seized. Doesnt that mean i shouldnt be able to push the kickstart down? When i try to kickstart it, it makea a puff sound every now and then..like its trying but just wont start.
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Old July 22nd, 2013, 11:11 AM   #14
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If you can push the kickstart down then the motor is not seized. I think there is still hope for the engine.
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Old July 22nd, 2013, 12:53 PM   #15
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The rings may be broken and leaving you with no compression. 80cc 2t engines turn over very easily, but should still give some resistance. Starting them by hand is possible, but if it just pushes thru the rings are probably welded to the piston. Has it always turned over or did it break free?

I'd still pull off the head & eyeball it. No pre mix oil usually leads to a ring failure ASAP.
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Old July 22nd, 2013, 01:54 PM   #16
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pic of the bike to confirm its a CR80 (2 stroke) and not a locked up XR/CRF80 (4 stroke - which are typically mega reliable)?
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Old July 23rd, 2013, 12:59 AM   #17
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The rings may be broken and leaving you with no compression. 80cc 2t engines turn over very easily, but should still give some resistance. Starting them by hand is possible, but if it just pushes thru the rings are probably welded to the piston. Has it always turned over or did it break free?

I'd still pull off the head & eyeball it. No pre mix oil usually leads to a ring failure ASAP.
It has always been free since the day it stopped. If the ring is broken/welded is that a little better? What does that mean i need to replace the piston?
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Old July 23rd, 2013, 01:10 AM   #18
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pic of the bike to confirm its a CR80 (2 stroke) and not a locked up XR/CRF80 (4 stroke - which are typically mega reliable)?
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Old July 23rd, 2013, 01:12 AM   #19
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I know its ugly but its a beast when its running. Its only a toy to fool around with. And if i get it running ima repaint it anyways.
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Old July 23rd, 2013, 06:09 AM   #20
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Ugly is a relative term brah.

Those are massive fun on a cart track in the woods. They make really good training bikes for the little ones too.

Totally worth fixing imho, even if you have to rebuild the lower end. The price of parts seem to be a bit high though. Rings would be my best guess also.

Subbed and good luck!
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Old July 23rd, 2013, 06:11 AM   #21
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yep, 2 stroke for sure. Hopefully just seized top end. Easy to pull the head and cylinder off and see the piston and walls of the cylinder. Can't remember if those have any type of exhaust valve (powervalve, ATAC chamber, etc), they can be a bit trick to put back correctly. my 125 and 250 did, but I don't think the 80/85 got them. might even get by with rings and a honing if it started and seized right away at low revs.

before anyone yells out hey man its a 2 stroke they don't have valves, some 2 strokes adjust the size of the exhaust port to make it smaller at low revs for throttle response and bigger at high revs for better flow. quick google search looks like no powervalve on the 80. pull the pipe off, pull the carb from the cylinder, and pull of the head and cylinder to get a look at the cyl, piston, and ring(s). 15 minutes to pull that off.
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Old July 23rd, 2013, 06:11 AM   #22
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I know its ugly but its a beast when its running. Its only a toy to fool around with. And if i get it running ima repaint it anyways.
just put new aftermarket plastics. only the frame would be painted.
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Old July 23rd, 2013, 07:16 AM   #23
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It sounds like it has compression but wont turn over. .
This is where people got misled. Not turning over would mean the engine doesn't spin. I guess you meant it wouldn't start?
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Old July 23rd, 2013, 07:22 AM   #24
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Simplest thing to do is get a compression tester and also run a leak down test.

I'd tear it apart anyway to look at the rings & cylinder. Just pull off the cylinder, leave the head bolted on to it. I think that was an option on these. If it has nuts around the base of the cylinder it is. Then it can be put back on for the price of a base gasket. $7 or thereabouts.

I'm betting the rings are seized to the piston. There was no power valve on these, the RM and KX 80-85s got them and were much friendlier to race/learn on.

Post pics of it if/when you take it apart. For a cheap fix, a drill hone thru the cylinder might make it passable if it isn't too bad.
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Old July 23rd, 2013, 07:23 AM   #25
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This is where people got misled. Not turning over would mean the engine doesn't spin. I guess you meant it wouldn't start?
Oh yeah, sorry. It wont start. But still the regular gas thing is what made it not start. I can still try to kickstart it. Which means the engine still spins I guess? It just wont start for nothing.
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Old July 23rd, 2013, 07:32 AM   #26
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Oh yeah, sorry. It wont start. But still the regular gas thing is what made it not start. I can still try to kickstart it. Which means the engine still spins I guess? It just wont start for nothing.
Yep, it'll start on regular non oil mixed fuel, but it destroys the parts that oil should have been lubricating so it won't run for long. Rings should go first, and that is your best case scenario. The rings being damaged will drop compression, so it won't start.

A piston/ring/gasket kit should be around $100-125. Hopefully the cylinder surface is still good.

Like I said, pulling it apart should be a 30 minute job, just package everything in baggies and label it all. The tank, seat, exhaust have to come off. I think the carb can stay as it is mounted on the cases... Then the rad hoses attached to the cylinder, the coolant of course... then pull the cylinder off.
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Old July 23rd, 2013, 05:50 PM   #27
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^

pretty much this, the tear down is easy. Get a piston kit but do some research first and make sure that the common aftermarket top end kit is plug and play for this bike. Most often the case but not always (example my 03 yz250 needs OEM piston stamped to match cylinder stamp) Make sure you stuff some clean rags in the bottom end whole so you don't lose any clips or anything down into it when tearing apart or putting back together. Make sure you wiggle the rod around while you have access to it and feel for anything that doesn't feel right, to much play, grinding, gritty feel ect... If so you might want to get a second opinion on the bottom end before going any further.

If the cylinder is still in spec get someone to hone your old cylinder for cheap or buy a kit to do it yourself, don't put a new piston rings in with out honing. Don't be afraid to clean your cylinder good once off, get in there with some brake blaster, tooth brush soap and water, but make sure you rinse it clean and dry it super dry, i generally use a blow dryer, don't put it back on until it is 100% dry.

It is easy just put everything back together the way it came apart but with new gaskets ect... Other things you should do, check air filter, prob needs replaced, or cleaned and sprayed for sure. Obviously change the crankcase oil in it, these are dirty bikes oil needs changed every so many hours of ride time, i generally do mine every 6hrs at least. Not sure if that bike has a sight glass, if so great, if not, find out how much goes in and measure it and put in that exact amount after a full drain. Find out what the factory recommends for your fuel mix. Generally 32:1 is fairly standard for 2stroke mx type bikes, People will tell you to thin out your mix if you are running "rich" This is false information, you do not lean out your bike by leaning out your fuel/oil mixture. Just like the ninja250's you lean out or richen your bike by adjusting the air fuel ratio by adjusting the carburetor. If your bike is jetted properly and you run it hard and hot like it is meant to be run 32:1 fuel oil mixture is generally great. Lots of racers run 28:1 but they really ring the necks of those bikes too. The problem generally occurs when someone leans out the fuel/oil mix lets say 42:1 or even 50:1 because they just putt around on their two stroke which they can get away with until that one day they ring it out and then seize the engine.

Thats a healthy start.

have fun, I would tear it apart and check out top end, bottom end and clutch, if any two of those are shot in the *** i would not waste my time fixing it up. top end is quick and easy, bottom end kit is closer to $300 maybe more but will probably need a shop to do some of the bearing work if they need pressed, and a whole clutch rebuild can cost up to $600- or higher if you buy premium parts. Just not worth it IMO.
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Old July 23rd, 2013, 06:26 PM   #28
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Decided to sell it while i can. Got a decent offer, and i have too many projects as it is. Have a 89 c2500 i gotta put head gaskets and brake lines in, 2 50cc mini motorcycle carbs i gotta figure out how to rebuild or replace, a 50cc scooter that needs carbs and a 99 grand prix gtp that needs its motor put in & need to get my harley a clutch kit anyways.. sorry for the wasted post but i got too much to do.
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Old July 25th, 2013, 01:01 AM   #29
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No worries, it was my opinion that you should sell it from the beginning anyway Dirtbikes are generally easy up keep but.... you have to keep up on and not let it all build up at once. When you take an old bike that probably hasn't had much up keep it can get pretty overwhelming once you start digging and finding out that everything is shot from clutch, top end to bearings and forks. You can buy a decent used mx dirtbike for $1700- $2500 or pay just as much maybe more to completely rebuild one that costs $1000 - $1500.
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