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2stroke No top end rebuild in 12 years...

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I recently bought a yz85 in great condition it just needed some carburetor work (the float needle did not seat properly). Now that that's fixed, I have a question. The bike is an '06 and the owner said "yeah it's still on the stock piston probably only has about a hundred hours on it" I cringed when he said this. But, nevertheless, I took a test ride and decided to buy the bike. When I kick it over, the compression is average for an 85 and it starts 2nd or 3rd kick cold and first kick warm. When riding it, there are no strange noises and I can hear no piston slap or anything out of the ordinary (listen to it in this video: https://www.youtube.com/watch?v=nx0VislGsg4&t=4s). I know a top end rebuild is a must on these 2 strokes so how has this bike lasted 12 years and still sounds like it's new? It doesn't bog, the only thing I have noticed is that it will hesitate while taking off sometimes when it's hot. I know I'm going to get the average "PUT A NEW TOP END IN IT NOW" 2 stroke guru, but is it really necessary? I have not taken the cylinder off yet but I put my finger over the spark plug hole and kicked it over and it has enough pressure to lift my finger but it's also really oily in there (oil ring left on my finger). So, what do you guys think? Does she got a few more hours or does it need a new piston ASAP?

 

 

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100 hours is getting out there on something like an 85, so yeah, it's past due. Top ends are cheap and easy, fix it before it tuns into something far more complicated and expensive.

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Cheap insurance to do a top end. Probably wasn't ridden much. If you go out an trail ride for 8 hours you would be lucky to have 4 hours of engine time most of the time. So unless it actually an hour meter it may have more like 50 hours.

Personally I'd ride it a few times then do a top end and swingarm, linkage and suspension service. Then you will be totally fresh on the major stuff.

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5 minutes ago, 1.21GW said:

Cheap insurance to do a top end. Probably wasn't ridden much. If you go out an trail ride for 8 hours you would be lucky to have 4 hours of engine time most of the time. So unless it actually an hour meter it may have more like 50 hours.

Personally I'd ride it a few times then do a top end and swingarm, linkage and suspension service. Then you will be totally fresh on the major stuff.

That's what I think because there isn't a scratch on the bike other than faded graphics from gas sitting in the tank (tank was gummed up when I got it, aka it sat more than it rode). I'm riding tomorrow so it's not like it will be changed immediately but I will definitely be ordering a new piston soon.

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Either it wasn’t ridden much, or it was and had a New top end not too far back. Never believe a seller based on their word. Either way, for 90 bucks I’d throw a New top end in.

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I'd put a new top end in regardless of what the previous owner says.

If he doesn't have an hour meter on the bike, then he's guessing.

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1 hour ago, MaybeMe said:

Just run ‘er til she blows!

Then send it to me ??

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I recently bought a yz85 in great condition it just needed some carburetor work (the float needle did not seat properly). Now that that's fixed, I have a question. The bike is an '06 and the owner said "yeah it's still on the stock piston probably only has about a hundred hours on it" I cringed when he said this. But, nevertheless, I took a test ride and decided to buy the bike. When I kick it over, the compression is average for an 85 and it starts 2nd or 3rd kick cold and first kick warm. When riding it, there are no strange noises and I can hear no piston slap or anything out of the ordinary (listen to it in this video: 
). I know a top end rebuild is a must on these 2 strokes so how has this bike lasted 12 years and still sounds like it's new? It doesn't bog, the only thing I have noticed is that it will hesitate while taking off sometimes when it's hot. I know I'm going to get the average "PUT A NEW TOP END IN IT NOW" 2 stroke guru, but is it really necessary? I have not taken the cylinder off yet but I put my finger over the spark plug hole and kicked it over and it has enough pressure to lift my finger but it's also really oily in there (oil ring left on my finger). So, what do you guys think? Does she got a few more hours or does it need a new piston ASAP?
 
 


I’m doing a top on my yz 85 and from Moro sport a piston rings and all that for just a piston is $86

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15 hours ago, Drzjosh125 said:

I recently bought a yz85 in great condition it just needed some carburetor work (the float needle did not seat properly). Now that that's fixed, I have a question. The bike is an '06 and the owner said "yeah it's still on the stock piston probably only has about a hundred hours on it" I cringed when he said this. But, nevertheless, I took a test ride and decided to buy the bike. When I kick it over, the compression is average for an 85 and it starts 2nd or 3rd kick cold and first kick warm. When riding it, there are no strange noises and I can hear no piston slap or anything out of the ordinary (listen to it in this video: https://www.youtube.com/watch?v=nx0VislGsg4&t=4s). I know a top end rebuild is a must on these 2 strokes so how has this bike lasted 12 years and still sounds like it's new? It doesn't bog, the only thing I have noticed is that it will hesitate while taking off sometimes when it's hot. I know I'm going to get the average "PUT A NEW TOP END IN IT NOW" 2 stroke guru, but is it really necessary? I have not taken the cylinder off yet but I put my finger over the spark plug hole and kicked it over and it has enough pressure to lift my finger but it's also really oily in there (oil ring left on my finger). So, what do you guys think? Does she got a few more hours or does it need a new piston ASAP?

 

 

 

3 hours ago, Hunter743 said:

 


I’m doing a top on my yz 85 and from Moro sport a piston rings and all that for just a piston is $86

 

I just did a little 12 85 I got it from the original owner, had 90 hours on it. Need the cylinder re-plated because he waited to long, and the piston slapped the nikasil off. 

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I had a simular situation. I bought my son a 07KX65. The bike looked brand new, still had dealer stickers on the fender and very little paint wear. The previous owner said his stepson was scared of it and the adults putted around the yard only.

Bike started and rode great. My son put abput 10 hours on it before it became hard to start. I replaced the piston and he got 3 hours on it before the crank bearing went, piston lip chipped.

Builder told me the cylinder coating was flaked off due to age and wear. This may have started the death cycle.

The short story is a $500 rebuild cost me $1100, cylinder needed to be replaced.

My suggestion would be to rebuild the whole engine, top to bottom. Seals, bearings, waterpump ect.... Who knows how much surface rust, condensation and corrosion may be hidden inside.

$500 worth of prevention for a summer of trouble free riding or possibly an $1100+ cure down the road.

Good luck, nice looking bike.

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