Polaris ATV Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
11 Posts
Discussion Starter #1
Hey guys. I bought a 2000 Scrambler 400 (2x4) and was told all it need was new rings. He told me it had been bored to an 85mm. When I took the top end off this is what i saw.

The first picture is the front of the piston (the side facing exhaust) The top left of the piston has a chip in it.

The second picture is of the left side.

The third is of the right side.

Does anyone have any idea on what happened?! The oil pump does not work. He didnt say if he pre-mixed or not. Also the cylinder looks like some of the piston is smeared on it. From all my research I think it is a combination of no oil and......either running too lean.......OR.....possibility maybe the piston was too big for the bore?!

Any help would be GREATLY appreciated.
 

Attachments

·
Registered
Joined
·
11 Posts
Discussion Starter #2
Also I forgot to add that the top of my head has a number of small dents in it. They are about 1-2mm in size and there are about 20 of them.

PLZ HELP!!!
 

·
Premium Member
Joined
·
2,544 Posts
I would say, from the pics and the last comment, that your engine was "oil-starved". Rebuild it and premix your fuel with a good synthetic 2-cycle oil at 50:1. That's my opinion.
 

·
Registered
Joined
·
143 Posts
Yea. Lubrication problem look for me.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #5
Alright thanks! Ya thats what I was thinking.

As for the cylinder I cant bore anymore out (seeing the im already .080 over-bored) how would you recommend getting the thin layer of melted piston off the walls? Some of it comes off when I run my fingure nail across it, but most does not.

Would honing it work, or any other method?!

Thanks again
 

·
Premium Member
Joined
·
2,544 Posts
Alright thanks! Ya thats what I was thinking.

As for the cylinder I cant bore anymore out (seeing the im already .080 over-bored) how would you recommend getting the thin layer of melted piston off the walls? Some of it comes off when I run my fingure nail across it, but most does not.

Would honing it work, or any other method?!

Thanks again
If the piston has seized and smeared aluminum on the cylinder you will need to remove it. You can do this with Muriatic acid. Just take medicine dropper and put just a few drops on the aluminum that has been smeared in the cylinder. The acid will eat the aluminum but will not hurt the steel of the cylinder. DO NOT GET THE ACID ON YOU . If you do get it on yourself, water and baking soda will get it off. Also don't get it on any aluminum unless you want that aluminum eaten up ! You can get Muriatic Acid at any home improvement store. They sell it buy the gallon, which will do about a billion cylinders.
Be sure to look at the top of the piston. If it looks like a rat has been chewing on it watch out. It means that the bearings in the bottom end are starting to go. If you put in a new piston it will just be ruined as more bits of bearing shed by the lower crank and rod bearings. The cure ? Rebuild the bottom end.
 

·
Registered
Joined
·
11 Posts
Discussion Starter #7
Ok Thanks Phil. I read on the internet about the acid trick you are talking about. I am planning on doing that asap. I ordered my new wiseco piston yesterday. As well as a complete gasket kit off ebay to rebuild engine.

Have everything tore apart but the only thing slowing the process is getting the clutch off. I am a college student at Ohio State and do not have alot of money to be throwing around (i have already put too much into this thing as it is). IS there a way to get the thing off without buying a clutch puller? I know everyone says "ohhhh its so cheap just buy it". ya well i cant afford it. Any help?!

Thanks
 

·
Registered
Joined
·
3,420 Posts
The clutch can be removed with a bolt or all thread rod about 10" long. I don't what size it is. It will be either 5/8" or 3/4" fine thread. A welding shop could make you one all you have to have is about 5" of threads or less. Also I have a 1995 400 explorer cylinder head and jug that can be bored if it will fit. PM me an offer on it if you need it. Thanks
 

·
Registered
Joined
·
3,420 Posts
Make sure your air box and boots are not cracked. That engine could have sucked dirt into it and caused engine failure.
 
1 - 9 of 9 Posts
Top