Tuckrb

Member
Jun 25, 2004
5
0
My son rides a 2002 RM85, and a couple of weeks ago, I noticed water flowing out of the radiator overflow tube. Upon checking the radiator, it was empty. A refill of water would only last 15 minutes or so, before it was empty again. When the bike is revved up, it pushes water out the overflow tube. We took the top end apart, and found a broken inner O ring between the cylinder and the head. I replaced the piston, ring, and all gaskets. On the first ride, the condition was the same. I pulled the head off again, and found the new O ring broken in the exact same spot as the old one. I've checked the cylinder and head for warpage, and all appears to be within spec. There are no sharp edges, or anything else that appears to be causing the O ring to fail. Has anyone ever seen this kind of condition? Thanks for any input.
 

Okiewan

Admin
Dec 31, 1969
29,555
2,237
Texas
Just curious.. how did you pick the "Using the Forums" area of the site to post that? FYI: there is a "Mini-Bikes" forum here, that you might have selected for this post.

Moved.
 

KCL

Member
Oct 9, 2003
27
0
The water pump impeller and seals are worn out. We replaced ours with a Boyenesen impeller, stock ones are plastic and get eaten away quickly. Might as well replace the seals also, they are stock items. This will resolve it.
 

cr2504life

Member
May 17, 2004
141
0
I dont' think he is talking about the seal or anything to do the the water pump. His is talking about the head gasket i think, but in this case it is an o ring instead.
 

Tuckrb

Member
Jun 25, 2004
5
0
The head gasket is failing. I have not been in the water pump yet, on the surface, I did not see where that could be causing the issue. Just incase the head/cylinder surfaces are not true, is machining these possible to 'clean up' the surfaces?
 

dog2

Member
Sep 26, 2002
73
0
I suspect the engine was overheated for some other reason (like a defective o-ring, radiator cap, or bad impeller). Once over heated the head can warp, and cause the head gasket to fail repeatedly. You should be able to have the head measure for flatness and cut if needed to correct the problem at a machine shop or two stroke engine rebuilder. It is hard to say if both the head and cylinder are bad, or just the head, without measuring.
 

ktmdad

Member
Feb 29, 2000
314
0
You can use really fine sandpaper on a flat surface to bring the head back flat, if it's not too bad. Also, take the advise already given and pull the water pump cover and inspect the propeller. The two piece stock unit will come apart. Replace it with the Boyensen unit. If the propeller is not working, it will cause the fluid to over heat.
 

Tuckrb

Member
Jun 25, 2004
5
0
Thanks for all the great advice. I took 400 grit wet (with WD40) sandpaper, and the head cleaned up really nice. Any idea where I can pick up the Boyensen water pump impeller? I've done some surfing, and have not had any luck. Thanks.
 

YZ165

YZabian
May 4, 2004
2,431
0
Okiewan said:
Just curious.. how did you pick the "Using the Forums" area of the site to post that? FYI: there is a "Mini-Bikes" forum here, that you might have selected for this post.

Moved.

:laugh: :rotfl: :laugh:
 

Tuckrb

Member
Jun 25, 2004
5
0
The problem is fixed! Here is a quick synopsis of what I did:

1. Used 400 grit wet/dry sandpaper with WD40, and cleaned up the head - although there were no major marks, this really cleaned up nice.
2. Removed the cylinder, and studs, and sanded the top of the cylinder as well.
3. Re-installed the head gasket with a light coating of silicone (Yamaha Yamabond).
4. Examined the water pump impeller, looks ok, will consider replacing later.

Thanks to everyone and all of their great suggestions.
 

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