1980 RM 100 question

berniepiet
Profile picture for user berniepiet
Posts
526
Joined
12/23/2009
Location
Atlanta, GA US
berniepiet
Edited Date/Time 7/27/2015 11:35am
Hi all. I have a 1980 RM 100 that we are re doing. We pulled the cylinder off and it is beyond the max piston size that wiseco makes for it.

Option 1: Could I put a 1980 RM 125 compete top end on it? Would it just be a direct bolt on or is there more involved?

Option 2: could I just bore out the 100 cylinder, Nikasil it, and use a 125 piston? I realize I would probably have to re shape the squish area of the head.

Anyone ever done something like this ?

|
CamP
Profile picture for user CamP
Posts
6828
Joined
8/16/2006
Location
Colleyville, TX US
CamP 7/24/2015 4:36am
7/24/2015 4:36am
You can have it nikasil plated back to the largest wiseco 100 piston bore size.
DrGreg
Profile picture for user DrGreg
Posts
68
Joined
1/7/2013
Location
Colleyville, TX US
DrGreg 7/24/2015 3:53pm
7/24/2015 3:53pm Edited Date/Time 7/24/2015 3:57pm
Option 1:
Sometimes it sounds easy to do something like this, but usually there are other things that complicate the process.
You definitely have to do your homework and research. Is the rod length the same between the 100 and 125?
Are you sure you can bolt the cylinder to your crankcases? Is the exhaust flange the same size on both cylinders, or will you need to have your pipe modified, and for that matter how will the 125 run with a 100 pipe on it?
Will you have to put a bigger carb on it ?, etc....

Option 2:
Cam is right, unless you've had some sort of catastrophic failure and have badly damaged the cylinder lining, you should be able to get it plated back to a size Wiseco has available.

I have sent several cylinders to Millennium Technologies in Wisconsin and they have done an excellent job with each.
I did have one that was beyond plating and they had LA Sleeve make a sleeve for it and installed it. I have never used them, but have read good things about Powerseal USA and Langcourt doing a good job on the plating also.
I personally will stick with Millennium for my cylinder repairs.

Option 2 is the easy way to go.
CamP
Profile picture for user CamP
Posts
6828
Joined
8/16/2006
Location
Colleyville, TX US
CamP 7/24/2015 5:44pm
7/24/2015 5:44pm
Hey Greg, I hope the leg is healing well!
DrGreg
Profile picture for user DrGreg
Posts
68
Joined
1/7/2013
Location
Colleyville, TX US
DrGreg 7/25/2015 1:45pm
7/25/2015 1:45pm
Hi Cam
Missed you at the TVRC party last week.
It's coming around. Definitely not healing as fast as broken bones did in High School. Hope to be riding at some point in the Fall series

The Shop

See All »
Mike P.
Profile picture for user Mike P.
Posts
756
Joined
11/3/2014
Location
Chantilly, VA US
Mike P. 7/25/2015 2:32pm
7/25/2015 2:32pm
I believe you have to use a different rod if use the 125 top end. A few years back I bought freshly built complete 1981 RM100 motor (same as the 1980). I wanted the motor for the bottom end (for my 1980 RM125, which is still currently in my 125). I have that complete top end somewhere around house (never used it0, but I'm pretty sure you will need a longer rod to use the 125 top end. Mike
WRH
Profile picture for user WRH
Posts
191
Joined
5/5/2014
Location
Saraland, AL US
WRH 7/27/2015 11:35am
7/27/2015 11:35am
I think the 77 /78 cylinders are the same , and the 79 / 80 cylinders are the same. It is possible the cylinder pictured is the 77 /78 model. Stroke would be off on the 100 to the 125 engine right?

Post a reply to: 1980 RM 100 question