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| RM100 Mods http://vintagedirtbikeforums.alp-sys.com/viewtopic.php?f=29&t=2233 |
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| Author: | JimN [ Mon Apr 06, 2009 10:29 pm ] |
| Post subject: | RM100 Mods |
I was at Glen Helen one day and my stepson was in his fourth race on a 79 RM100. He wasn't doing too bad for his fourth race. The race announcer started saying how that year RM100 was the crappiest bike made bake then with a strange power band that isn't at the top and isn't at the bottom but just somewhere. He went on to say that the fact Nick was riding as well as he was says something about his riding ability. Of course Nick heard all about the announcers comments during his race and wants to do something about it. We talked about stepping him up to another bike but he also asked about modifying this bike. So I'm looking to improve the performance of a 79 RM100. I head that the cylinder and head from a 125 would fit on the 100 bottom end but I would like to confirm that before asking if anyone has those for sale. I am also very interested in hearing if you have any tips on improving engine performance of this bike. |
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| Author: | rayivers [ Thu Apr 23, 2009 6:05 am ] |
| Post subject: | Re: RM100 Mods |
Jim, First off, let me tell you that I've never even seen an RM100, and I have no idea if the 125 top end will fit - so I waited to reply in case someone else had specific experience with this mod. One thing I'm fairly certain of, though, is that the RM125 piston will be heavier - so the crank will be out of balance, probably resulting in substantial vibration. The route to more power is pretty much the same for all internal-combustion engines: 1) Get more air/fuel in 2) Compress it more 3) Ignite it better 4) Extract the burnt gases more efficiently A bigger carb - perhaps the one from the RM125 of that era - may bolt right on, and should give you more top-end power. If you take the time to jet it correctly, the loss of low-end will be minimal. More compression can also help with low and mid-range power, and adds 'snap' coming out of corners. The best way to do this is to have a machine shop mill material off the top of the cylinder, or use a thinner head gasket if you can find or make one. .010" off the cylinder top or gasket thickness is a good starting point. If you can find an aftermarket exhaust or reeds, that would be great, but it probably will involve a hunt on eBay, Google, etc. The bike already has an electronic ignition, so that's good. Ray |
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| Author: | JimN [ Fri Apr 24, 2009 8:48 pm ] |
| Post subject: | Re: RM100 Mods |
Ray, We found a 1979 CR 125 that we may just pick up instead of doing something to the RM 100. In which case we'll just sell it. Thanks for the reply, Jim |
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| Author: | Mikeee P [ Wed Sep 09, 2009 1:23 pm ] |
| Post subject: | Re: RM100 Mods |
We've got an early model RM100 - It's the first year so I think it's a 1976? I asked the same question all over the internet and was told the RM125 cylinder, cyl head and carb bolt right on - apparently the only diff between the 100 and 125 are carb size and bore size the cases, crank and all of that is the same. What I don't know is if this is true of the 1979 model - find a parts finder on a site and compare the crank on the 79 100 and 79 125. Then compare the base gasket - if they are the same start looking for parts. Then you'll have two post or evo racers! Mike |
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