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1989 NSR250R engine rebuild


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F@ster

 
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1989 NSR250R engine rebuild

Thu May 04, 2023 6:36 am » Post: #1 » Download Post

HI Guys,

I'm new to the forum, but not new to NSR's. I rode an '88 MC18 R2J in high school in the 90's, but unfortunately the bike was damaged beyond repair in 2009 in a crash. I've recently bought a 1989 MC18 R5K in crates, and intend to build it up and restore along the way. The biggest issue I'm, facing at the moment is that the engine was stripped for rebuild (I have a local guy in South Africa to re-do the cylinders) but the crankcase has not been split. As there is corrosion on the crankshaft I think it would be prudent to rebuild the bottom end while it's stripped this far. From what I can tell on the rebuild pages on this site, a special tool is needed to remove the clutch, what they call a "special fabricated clutch holder" but there is little information on how to make the tool. My question at this stage is this: Where can I purchase the clutch holder, and the flywheel puller from that ships to South Africa?

I have the parts catalogue (in japanese) and workshop manual (in english), but any leads for required bearings and seals for the crankshaft rebuild would be much appreciated.

This is going to be a long-term project for me, as the seller unfortunately did not have any bodywork for the bike, and the exhausts seem to be modified from an R2J to fit, so will most likely need replacing to achieve the finish I'm aiming for. I don't have much to show at this stage besides a pic of some crates!
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RobH

 
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1988 Honda NSR250 MC18
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Thu May 04, 2023 4:42 pm » Post: #2 » Download Post

You'll need a flywheel puller and a clutch holder tool. Wemoto in the UK stock them
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RobH

 
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1988 Honda NSR250 MC18
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Thu May 04, 2023 5:02 pm » Post: #3 » Download Post

The challenge that you may have is parts to rebuild the crank
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Andy
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1991 Honda NSR250 MC21
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Fri May 05, 2023 1:40 am » Post: #4 » Download Post

Hello F@ster, and welcome to NSR-WORLD.COM Smile

The clutch tool can be fabricated from an old steel clutch plate. See the topic/post here:

http://nsr250.net/forums/viewtopic.php?p=104915#104915

If there's corrosion on the crank from water damage/damp, it's almost certainly scrap I'm afraid. Officially NSR250R cranks are (were) classed as a consumable item, and therefore non-rebuildable. Some OEM parts have become available (the Koyo main bearings) in recent years, and some owners have managed to adapt third party parts such as big-end bearings and thrust washers, but none of these are available officially from Honda. The biggest problem though, is that the main bearing pins are integral to the crank flywheels, and cannot be replaced. Any pitting whatsoever on the pins (which is highly likely if there's corrosion on the crank) renders a rebuild unviable.

1989 R5/6K cranks are similar to MC21 and MC28 cranks, but not interchangeable. It is possible for a good machine shop to turn down a new MC28 crank to fit in 1989 cases, but it's not recommended as the cranks are obviously balanced at Honda, and you always run the risk of getting swarf in the bearings, no matter how careful you are.

Don't just let any old muppet rebuild it! They need to be experienced with NSR cranks.

Fingers crossed, when you split the cases, the crank [at least outwardly] appears in good condition with no immediately apparent corrosion. It will need rebuilding though, that's a given.
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