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SL100 advice please

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I have decided that it is finally time to do something about our Honda SL100. It is VERY low on power and needs new piston/rings/ clutch plates.The bike has abotu 30k on it with the motor having 15k. What I was wondering is weather or not I should leave it at 100cc or just get a 125cc piston/rings/jug.

My dad has a SL125 and I have the Sl100, so we have a set but I think it would be cool to have a little more power.

Anyone know the HP difference? I know our 125 is LOADS faster than our 100, but the 100 is mega tired.

Let me know what you think, here is a video I did last year.

Thanks :)

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Well, right off the bat, the parts for the 125 are not a drop-in replacement, because the 100 has a smaller diameter wrist pin than the 125. Con-rod replacement is required to use 125 parts on the 100.

That said, there are big-bore kits available from Powroll specifically for the 100, even stroker work too. The vintage 100cc class has generated a renewed interest in hot-rodding the 100.

However, the 125 engine is a bolt-in swap for the 100 engine, so perhaps picking up a spare 125 motor and rebuilding IT would be the way to go.

That's what I'm doing on my OWN cafe project - rebuilding an SL125 with a NOS big-bore kit (150cc). I'm using a later model 2-piece head for it's better porting and bigger valves than any of the early 1-piece heads. Plus, a better selection of cams and springs for the later heads. 26mm carb from an XL175, too.

On the other hand, a straight-ahead rebuild on the 100 would get you back in business quickly and cheaply, if your needs / wants are mild...

Good luck with whichever way you go.

Kirk

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Hey, I was wondering about the 2-piece head you mentioned. I have a few 100's and was considering doing similar work on one of them. I have my '71 SL100 that I bought in 1974 and rode to school. I also have a '71 CL100, and 2 more SL100 parts bikes.

I have read quite a lot about stroke and bore options but I am not familiar with the head you mentioned. What years and models were they used on and any other info you have. Thanks, Marvin in GA.

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Hey, Marvin,

We've discussed this quite a bit here in the Vintage forum, but not for 6 months or so... Do a bit of searching on my name (KDN) and you'll find the threads. Lots of input from some real experts, ie, not me. :)

The short take is the first few years (74, 75, 76) of the XL125 came with a two-piece cylinder head that had much better ports and much larger valves than the one-piece heads found on any of the SL series and on the later CB/CL/XL 100's. The head splits right along the cam centerline rather than taking the cam out the side of the head.

They interchange onto the earlier SL's but the cam sits lower in the head, relative to the head gasket, so you'll need a shorter cam chain and shorter cam chain tensioners (front and rear) from the 2-piece head models to interchange them onto a one-piece model.

Later models (78 or so, on) also had the 2-piece head, but changed the way the head attached to the frame, and are not as interchangeable. Later yet, the points moved from the end of the cam to down under the flywheel, so they're even less interchangeable.

Good luck with yours!

Kirk

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I raced an SL100 dack in the day , late 60's , and at that time we would take one piston from the old honda 160 scrambler ,it had to be machined so that the valves would not hit,other that that it would fit the 100 cyl.

It considerbly raised the compression becaused it was a domed piston.

Made lots of power for the $ spent.

Don't know if you could get a 160 piston ,maybe Wiesco.

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