Replacement engines (of any cc) for eos 125cc MK2

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ssymes007
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Replacement engines (of any cc) for eos 125cc MK2

Post by ssymes007 »

Looking to fit a bigger engine to my eos 125 mk2. I know the quadzilla 250cc fits straight in but are there any other decent engines that also fit? Ideally a V-twin even if it does take a bit of fabrication (but not too much).
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Eamonn
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Re: Replacement engines (of any cc) for eos 125cc MK2

Post by Eamonn »

In my experience trying to fit a different engine is a difficult task on a number of levels. Firstly, you have to find an engine that would fit the existing frame (possibly with custom made engine plates) ensuring the final drive chain matched the position of the rear wheel and isn't too tall so that you can change spark plugs without removing the engine again.
Secondly, with an increase in power, you should also review the stopping power - this may require a bigger disk and the associated calliper and larger brake fluid reservoir.
If you get all of that sorted, you then have to tackle the legalities of updating your insurance to cater for a bigger engine in a bike that wasn't designed for it. You may find that some insurance companies would only offer very high terms in this situation.

As a general rule, it's easier/cheaper to sell the smaller engined bike and buy a bigger one - it all depends on how determined you are and if you have suitable workshop tools/experience.
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SPRIDDLER
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Re: Replacement engines (of any cc) for eos 125cc MK2

Post by SPRIDDLER »

My thoughts mirrored all those of Eamonn to buy a bigger engined bike.
However, it would be interesting to know why you want a larger engine: Is it for more grunt when loaded with pillion and/or camping gear, or faster acceleration, or to increase top speed?
If it's for an increased top speed and you are determined to fit a 250 engine you may need to raise the gearing by fitting a larger output sprocket or a smaller rear sprocket, in which case you'll need to verify that the chain won't foul the frame.
You may also need to fit the 250's engine electronics.

In 2018 I rode my new Honda CBF 125 1,800 miles to Spain and back but wanted a bit more grunt as the cacophony of 8,200 rpm at 65mph on the 125 was very tiring, plus the zillion gear changes necessary at every slope, bend and head wind to keep the speed up. When traversing the Pyrenees I was changing gear up and down about every 50 yards. :roll:

I replaced it with a new Herald 250 Classic (no longer available) which is a more relaxing ride and has the Suzuki GN 250 engine. The Sinnis Retrostar 250 is the same bike but with different graphics. Both are available s/hand.

Herald have just 125's and 400cc models now.

https://heraldmotorcompany.com/our-bikes/

Sinnis now have 125's and 380cc bikes.

https://www.sinnismotorcycles.com/sinnis-motorcycles/
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Greybeard
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Re: Replacement engines (of any cc) for eos 125cc MK2

Post by Greybeard »

Eamonn wrote: Tue Nov 23, 2021 9:20 am As a general rule, it's easier/cheaper to sell the smaller engined bike and buy a bigger one
That would be the sensible approach, Eamonn. There again a bigger bike wouldn't have 125cc on the V5 - just sayin' :roll:

Steve (a confirmed cynic)
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Eamonn
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Re: Replacement engines (of any cc) for eos 125cc MK2

Post by Eamonn »

100% agree Steve. In the 70's we would never have put RD350 engine in a 250 frame nor would we have put an S2C engine in a KH250 frame, that would have been illegal after all...!

:D
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ssymes007
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Re: Replacement engines (of any cc) for eos 125cc MK2

Post by ssymes007 »

Really appreciate all the replies. My main motives is to have a bit more power through the gears. The Eos seems to be built for a bigger engine for example the carbs and brakes.
ssymes007
Posts: 8
Joined: Mon Nov 22, 2021 7:08 pm
Location: Wirral, Merseyside

Re: Replacement engines (of any cc) for eos 125cc MK2

Post by ssymes007 »

Really appreciate all the replies. My main motives is to have a bit more power through the gears. The Eos seems to be built for a bigger engine for example the carbs and brakes.
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