Engine Transplant ?

[grewth]

Hello to you all!
I've just joined today.
Basically I've got a small collection of XS650 Specials, and I'm on XS650.com under the same user name.
But also at the back of my shed I have the mortal remains of a XS250 Special from about 1980.
This is a UK market version of the XS400 Special, built with a smaller engine for the UK "learner" market, which had a 250cc limit at the time.
This was only an incomplete rolling chassis when I bought it, but what has been happening is that as I've been buying, selling, and swapping XS650 stuff, I've also been picking up XS250/400 stuff along the way.
I don't have an engine for it at present, and although there is plenty of XS250/400 stuff floating around here in the UK, I'm wondering if I could squeeze something else into the frame instead.
Maybe something like a mid size four pot, perhaps 500 or 550cc ?
I haven't tried anything yet, but I'm wondering if anyone else has built a successful XS400 hybrid yet ?

 

[CaptChrome]

Well, I can't help you with the transplant info you need, I certainly can offer a welcome to the group! I for one will be interested with what you come up with and do with the bike.

 

[flea]

cant help you but will follow this with great intrest as the xs250 is as gutless as

 

[festasextremis]

The xs250 is a tiddler for sure, and while not any kind of whelming, under, over or other- it has options.

The xs250, 360 and 400 share the same conrods, cranks and cams. The valves may differ, but i cannot remember by how much, or if by much, if at all.

The 250 barrels can be bored out to about 450cc (roughly, just check it isnt hard.) and same for the 360. The 400 might be able to go bigger, but whatever...

The top end of the 250 has smaller ports, but thats a super easy fix. Just machine out a few extra mm and have some porting work done.

The cam, like an early cb250, xs650 and so on is super easy to get ground to a nicer profile. I send it to a machine shop in Ballarat, and they are around the corner from the re-sleeve/machine shop.

Put a thin base gasket (or do a base gasket delete) and a thin copper head gasket on, have a straight through exhaust fitted or made up and jet the (new- round or flat slide) carbies till the plug chop is a nice light brown/grey.

This is now a perky, loud and light bike.

You will need a number plate flipper in the U.K. if you want to avoid AI generated fines and compliance breaches.

Alibay and probably temu have pistons, it shares the same config of wrist height, etc as the yamaha majesty and some others. Wiseco make nice pistons and there are a few vendors in the UK that sell complete gasket kits.

As for being gutless, i ride a 2004 honda CB250 "nighthawk", i weigh 141kgs dry, and that thing struggles to get up past 127km/h on the flat. I have done a stage 1 (carb and exhaust mod) and it accelerates fine... If a Toyota yaris is "fine". It is loud, reliable and quick through traffic, and costs bugger all to run, register, and insure.

The XS250, feels nearly 2 times quicker, but a little heavier and a tiny bit faster... Plus, it's a better looking bike, i think. It's funny to think that the kawasaki gpx/ninja 250 is nearly 2 times the HP of the honda 230cc "cb".

Not many other engines would straight up fit, and you are going to need to cut and weld, and machine new brackets and so on. But basically anything would fit, but why? It's less hassle making a bike go faster by working the motor.

Remember the indian scout 101 would have been barely 30hp in 1920 at 600cc, yet a crafty kiwi made his go 200mph! Sure,it was 1000cc and had a custom OHV mod, but still. Enough time and energy and mountains do move.