What motorcycle engine?

[Tim-vvgqc]

I will probably be selling my bike after my accident, and think I will use it as an opportunity to buy a motorcycle engine or two. I always enjoy building & maintaining bikes as much as I do riding them but I have never done a full rebuild of an engine.

Does it matter what I get? Are some much harder to work on than others, or is it much of a muchness? Is it easier to learn by repairing a broken engine or just rebuilding a working one?

Thanks

[Super Sonic]

Air cooled two stroke single.

[Mad Scientist]

How about a fireblade 929?

Got one in bits in the loft that I’ve moved house with twice. Had some bore scoring but despite apparently being nikasil liners we managed to hone it off.

Yours for a drink if you want it.

[OutInTheShed]

What's a 'full rebuild'?

Could be just assembly from parts, or it could involve diagnosis, getting things machined, a certain amount of manual metal work, shimming, selective assembly, blueprinting perhaps.

You can do a strip/clean/re-assemble very cheaply sometimes.
Putting an engine back to 'as new' or even 'within service tolerances in the manual' can cost a lot in parts and machining services and I'd want to be sure the end product was worth it.

My first 'full rebuild' was building a bike from one with a knackered engine and one with a broken gearbox. Very few new parts needed, just a few gaskets.
Some might say it wasn't a 'full rebuild' because I didn't take the big end out of the flywheels.

[J__Wood]

Super Sonic said:

Air cooled two stroke single.

Yep start with an old air cooled two stroke single, then move on to old four stroke twin?

Stick with carbs that way easy to bench run without faff of water cooling constraints and ecu wiring (as long as you get coil(s))? Plus all the fun of cleaning jets...

No point rebuilding unless you can test your hard work.

[Birky_41]

Super Sonic said:

Air cooled two stroke single.

Can't beat a big one of these. I got 3 all over 400cc and they are lovely engines which go for hours and hours before needing even a ring

[KTMsm]

What are you looking to achieve ?

If you have room for a bike I'd buy a complete non runner then you should at least get your money back

I've engine swapped a few cars but I've never rebuilt an engine as it generally doesn't make financial sense

If you just want to strip and rebuild something I'd start with a lawnmower

[Super Sonic]

Birky_41 said:

Can't beat a big one of these. I got 3 all over 400cc and they are lovely engines which go for hours and hours before needing even a ring

CR?

[Birky_41]

Super Sonic said:

Birky_41 said:

Can't beat a big one of these. I got 3 all over 400cc and they are lovely engines which go for hours and hours before needing even a ring

CR?

No I have Maico engines. A 440 piston port and 2 x 490 reed valve (1 has a CR500 reed valve welded onto it)

I do have 2 x CR250 (1995 and 1996) and 1 x CR125 (1997) but these are all watercooled

[Birky_41]

There ya go. Here's one we're working on now. Real strong power and very simple to work on

This is the practice bike 490. The race one is ported more aggressive with higher compression

[spoodler]

KTMsm said:

What are you looking to achieve ?

If you have room for a bike I'd buy a complete non runner then you should at least get your money back

I've engine swapped a few cars but I've never rebuilt an engine as it generally doesn't make financial sense

If you just want to strip and rebuild something I'd start with a lawnmower

Exactly.
Ask yourself what you want from this. Old British engines and Harley engines are simple to rebuild (in theory, but sometimes less so in practice) and will always find a buyer once built. In demand Jap' sports bike engines may recover what is spent on them. But, they are not cheap to buy in the first place and you could get hold of, and rebuild, some complete bike for a similar cost. On the other hand, you could rebuild a small cheap Japanese engine and find there is no market for it once done...
You will probably find few folk willing to pay well for your completed engine, most, unless it's dirt cheap, won't want to take a chance on your "fun, just to gain a little experience" project.
If it's just for fun and the experience of making something work again, the lawnmower suggestion is a good one. Old Qualcast/Suffolk Punch stuff is well supported (with owners groups, spares etc) and it's something that you could use (presuming you have a lawn) when finished.