Boring worn/old engines

[Jamiyjames]

Ok I'm looking at getting an old bike to start doing some track days here and there, and for the price in looking I know I'll probably see some shocking bikes,, however if I see one I like and the engine needs some work I might consider it, so my question is if I needed to overhaul an engine and decided to bore it out 1) would it be expensive? Or would it be cheaper to buy a near new bike? 2) if it was bored out I would assume it would need a new sized piston to create a proper seal? 3) is there any things to consider if I went ahead with boring the engine, like bore stroke ratio, insurance (as is be riding it to the track most likely) eligibility to get on the track, higher torque /top end power etc?

And if you have any Experience with this please could you share?

Thanks :-)

[Sensibleboy]

Probably better to just get a used engine than rebuild the existing one.

[Jamiyjames]

well if that's because its a lot of hassle then that doesn't bother me its the financial cost that bothers me the most.

[paintman]

Assuming the bore can be re-bored then you will need a new piston for each cylinder. Plus replacement bearings in the little ends of the conrods to go with the new gudgeon pins.
Be as well to check cams/camshaft/rockers/big ends/big end bearings/mains/main bearing - basically all moving surfaces.
Can be cheaper getting a recon engine.

[BritishRacinGrin]

Nobody really overbores engines any more. If you wanted to do the engine as a project, you can often get away with honing the bores and fitting a new set of rings. Same amount of labour / practice but much less cost and ultimately still beneficial to the engine provided the bores are still round and aren't very severely worn or scored.

[Tango13]

Big bore kits for mainstream sportsbikes are so so common you're spoilt for choice.

If you can get your hands on a halfway decent Suzuki GSXR 600/750/1100 then the world is your lobster. So much work has been done by tuners here and in the US that all the problems we solved years ago. You can bore and stroke them for an extra 25/30% capacity and providing it's put together properly you won't lose anything in reliability.

If you're feeling devilish get something like a tatty old GSX 600/750 and cram it full of GSXR internals, sort the suspension and you'll have a bit of a sleeper.

As for telling your insurance, most bike insurers are used to modifications so they might charge something but most won't really care, nor will the people that run the track days.

[chippy348]

I have a bit of experience in re-boring motorcycle engines, but you are best to start with what make and model it is first.