My CBR1000F engine had been burning oil for some time, i got round to check the compression and the results are even but only 95 PSI.

The book suggests around 160 PSI.

So, i need to fix it and am unsure what to do. I would like to order the bits ready for me to start, but at this point im unsure if i need larger pistons or just standard piston rings? any ideas? worth me taking the risk and ordering the rings only.

Also, any idea how much power i would loose with these results.

Worn bores is my bet. Which means a re-bore and oversize pistons and rings. Though I am not sure that you can buy oversize pistons and rings for bike engines, I have heard a few bikers mention that they couldnt get them, but it is very probably dependant on the make and model.

David

How many miles has the engine done? It sounds, as Flak says, like worn bores. There are overbore kits for many engines, but not all. It may be worth getting a new engine over the rebore, but that depends upon price.

david silver spairs show an oversized piston for the engine. But how much is a rebore?

Also, maybe talking poop here i have a spare engine but dont know its history. is it worth me taking the bore block and pistons out of it and stick them in my engine. (swapping the engine is so much more work and also riskier then the above)????

Compression pressures that low normally indicate broken compression rings or burnt or bent valves however these faults usually only occur in one or two cylinders, which makes me think perhaps the test is giving a spurious result..
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Did you have the throttles wide open and all the plugs removed when doing the test?

How will changing the engine be more work than taking it out to split it in half? And then still putting it back in!

Have you tried putting (a little) oil in through the plug holes to help seal the bores? If that improves the readings it's worn bores... If not it's something else.... Otherwise, was the engine hot / cold as stipulated in the manual for the reading of 160 (or whatever it is!).

I think British Trident may have the answer here!

If your getting even results at around half the specified compression it sounds to me like the test isn't being done correctly. You need to have the engine at normal operating temperature, then (as above) remove all the plugs and test each cylinder by cranking on the starter with the throttle fully open. You need to allow 4-5 revolutions to get max compression pressure. if you're using a dial type gauge then ask an assistant to watch the gauge while you crank and let you know when the reading stops rising.

Puma Race Engines have an excellent guide HERE on compression testing an engine - well worth a read.

Obviously you may alrady know this and be doing the test correctly and indeed have a seriously worn engine. However I didn't know when first attempted it and spent a few weeks thinking my freshly rebuilt engine was no good.

warmed up, all plugs removed and full throttle. Also i could see the guage from the drivers seat on all the tests. I am positive its the correct result, just trying to see what needs doing before i take the car off the road.

i wont b splitting the engine out of the car, but leaving it in and taking it apart there. i need to do the cam chain tensioner anyway so its comming apart. I am also turbo charging it soon and might lower the compression at the same time.

Is it possible the engine timing is out?

I know nothing about bike engines. But it sounds like the engine timing is out.

Is it possible to do it in place? Do you not have to split the box/crank case from the inside? I may be wrong of course, but most I've seen you have to get at half, if not more, of the bolts from inside the gearbox half.