[rictus01]

Hi Laura,

I'm prosuming you have standard rings/pistons & bores ? and not something over sized ?

also you don't say if this is a new problem or something the bike has been suffering from for a time ?

I've worked on about 30 SV lumps and never see one with worn rings to the extent the garage was talking about, and there are many reasons for low compression, although as stated above valve clearances should have already been checked at your mileage.

"Trapped valve" and what is that then? are you talking about a valve not seating properly? which could be down to clearance or being bent, the clearance issue is easy to check, if it's bend then the question is to ask why that would be.

As to lapping in the valves, generally new engines don't require this as the seats are hardened..

So to clarify,

28k won't normally see a cam chain go, but the SV's tensioner are a known weakness, reset it and it should be fine (do this first as it may effect the stuff below / about 20 minute job)

As to the piston problem,
are you suffering any performance issues or high oil consumption ? these could point to problems. you will also have higher crankcase pressure as combustion will leak through. if not then it isn't you rings/piston causing the problem.

I'd first check the valve clearances (do a search/ perhaps an hour at most with basic tools), colour of the plugs (this will tell you if the bike is running rich (causes backfiring) or not), then airfilter (this will lead to rich running if blocked), then check the crankcase pressure.

as the rocker covers can be removed with the engine in the bike all the above shouldn't take more than an afternoon and have a minimal expense, but could save you a fair amount.

Cheers Mark.