Pulled the top end on that black DTR i recently bought to change the head gasket as it was leaking(why do DT owner's find it so had to put a gasket on).
Once i got the head off i was in for a big suprise, the piston only had 1 ring on it. The bore is standard 56mm but it's clearly hit the pv?
I took some off the PV and put a new(decent condition one i had in my shed) piston on it, put it back together didn't change the head gasket in case i have to pull it again soon(£25 an OEM gasket now).
I started it up for 15 mins, let it cool down re torqued the nut's. Started it up again revved it up to 10k this time, all seem's fine might take it for a ride in a bit to make sure.
What i'm really suprised about is it ran pretty dam good on 1 ring although the band did kick in around 8k and didn't pack as much punch, but i thought that might be gearing as iv'e been on 13-55 for ages
Also how the hell did a 56mm piston hit the PV? The bore seem's fine, but the head took a pounding.
p.s I would definately go for a rebore/new piston if i planned on keeping this bike for the long run and used it for more than sundays. May have to though if this piston goes
That cylinder head looks rough. Is that pitting in the cylinder head?
You're surprised it ran good on one piston ring? YZ 125's and lots of other motorbikes only run one piston ring.
Yeah that shouldn't have hit the piston. That powervalve has some extra markings on. Are you sure that the right one. I don't know but that's the only reason I can think.
And yeah I've moved off OEM gaskets now. For general rebuilds mate use Athena. very good quality does not blow like pattern. I guarantee that. And it's only a 10er.
Probably then a likely scenario is that the piston ring failed and snagged the powervalve on its way out.
Could have been installed incorrectly. Piston ring end gap not correctly measured etc etc.
I'd bin that head. It's ruined. Naturally this sounds like a doer uper and if it runs, it runs can get a sale. I'd feel sorry for the person buying it but that's life I suppose.
might take it for a ride in a bit to make sure.
