WTF rz backfire

[rz250r]

ok so now i have looked through the forum trying to find some info but have come up with nothing? so my bike used to start first time every time with out choke now it backfires on the right side??? idles lower, stops running after a ride seams to have a bit of viberation slight power loss hmmmm grrrrrr WTF was running fine over the weekend but did stall when i pulled up in my driveway i have no idea can anyone help out??? o it a 88 rz250r

[Desmo]

You've done your rings.
Don't ride it until you have fixed it.

[ritza]

i concur,dr jim

[rz250r]

yep thanks desmogod took the pipes off to have a look and guess what top of piston kaput will get pics when pulled down, now the question is, is there anything that i should be checking when rebuilding it???

[Desmo]

Yeah, check your bores for scoring and wear, will also be interesting to see the top of your pistons, haven't you recently upped the horsepower on this bike?
If you have, I'd say it's leaned out and melted your piston crown.
Sorry to have to tell you, but you'd really want to be splitting your cases and cleaning inside because there is a good chance it's dumped broken bits of metal down there.
Not the thing you want in your crank bearings.

[ritza]

usually the ring will break up at the exhaust port and get spat into the pipe, i've got some good 250 pistons of various sizes, if the bores are ok. new rings on both sides and small ends,clean up the pv's, assemble....get on and ride.....

[rz250r]

ritza i'll take you up on that offer, but i need to bore out a bit but if you have some think little over size, name your price..

Desmogod here some pics for you to look at have not got any of the bore yet...

[Nath]

Ouch

If Ritza doesn't have what you need you can still get them from Pro-X, Steve at twostrokeshop.com can get them for you.

Go see Ray Easson for the rebore if required.

[Satan1]

He is in Adelaide dude....

[Nath]

Ok, well don't speak to Ray then..

[Desmo]

ritza i'll take you up on that offer, but i need to bore out a bit but if you have some think little over size, name your price..

I don't think you'll be able to bore them out mate, as far as I know, the RZs have a nikasil plating on the bores, hopefully yours will be serviceable.
You'll definitely be looking for a new head though, damage like that is just begging for detonation if you re use it.
I'd seriously consider tearing the motor down and giving the bottom end a flush out, but that's just me.
Is the bottom of the piston broken off in that first pic?
What you really need to figure out is why it leaned out and did this damage in the first place.
Done any engine/performance mods recently?

[Nath]

You are thinking of RGV/RS Jim... RZ was invented before Nikasil

Just good old fashioned steel and dinosaurs..

Agree with everything else though, head is fucked, you wouldn't want turbulence like that in the squish... and no doubt there are little bits of ring in your crank somewhere..

[rz250r]

na have not done anything to it but move the pv but i did ride it hard over the weekend sitting in power band most of the time, bottom of piston is broken, not sure what plating on the bores are?? (yet)

[Nath]

I'd be stripping it if only just to clean out the debris that has fallen into the crankcase.

[Desmo]

Nath knows his RZs better than me, so prehistoric iron it is
You may get away with with just a hone through your bores, won't be able to tell until you rip them off.

EDIT: Wath Nath said, no point in giving it new pistons and rings to have it seize when your big ends let go.

[Desmo]

Here is what a newly honed bore looks like, if you can't see the cross hatching on your, it's time for a hone.

[rz250r]

yeah reading up now on how to split the case???? can i get the head polished???
i think i'll bore it out anyway, there is no cross hatching that i can see, hmmm whats the difference between hone and bore???

[Desmo]

No real benefit from polishing the head, just make sure it's nice and clean.
Do you have a manual for your bike?

[Nath]

Removing material to get the dents out will change the dome volume and mess up a few things unless you recalculate the volume and adjust the squish accordingly.

I would skip it and find a new 250 head, heaps of those around.. probably got a spare laying about.

[rz250r]

lol spare parts here in adelaide yeah right this place has nothing i drove 50km just to get a clutch cable not much here to do with rz any more, have been looking around for a head and found nothing yet