ZZR250 overheated, blew head gasket

[imthatguy]

Chances are the head is fucked. Usually with little Jappas like this the heads go soft after overheating and they go wobbly too. But worth having it checked if you really want to play with the motor (nothing wrong with that idea spanner time is good)

You'll want to hone the bores and re-ring it. So you'll need a set of micrometers, feeler gauges and a decent vernier caliper. (probably cheaper to borrow), I hope it's a poor photo because that bore looks glazed and I cannot see any cross hatching at all

I'd pop the barrels off it and have a good look on the thrust side of the pistons for signs of seizing (nice tasty marking) which I imagine it has done. If it has, pistons are toast unless you want a hand grenade motor. Checking the bore size all the way down is nice and easy, just calculate it with the ring gap

You can buy forged pistons for these with a number of different compression and squish arrangements
Also if it has been seizing, there is a very, very high chance that it has damaged the mains and big ends, they're not huge fans of suddenly stopping.
The rods will have to be very carefully inspected too as they're very petite around the small ends and seizing never helps
And after going that far, I would be investing in some beer to pay a decent mechanic mate to split the cases, because you'll learn a lot if you do.


And that's just the beginning

Thats the spirit haha

All great advice.

Just to clarify, Ive been though heat seizing before, as I mentioned this happened in my previous motor, it was characterised by an immediate sharp decline in power, up until it stopped completely, then it would be unturnoverable for 40-50 minutes afterwards while it cooled down.
This isn't what happened to this engine, apart from the fuel thing, I didn't really notice any loss in power until I pulled up next to the pump, then it stopped but it didn't feel like it seized, it just.. Died, like it would from running out of petrol (but not, because there was still petrol in it). When I went to try start it ~10 minutes later it turned over freely, just didn't want to actually catch and fire, like it was running low compression ( and the bubbled in the coolant as it was turning over would indicate that same). I would have thought that it it really overheated it would have exhibited the same symptoms as the original engine and not turned over at all, or atlas felt like it was rubbing..

Photos were taken on my phone in a dark shed, Ill do my best to get you some more tomorrow. It actually looks more or less ok from what I can remember..

Maybe Im just being unjustifiably optimistic, but, even if its completely toast as you suggest its still been an interesting exercise

Thank you for all your help!

[imthatguy]

Yeh, reckon that could be the case; which would take water out of the equation (but in a good way this time). So after it stopped from overheating, did you try and run it again once things had cooled? if so what were symptoms, compression etc.

Check page 3 haha

[ducatilover]

It is pretty hard to fix motors on the internet sadly but I reckon it'll be a bit of a giggle for you. I'll let ya know if/when I come over that way

[imthatguy]

It is pretty hard to fix motors on the internet sadly but I reckon it'll be a bit of a giggle for you. I'll let ya know if/when I come over that way

Its the journey not the destination right?

Sweet man, I appreciate it!

[imthatguy]

Its the journey not the destination right?

Sweet man, I appreciate it!

Im about to head into an exam so this'll only be a short update, but Ive spent the last few days pulling and inspecting the top end and putting it all back together again.

I had the head planed as it was significantly warped. Somewhere (ill upload photos later) I have a photo from the machinist of the damage.

Pistons seemed alright and there was plenty of gauzing left on the bore, so I decided to put it back together and see what happened. Low and behold, after my throughly flat battery had been given some juice, it roared back into life!

All up the total cost of the rebuild has been about $80 not including tools ($250) and im going to change the oil/filter/coolant ($60).

Its anyones guess how long its going to last, ill saver my victory while it lasts

Thanks for all your help guys!

[Bender]

Well done that man.

[BlackSheepLogic]

Just to clarify, Ive been though heat seizing before, as I mentioned this happened in my previous motor

There's a maintenance issue you should fix.

[imthatguy]

There's a maintenance issue you should fix.

This was, you understand, on the previous motor? Not on the one thats in there now. I will pull the head off the old one at some point and take a look, but this discussion was based around the new motor.

[ducatilover]

Well done that man.

+1