Heat seize?

[ukchad]

Bad news.
Engine was always running a bit hot, but I topped up with coolant and decided to take advantage of the Sunny weather yeasterday.

Hit 60 on the main road and bam! Back wheel locked solid.
Managed to keep it upright.

Coolant all around back wheel.
Temp gauge off chart.

Wheel seems to be freed up now when in gear, but can't kick down gears into first.

Not tried to hard to do anything, but did kick it a couple of times after cooled - never sounded close to firing.

I'm a total novice in these things, but what's the worst case here!

[declan]

@ukchad worst case is of course your entire engine is scrap how ever you won't know till you dive in a hard seize will most likely have bent your con rod and that's when it starts to get expensive and tricky

[Calum]

@declan Highly. highly doubt this is the case.

These engines are solid.

I agree that's the worst case. But that's only going to happen if the engine was well due a rebuild and it was revved with no oil to 20k rpm.

Nah, I'd say in this instance, you've scored the bore and the piston.

If the piston isn't fried, then you could get away with running it, albeit down on power.

But it'll need a top end rebuild.

So long as the piston remained in once piece, it'll need a rebore and a piston and that's about it.

If the pistons come dislodged, it may have gone down the bottom end, in which case it's going to need retrieving.

But I've had this happen before and got away with just a piston and bore change. Bottom end went on for a while after.

Depends on your budget. These engines are pretty strong.

[ukchad]

Thanks guys
A Yamaha Garage to do this?

[Calum]

@ukchad Any place with the ammenities for a rebore. I used Yamaha Skellerns Cheltenham because these guys are super into it, but they probably send it away to be done as it's specialist job.

PJME will offer a rebore service. But first thing is to see what has failed.

[declan]

@calum he did ask for worst case lol

[ukchad]

Ok

Bike went to garage, and needed rebore skim new piston and genuine Yamaha head gasket. Power valve was shaved to stop wider piston hitting it.

Bottom end was OK

Rebuilt and filled with silkolene Comp 2 stroke oil and coolant.

Managed to find 3 wire servo, cables pulley etc, which the garaged fitted correctly for me.

Electrics were fixed and tidied up while they were at it - total cost was £360. Incl vat

Now I have full power!!

Not that I have fully tried it yet as the mechanic told me to run in at 200 miles under 6000rpm, 200 miles at under 7000rpm and 200 miles under 8000 rpm.

Does this seem a bit excessive - I want to get that power valve fully opened!

[declan]

@ukchad people swear to take it easy but in my opinion it's excessive I done about 40 miles then thrashed mine and it's brilliant no issues with the top end but tbh is it worth the risk?

[finnerz89]

@ukchad that does sound excessive. I'd say use the whole rev range but don't labour the engine or run WOT for any length of time. Do that for 2 tanks of fuel then let her rip!

[ricky0115]

This happened to me, me being a noob I just bought a refurbished engine from eBay £250. Stripped the bike down and rebuilt it, currently on the wiring loom & hoping to have it running by 3 o'clock

So I have a few bits for sale I'll be posting tomorrow!

[Calum]

So if this were a four stroke engine I'd be like yeah, break her in.

But sorry, piston and rings is simply maintenance on two strokes.

I would bed the rings in to the new bore, or give the bottom end a good run in (which you haven't built so no need). I'd do the rings and piston in 10k miles.