Problem Solved

[bonceunounce]

Well we have the top end off the bike i detonated (poor tom wasnt too pleased that we had to drop the engine out )

Well, the piston and rings i guess are totalled, the piston is very burnt around the top area, the bottom ring is stuck to the piston, the top ring is also, but a piece of the top ring and some chunks of the piston around where the top ring goes.Also two big score marks about half inch long down the sides.

Ive worked it out as, when the bike turned the corner, it promptly kind of siezed but didnt seize solid , then, a piece of the top ring and bits of the piston, where taken up and crushed against the cylinder head ( explains the 6 or 7 deep scratches in the head) then the piston went back down and the bits of ring and that went out the exhaust port ( i found bits of ring and stuff in the mouth of the exhaust).

So, i take it im going to need to buy a new piston and rings for sure but what about the cylinder head? It has id say 6 - 8 chip marks and scuffs, kind of deep though spread all over it.

The barrel lookes fine, although where the exhaust port is its split in two and there is is a piece of metal running down the middle, this seems to me like its had a good scraping as its more shinier than the rest of the barrel.

Shall i replace the hole top end or just the piston and rings?

I can get pictures tommorow if need be.

Thanks

[Kickstart]

Hi

If the bore is scored then you will need to repair that, either with a new barrel or replating the existing one.

The head is probably going to be OK. Clean off any raised bits of metal and see how it looks then (raised bits would get hot and cause detonation). A few small minor pits in the head are not going to be relevant in normal use.

Also have a good look inside the engine for any bits of piston ring. Maybe get one of those magnets on what looks like a car aerial.

All the best

Keith
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[bonceunounce]

Cheers chap.

I went into the bike shop to check how much one was going to cost, but Tom is going to pay for it because its just coincedence it happened when i was riding it.

Need new barrel,piston,rings, small end bearing is going to be replaced too and a full gasket set, talking £170 ish quid.

While im in this thread, we had to drop the engine out, which ment removing front sprocket and chain, but now we have the sprocket back on, the wheel will only spin in neutral if we put it in gear it doesnt move, the bike didnt seize solid so its not that.

Have we put the front sprocket on the wrong way round? We put it with the numbers on the front, there is 13/28 written on it or something, we have that facing the front, shud it be the other way round?

Cheers

[Kickstart]

Hi

Think that someone said a barrel and piston kit are just over £100 from Dave Silver spares. Might be worth a try.

Is the engine still out? It will be very difficult to turn the sprocket by hand with the engine in gear, even with the top end off the engine.

All the best

Keith
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[bonceunounce]

We just couldnt get the back wheel to turn while it was in gear, the engine is back in the bike but the top end is still off, so there is just the conrod sticking up.

[bonceunounce]

What we really want to know is, why did this happen in the first place? The top end going.

I gave it a bit of stick down the dual carrigeway took it up to 70mph, went to a junction, turned right and conked out

The bike has done 29,899 on the clock if i remember rightly, and there is no record of it being rebuilt

So the fact the top end went, is it because of being worn out and needing replacement or is it because of something else?

I remember when tom first dropped it off to me, it had trouble ticking over and spluttered on accelerating, it packed up altogther 3 hours later. Is it just a case of it being worn out?

[McJamweasel]

Probably. Either that or you forgot to put 2t oil in it.
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[Kickstart]

Hi

2 strokes do wear out the piston rings. The larger the ports in the barrel then the more wear there will be on the rings. The higher the state of tune then the larger the ports will be (and the ports on an RS125 are a fair bit bigger than an NSR, especially the exhaust port).

I suspect it is likely that wear was a large part of it. Also you should never thrash a 2 stroke engine from cold as otherwise you will have a large chance of trashing the rings.

Not sure about the sprocket. Cannot remember from memory. What does the manual say (I sent a copy to Tom ages ago).

All the best

Keith
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[bonceunounce]

I think it is down to wear and tear. He was running it on Castrol Super TT.

Don't worry about the sprocket and that we will sort it all when he comes back from holiday.

Thanks again

[bonceunounce]

Just speaking to a bloke i know, he says make sure you do up all the top end bolts with a torque wrench to the required amount.

Is this really necessary?

[Hex]

[bonceunounce]

Aint these tools the expensive things? Bout £35?

How would i find out how tight to do the NSR engine bolts anyway? I have to rebuild it while Tom's away.

These things seem really complicated and hard to use?

[Hex]

A torque wrench ain't complicated to use, you just set the desired amount of torque and use like a normal wrench. When it gets to the set torque level it clicks, and thats when you stop (there are other types which click 3 times etc but the majority just click the once when at the set level).

They are expensive to buy, I don't know where abouts you are but its possible someone may have one you can lend?

I can't tell you the torque amount for the NSR as I don't have the haynes/workshop manual though I'm sure someone here will let you know when they read the post.
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[Kickstart]

[Hex]

[Kickstart]

Whats an "Alcohol kid"? Is that like the child of an Alco Pop?

All the best

Keith
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