Right guys, Pulled the heads on the race bike.

Diagnosis time. Lower cyl:

To me it all looks fine except for the bright ring on the piston and corresponding one on the head! how the heck does that happen? no play with the rod on the crank, could the crank have worn bearings causing that damage? (i assume its contact) This is the cylinder that doesnt belch heaps of smoke. The other one when I pulled the exhaust sloshed so i tipped it up in a bucket and got like ~50-100ml of super tar black oily liquid (the spray that was coming out the back of the bike I presume).







Upper cylinder to come soon/tomorrow:

Great pics, it does look like contact, however will leave it to someone more learned on these matters. I would however think that the liquid out of your other pipe is infact un burnt fuel. I had a stuck float in a carb once which flooded one side. It was a pain draining it, as I was concerned it might cause a fluid lock if I ran it. Cheers.

Piston to head contact.
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And now for the top cylinder (pushes air most of the time instead of firing), argh.

Crown showing more impact damage than the other one? At least he same ring.


Signs of seizure??


And the real damage, heavy scoring down the length of the piston - rings are free still though.


.. And corresponding scoring down the length of the barrel quite deep indeed. Also out of focus, patch of plating that has gone there is another smaller patch missing on the other side ..


The locating pins for the rings are present, the only thing to cause that damage would be something injested or the tip of a plug getting down right?

AFAIK it was run with airbox but no filter..

looks like someone forgot to fit the wrist pin circlip

FFS, you're not wrong .. Just went out and gave it the pin a push and it popped straight out the other side.

Bloody hell, least I know its nothing more than incompetence

Whats your opinion on the piston to head clearance reasons? the rod doesnt seem to have any play on the crank.

I wouldn't have thought that the standard squish would be close enough to cause this, so maybe the barrels/heads have been altered. I think there may have been different height barrels SP/R, but once again will leave this for the experts. Running an extra or thicker base gasket may be sufficient to get the squish right. The fact that it's on both cylinders means atleast whatever the person did was consistent...

Haha I said the exact same thing to my mechanic/machinist Shmokica.

There has been some DIY work on the ports, so I wouldn't put **** headwork out of the question.

Took the top off one and it's running a single gasket up the top (were they multi layer originally by chance??)

The gouge in the port isn't high enough to affect compression apparently either. So my friend/acquaintance (from my previous 2stroke addictions ) is going to sort the head out to stop it contacting (machinist by trade) lap the gasket surface flat and get it in a state to be used. I trust him well and he is pretty onto it preparing 125GP and RS250 machines on a regular basis, so he can make my bunch of bones ring a ding ding once more!

hang on a mo. Can you take a picture of the exhaust port? I mean fire a shot from the outside in.

Actually I can't, barrels are at the guys place for the heads to be lapped flat etc.

What're you thinking has been done Matt?

One of them has a crack across the exhaust bridge up the top of the joint, goes about halfway across the width of the bridge.

MATT!!

I know what you're thinking! Not easy to see, but take a close look at the bottom of picture one... I think those barrels should be running single ring pistons!
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OK what would I be looking for, keeping in mind my knowledge about NSR's is entirely from what i've read searched for on this site in the last week or so.

One of the barrels on the bottom has a symbol on it that the other doesn't, looks to be scribed into it a 7 with a line thru it. Almost japanese looking, probably not what you're thinking of?

Post some better pictures of the barrels please. (My comment was to Matt... he'll understand when he sees it!)
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FruitLooPs wrote:Actually I can't, barrels are at the guys place for the heads to be lapped flat etc.

I guess it'll forever remain a secret! Once the barrels are back i'll be sure to

NSR base gaskets are single piece, stock is 0.5mm, HRC do 0.4's and 0.6's as well.
Head gaskets are just head gaskets, I've got a used one here, it mic's up at 0.3mm.
Stock squish is always within 0.1mm of 1.2mm.

So we can see no matter what you do you'll never get piston/head contact and your barrels are too short for stock pistons by over 1mm.
Clearly your barrels are butchered to hell or not intended to be run with standard NSR pistons. That's why Matt wants a clear pic, so he can see what they are.

But possibily of more importance to you right now is to realise that without quite a hefty amount of work (or just running multiple base gaskets) you'll struggle to get both the squish and the head volume right.

When you get the barrels back measure how tall they are.
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