hi all,
just joined the forum today so hi to you all, i have afew questions for you all, as my ive just had to take my mc15 r5k apart again, i had my barrells plated by langcorts about 500 miles ago and just had a minor nip up, ive taken the barrells off to inspect them and both have marks on the pistons and rings where they have been passing over the exhaust port bridge, im guessing they were never releived after they were plated, my question is can i releive them myself with, say 400 grit paper, if so how deep should i go ? 0.05 mm perhaps ??? and lastly will i wear through the nikosil doing this and does it matter

thanks for any light you guys can shed on this for me

steve

mc18 sorry

Hello!

Not sure what you mean by releived, or what you're trying to do.

How deep are the marks? You'll get better information from here if you can figure out how to post pictures.

Check for cracks on the exhaust bridge. They're bad and will be a major cause of the wear of which you speak.

mc 15? What is that? I haven't heard of one and google images would have me believe it is some sort of ultralight, a subwoffer or some really ugly girl pulling faces.
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MC21 Honda NSR250. TYGA 300 conversion.

Oh, mc18, my bad!

If you have hone marks on the exhaust bridge send it back to the platers as there will be no clearence for the brdge to expand out when hot.

I would assume relieving the exhaust bridge needs to be done before plating. Either way, I wouldn't screw with it if I were you.

Hi Steve

Sorry to hear your bike nipped up.

Yes, ideally the exhaust port bridge should be relieved after being replated and before use - to give the thin bridge room to expand. (As the bridge is thin it heats up faster than the rest of the cylinder and expands faster, & can sometimes rub the piston). I'd be surprised if the plater hadn't done this though, they usually know their stuff - it's their business to know. If the seizure is very light, you can often get away with super fine wet and dry if you are patient. If it has broken through the chrome, the best thing is to get them replated. On the piston, it's good practice (if you are racing) to relieve the piston ring groove at the point where it runs over the bridge. This you do with a small triangulated fine file, again this allows the ring to run freely in the groove should it get hot or the groove start to peen over.

Cheers

Dan
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www.geckomotorcycles.co.uk

And countersink the drilled holes on the piston .it helps the oil collect there and lube the exhaust bridge .