Hi Guys,

I have just removed the front cylinder on my MC21 because I need to have a snapped exhaust stud removed ...and found the barrel probably needs re plating as the nikasil is worn on the exhaust port bridge.

My question is "what are the chances"...that the rear cylinder might be OK? Is it always the case that the wear on the front indicates the rear needs ripping down or does the front get more wear due to being canted forward? 🤞
There is no further damage on the barrel/head/crankcase in fact it looks clean, can't see one det mark! The odo is showing about 16,000 miles and the rest of the bike tells me this is about right...

Cheers for any insight!

Max

PS. Ive not quite worked out how to add an image on here yet....when I click to add it just disappears...If I figure it Ill drop an image.

id say having a look is the only way to know for sure

prelude2.2 wrote:id say having a look is the only way to know for sure

There's no excuse not to really is there....😟

[/quote]There's no excuse not to really is there....😟[/quote]

its the only way im afraid. i had to get mine redone last year. i wonder did anyone ever try inserts
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John 3:7

For the minimal cost of a base gasket (you can keep the head on to save the cost of the more expensive gasket), it just makes sense to check the other barrel. It's probably fine.... but probably doesn't mean definitely!
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Andy.
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All wise words and of course you are both right...off she comes then.

I just know that when I remove the rear cylinder it might/might not be ok on the plating side of things... but am I really going to rebuild it with only a base gasket? really? whilst throwing a new top end at the front cylinder...do a half top end refresh?
I feel like the proverbial cat on the edge of the bath...the inevitable is coming, that is why I am reticent and posting on the forum looking for lifelines but instead you all show me the mirror of reality and... plop ! I'm all soaked in the bath!!Doh!

Relax Max, all will be fine, you'll swim, not sink in that bath, and when you get the other barrel off and all is fine, you may as well throw a set of rings in that one as well, personally I would do a new small end as well, along with the all important new circlips.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto

Being a cat owner, or rather, butler, I appreciate the analogy!

Without knowing the service history, as Les says, it would be prudent to at least do the rings. It's easy to say "just do the whole top-end", but there's no point replacing perfectly good parts that are within spec when you're not trying to win races on a street bike, and the cost of spares is ever-rising; some to almost extortionate levels! I guess it depends on whether (a) you are able to accurately measure the wearing surfaces, and (b) how comfortable you feel with the condition and history of the current components.
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Andy.
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Well I have had both cylinders off and they show equal amounts of wear. I took them to a pal who has a lifetime of skill and still builds, races (and wins!) 2T's at national level. He was happy to give them a thumbs up 👍 and recommend that I put it all back together. Aptec and GT said similar after emailing them...so I am going to take it as a done deal.

Andy: can I ask why you would replace the rings at least?

Regarding rings, I see a D shape in the top ring groove on the piston, which I assume is the mark for aligning the ring gap....should I see similar on the bottom expander ring groove?

Max wrote:
Andy: can I ask why you would replace the rings at least?

Well why wouldn't you, while it's all apart?

Max wrote:
Regarding rings, I see a D shape in the top ring groove on the piston, which I assume is the mark for aligning the ring gap....should I see similar on the bottom expander ring groove?

No ring expander on the MC21. (It was only ever a thing on the MC16, and long discontinued.)

There's a peg in each groove for ring alignment. Note that the grooves are different shapes when you refit the rings. And yes, we have seen a flat ring jammed into the keystone groove before!


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Andy.
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Thanks for the info Andy, good to highlight the ring shape difference. I'm sure people put them upside down and back to front all the time!!