A while back I pulled my chambers off to take a look at the pistons, and noticed that the top cylinder had some scratching on the exhaust side. So tonight I decided to pull the cylinders off and take a closer look at both.... This is what I found.

Top piston:


Bottom piston:




Bottom cylinder:



I was hoping I would just have to hone the cylinders and do the usual top end rebuild, but my friend caffeinejoe noticed that the top cylinder has a crack in the exhaust port bridge Can this be fixed? Also what's the diagnosis on the bottom cylinder, does it look badly worn? The bike did not seize, I pulled it apart to see what condition the top end was in.

The bike is a 28SE, with TYGA chambers, TYGA reeds, an MC21 flywheel, modded air box, and 152s on the MJ. I have been running BR9ECMs, 95 octance fuel, and castrol TTS oil. I live near sea level, and it's winter here so the bike has been used a lot in temperatures around 0 - 10C.

Check http://www.flickr.com/photos/45725426@N07/ for more pictures.

Thoughts, comments, advice please.

Cheers
Tom

If had to guess, I would say the top piston did seize. It doesn't look too bad but is stuffed. Cracks in the ports are easily welded up but I think they will have to be re-nikasilled if welded.

I am no expert on this but if it was me I would weld the crack(s), have both cylinders recoated and do a full top end rebuild.

But thats just me.

Andy

Bandit7

Yeh looks like that top has siezed or partly i would say . Get the cylinders redone or buy some good second hand ones .

Major_Tom wrote:
I was hoping I would just have to hone the cylinders and do the usual top end rebuild, but my friend caffeinejoe noticed that the top cylinder has a crack in the exhaust port bridge

See, I really do have a friend......Yay!

Bump
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MC28SP
KLX110 hotrod
CAG Minimoto
1997 WRX
21 Speed Bike
162 Smurfs

no pics of top cylinder?


Can't add much more beside what has been said already, possibly rings out of spec relativve to barrel?

Just got off the phone to NZ Cylinders and they are quoting $645 NZD to weld and replate the cylinder, ouch! It's my birthday soon, anyone want to give a poor student a cylinder?

Back to reality, what can cause an exhaust bridge to crack? Running lean > too much heat > too much stress > crack? Something like that? I know for a fact that the top cylinder has been running slightly leaner than the bottom.

Hey mate, mine have gone the same way and yes, it going to be aprox 1300 nzd to fix plus top end rebuild kit.
Nobody said it was going to be cheap

Well looks like I have a very expensive paper weight now then.

I'll give you a couple of grand for it Tom

For you Malcolm only $10k

Most common cause of a cracked bridge is the bike not being warmed up enough before being riden.

I've had a number repaired and replated only to find the new weld cracks again very soon. Not always but in most cases.

Personally I'd be looking for another cylinder.
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If I have to take the carbs off once more...

StephenRC45 wrote:Most common cause of a cracked bridge is the bike not being warmed up enough before being riden.

I've had a number repaired and replated only to find the new weld cracks again very soon. Not always but in most cases.

Personally I'd be looking for another cylinder.

My warm up process is to start the bike, blip it up and down up to about 4500 rpm, led it idle for a bit then take off once the temp is about 50C. Then I wait till it's above 60C before I give it beans. It always hesitates in second gear for a bit, then pulls cleanly in 3rd and I know she's good to go.

Sound about right? I'd hate to break another cylinder.

Ha! Don't let it languish in the garage though, otherwise you might as well pass it on. You sound like you're being pretty kind to it, doesn't sound like your warmup is the problem. Do you rape it into the redline much?

Major_Tom wrote:The bike is a 28SE, with TYGA chambers, TYGA reeds, an MC21 flywheel, modded air box, and 152s on the MJ............95 octance fuel,..........0 - 10C.

Discussion of jetting in general is banned but;

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Please do not PM me technical questions, if you can't find it on the Forum start a thread

Yeah it's cold here at the moment..... The engine sees the redline every now and then, but rarely do I go past it.