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Blown yz125 Replated or Replaced?

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Hey guys, so I pulled apart the yz125 i just bought and top end is gone. The piston looks like hell so obviously I'll replace that, but i'm wondering if I should replate the  cylinder or just buy another? It's really not in terrible shape in fact it has most cross hatching still in, but there is one minor scar in the side wall. Also i'm winding how important it would be to also replace the   cylinder head, as is pretty chewed up... I tried to attached some pics of these. Would you replace both or should I just replate them? Let me know what you would do with this engine as I'm new to two smokes.

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Edited by xtactical

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Have you dis-assembled the bottom end?

The damage on the piston's crown and cylinder head may suggest a bearing failure.

 

Depending on your location (cost of shipping) 

buying new could be a better option than having your damaged cylinder replated.

Edited by mlatour

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52 minutes ago, mlatour said:

Have you dis-assembled the bottom end?

The damage on the piston's crown and cylinder head may suggest a bearing failure.

 

I'll have time to get into the bottom end late today, I can't see or feel any issues yet with it but i'll open it up to see what's going on anyway.

Guy I bought it from told me both top and bottom were done less than 3hrs ago, so he either lied or blew the thing up himself. I know he has been running it the way you see it, and of course was a PITA to start and would bog out at idle prob due to piston damage...

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55 minutes ago, P84ONE said:

Re-plate and send or buy piston from re-plater. Clean up head, and you should be good. 

Is it possible to save the head if I buff out the scratches myself or will that mess up compression?

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37 minutes ago, S.O.A.N.Z said:

2000 model ?

 

I believe it's a 99, at least the cylinder is, engine was built by some performance garage in Miami called Zambrama and I found some wierd things when I opened it up.

I think I found the cause of the cylinder damage, was a nut that fell off inside the clutch housing where they drilled the clutch cable mount through, so dumb...

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11 hours ago, xtactical said:

I believe it's a 99, at least the cylinder is, engine was built by some performance garage in Miami called Zambrama and I found some wierd things when I opened it up.

I think I found the cause of the cylinder damage, was a nut that fell off inside the clutch housing where they drilled the clutch cable mount through, so dumb...

I'm lost...

Please explain how a nut in the clutch housing can damage a cylinder? 

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depending on if you want to go a stock cylinder and piston or go over size??? if your looking to stay original then get a new cylinder, piston and head just to be safe.

the head combustion chamber can be fixed but to avoid compression loss(for the nominal amount of difference) the head to cylinder face would have to be machined back to within original tolerances of the combustion chamber easy enough for a machine shop. those dags in the head would cause pre ignition as they heat up a lot more than the rest of the head around them.   id say the marks in the piston and head are caused by the ring locating pin from the piston. usually what does it.

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2 hours ago, P84ONE said:

I'm lost...

Please explain how a nut in the clutch housing can damage a cylinder? 

Ohhhh right it's not a 4 stroke, yammys 4 strokes share clutch/engine oil. Can you tell i'm new to 2ts haha

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After further digging into the engine I realized that it had been modd'd by the race builder. So I ended up putting the  cylinder, piston and head in mail to millennium today. I'll update once received back and the cost, hopefully won't cost as much as replacing them all new but it's going to be darn close.

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16 minutes ago, KTM_rider_EK_17 said:

DO NOT RE-PLATE!!! In the long run, re-plating can cost just as much if not more. Just buy the cylinder and a top end rebuild kit. 

Besides the cost is there any other reason you'd recommend not replating? I was under the impression that replating might actually last longer/be more durable than stock?

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Been re-plating AKA, having it done for years. New cylinders can be over 400 with a piston. Re-plate is 185 for 250cc, and 155 for 125cc, add a piston for 100, top end gaskets for 30-45. So, you do the math.

Re-plate is fine on the engine, good on the wallet. 

Just send, or purchase piston from re-plater for a match to bore. 

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Thanks for the feedback fellas, the parts are already  on their way to millennium for replating. Becuase of the scuff in side of  cylinder they said it would prob have to be welded, so basically i'm looking at $275 for  cylinder repair, $115 for piston, and $50ish to resurface the head plus shipping costs. If I were to replace all three i'd prob spend another $50-100

The main reason I decided  on the replate is the engine was obviously built for a race driver and has been pretty heavily modded.

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17 hours ago, KTM_rider_EK_17 said:

DO NOT RE-PLATE!!! In the long run, re-plating can cost just as much if not more. Just buy the cylinder and a top end rebuild kit. 

Pure nonsense. 

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