Need help/advice 103 rear piston shattered
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Tourer
Joined: Jun 2008
Posts: 275
Likes: 0
From: Southern MD
Need help/advice 103 rear piston shattered
I did a SE 103 piston kit a few months ago did Fuel Moto cams a few years ago. Well after about 700 miles after the piston kit on the way to bike week (i was pushing it hard 80 + for for about 25 miles then stopped to take off my jacket and ran normal for about 35 miles 70- 80) The top end started to make some noise so i pulled in the clutch gave the bike a little gas (to listen to the noise) and it then locked up/stopped running. It would not turn over with the starter.
So i tore it down yesterday and the rear piston is in nothing but chunks and a piece stuck in the exhaust valve (telling me that valves/cams were fine until it broke as it was trying to push the piece out the exhaust). The wrist pin still in the connecting rod with no issues. The connecting rod not banged up or nicked. Oh and after sitting a week the heads/rockers still covered in oil so i dont think i lost oil pressure. But still hard to say.
Does anyone have any experience with bad pistons or know something i may have done wrong. Again i road local for about 400-500 miles and then off to bike week. So i would think that was plenty of break in miles after heat cycles and stuff.
Thanks in advance
So i tore it down yesterday and the rear piston is in nothing but chunks and a piece stuck in the exhaust valve (telling me that valves/cams were fine until it broke as it was trying to push the piece out the exhaust). The wrist pin still in the connecting rod with no issues. The connecting rod not banged up or nicked. Oh and after sitting a week the heads/rockers still covered in oil so i dont think i lost oil pressure. But still hard to say.
Does anyone have any experience with bad pistons or know something i may have done wrong. Again i road local for about 400-500 miles and then off to bike week. So i would think that was plenty of break in miles after heat cycles and stuff.
Thanks in advance
Thread Starter
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Tourer
Joined: Jun 2008
Posts: 275
Likes: 0
From: Southern MD
It looks just like the parts/pieces of the piston hit it. After it came apart. Nothing horrible.
Just asking but you did get the correct piston in the correct hole right? and pointed in the right direction?
Pistons usually just don't come apart. Dropped valves, valve float, piston to piston contact, piston to head contact, oiling issue are some of the culprits of a broken piston.
Pistons usually just don't come apart. Dropped valves, valve float, piston to piston contact, piston to head contact, oiling issue are some of the culprits of a broken piston.
Road Master
Joined: Mar 2010
Posts: 934
Likes: 54
From: SE Wisconsin
Adjustable pushrods? If so, I'd double check to see if the front set matches the back set in length.
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Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
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From: Phoenix '53, '88, '09 Big Twins
you could bother with forensics...but in the end you are going to be rebuilding the whole darn thing ( no used parts incl con rods...get the bottom end checked, trued, welded)
my guess would be a valve timing error and a valve smacked the piston- whether rods, cam install etc. doesn't much matter at this point.
when you buy new pistons , get forged, not cast. forged are stronger
once saw a loose nut from an air cleaner assembly go all the way through an evo and out the pipes...still ran but
piston, head and valves were damaged
good luck
mike
my guess would be a valve timing error and a valve smacked the piston- whether rods, cam install etc. doesn't much matter at this point.
when you buy new pistons , get forged, not cast. forged are stronger
once saw a loose nut from an air cleaner assembly go all the way through an evo and out the pipes...still ran but
piston, head and valves were damaged
good luck
mike
Last edited by mkguitar; May 22, 2013 at 04:37 PM.
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Usually ... if anything mechanical was wrong with the assembly like valves hitting, p-rods too long, rockers, etc... it usually bends a valve real fast & goes bad pretty quick & not at 700 miles. Anything that hits the top of a piston will leave a witness mark, if you can still see it.
I have seen pistons fail with no external causes... just a bad piston casting. These can take many miles to fail & usually do so with no warning. Unfortunately the only way to accurately determine a piston failure is to send the pieces to a forensic metal lab & have the put it back together & x-ray the assembly for material defects. Not a cheap process.
The motor will need complete disassembly & everything checked. Damage can be done that the eye can not see.
Sorry it happened...
I have seen pistons fail with no external causes... just a bad piston casting. These can take many miles to fail & usually do so with no warning. Unfortunately the only way to accurately determine a piston failure is to send the pieces to a forensic metal lab & have the put it back together & x-ray the assembly for material defects. Not a cheap process.
The motor will need complete disassembly & everything checked. Damage can be done that the eye can not see.
Sorry it happened...
Grand HDF Member
Joined: Jun 2008
Posts: 4,012
Likes: 298
From: Central Fl
you could bother with forensics...but in the end you are going to be rebuilding the whole darn thing ( no used parts incl con rods...get the bottom end checked, trued, welded)
my guess would be a valve timing error and a valve smacked the piston- whether rods, cam install etc. doesn't much matter at this point.
when you buy new pistons , get forged, not cast. forged are stronger
once saw a loose nut from an air cleaner assembly go all the way through an evo and out the pipes...still ran but
piston, head and valves were damaged
good luck
mike
my guess would be a valve timing error and a valve smacked the piston- whether rods, cam install etc. doesn't much matter at this point.
when you buy new pistons , get forged, not cast. forged are stronger
once saw a loose nut from an air cleaner assembly go all the way through an evo and out the pipes...still ran but
piston, head and valves were damaged
good luck
mike
I am thinking similar to Mike. I'd be looking for something the engine may have swallowed. +1 on the forged pistons as well. In any event good lick with the rebuild.