I had a problem i guess

MikeG · Dec 9, 2023

Big_Jim59 · Dec 9, 2023

That's so strange. Was it making noise? It looks like it has been that way a while. Is the cylinder scored?

Torontonian · Dec 9, 2023

I think the first photo is the damage to the cylinder , where the circlip went on vacation .
Now the engine has to come apart to find the missing circlip piece (s ) .
My condolences , labour and money , as per usual .

marshg246 · Dec 9, 2023

Torontonian said:
I think the first photo is the damage to the cylinder , where the circlip went on vacation .
Now the engine has to come apart to find the missing circlip piece (s ) .
My condolences , labour and money , as per usual .

I thought the same, but he shows the piston with the circlip in place and there's only one picture in the post. In the piston thumbnail, it looks like the end of the middle rings is broken with a small bit missing.

DennisMo · Dec 9, 2023

The circlip only has one eyeleyt. Looks to me like part of the circlip with one eyelet has broken off which explains the damage. I have never seen a broken circlip like that before

marshg246 · Dec 9, 2023

DennisMo said:
The circlip only has one eyeleyt. Looks to me like part of the circlip with one eyelet has broken off which explains the damage. I have never seen a broken circlip like that before

Didn't notice that - good catch. I still wonder about the middle ring. Either may have started the issue.

Big Phil · Dec 10, 2023

marshg246 said:
Didn't notice that - good catch. I still wonder about the middle ring. Either may have started the issue.

Had a circlip come away on the right inside wrist pin last year. It didn’t break but just sat against the inside of the barrel which wore a huge groove. The debri fell on to the Cam Lobe below and wore that away along with the adjacent follower. Ended up rebuilding with new barrel sleeves, pistons, cam and resurfaced followers along with new seals etc. etc. as well as the purchase of various special tools. Only sign of anything wrong was when it began smoking all of a sudden from the right exhaust. Originally thought a valve seal had failed. Anyway, engine rebuilt now and all good so far after 1,200 miles. I was gutted at the time but it was a great learning experience as I had never rebuilt an engine from splitting a crank shaft and cleaning a sludge trap all the way up. In all honesty it was a great winter project and I thoroughly enjoyed the experience, well mostly. A few hiccups but got a huge amount of help from local Norton Cambridge Branch members which I will be forever grateful for.

kommando · Dec 10, 2023

Very difficult to sort out cause and effect but the damage to the piston looks initially to be caused by part of the circlip coming loose and then bouncing around in the gudgeon pin hole area. That piece of circlip also took gouges out of the bore wall which then took a piece of the ring away.

So somewhere in the engine and/or the filter is the circlip part, bore swarf , piston swarf and a bit of piston ring.

The circlip must have had a weak point at manufacture from either the base material or the processing, just left strong enough to be able to be installed and not break but then to fail under the stresses of normal running up and down the bore ie a fatigue crack of the original weak point.

concours · Dec 10, 2023

kommando said:
Very difficult to sort out cause and effect but the damage to the piston looks initially to be caused by part of the circlip coming loose and then bouncing around in the gudgeon pin hole area. That piece of circlip also took gouges out of the bore wall which then took a piece of the ring away.

So somewhere in the engine and/or the filter is the circlip part, bore swarf , piston swarf and a bit of piston ring.

The circlip must have had a weak point at manufacture from either the base material or the processing, just left strong enough to be able to be installed and not break but then to fail under the stresses of normal running up and down the bore ie a fatigue crack of the original weak point.

The failure mode on Mike's piston is improper installation of the circlip. Squeezed too hard with the tool, the clip was bent at the thinnest area just behind the loop. This leaves the loop end unsupported by the circlip groove, where it flexes with each start/stop at the end of each piston stroke. Eventually it fatigues & breaks. Then, it does it's visible damage as shown by the witness marks.

MikeG · Dec 10, 2023

this is the other side of the piston and cylinder. Gouged both sides. Bike smoked a bit on over run but not excessively. No signs of debris anywhere. Ive owned this bike 8 or 9 years, first time into engi ne. It never gave any indication of trouble. Only pulled the head to repair exhaust port threads

kommando · Dec 10, 2023

So the circlip piece was small enough to pass through the centre of the pin and mark the other side of the bore, some consequences from such a small piece.

concours · Dec 10, 2023

kommando said:
So the circlip piece was small enough to pass through the centre of the pin and mark the other side of the bore, some consequences from such a small piece.

Correct.

MikeG · Dec 10, 2023

FWIW when I bought this bike I was told the engine had been redone by one of the best-known in the Philly area. Can't prove or disprove but it was definitely apart at one time and put back together with non superblend bearings and factory style +.020 pistons.

Schwany · Dec 10, 2023

MikeG said:
FWIW when I bought this bike I was told the engine had been redone by one of the best-known in the Philly area. Can't prove or disprove but it was definitely apart at one time and put back together with non superblend bearings and factory style +.020 pistons.

I feel for ya. Can't trust anybody. Well, I can't anyway.

Professional best-known

work I suspect. Ugly result.

I've never seen a piston pin circlip come undone on anything I have owned and/or done the work on. I've read about it many times though. I've screwed plenty of things up, just not that particular thing.

Good thing said mechanic didn't try to install spiral locks. Fiddly little things.

grandpaul · Dec 10, 2023

Just when you think you've seen it all...

acotrel · Dec 10, 2023

I once bought a Triumph 650 barrel which had a groove in it from a loose gudgeon pin. I usually push the gudgeon pin against the circlip to make sure the clip is seated. They can go in skew and sit up. If you don't notice , things can go wrong.

cliffa · Dec 10, 2023

Over the years I have been a member here there have been about 5 similar issues reported. Therefore I'm really surprized one of our favourite suppliers hasn't started making Teflon buttons (or other materials) to stop this happening.

marshg246 · Dec 10, 2023

cliffa said:
Over the years I have been a member here there have been about 5 similar issues reported. Therefore I'm really surprized one of our favourite suppliers hasn't started making Teflon buttons (or other materials) to stop this happening.

I've often wondered why a circlip at all. A pin the width of the piston with a rounded end seems like it would work or even a longer than standard one with something like you mention.

I watched a video of an old WWII airplane engine where the pin was an interference fit and no clip - the pin was flush with the piston so even if it did move it wasn't going to hurt anything. A PITA to install/remove but much simpler.

Richard Tool · Dec 10, 2023

I’ve seen large diesel engines with the buttons on the wrist pins - always wondered why and now I see …

MikeG · Dec 10, 2023

Schwany said:
I feel for ya. Can't trust anybody. Well, I can't anyway.

Professional best-known work I suspect. Ugly result.

I've never seen a piston pin circlip come undone on anything I have owned and/or done the work on. I've read about it many times though. I've screwed plenty of things up, just not that particular thing.

Good thing said mechanic didn't try to install spiral locks. Fiddly little things.

Cant speak for the installer, especially if its the one i was told it was. He's been gone since 2010 and back in the day he was a dealer, racer, and very helpful and knowledgeable guy. If it was or wasn't it's hard to place blame after thousands of miles, some not so gentle.

I had a problem i guess

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