Piston Gudgeon Pin Circlip?

[PEZBerq]

In the latest Transmoto mag there is an article on rebuilding the top end of a modern four stroke that shows a regular circlip used to secure the gudgeon pin.  How common is this and can it be used for any piston? Certainly make life easier than struggling with the wire clips that are a bugger to fit and remove. What does the brain trust reckon?

[oldyzman]

Just a question, I have usually put the piston onto the rod pin and 2nd clip on then slide the cylinder on (two strokes by the way) is it easier the other way?

[evo550]

Yeah, I saw that as well, but just thought that's what was supplied with the piston, so use it.
What I thought was interesting was the advise about the placement of the circlip opening, mine just end up where they end up, but I doubt the opening ever ends up at 12 or 6 o'clock.

[pancho]

 I would never use those type of circlips because I have had problems in the past. They shatter at high revs/piston speed.
 Likewise wire circlips with tangs turned up I have had the tangs shatter. They are fairly hard and make realy 'groovey' tram tracks up and down the bore. The ones that are a pest to get out are the only ones that I use.
 
 Over the years I have had a lot of experience with dramatic failures!!!!
 cheers pancho

[smed]

The Yamaha YZ400F that started the modern 4T revolution used them as stock,I don't know about the other modern 4T's but my CRF250 has the old style we all love to hate,I was in the industry when the 400F was a couple of years old & worked on a few,I loved those Circlips,so easy to install ,I installed the piston the same way as the article, much easier,perhaps thats why they used that design circlip,as an aside another interesting thing about the 400F motor is that the shift fork was fixed to the pin it would normally slide on & the pin itself floated in the cases

[brent j]

The groove is usually cut to suit the profile of the circlip.

The wire clips fit into a half round profile groove and the type shown fit on a square profile groove.

[OverTheHill]

didn't wiseco have thin flat circlips that were something like 1.5 turns & you sort off wound them in--or did i dream it.
I'm sure i've seen 4 stroke pistons over the years with teflon buttons in the gudgeon pin ends with no circlips--that'd make it easy to assemble.

[TT5 Matt]

yeah wiseco used those flat circlips in 4t pistons,easy to get in but a ladies thing to get out

[matcho mick]

i've allways put circlips ends in the vertical,simple logic!!,not keen on ceegar style,but if you do use them,they ,like all of that type are stamped,ie inherit a sharp edge,that which is place in the direction of thrust,(ie,more push,more locking),place the other way,force deforms them inward,thus releasing their grip!!,(ouch, thats where pancho's warning kicks in),i try & use teflon buttons in all my r/r 4t's,std honda circlips are ok,those wiseco spiral circlips are safe too,
ps Amaroo hillclimb bitd,matcho on the line,engine running,swish swish noise,wtf??,circlip walked out,tramline up the barrell

[BultacoMacca]

I have had to use these circlips in lots of aftermaket supplied Jetski and bike pistons and haven't had any problems.
As Brent J  says the groove is generally machined square to suit the square profile of the clip.
As Matcho Mick says if you use a circlip have the sharpest edge of the clip facing outward.
The most important point is that the clip needs to be held very, very firmly in the piston groove, no easy rotation, and fit at top or bottom away from any access slot.

[TT5 Matt]

the other thing about circlips is never re use them not matter what type they are and lets face it there only 2 or 3 bucks each anyway

[OverTheHill]

been guilty of re-using wire/with ears piston circlips many times over the years & "i know" i'm gonna come unstuck oneday [only on my own junk though]. When talking 'flat' circlips--not only piston but mainly thinking gearbox flat type in my case i always adhere to the sharp side away from the thrust--if that sounds right [i know what i mean haa]--so less chance of getting ramped out. In saying that--would grooves be machined absolutely square or have slightly rounded edges of bottom corners of groove!!--anyway.

[Simo63]

I'm sure i've seen 4 stroke pistons over the years with teflon buttons in the gudgeon pin ends with no circlips--that'd make it easy to assemble.

I recall rebuilding an XL175 motor and installed a big bore kit that pumped it out to 232cc way back when I was still a teenager (yeah THAT long ago  ).  The piston in that kit used the teflon buttons.  These were a white-ish teflon.  Certainly made it easy to install but I was highly doubtful about using them but as the piston came without any traditional circlip groove machined into it, I used them.  After assembly I ran it for a couple of tanks and then pulled the top end down to check everything was all okay and I could not believe that those buttons had marked the bore.  Nothing hugely serious but you could clearly see lines where they had been rubbing on the cylinder liner.  I didn't like that at all 

[shelpi]

didn't wiseco have thin flat circlips that were something like 1.5 turns & you sort off wound them in--or did i dream it.
I'm sure i've seen 4 stroke pistons over the years with teflon buttons in the gudgeon pin ends with no circlips--that'd make it easy to assemble.

Yep I was useing them upto last week before we went to the next O/S they are ok when ya get used to them, but love the idea of the circlips why didnt we think of it earlier?

[pancho]

been guilty of re-using wire/with ears piston circlips many times over the years & "i know" i'm gonna come unstuck oneday [only on my own junk though]. When talking 'flat' circlips--not only piston but mainly thinking gearbox flat type in my case i always adhere to the sharp side away from the thrust--if that sounds right [i know what i mean haa]--so less chance of getting ramped out. In saying that--would grooves be machined absolutely square or have slightly rounded edges of bottom corners of groove!!--anyway.

 Another trick I learned at a GM Holden school years ago, that I never saw in any manuals, was that if you grab a circlip between thumb and forefinger and squeeze the circlip will form a dish. So you mount the circlip in the groove in a way that the thrust on it forces it into the groove. Mainly applies to larger circlips but the principal applies.
 
Of course the other thing is Seegar circlips fit into a square machined groove only.
 cheers