Loose Piston

[aardvark]

My lads PW50 has been making a gentle rattling sound from the top end for a while. So tonight I decided to pull the top end off. It would seem that the piston is ever so slightly loose in the bore and this is causing the rattle.

I guess the questions are:
Is this a major problem?
Will it be ok to ride for now?

[Gosling1]

Yes, and
Maybe for a bit....

the rattle will just get worse - if you let it get too bad, you run the risk of damaging the bottom end, and maybe also having to replace a barrel instead of just getting it bored & honed and a new piston fitted.

A top-end rebuild on a PeeWee shouldn't set you back more than a few hundred bucks mate, if you do all the spanner work ?

[aardvark]

Thanks Gos. Seiko came around and had a look and we're not convinced the piston is that loose. The sound seems to be coming from the top end and is similar to the sound some loose washers would make.

Buggered if I know. Taking it away this weekend. If it blows up, it blows up.

[Wattie]

You let seiko the computer geek offer advice on mechanics??

[Glen]

That's like letting Firey tighten your nuts..........

[MadKaw]

Could be the cage bearing on the rod at the crank.
Had one let go on the kids LEM and those little bars in the bearing do a lot of damage..

and on the LEM, its a pressed crank / rod set up so you have to replace the whole crank / rod assembly..

[aardvark]

You let seiko the computer geek offer advice on mechanics??

It really wasn't any different to me offering myself mechanical advice!

Could be the cage bearing on the rod at the crank.

Sounds more like it's coming from the very top end. Like a broken ring, or the piston hitting the head. However I checked both of those and they are both fine. There's no real scoring in the barrel, although there is a lip at the top which seems to be the maximum height that the rings reach at the top of the stroke. I'm wondering if the rings are hitting this lip?

The gudgeon pin does seem to be very loose as well.

Might be a full top end rebuild when we get home. Or by the time we get home, it could just need a new engine. In which case, I'd better replace the headstem bearings in the 80.

Meanwhile, the lad sits on the couch playing Lego Batman on Xbox.

[mike-s]

I doubt it'd be the lip, that lip is from wear from piston/ring movement, and at most might be a bit noisy when cold, but would go back to normal in short order. I would take the barrel off and check the rings and gudgeon pin out myself. also if you have a vernier caliper (digital are best) perhaps check the barrel from wear? it might be bottom end slop (oval wearing of the bore due to higher wear in the fore/aft direction than side to side).

Aside from that i'm not sure what to check. You may want to use the big-arse-screwdriver-as-a-stethoscope method to try and figure out where the noise source is as well.

[seiko1]

You let seiko the computer geek offer advice on mechanics??

How rude!
Anyway the cage bearing is what I could not remember the name of Jase
If it is that it would transmit the sound up the connecting rod to the piston and appear loudest there
Sound's good...but might just be all shit as Wattie said
Everything is so bloody tiny it's hard to tell anyway

[Tack]

Just BTW, if your checking for slop, the piston will be loosest in the "belly" of the cylinder not necessarily at TDC.

[potta9]

I doubt it'd be the lip, that lip is from wear from piston/ring movement, and at most might be a bit noisy when cold, but would go back to normal in short order. I would take the barrel off and check the rings and gudgeon pin out myself. also if you have a vernier caliper (digital are best) perhaps check the barrel from wear? it might be bottom end slop (oval wearing of the bore due to higher wear in the fore/aft well.

Digital Verniers are ok but for a 100% accurate measurement I'd use normal Verniers. A rebuild kit for one of these complete top end is cheap. Check out www.pwonly.com.au

[Jonno]

Inside micrometer for accuracy or at least telescopic "T" gauge and use outside micrometers, verniers are for pickin ya nose ffs and measuring basic stuff for a general idea and you wont get them down the bore far enough.

Just pull the bore off and take it and the piston to an engineering/machine shop that do cylinder re-bores and let them measure it, offer them a $20 and I am sure they will do it free.

[Gosling1]

.... The sound seems to be coming from the top end and is similar to the sound some loose washers would make....

probably the little-end bearing then - especially if the gudgeon pin is a loose fit ?

But that sound you describe - that sounds like 'detonation' to me - the arch-enemy of all stinkwheels ! either the fuel you are using is too low an octane, or the timing is out - those sort of things can cause detonation.....are there any pock-marks in the top of the piston ?

[seiko1]

.... The sound seems to be coming from the top end and is similar to the sound some loose washers would make....

probably the little-end bearing then - especially if the gudgeon pin is a loose fit ?

But that sound you describe - that sounds like 'detonation' to me - the arch-enemy of all stinkwheels ! either the fuel you are using is too low an octane, or the timing is out - those sort of things can cause detonation.....are there any pock-marks in the top of the piston ?

Pock marks on the piston?
or Jason's Piston?

[Sulli]

Ardie send it to a reputable repair shop they will do the job and guarantee it not worth the hassle to do your self its only a top end rebuild FFS or R and r it your self and get the shop to do the other stuff