Suzuki FZ50

[BooG]

I am doing up an old ped to sell. Got the engine started, and there appeared to be a metallic knock/slap from the cylinder head that disappeared as the engine warmed up. My thoughts are either Big/small ends..Piston rings...
anything else it might be??

[nhmaf]

Hmmm, I am not familiar enough with these to offer anything more helpful, I guess.   I do know that some little bikes' design tended to have a surprising amount of piston slap when cool because of the chosen metallurgy.  Has the bike been sitting for a very long time?  

[montmil]

As the "slap" disappears after the engine has warmed up, I'm with Mike's idea that it's piston slap.

Big/small end bearings would probably continue to complain during ops. Is the oil injection system working?

Depending on how much time, money and effort you plan to invest before flipping the bike, it might be fairly simple to pull the 2-stroker's head and cylinder to check for a broken ring. Feeler gauge might also confirm piston to cylinder gap. If the little ring-dinger was abused by PO's, there could be cylinder wear issues.

[BooG]

How do I check the wear between the cylinder wall/ring/piston? Do I need an oversize piston? Will check the oil feed is working...good call on that. Its been standing a while (2 years ish) so one or two things are "tight'.

[BooG]

I've found out that there is supposed to be an "expander ring" under the lower piston ring itself. Could be the prob I'm experiencing. Will remove piston shortly to verify this.

[Barry]

Multi piece oil control rings are common enough. The slotted ring has an expander spring behind it to force the ring against the cylinder wall. Not sure it's absence would cause piston slap though.

[nhmaf]

While some may argue that slipping feeler guages around the piston while still in the cylinder can be good enough, I think the only way to get to the bottom of things like this is to remove the piston and carefully measure it, and the cylinder bore separately.  It also enables you to see the entire cylinder surface, especially around the transfer port area, for wear.

From what I have heard, these machines were somewhat of a "hotrod" among the moped/50cc crowd, and some owners tended to treat them with a heavy wrist.

[BooG]

Piston rings wrong way up!! Swapped em around and I'm in business!!
Compression is a massive 110psi...cleaned out the carb and she fired up willingly. Only have to track down why the indicators aren't working now and she'll be ready for MOT!

[montmil]

You rock, BooG!

ringa-ding-ding

Turn signal bulbs installed, "wrong way up"?