Since drowning, my little old 1987 TT250 has been burning way too much oil.
I finally had a free weekend to spend on the TT, so it was time to pull the engine down and install a new piston & rings… maybe.
Andt had scored a new Wiseco piston kit off ebay for AU$30, so I figured the easiest & cheapest option would be to drop that straight in.
Since I’ll undoubtedly be doing this again in the near future, I wanted to find some useful shortcuts, like removing the whole top-end with the bottom-end still in the frame. Nothing wrong with a few shortcuts is there? MMmm, well ok, I was being careful too.
After getting the top-end off, I removed the old piston and had a look at everything. The old piston looks pretty good; just some carbon deposits and a couple of very small chips on the top surface (not near any landings). The ring grooves still look pretty good, but the old rings do feel a bit floppy. Both compression rings have about 0.15mm of side clearance (in the groove), which is too much.
I did 2 “test installs” with the old piston; remove top-end, remove gudgeon pin, remove piston, remove rings, install rings, install piston, install gudgeon pin, install top-end. By the 2nd test, I was pretty good I recon. Holding the top-end while compressing the rings and lining everything up was a challenge, but it eventually sorted itself out :-)
It might be worth noting that the piston was very easy to remove by hand. No pressing or anything, which was good. The only restriction I had removing the pin (after removing the lock collar) was a “hydraulic lock” from the oil galleries around the pin. I blew compressed air randomly into the bottom of the piston/pin, and the pin came out very easily.
Now ready to install the new piston and rings.
Bam - first mistake. I got too excited, and installed the piston onto the conrod.
Andt had also made a similar mistake months ago when he got the new piston; he’d already put the rings on. So I assumed it was all ready to rock (stupid, I know).
So new piston is on the conrod. Now I just need to chuck the top-end back on, right?
It wont go on, like the piston is just getting jammed… hmmm. After stuffing around for way too long, I realised that I need to set the ring gap correctly! DUH!
So I take the new rings off the new piston, put the top compression ring in the barrel. Whaaat? It doesn’t fit. How can the gap be so far out!?
I check the piston… whaaat!? It’s a oversized! Hahahah.
New great new wiseco piston and rings is an oversized kit. Geez I’m an idiot.
Oh well, I put everything back together (with the old piston and rings) and make sure it still runs (burning oil) - yes, and yes. So at least now I know how to do it.
What now The old/current piston is in ok condition, and the bore is ok too, even still a perfectly visible hone pattern. So I’ll try to find a new set of standard bore rings and install them.