Somebody talk me out of this...

[JetdocX]

Have you pulled the oil filter and drained the sump yet?  I can't believe there is no metal in the oil after an event like this.  It's really easy to cut the filter element off the spool, let it drain into a rag for an hour or so, then check between the pleats for shiny things.

What caused the piston to break right there?  Could be a casting defect, but not really sure based on your photo.

[Mustang]

I suspect abuse as the culprit that broke the piston ....hard  to tell from a photo
the plug color means nothing until you have a good piston and rings in the #1 hole
he may have had that advance set too high like 5 degrees and running cheap gas and got some detonation going on would be my best guess as to why the piston failed
if you are going back stock pipes and timing advance with stock air box just use 98-105 for main jet sizes with the right hand snorkel covered
although 98 is too small a main even though that was stock  on keihin carbs
 102's or 105's and you will be golden
shim the needles up approx .030 of inch with a flat washer will take out the mid range bog from 4k to 5k  and set the pilot screws at 1 3/4 to 2 1/4 turns out , whatever works best for your bike
it will run fine

don't forget the hylomar for the cylinder liners or you will have a coolant leak into the crankcase

[JetdocX]

Forgot about the aftermarket timing advance plate.  However, I'd expect to see some melting of the piston dome and probably some scuffing of the piston skirt areas if detonation was actually happening.  

Are there yellow deposits along the top of the piston, or just normal colored soot?

[pKp]

I suspect there may have been metal in the oil - a few spots of yellow-colored bubbles rose to the top of the catch basin. Not immediately, but after sitting a few hours waiting to be dumped. The filter looked new - I'll check again for metal specks. The top of #1 looked fine - I really had to probe to find where it was broken. Actually the split in the oil ring led me to the cracks.

At any rate, removing #2 and #3 tonight - ran out of parts baggies! Will post the results.

Also, what is the recommended re-conditioning for the sleeve. It looks fine, no scratches other than the x-hashes that I believe are supposed to be there. Should I take them to a machine shop for inspection? They seem pretty tough.

[Mustang]

mic the bores  for size .use a dial bore gauge and if # 1 matches the size of number 3 than I would just give it a light honing and reassemble

#2 should be a bigger size than #1 and #3
they should all be straight (no taper) and round


per the Triumph Service Manual:
the bore should be 76.03 mm-76.05 mm with 76.1mm being the service limit
liners should be checked at top ,middle and bottom of bore

[Bixxer Bob]

I haven't time to do the search right now but I distinctly remember reading a post about the back of pistons failing between the rings.  If it wasn't on here it was on RAT, and I think EB made some contribution.  If I get a chance I'll do some digging later.

[pKp]

Hey - maybe I should contact Triumph - get some free pistons? Bike has only 18,000 miles - but with the mods I'd probably be wasting my time.

[BruKen]

:D nothing wrong with living in hope, it staves off despair.

[Mustang]

Hey - maybe I should contact Triumph - get some free pistons? Bike has only 18,000 miles - but with the mods I'd probably be wasting my time.

you would be wasting your time ..it's 12 years old !!

[pKp]

Quick update - #3 was blown as well - looked just like #1.

#2 seems fine - looks new. Might be new...maybe the PO had to change it out before me.

I read a post over at RAT that talked about cast pistons vs forged pistons - seems the cast ones can not take any sort of timing advance without failing at the ring land. Others have had the same issue as me with different bikes.

...two pistons and hold the mayo...!

[Mustang]

not quite .................I've got 65 thousand miles on a set of pistons just like yours with 4 degrees of advance . It has been set up that way since mile 3000.

I think previous owner got greedy for power had advance set at 5 degrees and was running low octane gas with main jets that were not big enough for the pipe andd advance changes ...........

[pKp]

The verdict is in -

112 main jets
38 pilot jets
3 turns
no shims (N3RF)
Yoshi cans
4 degrees advance

Throw in some regular gas and you get broken pistons on #1 and #3

[Bixxer Bob]

This is exactly why I don't meddle with timing.  I understand what I'm doing with fuel maps and know that providing I don't lean it out beyond 14 to 1 (stoichiometric is roughly 14.7 to 1) it might run rough, but I'm not going to do any lasting harm.  I've never read up on timing changes and the possible effects, so I don't go there.

[Mustang]

I've never read up on timing changes and the possible effects, so I don't go there.

it's all about horsepower and throttle response if you do it right  :D

[ramseybella]

I am totaly dumb to this stuff, just waiting on Rubber, Chain and sprokets then Ride!! :?

But please do explain!! :)