Broken 268XP

[Dragonz]

I just picked up a broken 268XP.
It has low compression & the bore has visible scoring with the muffler off.
I will strip the saw over the next couple of days & post pics as I go.
I'm figuring on rebuilding with a 272XP top-end, but want to know what mods people have done to these saws to get the best out of them.

I have searched the forums, but most of the images are gone from peoples posts (most posts on this saw are several years old), so if anyone can post pics of muffler mods, or any info on porting, that would be really appreciated.
There are precious few people here in New Zealand who mod saws for performance, generally the thought is "just buy a bigger saw" so not much local help to be had.
I've been playing round with 2t bikes for many years, & have rebuilt an 028WB with a little help from members here who shared manuals for the saw with me.
Also have recently got a beater 200T that I have just got running, so may put up a couple of threads on those saws too in time

 

[cus_deluxe]

If the cylinder is salvageable id stick with it. Should be a pretty good performer out of the box. Check if theres room to leave out base gasket and have good squish clearance. Maybe a little timing advance and make sure muffler is nice and open.

 

[cus_deluxe]

But make sure you know why it melted down in the first place.

 

[Dragonz]

Cylinder is toast, looks like a classic "straight gassed saw" some melting of the piston, ring locked up in the grove, & big scores on the piston & cylinder, along with some ali left in the bore. Will get pics off my phone a bit later, cos we all know a thread is worthless without pics right?

 

[cus_deluxe]

os we all know a thread is worthless without pics right?

Truth. Lol. Ive cleaned up some pretty gnarly ones. Worth a half hour of time to give it a try anyway. Lookin forward to pics

 

[Dragonz]

 

[cuinrearview]

I wouldn't hesitate to go at that cylinder with some sandpaper and scotch brite. What do you have to lose?

If you can't save the cylinder, then a switch to 272 could be justified. But the tiny increase in performance isn't worth the investment in time and capital otherwise in my opinion. Either way, as stated above, I would be damn sure of the cause of failure before putting time and money into it and firing it up. I don't disagree that it could have been straight gassed from the pictures, but dirty air/fuel could have caused that too as well as an air leak.

 

[Dragonz]

The cylinder is scored pretty deep in places, definitely through the plating.
I've got a 272 p&c coming (after market) coming from a supplier that seems to have good stuff at a decent price.
Will set up a wee jig & blanking plate tomorrow & check for leaks on the crankcase

 

[cuinrearview]

Sounds like you have it all sorted. Good luck with the build!

 

[Dragonz]

Hope to get the new cylinder & piston tomorrow.
What muffler & porting mods do people do on these motors?
I see dual port mufflers suggested, base gasket delete with slight tweak to transfer heights & exhaust port height accordingly, but what else is common/recommended?

 

[drf255]

101/122/77 works well on a 272 jug. About 25 out of the band.

The 266 vs. 272 has a very different intake setup. The 266 has an intake block bolted to the jug, then the carb and elbow bolted to the block separately. The 272 has the traditional block with nylon sleeved through bolts that go all the way back to the intake elbow.

Not sure on the 268. The 266 Tilly carb had a smaller bore than the 272 carb but worked just fine.

Been a while for me, but I think I took 25 off the crank key as well to advance timing and the muff mod was easy peasy.

FWIW, the 272 decomp jug will not function with a decomp and the metal flag brake. You will have to plug the decomp or get a newer nylon flagged brake. The 272 jug also has a different spark plug angle than a 266 (?268) but the top cover should still fit. The plug boot will sit against the stock cover.

 

[Dragonz]

The 272 intake you describe is identical to the 268 I have.
Everything I have read says the 272 is directly interchangeable with the 268, guess I find out when the new jug arrives.
Thanks for the advice on the port opening degrees, I will plot out what I have when I get it all & compare.

 

[drf255]

Everything may have changed when the 266 became the 268 except for the 50mm bore. I simply don’t know that.

The carb setup looked the same externally when I did the swap. It wasn’t once I pulled it apart.

This is my finished jug. I’ll look for an intake flange pic. I may have both 272 and 266.

 

[drf255]

Looks like I have outer pics of the 266, and only pics of the 272 flange from assembly.

 

[Dragonz]

Well it's all back together & running.
I need to map out the ports to recheck the timing, but I focused on cleaning up the ports, & matching to carb manifold & exhaust more than size or durations at this stage.
The AM cylinder had limited meat at the rear of the cylinder, so there is a limit to what I can do with the transfers.
Squish is at 0.68mm (0.0267") without the base gasket. I can always put the cylinder in a lathe & trim the base down to reduce later.
Still learning with saws, so not trying to be too radical at this point. Most of my 2t tuning has been for piped engines for bikes, so the port timing is different when you don't have that nice tuned exhaust to stuff a whole bunch more air & fuel back into the cylinder. Fun to learn though.
I put a 24" bar with semi-chisel chain on it.
Gave it 2 heat cycles yesterday, will give it another today, then go find a tree to run it through & test/tune fully loaded