warped cylinder head

[RZtuner]

Yup that's spot on, running really lean. Small specs of aluminum on the nose from the piston crown starting to melt. The edges of the center electrode still look nice and sharp and the plug is not completely burning off all the deposits off the ceramic so the plugs heat range is perfectly fine. Richen up the map and you should be fine.
Sounds like you have a cool project with the Fuel Injection. How about some pics of the bike?

[jumjum01]

Thanks, here are some pix

[brrrappp]

lesson learned: Fit the plug heat range the engine needs, not what someone in a book tells you.

Gordon Jennings wrote the bible on how to read plugs and select them. If you are interested in this, I recommend you read it through a couple of times. It’s quite long but very informative.

https://www.strappe.com/plugs.html

Excellent write up!

RE: Gordon Jennings.....his was the first column I would read every month when my Cycle World or Motorcyclist (he wrote for several different mags over the years) magazine would arrive in the mail. I had such a hard time believing his research about richer 2-stoke oil mixtures resulting in an increased horse power output that I felt compelled to call him.
Unbelievably, he answers his calls personally. We spoke for about a half hour. I re-jetted my KX250 motocross bike for 20:1 the next day.

Sorry to divert the subject

[RZtuner]

Ah yes, the glory days of Cycle World when they were 265 pages thick and full of technical articles from Jennings and Cameron and only about 10 ads!

Gordon was a brilliant mind and even though that article was written in the 70's based on experiences racing Kawa triples and early TZ's it is still very relevant today to any two stroke guy. Everything he writes is spot on.

[JanBros]

Gordon was a brilliant mind and even though that article was written in the 70's based on experiences racing Kawa triples and early TZ's it is still very relevant today to any two stroke guy. Everything he writes is spot on.

except his exhaust port formula's. don't use them as he uses the entire port and you should only use the blowdown-part of for calculations

[RZtuner]

I am disappointed to read this. Really not a fair comment trying to compare data from Gordon's Two Stroke tuning manual published in 1975 to the latest two stroke computer simulation information currently available. At the time Gordon was a pioneer in the field and had quite the life. Never a good idea to speak ill of the dead.

https://www.superbikeplanet.com/from-ma ... 1931-2000/

[(F5)]

It's just a statement of fact that understanding by the human collective evolves. I remember his writing, and could open the cabinet a metre away and pull out that book. And I think very much he would, if magically alive and 40 again, would be striving to reinsert himself into current understanding, gleefully discarding and replacing better models. When you change a variable that you had previously settled on, then other parameters may go in other directions. Crankcase volume would be a good example. As would be the dreadful transfers. But there you go.

[RZtuner]

Exactly, we build on the strengths of the pioneers who went before us. Gordon was one of the fast guys of that era! Set a Bonneville record at 137 mph on a Triumph Bonneville back in the day. Nothing but respect from me.

[JanBros]

you feel my comment was disrespectful ?
you say it is still relevant, It still is a good book to understand better how a 2-stroke works, but people who don't know better may use his book as is and calculate stuff with formula's which history has proven to be wrong.

[RZtuner]

I wasn't referring to his book, I was referring to his spark plug article [Gordon was a brilliant mind and even though that article was written in the 70's based on experiences racing Kawa triples and early TZ's it is still very relevant today to any two stroke guy. Everything he writes is spot on.]
I still hold that opinion, plug technology has not changed. We are still using the same plugs I used in my 1977 TZ250 back in the day.

Obviously, 60 years later two-stroke development has changed, and yes, I think it's really not a fair comment trying to compare data from Gordon's Two Stroke tuning manual published in 1975 to the latest two stroke computer simulation information currently available. At the time, it was as good as it gets.

[jumjum01]

Top end rebuild is now complete. Cylinder was bored to 64,75mm and 2 new ProX pistons installed. The warped Y3 cylinder head was milled 0,4mm to set 1mm squish. Compression test is now at 130psi on both cylinders. Due to ensurance I cannot ride the bike and do engine break-in until 15th of March Thanks for all your inputs

[(F5)]

Good to hear it's back together. . . But I'm concerned.

Many bikes you correct the squish clearance to sensible (like 1mm on a 350 twin) and the compression ratio will shoot up to too high. My 1UA needed some metal removed from the chambers. Was over 20yrs ago and cant comment on your model. But I would 100% measure the actual compression ratio and adjust if required. Is hate for you to melt it again for the want of a little checking.

Oh, now I'm going to have a quick rant about compression testers.
They are a very blunt tool. You can use them ( once correct method used) to test for catastrophic failures, and with care, if you rebuild and test measure, you could then use that as a gauge of engine wear. But only noting changes as a broad guide.

You can distort readings with improper technique, or just some oil collected in the crankcase as often occurs thrown up showing a better seal.

But you cant trust them to gauge compression ratio. Heres an example. I measured my 200cc dirtbike as an experiment after skimming the head. It read 190psi. I measured the volume and it was too small so I took some metal out and got the volume correct. I then used the guage again ( some German brand which was screw in and moderately expensive back in the day). 195psi. I removed metal and got a higher reading.

They aren't a tuning tool. They are a diagnostic tool.

[RZtuner]

Maybe invest in a better quality gauge. I have a Snap-on gauge (not cheap!) and find it extremely accurate.
https://shop.snapon.com/product/Compres ... et/EEPV500

Mine gets used all the time for racing. It's a quick and very reliable test of piston condition.

[(F5)]

Perhaps. But a very poor test of compression ratio.

[jumjum01]

Yes, I need to measure the head cc after and find the CR. Hopefully it will be ok since I used an Y3 head which has lbigger champer volume than my stock Y2 head. I know that the compression test is not an accurate indication of the CR, but before top end rebuild the test was 100/110 psi, so I am happy that the psi is a more healthy level now