Lynx starting woes

[tornitore45]

This engine did run breafly when first assembled, then I decided to take it apart clean it up and reassemble it with thread-locking compound and Loctite 580 sealant around the crankcase to avoid oils seepage. This tells me there is nothing wrong with the Ignition or any major construction details.

Now,driven with the drill, my Lynx sputter a handful of pops at a time but no sustained running.
If I slow down the drill I get it to a point where it has sustained ignition under power drive but will not run, at higher RMP will go back to hit and miss.

Compression is not great but I have run engines with little static compression that exhibit sufficient compression at running speed.

I know the valves seal because I can feel pressure plugging the exhaust.

The fact that it seems to have problems at high speed leads me to advance a theory that the valves do not return quickly enough. Again is a theory, but I wander if the springs have weakened or oil accumulating under the poppets creates such a vacuum suction that slow down the valves return.

The spring were tempered at 400F. Possibly too much.
Any of you had experiences that may confirm my suspicions, or any suggestion to offer?

 

[Cogsy]

On my recent build of the Rupnow Vertical I had little problems starting and running it initially but when I later pulled the carb apart and fitted gaskets to it I had quite a bit of trouble finding the proper settings to run it again. So in my case all my air leaks added up to the right carb settings but when I fixed them the carb was way off. Possibly you're experiencing something similar?

 

[tornitore45]

Another example of the wisdom of "If ain't broke don't fix it"!

 

[tornitore45]

Suspecting that the spark plug protrudes from the head just enough to touch the sleeve and prevent the head from sealing against the sleeve I plan to make a thicker copper washer to back it up a little. Found lots of oil under the head and into the screw holes.

The plug is angled, therefore is somewhat buried in the hole.
Mi question is: Can ignition suffer from backing up another mm?

Next question: How you make sure the head seat straight when tightening the 8 screws?

I follow the practice to start finger tight and tightening a little at the time going in a cross pattern. Is there a better way?

 

[gbritnell]

If the engine ran before then I would have to think that the plugs didn't protrude too far at that point. You can add a thin copper washer and it won't hurt anything. Tightening the bolts in a crisscross pattern will make them even but on a small engine it won't generally have much affect.
gbritnell

 

[pickleford75]

one possibility is that if the spark plug has a compressible washer on it after tightening and loosening it and then re-tightening it again the ground electrode may have ended up in a different clock position then before causing interference that was not there before.... just a thought

 

[mcostello]

If the plug as tightened against something there might be a shiney spot to look for.

 

[tornitore45]

Good point. The Sleeve top has a nice layer of Loctite 518. Is velvety red with no signs of spark touching.
Knock down that theory.