Angle head over intake

That's correct crassius. If there was piston slap that could only mean one thing...the piston is too loose in the cylinder. Ideally if the chrome stayed on the bores ,(which I've yet to seen happen), the cylinder would last forever and only the piston and rings would wear out. What I wish these motors had was a cast iron cylinder sleeve or the whole cylinder being made of cast iron. I have thousands of miles on my motor and it runs great, although the chrome on the cylinder is flaking off in a few places.

I've heard that same popcorn popping sound on my motor at high revs Crassius. Glad to hear it is likely to go away. I wondered if it was spark knock, but you describe it well. I looked down the bore when I had the head off and all is well. I flipped the head again as a double blind test (takes 5 min!) and motor runs better and cooler and less popcorn noise with the sparkplug to the rear.

Had a look at a the rings thru the exhaust port and are still mostly black. Only 3 tanks of fuel on it and overly rich on oil and fuel. Will back off oil to 32:1 on tank 4. Top speed capable in either direction on a flat is 59.9kph. Could not get it to hit 60kph in both directions! It is faster with plug to the rear, which surprised me. It felt like it wound out better plug forward but was actually 2kph slower.

Piston was tight on assembly and squish was in the reasonable 0.020" to 0.040" range. Checked on assembly and cannot remember exactly now. Many Japanese engines are 0.130" to 0.070" as bought new. Too tight a squish will give and odd noise at full throttle and speed. Don't know what the popcorn noise is. I assumed detonation and backed off.

Steve

Sorry folks... It's true that the angle heads have higher compression than the old center plug heads. (Just look at them both side by side & you'll see the difference).


Also, if you're hearing loud 'pinging' at high RPMs?, try adding a 2nd head gasket to lower the compression a little.

haven't measured all I've seen, but though they look diff, both heads hold exactly the same amount of water, so all I've measured are same compression ratio

Often hard to tell volume just by looking and CCs do not tell the whole story.
I don't think you can begin to guess which head is which volume here.
One is 23-25cc and another is 18-22cc, I cannot remember exact numbers now, but hard to tell just by looking.



So the stock Blaster head on the right is 23-25cc. Squish distance was over 3mm. I filed 1mm off the head (still over 23cc IIRC) and ended up with detonation. (1mm = 0.0394" ~0.040")

The head on the left is a chamber shape I had cut in a spare head. With this shape I was able to reduce the volume as low as 18cc with no detonation.

This is how you CC an head:



Note that the frosty amber liguid is for the technician and is totally optional.
A greased plate of any flat liquid tight material (glass or aluminum etc) and water is measured into the sparkplug hole. When it is filled to the bottom of the threads, you have your volume. You can calculate the headgasket and piston deck height volumes.

Different chamber shapes return different results. One of these is a low RPM torquer and the other is a peaky revver.



I am kind of excited to try this same sort of experimentation on the Grubee.

Just throwing an extra headgasket on my seem to be a quick and easy answer, but often doesn't work because of issues with quench distance.

Steve

The heads you have pictured above aren't stock heads... (& aren't what I was talking about).

Also... when I advised about adding a 2nd head gasket, keep in mind that these are cheap $100 'stock' china girl engines that I'm talking about & not high tech motorcycle engines... Adding a 2nd head gasket will work fine.

You can use Permatex copper spray-a-gasket to stick 2 head gaskets together to lower compression. I initially wondered if the popcorn popping sound you were hearing was from too high compression for low octane fuel, but my motor has 130 psi, and I have no "pinging"?

I posted some of this info in other posts, and I apologize for the poor cellphone photos.

I eventually did blow a headgasket as Crassius suggested might happen.

Head was considerably warped when checked. During the hillclimb tests it had gotten quite hot and a lot of popcorn rattle was heard. Planing the head (sanding it on a sheet of sandpaper) reduced the squish distance to near contact (0.015") and a terrible shape trapping charge gas out near the cylinder wall. To solve this I sanded the outer edge of the combustion chamber bowl with a piston backing the sandpaper.



The result is a larger and better shaped quench (or squish) band. Ideally you will take this band out to the edge of the headgasket. Here is a (poor photo) comparison:

Stock head on the left, modified head on the left with the sooty chamber.

I again tested the squish. It was at 0.038" which is near perfect.

The result was a cooler running engine, no popcorn rattle, and more power on long hills. Very worthwhile work. Incidentally, now with 4 tanks of gas all black on my rings is gone. I have changed from 20:1 oil to 40:1 oil and engine works better, especially at low speeds, no ignition skipping.

Steve

I have a lot more miles on my bike now, even in spite of it being winter in Canada. I have been running the plug to the rear with mostly no problems. I did blow another headgasket when temps dropped down to -7c and I didn't richen the fuel mixture. Piston overheated and headgasket popped. No headwarp this time, New gasket and don't ride below -4c seems to be working.

An idea came to me about the plug forward/backward thing. The exhaust side of the head always runs hotter, so if the plug threads are over there, it will run hot. Why not try plug forward with a colder plug?

Too much snow for me to ride lately, so someone else try it?

Meanwhile, some good plug info:






Steve