No start after head resurface

[lucky16]

Build:
Yamaha Vino 2T (YJ50) minarelli horizontal engine
70cc BBK Athena sport aluminum
Yasuni Exhaust (derestricted)
Polini Air intake cone filter
Dellorto 21mm carb
BR9HS spark plug

Scoot has been running with the above setup for a few years. I have not been running a head gasket in order to achieve the correct squish with the Athena kit. (Apparently it's a known issue with that kit) Instead I've just used gasket maker. Whenever I don't drive the scoot for a few months and I go to start up it blows the head "gasket". It'll normally idle but bogs and dies with any throttle. And I can feel the compression leaking out the sides with my hand. No big I just reseal it and good again.

This time around I noticed burring on the surfaces where the head mates up so I got the good idea to wet sand them out flat again on a glass table and maybe I can actually use the head gasket with the material that's removed. The sanding/finishing worked good and I achieved the correct squish actually using the head gasket. Sealed it with copper spray sealant (they're all metal gaskets) Waited 48hrs but now it won't start. I also tried to put a thicker gasket between the cylinder and block with no head gasket but same thing, can't start.

It doesn't even sound like it's trying to start. I'm picking up some starter fluid tonight and I'll advise if that gives it any signs of life.

- Confirmed I have spark (tested with spark plug plugged in and touching it to the frame while cranking
- compression is 90psi regardless of how I set up gaskets
- squish tried .7 and .9
- carb setup is unchanged and I'm hesitant to change it since it was working a few days ago. I'll likely try to clean the carb and let y'all know the jetting, but again it was running before so I'd think I'd at least get to idle.

I figure the only variable is my resurfacing of the head so maybe I jacked it up with that. I went ahead and bought a new 70cc bbk (cheap eBay knock off) I may get a knock off 19mm phbg carb while I'm at it because the 21 was a real pain to set up..

Anyway open to any and all suggestions to get this thing running. I literally just need it to run for 3 weeks. If I can find a solution between now and when the bbk arrives I can return it else I'll slap it on and see what happens.

Has anyone else tried to resurface their head and had good or bad results?

[lucky16]

Further data:

Batt 11.84v (12v)
Squish 1.0mm
Authentic 21mm dellortho PHBG carb
W7 needle 3rd from top/2nd from bottom
40 slide
60 choke jet
262AU atomizer
95 main jet
36 idle jet
Fuel screw 1+1/4 turns out
Idle screw set for 1300 rpm (previously)

[aeroxbud]

Is the plug getting wet when you try to start it?
Only getting 90psi isn't a good sign. You would usually want at least 100.
I have surfaced heads before with out problems.
Perhaps do a leak down test.

[lucky16]

The plug does get wet when I crank it. Although not as we as I expected on some of the tries where I cranked it a lot.

I know 90 isn't great but I was hoping it would at least start since I think it had to be worse before the head resurface since I could feel the compression leaking out the side. Sadly a leak down isn't super feasible for me since I don't have an air compressor :/

Other symptoms
- Took off the reed block and it looked like there was some copper gasket sealant stuff that made its way back there. Looked like shiny copper specks mixed in with the oil/gas. Not great. Spent like 2 hours cleaning all that out as best I could. Last time I ever use that stuff.
- the squish seems inconsistent in that it's thinner closer to the spark plug and flares out at the very end near the cylinder wall.

Here's some other stuff I tried:
- Starter fluid
- Cleaned the air filter
- Tried an extra washer on the spark plug making it less deep essentially (brought up in a different forum that the spark plug could be contacting the piston. Don't think so because it turns over smooth, but couldn't hurt to try)

Also was brought up that 11.84v may be a dead battery. I'm getting spark so idk, but new batt can't hurt either because the current one is over 5 years old.

Happy to hear someone has done a resurface successfully! I think I just took off too much on the head side (not the cylinder side). I essentially did the resurface twice because the first surface I used wasn't completely flat (table) and it got messed up. The second surface (glass) worked money but I think it was just a lot of material to fix the initial mistake.

Please keep the ideas coming. I'll advise if the new top end or batt fixes the issue

[aeroxbud]

A good battery is usually over 12.5V. You could try charging it.

[chehystpewpur]

i could be wrong. but ive never ran an engine without a head gasket. the cylinder pressures get insane during combustion. sanding the surfaces also removes material so you effectively decked the block and head. if it was me i would remove the gasket at the base of the cylinder and test it with shims to see how much thinner you should go. put the headgasket on or a thinner one. the base of the cylinder isnt under much pressure so some people use shims and a tiny bit of sealant with good success. you can still get good squish clearance like that.

also if your dead set on no headgasket depending on how smooth you sanded it it may be too smooth for the gasket mater to adhere to most heads have a pretty rough surface from a machine shop blocks too.

[lucky16]

Certainly not dead set on no head gasket - only tried it because that's how it was working before all this to get the squish just below 1mm.

Now I'm running a head gasket after the resurface and just adjusting the thickness of the base gasket to set squish. (I tried without the head gasket during troubleshooting when it didn't start up with the head gasket on, but that didn't work so I'm back to the head gasket setup now)

I got a new battery on the way so I'll see if that works. Wish me luck. If that doesn't work I'm going to break open the new cheap bbk (ncy) I got and I'd be surprised if that doesn't work.

[aeroxbud]

Piaggio don't use head gaskets on its air cooled bikes. But They are designed like that I guess. I just used copper spray when fitting an aftermarket kit to the standard Piaggio head.

[chehystpewpur]

thats funny cause ive never seen an engine without them but also dont own piaggio. with enough cylinder head bolts i could see it being possible but most vehicles use 4 nowadays and thats known to be too few. all the newer gm headgasket problems are mostly stemming form that. they used to do 6 per cylinder and it held well but they lowered it to 4 and it doesnt clamp well enough to stay sealed up. hopefully you can get it going again. i remember when i had a pos 4t scoot and put a bbk on it to solve problems i had and the bbk had more problems than the chinese crap it had on it. these 2t are almost indestructible once you get them going.

one thing i will say though. as i had a major headache for like 2-3 days one time check your reeds. even chipped corners can cause a no start. i had a set that went bad very quickly they were new and just fell apart. put a cylinder on it changed the stator the rotor carb all kinds of stuff couldnt get it to run right or at all and was like ya know lemme look. the reeds were done. now i run custom reeds and havent had a problem since then with reeds.

[lucky16]

Got the battery tested and came back 11v and 1cca which I don't think is going to cut it... Wild that the battery finally gave out at the same time I was doing the head resurface.

That said, I also found that due to my failed 1st resurface, the squish is inconsistent. The surfaces are truly flat now, but not perfectly square which leads to smaller squish at the bottom of the cylinder than the top.

I expect it'll start but run like crap and eventually break itself. Thus I'll chalk that up as a $150 learning point and end up installing the new cylinder.

Before I do though I want to test the janky one with the new battery just so I can see if it'll start up. That would make me feel a little less crazy.

I'll let y'all know how it works out. Hopefully with good news

[lucky16]

Alrighty. Got it running.

Put everything back together on the old cylinder including the head gasket and a new gasket for the reed valve. That got compression up to 100. Hooked up the new batt and it coughed a few times but still wouldn't start.

I believe I f'ed it away on my 1st resurface attempt and subsequent one to fix the first. Ended up taking off too much material and after flattening the first it was not perfectly aligned: although the surfaces mated perfectly, squish at the bottom was .6 and at the top was 1.4...

Threw on the new cylinder and it started right up on the second kick. For what it's worth, I tried the old battery as well and it still worked

Lesson learned is if you're going to resurface the head ensure you use a glass table or something machined truely flat the first time and take off as little material as possible. Also I think I could have avoided this whole thing if I used a head gasket to start and accepted a slightly bigger squish.

Other lesson is I'm definitely not going to use copper spray sealant ever again - made a mess from excess that must have seaped out and dissolved in the case which was a real pain to clean.

[lucky16]

Btw with the new cylinder compression was up to 140!