Think I blew my first head gasket yesterday...

[mapbike]

Took the new engine for a 16.5 mile ride yesterday, on the last of it I stopped for a couple minutes and noticed when I rev the engine I'm hearing a high pitched whistle sound when I jack the throttle, it's definitely the sound of air squeaking past a small opening somewhere, exhaust gasket looks good and I know carb gasket is sealed, pretty sure it's got to be the head gasket, I also noticed that the top of my spark plug is turning a blueish color so I will have to pull the carb and drill the jet up a size for sure also, I think at a cruise speed of about 32-34mph mix is not to far off, but when I hammer it and run it up over 40mph and keep it at the current top speed of 42mph it's a bit lean and gettingf very hot as well, gonna guess overheating is what has got my head gasket and possible warped the head a bit, no big thing, gonna pull that head resurface it and put aside for another engine, I'll just put the Puch head on and rejet the carb up a bit and that should solve my probelms.

The carb was tuned perfectly on the engine it came off of but it doesn't have nearly the port work that this one does so this tells me that my porting has really helped it flow better because of the lean condition I'm now having, lots more air flowing through the engine now.

Really curious to see what this thing is gonna do when I get the carb tuned in right, more compression and my expansion pipe exhaust built for it, I'm betting on 45MPH with the 34T sprocket possibly, need to get my Tach hooked up on it so I'll know what kinda RPM's I'm turning it at what speed.

Sure am loving the Dax......... best and smoothest running engine I've had yet...... gonna end up with one of them on all of my personal China girl builds, as I will replace the engines I currently have, they are good running engines but I just really like the extra smoothness of the balanced Dax lower... really nice.

map

 

[maniac57]

I'm quite thrilled by your glowing reports on the Dax balanced bottom end assembly.
Sounds like I need one too!

 

[mapbike]

I'm quite thrilled by your glowing reports on the Dax balanced bottom end assembly.
Sounds like I need one too!

If you get one and put a well ported jug and everything else well tuned you'll be a happy camper, I know I am, the dax lowers ain't snake oil, they really are smoother running and mine will hit 42mph pretty dang quick, the carb, compression and exhaust is what prohibits it from more speed, it isn't the vibe issue that prohibits most of them like my others, I have one that has hit 42mph but it feels like the bike is either gonna break apart or blast off by the time it gets there, my dax engine has less vibes at 42mph than my others do at 28-30mph, that aint nothing to sneeze at in my book........ Im serious when I say Im gonna replace all my lowers with the dax lower when I can, I'll use my current upper cylinders and pistons but I'm not gonna fool arou d with the e tra vibes at higher speeds when for a couple hundred bucks I can have all my china girls running better and smoother, im gonna say they're probably gonna last longer also.

 

[Jumpa]

Are they a special lower or just the basic ones they have on the web site there? Also Shan how much are the lowers I have almost the same upper set up as you with the short aluminum intake But I have a "NT speed carb" and the aluminum fin header. I'm heating up big time and don't like it. Also when it heats up and only when it heats up I get a slight knock I can hear it don't like it . I gonna tear it down today since its my day off go deep besides I've been wanting to swap out bikes for the suspension and disc brakes Gary Fisher I have sitting in the corner .. f my darn idler would ever get here!!

JK

 

[mapbike]

Are they a special lower or just the basic ones they have on the web site there? Also Shan how much are the lowers I have almost the same upper set up as you with the short aluminum intake But I have a "NT speed carb" and the aluminum fin header. I'm heating up big time and don't like it. Also when it heats up and only when it heats up I get a slight knock I can hear it don't like it . I gonna tear it down today since its my day off go deep besides I've been wanting to swap out bikes for the suspension and disc brakes Gary Fisher I have sitting in the corner .. f my darn idler would ever get here!!

JK

Dax lower is a basic china girl case with high quality beraings and it has what they call a GP360 hand drilled and balanced crankshaft, its not a butter smooth running set up but it is much much smoother than any stock regular china girl engine I have owned, comfortable smooth at over 8000rpm is what I ended up with mine.
Be glad when Duane gets some more made up so more people can enjoy one or at least get some cranks for sale so people can upgrade to a better balanced crank assembly if they want.

Check the spark plug for color and if it shows a lean run condition try lowering needle clip one notch and if it still runs lean probably need to upjet.

Map

 

[FMB42]

Ya, I'll probably try a Dax Gen IV crank once I'm farther along with test/tune/tweaking my plain old 66cc China Girl. Meanwhile, sounds to me that Dax is not only balancing these Gen IVs, but truing the cranks as well (maybe Dax can answer this). A finely trued crank on any 2 cycle will, of course, also result in a much smoother running engine (the smoother the stronger). Btw, race mechanics spend a lot of time fine truing cranks for the riders they tune for. Anyway, I'll be interested to see just how true, or untrue, my plain Jane 66cc crank is when and if I get around to checking it (there's an old saying among general auto mechanics that goes something like this: "compression testers, dial indicators, and leak-down testers are bringers of bad news")...

 

[mapbike]

Ya, I'll probably try a Dax Gen IV crank once I'm farther along with test/tune/tweaking my plain old 66cc China Girl. Meanwhile, sounds to me that Dax is not only balancing these Gen IVs, but truing the cranks as well (maybe Dax can answer this). A finely trued crank on any 2 cycle will, of course, also result in a much smoother running engine (the smoother the stronger). Btw, race mechanics spend a lot of time fine truing cranks for the riders they tune for. Anyway, I'll be interested to see just how true, or untrue, my plain Jane 66cc crank is when and if I get around to checking it (there's an old saying among general auto mechanics that goes something like this: "compression testers, dial indicators, and leak-down testers are bringers of bad news")...

Yeah I figure he probably does some amount of truing the cranks also, I have a second lower I haven't built up into a complete engine yet so ill be curious to see hwo the second one does compared to my first one, my first one is giving me smooth comfortable power and speeds of over 40 mph. Been clocked at 48mph my older standard HTs top out at around 38mph and wicked vibes at that speed.

Map

 

[maniac57]

Yeah, I'm extremely budget limited so I'd love to be able to buy just a crank. I can easily source good bearings locally, but getting a crank trued and balanced is another story.