Break In Port timing suggestions?

DirtyBum

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Hi this is my first post!

SO I am fairly new to porting, I built a piston port 80cc which blew up (spun the bearing which in turn destroyed my piston and cylinder). I bought the cheapest cylinder, new piston, bearings, rings, slant head, reed valve, jets and a new sparkplug from Amazon and I am cracking my case today to clean out the residual bearings and such... I'll be balancing my crankshaft and planning down the mating surface while I'm at it. Parts won't be in until tomorrow and I'd like to port my engine for optimal performance at low rpms/climbing hills and was hoping someone could just give me some decent ballpark port durations for running a reed valved engine uphill, I've got a lot to do and I'm honestly just not trying to research and understand why exactly those port durations do what they do. I will be windowing the piston and I'm open to putting a trench/boost port in but I want to do this in under 6 hours as I am damn tired of working on the engine.

I'm going to be taking this baby on a road trip through the Appalachians (about 900 miles) in a week or two so not trying to do anything extreme or wonky which will make it unreliable.

Please limit answers to port duration suggestions as I already know it's not the best idea to go on a road trip that soon, I'm cold and the bike has been pretty damn reliable until the bearing finally gave out (modded too hard, I know what I did wrong and I don't wanna talk about it 🤣) and I am heading for greener pastures.

If I don't get an answer soon I'll keep my durations and just do a little cleaning and up and widening of the ports, that got me 35 mph before and was great going uphill until the cataclysm.

Thank you!
 

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Just for full transparency. I'm probably one of the best for these questions. Impulserocket has some different technical knowledge but ask anybody I'm known for taking each motor to they're limit. If I HAD to do this it would be on this. I actually built another one last night. It's a 49mm iron sleeve. Upgraded BULLETPROOF pk80 top end. I've travel over 75 miles on 1 day in 90°+ weather tru difficult terrain with a full load including a belt sander I had to buy 25 miles away. It ran perfectly. It's THE most dependable 2 stroke they're is. I'm not exaggerating when I say ask anyone here I've owned and test virtually ever motor with every option. Showed absolutely no mercy. If it needs to be 2 stroke do it on an iron sleeve 1. No chrome to wear away. 2. Even with a part failure high likelihood it stays running. There's just so much to say about this. Keep vigilant any sign of change in operation has to be caught immediately.
That's awesome I've got a "50mm" piston (it's measuring 49.5) I'm thinking about boring out the old jug... stepfather has some equipment but idk if the jug has enough meat to sleeve with the 50 mm bore. Might sleeve it to fit the 47mm. Is the increase in width really that much more powerful? Seems like the balance might be an issue, but willi g to go the distance here.

There alot to unpack here 1. Red RTV isn't gas resistant. Even grey isn't very good BUT if you hafta then use grey. To seal surfaces against 2 stroke mix loctite 518 or dirko ht red are advised (they seal chainsaw cases). 2. A road trip motor should be focused on. simplicity. Adding ports and reeds is adding failure points. If you have a faulty reed(which is likely for a g2) your mega f***ed in some cases. Your asking alot from a little motor. 3. You will need a spare almost everything. 4. Doing anything from a dead stop is not advised. I hope you have an escape plan.
I'm gonna tote the entire old jug and spacer just in case, also going to have some spare bearings on deck though the new upper bearing is clearly WAY better quality, and I got some of those fancy washers that keeps it in place and protected. Completely saturated the case with red high temp bearing grease before starting up lol. I made some washers out of old piston but the steel ones fit better... She vibes a bit more but not much to talk about. Took her about 10-15 miles last night breaking in the new rings, gonna retorque everything and go for a few short rides here in a few. Tuned ever slightly rich, I'm really pleased with my improvised spacer.

I'm sure my primary compression decreased with the spacer and probably slightly different porting numbers. I'll check it with the wheel when I get a chance.

I think I'm addicted
 
I flipped the pin so the other side would wear and switched from 32:1 93 to 50:1 87. Got about 50 miles on 50:1 and this happened the next day.
NEVER run any less oil than a 32:1 ratio after breakin on these China Girl motors, even if it is full synthetic oil.

These motors WILL self destruct just like yours did.
 
That's awesome I've got a "50mm" piston (it's measuring 49.5) I'm thinking about boring out the old jug... stepfather has some equipment but idk if the jug has enough meat to sleeve with the 50 mm bore. Might sleeve it to fit the 47mm. Is the increase in width really that much more powerful? Seems like the balance might be an issue, but willi g to go the distance here.


I'm gonna tote the entire old jug and spacer just in case, also going to have some spare bearings on deck though the new upper bearing is clearly WAY better quality, and I got some of those fancy washers that keeps it in place and protected. Completely saturated the case with red high temp bearing grease before starting up lol. I made some washers out of old piston but the steel ones fit better... She vibes a bit more but not much to talk about. Took her about 10-15 miles last night breaking in the new rings, gonna retorque everything and go for a few short rides here in a few. Tuned ever slightly rich, I'm really pleased with my improvised spacer.

I'm sure my primary compression decreased with the spacer and probably slightly different porting numbers. I'll check it with the wheel when I get a chance.

I think I'm addicted
Let be clear here CRANKSHAFT BEARINGS!!! 6202 2rs. Pgn makes them for 2$ a pop rated up to 23k rpms lol. Shoot me a message and I'll bring you to the other side of this BUT you have some work to do I HIGHLY recommend you spend 70$ on a brand new iron sleeve then keep the remainder of your for the parts you will likely need for a journey. From now on I seriously recommend as uncle Damien has advised 20:1 conventional(valvoline is the good stuff) then 32:1 synthetic(dominator kicks major ass). We can talk more about ratio and fine tuning later lol. This is just what I recommend and I ride the wheels of these lol.
 
I have a great job opportunity here so I may not be going on this trip just yet, I realized theres a lot that I need to get right before trying a trek like that. Mostly resources and experience. Thanks for all the great advice y'all
 
I have a great job opportunity here so I may not be going on this trip just yet, I realized theres a lot that I need to get right before trying a trek like that. Mostly resources and experience. Thanks for all the great advice y'all
Just another thing to mention...During breakin, I always use Valvoline 2 cycle multi-purpose oil for the first 300 miles at 20:1 mix ratio, I then change over to Amsoil Dominator 2 cycle racing oil and recommend nothing less than 32:1 on regular China Girls...You will find there are others here that also use the same stuff and same amounts I recommend and have great results such as @Mike Cyanide.
 
That piston looks like a piece of casting flash broke off and rattled around in there until it finally burnt up. In the mean time it chewed on the piston and head.
It was the upper bearing, there were still about 6 needles and half the shell that hold them in there. Some of it was embedded in the head and I removed it with needle nose pliers. I honed the cylinder out with the old piston, made a 5mm spacer and put the low wrist pin piston in. it's running great! I finally conquered the steepest hill in my hometown with that setup and the crankcase stopped leaking??
I'm guessing that's because of reduced primary compression or possibly the seals getting filled in with junk from the copious amounts of grease I put on all the bearings after cleaning the crap out of everything. Either way, I'll take it. I haven't even tried the new jug yet but I'll update when I do. Going to take my time getting my ports just right and make sure it's properly jetted.
 
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