31cc weed eater bike, few quesions

[keatonx]

I'm screwing the spark plug back in and i feel a bit of ressistance in this one spot. So i take it out, spray it with some fogging oil, then twist it with my fingers till it screws in freely. But I aimed a flashlight at the threads and the bottom 1 -1/2 winds of thread were broken off. (they either fell into the engine when i took the plug off or the engine gobbled em up!) The engine had 5-6 winds in total, so now it has 3 to 4 winds left holding the plug on. And this is on an engine with a poop load of compression! (mtd 31cc, but same engine as ryobi 31cc). Will the 3 to 4 remaining winds hold the plug on, or will it shoot off like a bullet?! I don't want to use a repair kit because the compression might leak!

Also, how can I make this thing more powerful? It already has tons but the more the merrier! I was thinking bending the reed valve retainer out so more fuel can get in the engine (but then i could get reed flutter at high rpms). So far I have sawed off a big rectangle at the bottom of the muffler, and removed the spark screen. I gave it my biggest carb, too.(about 11 to 12mm at the butterfly)

But I really love this thing! So far it goes around 60 kmh, but i'm getting a pocket bike clutch in the mail for it, and adding GEARS! (3 speed pedal crank cassette on rear wheel). The engine has tons of leftover power with the 1 speed. I'm going to make a post about it (It's chain drive with a primary reduction from an angle grinder).

 

[double trouble]

that plug

It will shoot out and make you wish you were a girl.
Yer gonna scream like one too.
Its all that lying about going 50k with a 33cc motor.
ya best glue that sucker in.

 

[keatonx]

Glue it in? Thats not happening cuz i won't be able to take it out. And i didn't get that third sentence

 

[keatonx]

''I gave it my biggest carb, too.(about 11 to 12mm at the butterfly''

It is actually 14mm at the butterfly (outlet at engine side of carb)

 

[bideronit13]

You can place a new sleeve in the head or have a shop do it without loosing compression.

 

[keatonx]

You can place a new sleeve in the head or have a shop do it without loosing compression.

Like a helicoil?

 

[HeadSmess]

its called a helicoil, its a fairly standard repair, plug threads in alloy heads are the joy of all apprentices and the bane of all tradesmen...lucky im neither

its an M14x1.25? i think... just about every mechanic will have a kit, and just about every mechanic will try and say its a $50 job even though it takes about 2 minutes.... this is about half the price of a kit itself... and the inserts are about 50c each...

only mechanics will keep the kits intended for plug threads.

oil/nickel antisieze plug threads! combine aluminium with iron at high temps and you get galling....which means stripped threads. stainless steel is worse... "galls" if you look at it crosseyed and forget to lube...hate that stuff! never insert a plug dry. i noted the fact you said you oiled the threads good boy

araldite works for 5 minutes

um...theres also the option of tapping out to the M18 plug thread...."A" series in ngk. sort of getting rare these days....

its hard to write about the same thing twice in a row and not repeat anything

14mm bore on the carb wont make a load of difference unless the manifold/inlets matched to suit.

id love to know where the reeds are on an mtd might need a picture or two...

id say make a pipe, i always say make a pipe problem with unified heads like an mtd has is measuring port times... its possible, but requires maths and i hate maths! so you can either guess it, make a pipe and never be sure if its better, or work with positive dimensions and be fairly certain you cant get better...

my personal method for getting an mtd to go fast is throw it in the bin that truck does 100 down the road!

double ended cranks all the way

 

[keatonx]

I also broke the bottom piston ring so i'm looking at buying a replacement engine. The trimmer i'm looking at has a simmilar looking engine, but it's a 32cc. Will a 1cc difference be a problem if i swap the rings and cilynders? The 1cc difference could be in the piston stroke.

 

[keatonx]

Also does anyone have any experience with 32cc craftsman(or yardworks) trimmers? Do they have much compression? Do they have 2 piston rings?

 

[keatonx]

My cylinder has 2 side by side ports on each side. Sould I grind those so they are 1 big port? I just did that on a scrap engine, and I'm going to test it in a few days.
(don't worry, headsmess, your pics are coming!)