Damn head bolts!!!

snobord28 · Jun 14, 2010

Ive only had my lil girl running just a little bit like a hour total, I go to check the head bolts with a tourque wrench at 12 ft/lbs and the last one stripped. I replaced every other bolt but didnt want to mess with theses ones at the time. Guess I will now, how many other people have had the same problem with these weak a** bolts? :-||

jauguston · Jun 14, 2010

Are they 6mm or 8mm? 12 ft lbs on 6mm Chinese studs is a bunch. I torque my 6mm studs to 9 ft lbs. I put the torque wrench on the head nuts every 2-3 times I ride it and get movement every time so far. The motor has about 100 miles on it. Its a slant plug Sky Hawk.

Jim

bairdco · Jun 14, 2010

i tighten mine with a little 10mm wrench, then check them after the first ride when the engine's hot. i can usually get a 1/4 turn out of them.

then i forget about them and they don't come loose.

if you keep trying to tighten them all the time, you'll eventually strip them. at least that's my opinion. and 3 engines on 3 bikes and a few thousand miles of WOT hasn't proved me wrong...

jauguston · Jun 14, 2010

I use a inch-pound torque wrench. They give you torque specs for a reason. My head bolt nuts are acorn style and take a 14mm socket. Still 6mm studs.

Jim

moronic_kaos · Jun 14, 2010

I tighten them about as tight as the flat head bolts are that hold the clutch arm in place. No air leaks.

jauguston said:
I use a inch-pound torque wrench. They give you torque specs for a reason. My head bolt nuts are acorn style and take a 14mm socket. Still 6mm studs.

Jim

Mine never came with torque specs. Mind sharing?

meowy84 · Jun 15, 2010

Also f you have acorns you might want to replace them with regular nuts because I found on mine the end of the studs were bottoming out in the top of the acorn. So instead of cutting down the studs a thread or two I just got the nuts instead.

corgi1 · Jun 15, 2010

What is the number you use on the inch pound torque wrench?

nidyanazo · Jun 15, 2010

My hand is my tq wrench.

jk I have a good one, but after countless engines built, I got a knack for it. (as most people do )
Worst time I screwed up was torquing a new 302 with alum heads to a steel block..., was supposed to go to 90 ft/lb but the last one stripped at 80ft/lb.

Darn that was annoying,.

Try this

Bikeguy Joe · Jun 15, 2010

Just be careful tightening them if the engine is hot, and the constant checking and re-torquing can cause them to strip.

jauguston · Jun 15, 2010

95 in-lbs is approximately 9 ft-lbs. 12in-lbs = 1 ft-lb. Anyone that thinks they can pull a specific torque spec with a hand wrench doesn't care much for the stuff he is working on. Can you sometimes get away with it-sure. There is the right way and the other way. I wouldn't let anyone put a wrench on anything I own that says he doesn't need a torque wrench he can do it by feel.

Jim 43 years as a heavy equipment mechanic and crane operator.

bairdco · Jun 15, 2010

guess i won't be working on your bike...

snobord28 · Jun 15, 2010

alright I replaced the studs,now i need to know was 12ft/lbs too tight in the first place? there 8mm bolts and 12 ft/lbs is what my engine kit recomends but they stripped so... thanks all

meowy84 · Jun 16, 2010

nidyanazo said:
My hand is my tq wrench.

Enzo Ferrari to his mechanic at Le Mans:
"Mamma-mia!!!! Why the {italian expletive} did the engine on that 250GTO grenade itself 50 yards from the finish line?"

Mechanic:
"My hand is my torqe wrench."
rotfl

j/k

Seriously though, most auto service manuals give you tq specs for every nut and bolt on the car including fender nuts and so forth. To put your fender on with a tq wrench is kinda cooky and pointless BUT during engine asembly a good tq wrench is a must and not using one is just asking for trouble.

Mind you on a low performance single cylinder 2 stroke you can get away putting a head on by feel without a tq wrench. Used to do it all the time when I was a kid with my dirtbike before I even knew what a tq wrench was without any dire results. With the low quality hardware on the HT engines I think you might sometimes actually strip the head fastener torquing it to what the specs say.

That being said the instructions for my PK/Zoom 80 call for a head torque of 8-10ft/lbs.

snobord28 · Jun 16, 2010

thanks for everyone's help, I got it back together and everything seems ok. Ill use a little less torque and continue the long process of breaking in.

brnot

tim turbo · Jun 16, 2010

I have had my china girl for two years now, and I have come to learn these little engine'sare pretty tuff. I lived next door to a motorcycle mechanic years ago and he never used a torque wrench, he told me depending on the application two, three, or four finger's on the end of a wrench will do quite nicely. If I was building a car motor that would be a differant story. What I,m trying to say is, your not building piano's these are cheap motors,with cheap parts,easy to get. Just saying..

moronic_kaos · Jun 16, 2010

Just got 3 feet of steel threaded rod (everything on my motor is M6) for $6. Replaced every single stud in 2 motors. So yea, loss of a stud is really not a big deal.

I'd be pretty scared to tighten up the studs (especially the rear ones) to 12 ft-pounds though, as it's a steel stud going into whatever BS metal these engines are made of. When I got the motor, some of the studs would actually come out just by loosing whatever nut was on it. So I'd say go it like this:

studs go in 1 to 1 1/2 turns past being able to wiggle inside the hole (given that they're pretty much bottomed out)
Nuts go on at what I'd guess to be 10 ft pounds.

You'd think the nuts would further tighten up the studs, but they don't.

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Damn head bolts!!!

snobord28

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jauguston

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bairdco

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moronic_kaos

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