Head bolt torque

[Walter F.]

Just got back from Harbor Freight, got a new Torque Wrench and I'm dying to try it out. Does anyone KNOW or have an expert guess at the torque number for the head bolts. I have a 49cc with M6 cap screws, I don't use studs, I can use either inch pounds or newton meters. It seems somewhere I saw a number like 12 newton meters, does this sound about right? Happy Trails Walter F.

[misteright1_99]

I believe for 6mm the figure is 8 ft lbs/ 96 inch lbs......That is what I have my head bolts (studs) torqued to. I believe the 12 ft lb rating is for 8mm studs.....

1 ft lb = 12 in lbs

[Bikeguy Joe]

I second that.

[Bikeguy Joe]

Here's a photo of my torque wrench.

Low torque setting (photo 1.)
High torque setting (photo 2.)

[seannp22]

how many ft. lbs. of torque is it for 10mm head bolts? I torqued mine to 10 ft. lbs. but it blew the head gasket due to not enough pressure. I'm debating between 15 and 20. any suggestions?

[richirich]

seannp22, out of quriosity what kind of motor do you have that has 10mm head bolts?

[2door]

First of all make sure your gasket surfaces are square. We suggest using a known flat surface, glass works well, or anything thet is true and warp free. Lay a sheet of 320 or 280 grit snadpaper on it then take the cylinder head and rub it across the abrasive surface. You'll see immediately if the cylinder head gasket surface is really flat. Work the head around rotatintg it in your hand so you don't sand an angle into it until the surface is uniform.
Do the same to the cylinder. If you don't want to remove the cylinder from the case then stuff a rag into the piston bore so you can capture the material you remove, and use a large flat file with sandpaper wrapped around it to true up the gasket mating surface.
I prefer to do this with the cylinder removed from the case but that's your preference. The studs need to be torqued into the case prior to reassembly. Install two nuts, back to back on the upper threads then torque the studs into the case to 120 to 150 inch pounds. Install the cylinder being careful to get the piston rings aligned with the pins in the ring grooves and into the cylinder. Lubricate the rings with a little oil prior to assembly. Once the cylinder is in place install the cylinder head and install the head nuts. Pick up some new hex nuts, preferably shouldered nuts with a wide flange, and lock washers, torque the nuts to the same as you did the studs, 120 to 150 inch pounds. Throw the acorn nuts in the trash or the scrap parts bin.

You should be good to go using this method. I always suggest using new, unused gaskets but others will tell you the originals will work. Install the spark plug, connect the seconday ignition wire and go ride your bike.
Good luck.
Tom

[Al.Fisherman]

Originally Posted by seannp22

how many ft. lbs. of torque is it for 10mm head bolts? I torqued mine to 10 ft. lbs. but it blew the head gasket due to not enough pressure. I'm debating between 15 and 20. any suggestions?

Is the stud a 10mm or a 6mm with a 10mm nut? Really no reason to have a 10mm stud in a small cast aluminum engine such as these. I said before 204 INCH pounds is max for 8mm studs in cast aluminum. First time I use 150 INCH pounds then if I have to go into the engine, I use 175 INCH pounds on re instillation. 6mm is from 50 to 60 INCH pounds.

OH and as said 1,000+ times...throwaway the acorn nuts and replace with locking nuts. For the record, I don't use lock washers, just flat washers. I have never seen a head installed with lock washers, except on these Chinese engines. Why I don't know..then again how can they make such a sloppy engine.

By the way... 10mm bolts/studs in cast aluminum is 25 INCH pounds.

Newton to inch pounds ..... Newton = inch pounds X 0.113

50 INCH pounds = 5.65 Newton
60 INCH pounds = 6.78 Newton

[Skarrd]

here's what i use (8mm studs)

step 1: 10 ft-lbs (Z pattern)
step 2: 20 ft-lbs (N Pattern)
step 3: 0 ft-lbs
step 4: 15 ft-lbs (N pattern)
step 5: 25 ft-lbs (Z pattern)

might be overkill, but it's worked great to make sure that:
A: the bolts are torqued evenly
B: there is enough pressure to hold the head gasket in place and prevent blowouts.


i know it's a bit over what is recommended for the head torque, but really if you go slowly and uniformly. you'll be fine going to around 25-35 ft-lbs.

just make sure you have a good torque wrench, and slowly torque it.