Head bolt torque

Walter F.

Walter F.

New Member
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.
 
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
 
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Here's a photo of my torque wrench.

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

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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?:-||
 
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
 
seannp22 said:
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?:-||
Click to expand...

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
 
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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.
 
Hey, read all the stuff and thanks! so this is what i came up with:
1, take off head and slide the cylinder up till you see the bottom of the piston
2, drop a 1/4 by 20 tap down the cylinder hole add grease to the cutter to catch chips
3, thread into stripped stud hole in block cleaning and regreasing as needed
thread in about 1 inch of tap then push tap back out of cylinder hole
4, slide the cylinder back down and install a 1/4x20 by 3" bolt with 2 washers
5, torque using the z then n pattern up to 10 PSI (48cc grubee)

this worked great and i did not have to deal will rings or reseating the piston you end up with 1 7/16th bolt head and 3 10mm. Thinking about doing all 4 this way since the larger thread pattern leaves more metal to hold what you guys think?
 
oh, also i did the glass sand paper thing and used a little perma-gasket on the head gasket figured it wouldn't hurt and for years its what we did with cars
 
jats said:
oh, also i did the glass sand paper thing and used a little perma-gasket on the head gasket figured it wouldn't hurt and for years its what we did with cars
Click to expand...

Head gasket...use this, or aluminum paint.


All other gaskets I use this...or something similar.
 
I suggest,

6mm studs 125 in/lb
8mm studs 145 in/lb

if your torque wrench only reads ft/lb don't use it, because it probably won't be accurate at these small values. Get one that reads in/lb.

Don't over torque the studs trying to stop a leak. If it leaks at these torque values, you got some other problem. Over torqueing the studs could result in distorting the cylinder bore, or stripping the block.

Retorque the head bolts several times after the initial start up.
 
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biknut said:
I suggest,

6mm studs 125 in/lb
8mm studs 145 in/lb

if your torque wrench only reads ft/lb don't use it, because it probably won't be accurate at these small values. Get one that reads in/lb.

Don't over torque the studs trying to stop a leak. If it leaks at these torque values, you got some other problem. Over torqueing the studs could result in distorting the cylinder bore, or stripping the block.

Retorque the head bolts several times after the initial start up.
Click to expand...

I think that 125 inch#'s on 6mm studs is way high.
6mm (Lowe Grade) 3-5 Foot pounds (36-60 INCH POUNDS)
6mm (Metric 8.8/approx US Grade 5) 7 Foot pounds (84 INCH POUNDS)
I use between 60 and 75 INCH POUNDS

8mm (Lowe Grade) 8-12 Foot pounds (96-144 INCH POUNDS)
8mm (Metric Grade 8.8/US Grade5) 17 Foot pounds (204 inch pounds)
I use between 150 and 175 INCH POUNDS
 
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I'm not sure what size my studs are. Engine is 66cc flying horse.. But I torqued mine to 96inch-pounds. Has been great so far. Still using the acorn nuts but I put blue thread lock on them so they aren't going anywhere.
 
Rocky_Motor said:
I'm not sure what size my studs are. Engine is 66cc flying horse.. But I torqued mine to 96inch-pounds. Has been great so far. Still using the acorn nuts but I put blue thread lock on them so they aren't going anywhere.
Click to expand...

All 66cc that I have seen the cylinder studs are 8mm, which doesn't mean some might be 6mm. Now most 49cc that I have run across are 6mm. I've even seen 8mm X 1.0, but it's not common.
 
seannp22, you didnt blow a head gasket because you didnt have enough torque, you blew the gasket because one of your studs wasnt bottomed out correctly. take your head off and your gasket, take a pair of pliers, grab each stud right above the jug, and see if you can tighten it. if none are loose, that means you tightened your bolts incorrectly. you must tighten in an x pattern, and tighten each bolt a little at a time until they are all snug and showing the correct poundage. 10 to 12 foot lbs should be sufficient torque for any ht engine. as far as acorn nuts are concerned, I always use a pair of dykes to cut the caps off. that way i can use the nuts that come with the engine. had my current engine for about a year now, no issues with the nuts or the locking washers.
 
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