head bolts

ZOOMCAT

New Member
Mar 14, 2008
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i bought my first bike motor it is a 70cc that i got on ebay' do they torque the head bolts at the factory or is that your job to do there seems to be gas in the spark plug is this good. and i am a newbie to this and i love it all your guys bikes look THE BOMB!!!!! thanks zoomcat:ride2:
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
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up north now
Welcome to the forum.

Generally, they are torqued at the factory. However, it's not a bad idea to check them especially after you've run it a few hours.

Find/borrow/buy a torque wrench. 15-20 ft. lbs. is the range you want to be in.

As for the gas in the plug...as long as it runs well, and the plug is a nice coffe/chocolate brown you are in good shape. If it seem to have a little gas on it, I wouldn't worry about it.
 

deacon

minor bike philosopher
Jan 15, 2008
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north carolina
Mine were torqued at the factory. Of course I screwed up the install and had to pull the head to correct it. So I can't say for sure but I think they are. If you have a torque wrench laying about it cant hurt to check them though. It should be 110 to 120 i'm told.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
Just to clarify-

110-120 in. oz. is in the same ball park as 12-15 ft. lbs.

If you don't have a torque wrench, use a 3/8" drive rachet and hold it so the rachet part is in your palm, not the handle and tighten it "pretty snug" that way.

These head bolts have been know to pull the metal out of the base if overtightened.

A little too loose will blow a head gasket (big deal) too tight will pull the threads and then you've got a mess.

Botttom line is don't worry about it unless you have a problem or the head needs to come off.
 

Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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Zoom
Its best if you have a inch pound torque wrench to use. I torque the nuts to a max of 110 to 120 inch lbs. When I've taken the head off I use aluminum spray paint to coat the head gasket on both sides this will act like a gasket sealer. Torque the nuts in a cross pattern start at 40 in. lbs. then go to 80 in.lbs. last I use 110 or 120 in.lbs. if I've had the head off more than once I will go to the higher setting. I watch the gasket area for leaks and if I find it leaking then I make a new gasket as the old aluminum leaks pretty easy once its been messed with. I use a special high temp gasket material for the head and exhaust gaskets and it bumps up the compression a little as its a little thinner than stock. My homemade ones have yet to leak. I'll have to get the name off the material if your interested. Most industrial gasket shops will carry this stuff and there is lots of scraps that you can get. For a lot less than you would pay for in a parts store.
 

Pablo

Master Bike Builder & Forum Sponsor
Dec 28, 2007
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i bought my first bike motor it is a 70cc that i got on ebay' do they torque the head bolts at the factory or is that your job to do there seems to be gas in the spark plug is this good. and i am a newbie to this and i love it all your guys bikes look THE BOMB!!!!! thanks zoomcat:ride2:
Frankly, mine were quite loose......Norm has da BOMB advice.
 

hartungej

New Member
May 31, 2011
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Madison, WI
Head Gasket/Cylinder Head problems-Help pls!

If anyone is still paying attention to this post . . . Here's a newbie looking for some help!

I'm running a Grubee Skyhawk 66cc with recently replaced cylinder and piston/rings. About 2 gal 24:1 through now, just switched to 32:1.

My cylinder head recently loosened up a great deal, to the point that I had air forcefully leaking out each side of the cylinder head. Upon retightening, I still seem to get pretty good power, but have lost about 5mph top end (31-32mph down to 26ish mph). Have I lost compression and possibly need a new gasket? What's the fix?
You should also know that I actually had 2 gaskets on this one since my new piston was topping out on the cylinder head my mechanic put 2 gaskets on and actually had to shave some aluminum off the head to make it fit!
If I do have a leak leading to reduced compression, how can I check for a leak?

Thanks in advance for any advice.
 

decoherence

New Member
Aug 23, 2010
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sebring,fl
i'm not an expert or even pulled my head off but,

the 2 gaskets lowered your compression.
also are you sure the piston was hitting the head & not the spark plug?
i would take a guess that if you took off the second gasket & pulled the plug out & turned the engine over it will be right as rain.
 

Drewd

New Member
Jul 25, 2008
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Colorado
I have a list of tips for builds that I religiously follow.

I always replace stock head studs and nuts. I then JB weld the upgraded replacement studs into the block. The reason I do this is that vibration almost always causes the studs to back out on their own. Lots of builders don't realize this and automatically tighten the head bolts.....with torque on less thread on the backed out thread, many end up stripping out the block threads.

With JB weld and replacement studs, I torque the **** out of my studs (25-30 ft-lbs) and I never have to worry about loose heads or leaking gaskets again!
 

Tohri

New Member
Aug 28, 2010
159
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People's Republik of Massachusetts
Seconding drewd. But make sure to use rated threaded rod for the studs, either B7 or grade 5 material at the Minimum, And heavy nuts on the top. The last motor I put together had M8x1.25 threads at the top (standard) and M8x1.0 fine threads where it mates with the cases. Big no-no on the designer's part, because grade 5 M8x1.0 allthread is next to impossible to find. I'm having to use bolts and cross my fingers.

Also, for studs, use Red loctite to mate them to the cases, better than JBweld. blue loctite if you ever have to remove something, red for a near welded bond.