Head stud kit

GoldenMotor.com

bikeme

New Member
Apr 11, 2011
7
0
0
Arizona
Hi, Can anyone tell me the head stud thread size for a
Grubee Skyhawk GT5 66cc slant head? SBP has three
listed as: M6-1.0, M8-1.0 and M8-1.25. I just ordered
my kit and want to get my order in to SBP. Thanks much.
 

matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
i may be in the minority and its not an answer to your question, but out of all the studs,bolts on my GT-5 the head studs are the only ones i didn't worry about. mine seemed strong and held up to my ratchet just fine when i took em out, no stripping or anything like that.

pretty much every other stud/bolt/nut i replaced on mine.
 

bikeme

New Member
Apr 11, 2011
7
0
0
Arizona
Thanks for the info Matt. I'm also planning on buying the SBP engine hardware kit that contains motor mounts, intake and exhaust bolts and engine case bolt and nuts. Did you
use this kit?
 

matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
i got all my stuff at the home depot for the most part, although it probably would have been easier to get the sbp kit. iv'e heard nothing bad about their kit so if you don't mind waiting a few days for shipping i see no reason not to grab it. i was getting things as i needed and go to home depot pretty frequently anyways so it was just convenient for me.
 

DaveC

Member
Jul 14, 2010
969
1
18
Boise, ID
I've got both kits. One thing I would recommend is tapping all the holes to the bottom. Most of the holes are very shallow tapped. As far as what size head studs mine was a hybred bas.tard of both sizes, M8 1.00 in the block and M8 1.25 on the head end. I got the M8 1.00. When I tried to screw in the stud it would not go in the hole, instead of being for a M8 was more like for a M7.9, just a little too small. I figure spec tolerances are pretty loose there in China :p When tapping the hole use a greasey type of lube so the chips get stuck in the grease and don't fall off in the motor.

Buy and use a tube of Blue Locktite. Locktite won't work on the exhaust studs, too hot. Just make sure you botton out the exhaust stud. Tightening up a too-shallow stud is what pulls the threads right out of the hole.:-||
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
DaveC,
Your engine is not unique as far as the studs being different threads on each end. In fact the majority of the 2 strokes I've worked with have had 8mm studs that had a 1 thread on one end and a 1.25 on the other. The fine threads went into the case and the course thread was on top, at the cylinder head.
As long as you're replacing those studs you might as well toss those stupid acorn nuts and replace them with shouldered hex nuts too. The acorns are notorious for bottoming out before they are tight against the head. My experience anyway.
Tom
 

bikeme

New Member
Apr 11, 2011
7
0
0
Arizona
Tom,
Are you saying the replacement head studs from SBP will not work because their threads are the same on each end? Where are upgraded studs with different threaded ends to be found? ~Bikeme
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Tom,
Are you saying the replacement head studs from SBP will not work because their threads are the same on each end? Where are upgraded studs with different threaded ends to be found? ~Bikeme
Just check your studs then compare them with what SBP sells. Whatever the thread pitch is in your engine case must match what you plan to replace them with. As for the top end, it doesn't make much difference if you replace the acorn nuts with hex. Simply match the threads. I hope this answeres your question.
Sick Bike Parts should be able to answer any questions you have about thread pitch. They are good folks to work with. Email or give them a call.

Tom
 

matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
my advice is take out all 4 of your studs, make sure they're all the same size, and go to the home depot, they got thread sizing test mats, helps people find exactly what they need.

bring em there, size em up, and order the proper size from sbp.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
I'll tell you this; you'll not find an 8mm stud with a 1 thread pitch. Yes, I've heard that some can "force" a 1.25 stud into a threaded hole with a 1 pitch, but that is what we call being a "hatchet mechanic". It's the same as "forcing" a 1/4 x 20 screw into a 6mm x 1 threaded hole. Yes, it can be done but it's not the right way to do it.
 
Last edited:

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
Good luck finding a 8mm X 1 bolt or threaded rod at Home Depot. You'll find that 8mm bolts or threaded rod will come in a 1.25 thread pitch. If your engine case takes a 1 thread pitch..."you're gonna need a bigger boat".
Tom
 

DaveC

Member
Jul 14, 2010
969
1
18
Boise, ID
Good advice. Thanks DaveC. What did you torque studs to?
I'm torqueing to 12.5 Ft Lbs, some will say as much as 18 Ft Lbs but to each his own. I think 15 Ft Lbs should be max.

The SBP stud is actually a section of all-thread. The M8 1.00 comes with 13mm nuts for more room for a socket and it turns out the size needed for a conversion to a Puch head, there's no room for a 14mm socket.

All I can really say is it's a bad idea to try and put a M8 1.25 into a M8 1.00 hole, even retapping the hole. If you must change threads then helicoil to the correct size. Cross-tapping a thread like that means the next step is JB Welding the stud in. :p
 

matthurd

New Member
Dec 13, 2010
817
2
0
manchester NH
Good luck finding a 8mm X 1 bolt or threaded rod at Home Depot. You'll find that 8mm bolts or threaded rod will come in a 1.25 thread pitch. If your engine case takes a 1 thread pitch..."you're gonna need a bigger boat".
Tom
it's not the studs themselves i'm sending him there for, simply for a sizing chart so he can accurately purchase the upgraded stud kit made for his motor. millimeters can be a bit hard to measure with out good equipment, better off to use someone else's good equipment then to purchase something that looks right but you're not 100% positive about.
 

2door

Moderator
Staff member
Sep 15, 2008
16,302
175
63
Littleton, Colorado
it's not the studs themselves i'm sending him there for, simply for a sizing chart so he can accurately purchase the upgraded stud kit made for his motor. millimeters can be a bit hard to measure with out good equipment, better off to use someone else's good equipment then to purchase something that looks right but you're not 100% positive about.
I see what you're saying and agree. Using the proper tools to measure the diameter/threads is a good idea. Simply comparing them side to side is also a way to determine what they have. Like SAE fasteners, the difference between fine and course threads are readily apparent when viewed next to each other. Also a tool to determine diameter would be beneficial if the person doesn't have access to a a caliper or diameter guage.