Broken motor mount stud

Sharksfan · Dec 17, 2009

Can any one tell me if all of the engine studs are the same diameter and thread pitch? I broke a rear motor mount bolt off of my RAW 80cc this morning and I now want to replace them with stainless steel all thread. Are all of the mount, intake, exhaust, and head bolts the same (except for length)? I want to go and get a long piece of all thread so I can replace as many studs as possible. On an added note, anyone here in San Jose very good at broken bolt extraction? I could sure use some help. (and some tools)

Thanks, Sharksfan. :-||

2door · Dec 17, 2009

Shark,
First of all stainless steel is not a good choice for fasteners for your motor. I know it is hard to cut, bend and work with but unless it is an aircraft grade allow, stainless is not considered good fastener material. The motor mounts, intake and exhaust are 6mm X1. The best option, instead of studs and nuts is to replace them with grade 5 or grade 8 Allen head cap screws. There is no requirement for studs and nuts. You'll hear opposing opinions on this but don't be fooled into believing that studs are better, won't loosen as readily, blah, blah, blah. The head studs/bolts are a different story. They are a strange item that you can't just pick up at a local hardware. Most of them are 8mm diameter but they have different threads on each end. One end is a 1. thread, the other end is a 1.25 thread. If you've been told to locktite your fasteners and believe in that then by all means use only the blue lable Locktite. The red lable product makes it almost impossible to remove a fasterner later without applying lots of heat. Hope this steers you in the right direction. Incidently, Ace hardware carries a good selection of metric fasteneres as well as our sponsor, Sick Bike Parts. Good Luck.
Tom

FileStyle · Dec 17, 2009

at my local bolt company I bought a bolt kit (my version) replaced bolts on the entire motor and also replaced the studs with socket head bolts. the total price in bolts, a whopping $5.78
just knowing that I have better bolts in the engine mounts gives me relief that I wont have any problems later. as for extracting a broken stud, have you got the motor off to inspect it, it may be out just enough to grab with a pair of needle nose vise grips or if flush, most auto parts store's carry drill bits and easy-out's (bolt extractor). its just a matter of drilling a straight hole into the stud without getting into the bolt hole and using the easy-out to back out the stud.

Sharksfan · Dec 17, 2009

2door, you are the man! I figure if I have the motor off ant way I might as well replace them all. I think will Keep my head bolts until after the horror-days. I am just glad I am going into winter break so I have time to fix this.

Sharksfan.

Sharksfan · Dec 17, 2009

FileStyle said:
or if flush, most auto parts store's carry drill bits and easy-out's (bolt extractor). its just a matter of drilling a straight hole into the stud without getting into the bolt hole and using the easy-out to back out the stud.

I will have to take a picture to show where the bolt is broken. I am not sure how I am going to get a drill any where near where this is broken because I think the clutch side of the engine is in the way.

Sharksfan.

Sharksfan · Dec 17, 2009

FileStyle said:
at my local bolt company I bought a bolt kit (my version) replaced bolts on the entire motor and also replaced the studs with socket head bolts. the total price in bolts, a whopping $5.78

File Style,
Do you happen to remember the lengths of the bolts you bought? I would hate to have the wrong stuff. I believe the rear bolts are 3" but I know the intake and exhaust are much shorter.

Sharksfan.

FileStyle · Dec 17, 2009

I think I used 3/4" long for the intake and the exhaust I left in the factory studs. the motor mounts are going to vary according to the bike you have! I had to use a diff. mount set up for the front and the rear, my seat stay was bigger than the mount and had to do some shaving of the mount itself. and then I used some 3 1/2" long for the rear, but I did use some spacers on those as they were just a little long. and they didnt carry 3 1/4" (80 something in mm). just place your motor in the frame and take a look to see what you got. somewhere in the length or a little shorter than your studs.

flybytaco · Dec 17, 2009

if you have access to a harbor freight they have set punch set use the rear mount spacer find a way to tighten the spacer down to the block with the good stud now the spacer becomes a guide must align proporly so the center of the set punch is center with broken stud i take it the stud is broken off flush? if not grind it smooth after ligned up hit set ponch with hammer and you have yourself a perfectly centered punch in the stud.if you have a drill press thats your best bet if not use the mount spacer as a guide take spacer off after you drill it extract it or heli coil it hope that helps

Sharksfan · Dec 17, 2009

flybytaco said:
if you have access to a harbor freight they have set punch set use the rear mount spacer find a way to tighten the spacer down to the block with the good stud now the spacer becomes a guide must align proporly so the center of the set punch is center with broken stud i take it the stud is broken off flush? if not grind it smooth after ligned up hit set ponch with hammer and you have yourself a perfectly centered punch in the stud.if you have a drill press thats your best bet if not use the mount spacer as a guide take spacer off after you drill it extract it or heli coil it hope that helps

This is exactly why I signed my self up with this site you guys are the greatest!

Sharksfan.

bairdco · Dec 17, 2009

2-door, i have a grubee starfire gen 4, and the head studs are the same thread on both sides.

also, another reason NOT to use stainless steel hardware, is it doesn't play well with aluminum. just threading a bolt in by hand can cause it to seize. the hard threads of the bolt cut into the soft aluminum and will destroy them.

xlite · Dec 18, 2009

Sharksfan said:
Can any one tell me if all of the engine studs are the same diameter and thread pitch? I broke a rear motor mount bolt off of my RAW 80cc this morning and I now want to replace them with stainless steel all thread.

Back when I was young and foolish and hadn't discovered stubby wrenches and also several people I did bikes for have broken bolts/studs. IMO your initial instinct to use allthread is right on. However stainless and grade 8 are bad choices. If you think stock chinese metal is hard to get out wait til you deal with grade 8. I tried several "hard" hardware before learning this lesson.

Using hard steel for this is the number one reason for needing a new engine. Not "seizing" or "wear". I suggest getting the cheapest 6mm allthread from McMaster ($2 3ft) and learn to use threadlocker instead of overtightening.

2door · Dec 18, 2009

bairdco said:
2-door, i have a grubee starfire gen 4, and the head studs are the same thread on both sides.

also, another reason NOT to use stainless steel hardware, is it doesn't play well with aluminum. just threading a bolt in by hand can cause it to seize. the hard threads of the bolt cut into the soft aluminum and will destroy them.

There's been some controversy regarding head stud sizes and thread pitch. I think it depends on the manufacturer but every engine I've worked with for the past two years have had the odd-ball studs. I was going to replace the studs with bolts but could not locate a source for 8mm bolts that long with a fine, 1.0, thread pitch. When you get to that length they go to a 1.25, or so my search revealed. And you're right about the stainless not being really compatible with the aluminum castings. I wish there was some way to get the message out there to folks to stay away from stainless steel fasteners. The old saying, "Stainless is Forever" is correct for some things but not high stress or vibration applications. Ask any mechanical engineer, he'll confirm that. I've seen hot rods with stainless fasteners used on critical steering and suspension components. They scare me to death.
Tom

john_the_great · Dec 19, 2009

when my motor mount broke I just dug a bolt outta the junk bin cut off its head with a grinder, drilled out the old one with a reverse drillbit and called it a day

Sharksfan · Dec 30, 2009

Thanks to all of you for your help!

I went and bought my self an "Alden drill-out micro grabit" It did exactly what it was supposed to do. After I got the bolt out I replaced the intake, exhaust, and both motor mount bolts with 6mm 1.0 thread pitch allen head cap screws. When I put the motor back on I used Christopherfowlers tip of using pieces of an old belt between your frame and motor mounts, it worked great. I have put 40-50 miles on since the repairs and everything is holding together nicely.

Thanks again,

Alson · Sep 10, 2010

I gust broke or they broke by them self the back motor mount studs, payed 20 bucks to get them out, anywayi went to Lows and got the right threds and lenth but there aphillips heads, I put a little locktite blue on the ends, and I broke my aluminum bac picel so I went to the mentel ones that came with my kit, will they hold they seem thin, anyway I orderd the replacement kit form Sick Bike, but there studs 5grade or more, do you think there better or should go with the allen heads, when you use the allen head boults do you use locktite, or just the warsher and lock warsher. My studs held for 6 mounths with locktite zpt

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Broken motor mount stud

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