Rear mounting bolt fell out...what now?

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jlew

New Member
Jun 7, 2010
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Ann Arbor, MI, USA
I was riding my MB today (almost 70 miles on the engine) and the right rear frame-to-engine mounting bolt ripped out of the engine. I don't really see how that could happen as there isn't any direct torque on that bolt while riding, but now all that's there is a hole where the bolt went in to the motor. despite stopping immediately and looking for over an hour (!) i could not find the bolt and its nut anywhere on the road.

So can i buy a replacement bolt? if so how do i mount it? i'm assuming the thread is stripped but i have no way to be sure. here's a picture of where it should be:



thanks!
 
bairdco

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
if you think about it, the right rear bolt takes the most torque, because that's the direction the chain wants to pull the motor.

you could just get another bolt or a piece of allthread if it's not stripped. i think it's 6mmx10, but i don't remember how long.

if it is stripped, you could tap it out to 8mm x 10 and get a bigger bolt.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
From your photo it appears that the stud is sheared right at the mount extension piece. If that's the case it is an easy fix. The broken stud can be removed with a pair of vice grips because there's plenty left to latch on to. Just unscrew it from the engine case and either replace it with 6mm threaded rod or a 6mm Allen head cap screw. You're lucky; most of them break at the engine case making removal a little harder. You have a good inch or more of material to grab. Lefty loosy...righty tighty. Good luck and let us know how you make out. Ace Hardware should be able to provide you with the fastener material you need.
Tom
 
Kevlarr

Kevlarr

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Jul 22, 2009
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From the gap around the mount extension it looks like you're having to pull the motor into the seat post when you tighten the mount. You should pick up a few 1/4" washers and try putting one on each stud between the motor and extension to close the gap before you tighten the strap.
 
ex-28

ex-28

New Member
May 23, 2010
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winnipeg, Manitoba
i had this happen to me as well rear right bolt stripped on me , i unscrewed the bolt and replaced it with threaded rod 6mm is the size for the engine zoom sells , i had a verry hard time finding it but a small town close me me bumper to bumper had it $3.50 for it , just cut off the lenth you need with a hacksaw file the burr off the end and then attach 2 nuts on 1 end of it and tighten them together, then you can use a wrench on the nut (as they lock together) and thread it into the engine through the mout. then remove 1 of the nuts and tight it all up again !
 
J

jlew

New Member
Jun 7, 2010
12
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Ann Arbor, MI, USA
so i finally got the threaded rod today, and dismounted the engine to find the original bolt HAD broken off flush with the engine block. I tried drilling through it like one would do with a screw, but my crappy drill can't even make a dent in the bolt. there's not enough bolt left to grab onto outside the engine. What should i do to try to remove it?
 
ex-28

ex-28

New Member
May 23, 2010
110
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winnipeg, Manitoba
canadian tire here sells a damadged screw removal tool it goes in your drill and you drill 1 end into the screw , then use the other end to screw it out , its called "GraBit Damaged Screw Remover" Product #54-3809-2
 
J

jlew

New Member
Jun 7, 2010
12
0
0
Ann Arbor, MI, USA
So i bought a couple bolt/screw extractors for my drill, both of them almost instantly stripped, and now all i have is a 1/5 inch hole into the bolt. I'm thinking of maybe putting a reverse-threaded screw into the hole and trying to take it out that way, but honestly I don't know what to do.
 
ex-28

ex-28

New Member
May 23, 2010
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winnipeg, Manitoba
hats what the other end of the screw extractor is , 1 end bors a hole the other end with threads is reverse thread hmm :( they kits always save me
 
B

broHSI

New Member
Jul 27, 2009
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USA, CA
jlew said:
I mean the hole is bored fine but the reverse threaded end strips...i guess the metal the bolt is made of is stronger than the extractor.
Click to expand...
Try drilling it then reverse the drill to back out the broken stud..

The only EZ outs that are any good are the square ones, especially in the small sizes.
 
F

fm2200

New Member
Nov 16, 2008
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new york city
If you over torqued that mount bolt you would have stressed the bolt. The over tightening of any bolt makes it prone to snapping. Another way of putting it, you were at the point of where you just needed a little more torque to just stripping it. The quality of some of the hardware in these kits are also sometimes to blame. You could have been subject to just that.
 
Al.Fisherman

Al.Fisherman

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Sep 9, 2009
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Calera, Alabama
jlew said:
I mean the hole is bored fine but the reverse threaded end strips...i guess the metal the bolt is made of is stronger than the extractor.
Click to expand...
If the stud is OEM there is NO way that the stud is stronger (this is one reason I recommend NOTHING stronger then a US grade 5 or metric 8.8). The key to using a extractor is to first drill the hole as large as you can without eating the threads in the hole or off the stud, second as deep as you can. Mark the drill bit at a depth or 1-1/6 inch. This will drill through the stud without penetrating the case. If this still fails, drill stud out with a drill bit that is the correct size to accept a 1/4" 20 or 28 stud. Tap to a 1/4" 20 or 28.

Sometimes using a left handed drill bit does the trick, and as it is drilling will extract the stud, then only a thread chaser is needed.

http://www.efunda.com/designstandards/screws/tapdrill.cfm
 
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spideyman

spideyman

New Member
Aug 29, 2010
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ontario
i have had several of these shear off right at the block i think my motor isnt balanced well i will know more over the winter but for now i just heli-coil them and it works really well
 
K

kallsop

Member
May 2, 2009
106
1
18
CT US
HarborFreight sell a stud extractor kit. It's fairly cheap and works well enough. After my second 6mm stud broke flush with the engine, I tapped the block for a 1/4"-20 helicoil and used two grade 8 bolts and blue Locktite to mount the rear of the engine. No problems since. Other things want to vibrate loose, that's the way it is with these buzz bomb engines, but the engine mount is solid.
 
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