Author Topic: Snapped cam chain tensioner bolt  (Read 3466 times)

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Offline Calumjs

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Snapped cam chain tensioner bolt
« on: August 19, 2014, 05:32:46 AM »
So after cleaning up a 400/4 motor ready to put in my 350/4 frame I noticed something rather shocking, the cam chain tensioner bolt has been snapped off inside the case!! Can someone much wiser then I advice me on my options? Much appreciated.

Offline 70CB750

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Re: Snapped cam chain tensioner bolt
« Reply #1 on: August 19, 2014, 05:52:15 AM »
If I may, I will tell you what not to do:

Do not use easy out!

I never saw one do anything but snap.

You could find left hand drill bit and drill it out, with some luck it will spin it out.

What is on the other end as inside the case?
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Offline 70CB750

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Re: Snapped cam chain tensioner bolt
« Reply #2 on: August 19, 2014, 06:18:01 AM »
Prokop
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Online calj737

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Re: Snapped cam chain tensioner bolt
« Reply #3 on: August 19, 2014, 06:18:41 AM »
That bolt is attached to the tensioner within the motor. Either your tensioner is not installed (can you see the sheared thread-end?) or you will be disassembling your motor to retrieve the tensioner and installing a new one, as I would be very hesitant about dropping something inside the engine that needs to be secured (part 16, 18)

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Offline Calumjs

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Snapped cam chain tensioner bolt
« Reply #4 on: August 19, 2014, 06:41:29 AM »
Yeah it's sheared off, so would this involve just taking the head and barrels off? Or do I need to split the cases? Alternatively I can hope that the can chain is tensioned  and just run it as is
« Last Edit: August 19, 2014, 06:46:15 AM by Calumjs »

Online calj737

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Re: Snapped cam chain tensioner bolt
« Reply #5 on: August 19, 2014, 06:58:02 AM »
Might get away with just head and barrels.

Kind of risky to expect it to be properly tensioned since the tensioning nut is missing.
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Offline Calumjs

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Re: Snapped cam chain tensioner bolt
« Reply #6 on: August 19, 2014, 07:06:36 AM »
Is say it's been smacked off rather then over tightened. So with out the nut there is nothing stopping the bolt from loosening? I was thinking if I lay the motor flat so when I removed the bolt numbers 18/16 will just lay on 9 if I'm really careful. 

Offline HondanutRider

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Re: Snapped cam chain tensioner bolt
« Reply #7 on: August 19, 2014, 07:21:08 AM »
If you are hesitant about disassembling the motor to retrieve the ring and washer (#16 & 18) and replace the tensioner locking bolt and nut (#12 & 17), then you could perhaps seal the broken bolt with some thread-locker paste and replace the blind bolt (#11) with a longer one and locking nut to adjust the tension.

Offline Calumjs

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Re: Snapped cam chain tensioner bolt
« Reply #8 on: August 19, 2014, 12:20:58 PM »
How long does the longer replacement #11 bolt need to be?

Offline HondanutRider

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Re: Snapped cam chain tensioner bolt
« Reply #9 on: August 20, 2014, 05:05:10 AM »
How long does the longer replacement #11 bolt need to be?

Length isn't such a problem as it can be longer to extend beyond the motor.  It needs to be long enough to reach down into the mechanism to apply pressure to the springs (the end can be narrowed and rounded to better accomplish this) and long enough to allow a nut to be mounted for locking it in place.

Here's a picture of the one I made for my 350-F:

Offline neevo

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Re: Snapped cam chain tensioner bolt
« Reply #10 on: August 20, 2014, 05:17:23 AM »
What's to stop oil coming out of this hole? Reason I ask is mine motor has had this happen at some stage and the PO cut a groove in the bolt/cases getting it out. Wondering if this will leak oil or if once the lock nut is tightened it should be oil tight?


Offline Calumjs

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Re: Snapped cam chain tensioner bolt
« Reply #11 on: August 20, 2014, 07:21:52 AM »

How long does the longer replacement #11 bolt need to be?

Length isn't such a problem as it can be longer to extend beyond the motor.  It needs to be long enough to reach down into the mechanism to apply pressure to the springs (the end can be narrowed and rounded to better accomplish this) and long enough to allow a nut to be mounted for locking it in place.

Here's a picture of the one I made for my 350-F:

Thanks bud, id say about 30-35mm long. Does any oil seep out of it?

Offline 754

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Re: Snapped cam chain tensioner bolt
« Reply #12 on: August 20, 2014, 07:28:36 AM »
Fix that saw cut with JB Weld.
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Offline HondanutRider

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Re: Snapped cam chain tensioner bolt
« Reply #13 on: August 20, 2014, 08:28:47 AM »
Thanks bud, id say about 30-35mm long. Does any oil seep out of it?

None noticed on mine.

Offline Bodi

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Re: Snapped cam chain tensioner bolt
« Reply #14 on: August 20, 2014, 12:26:51 PM »
The hole goes to the tensioner actuator rod. There's no oil pressure in there, and a pretty long thin path to the inside of the cases. I would say that oil leakage is not a serious problem here.
As for getting the stub out: opening the cases is not going to help, you have to attack it from the outside (been there, done that). A reverse drill bit is likely the best approach, the easy-out that fits in a 6mm bolt is really small and delicate: once you snap off the hardened steel easy-out you have more trouble that you started with since you can't drill it out. The bolt itself is soft steel and drills easily, keeping the drill centred and straight is the problem. The hole and bolt are odd, the bolt has a 6mm part at the end that actually screws into the case, and an 8mm thread close to the head where the locking nut goes. The case hole has a bore to clearf that 8mm thread, I made a drill guide by machining a steel rod to fit snug in the bore then drilled a smaller hole through to guide a drill roughly the size of the thread root. I have this kit somewhere but can't find it now...

Offline Don R

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Re: Snapped cam chain tensioner bolt
« Reply #15 on: August 20, 2014, 01:03:40 PM »
i'm not up on the small motors, does the bolt that is broken push on the tensioner like a 750?  if so, then what would be loose/missing inside the case?
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Offline 70CB750

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Re: Snapped cam chain tensioner bolt
« Reply #16 on: August 20, 2014, 01:15:37 PM »
Check the link from Cal, the broken bolt works just like the M6 on CB750 engine, the bolt with a nut on it.  It tightens against the notch of the tension rod.

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Offline Calumjs

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Re: Snapped cam chain tensioner bolt
« Reply #17 on: August 20, 2014, 01:55:08 PM »

The hole goes to the tensioner actuator rod. There's no oil pressure in there, and a pretty long thin path to the inside of the cases. I would say that oil leakage is not a serious problem here.
As for getting the stub out: opening the cases is not going to help, you have to attack it from the outside (been there, done that). A reverse drill bit is likely the best approach, the easy-out that fits in a 6mm bolt is really small and delicate: once you snap off the hardened steel easy-out you have more trouble that you started with since you can't drill it out. The bolt itself is soft steel and drills easily, keeping the drill centred and straight is the problem. The hole and bolt are odd, the bolt has a 6mm part at the end that actually screws into the case, and an 8mm thread close to the head where the locking nut goes. The case hole has a bore to clearf that 8mm thread, I made a drill guide by machining a steel rod to fit snug in the bore then drilled a smaller hole through to guide a drill roughly the size of the thread root. I have this kit somewhere but can't find it now...

Thanks for the info, but when I remove the bolt won't parts 18/16 fall into my motor??