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Old 08-16-2011, 03:06 PM   #31
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Re: Pop top scissor bolts snapped & will not rise

I'm not too smitten with the design. Could use more help understanding it though. Can someone post a sketch to show the installed scissor and roller bolt configuration?

Seems to me that the bolt (scissor?) goes through sharp edged metal holes in the tube, which rotates in a cutting motion around the top portion of the bolt as the roof is raised and lowered. In other words, the tube hole facing toward the outside of the van is resting on the threaded section of the bolt, and the tube hole facing inside the van is resting on the shank section of the bolt.

The broken bolts display a ductile fracture (the tiny tip at one edge of the otherwise somewhat flat breaking surface). This means there was some pulling stress present. As everyone has noted, the failure is in the threaded area. I'm assuming the metal edge of the tube hole was literally cutting into the bolt there - if ever so slight.

Also as everyone has noted, it is most likely that the bolt bent before it broke and that was the primary source of stress (a nicked thread area provided the weak point for a crack to promulugate). Basically, the bolt is serving both as an axle for the tube frame and a wieght bearing attachment point for the chain to spring mechanism. It's my guess that forces from the chain exceeded the design rating of the system. So someone needs to fess up on the maximum amount of weight they have placed on their roof when lifting. SMB published the design rating for comparison and I'd like to know if that is the root cause of the problem.
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Old 08-16-2011, 05:03 PM   #32
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Re: Pop top scissor bolts snapped & will not rise

Just so happens I went out and looked at my penthouse scissor mechanism for the first time today....since I have not had a failure. Knock on wood.

Over View The lift arm and the slave arm


Lift Arm showing tension spring


Next three pics are various views of the attachment point between the lift arm and tension spring. Note: bolt end is bend as installed...no flat seat.




Compression assist spring


Compression assist spring in constraining channel


Slave lift arm


Next two pics are of the pivot point attachment on the slave arm



Next three pics are of the scissor bolt asm




Would be nice if a few other people who have had penthouse lift mechanism failures could post pics.

Kevin - Did the tension spring "let go" or did you mechanism just bind up. Did it bind up while lowering the top or did it bind the next time you tried to raise the penthouse??
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Old 08-16-2011, 05:19 PM   #33
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Re: Pop top scissor bolts snapped & will not rise

So the inside wall (to the scissor) of the master arm is not on threads, the outside wall is- regardless of which length bolt is used. Does that really make the shorter bolt more prone to failure in this application?

I think the chain/foot bolt loosening (deformation of the washer into the chain) could cause fatigue. Combined with other factors (sticking in the track, nicked or defective bolt, age, use, etc).

But a few failures out of thousands of tops I don't think is cause to question the design or fear the failure of your own top. A reason to inspect and service, yes, but I don't see that failure is inherent or imminent.

Incidentally, Len, your master support bar is very, very straight compared to mine which shows a distinct bow...
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Old 08-18-2011, 02:29 PM   #34
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Re: Pop top scissor bolts snapped & will not rise

Thanks for the details LenS. I agree it would be even more helpful to see others, especially failed ones (preferrably first hand by an original owner who can speak freely without worry of warranty nullification issues, and fresh after it happened). Photos are wonderful. Macro face shots on each surface of the break would be helpful too - that lets you see how much ductile vs. brittle fracture occured (i.e., percent of area rippled).

There's one other roof failure reported at http://www.sportsmobileforum.com/vie...4b31c240340e15. In that case it was an 11 year old manual lift top and one roller bolt broke while the owner was lowering the roof. No other information on the failure was provided. Additionally, a vendor on the site claims to have fixed more than one broken SMB roof and thinks they need stronger tubing and bolts.

To recap on this case though, owner (second owner?) was lifting (manually or with hydraulic lift?) roof (unloaded? how old? any previous accidents or work done on it?) while parked (on level or uneven ground?) when one scissor bolt broke. Owner noticed binding problems when previously lifting roof and shows some evidence of a plastic roller track snag. Don't understand the track config well enough yet to see what caught on it and how. During attempt to resolve break, owner broke second scissor bolt. Don't understand, probably missed it, but when and how did the roller bolt break? Note all bolts exhibit bending and brittle fracture at top of thread area, with a very small amount of ductile stretch displayed on the outside of the bend - suggesting failure was initiated by bending (stretching) the bolt, and then it snapped.

At this point, I wouldn't worry about imminent failure much either Jage, though I always use the support legs when the top is popped and it only takes one time for somebody to get hurt. Still don't like all aspects of the design. Those exposed tube hole edges bother me. Due to installation variations I've seen so far, we can't be sure what the bolt configuration was on the failed units. The roller bolt looks longer than the scissor bolt. It's still possible that the threaded portion nearest the shank got nicked by the tube hole - perhaps during the bending process.

LenS has a beat up washer at the roller arm connection and I'm curious about how that ocurred. Don't know that the unit is worse for wear, but it's an indication of something gone awry during the lift/drop process (e.g., chain folds up and unchinks, bending washer in process), or someone doing a bang-up install job (which I think LenS was indicating is what happened), or hard living going on in the van (e.g., heavy lifting of hard objects banged into washer). Also, cut-off scissor bolt end has left you short a couple threads for a sound nut connection. The nut is cut into some too. SMB did not do this on my rig. Is that a square lock washer beneath your scissor bolt head LenS?
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Old 08-27-2011, 10:40 PM   #35
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Re: Pop top scissor bolts snapped & will not rise

Mine had black allen bolts installed in the cross-section tubes. I assume they are high tensile ones, and called SMB about it. They said they wouldn't break.
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Old 08-28-2011, 12:47 AM   #36
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Re: Pop top scissor bolts snapped & will not rise

Is this on electric, manual or both versions?
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Old 08-28-2011, 09:15 AM   #37
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Re: Pop top scissor bolts snapped & will not rise

I to have made this repair to smbs in the past. This and bending bars seem to be a normal problem for these tops. You have to watch going with a bigger bolt the bars are already a borderline weak spot and opening up those holes makes an already weak designed bar and makes it weaker. As said before these tops are heavy and will really hurt someone if it comes crashing down on you. When ever customer's come to me with this issue I always think about the smb web site say's on their penthouse page

"What's the durability of the Penthouse?
We really don't know. Since we introduced our third generation model in 1974, we have never replaced a part because of wear. The top itself is made of reinforced fiberglass with built-in wood stringers. Metal parts are all heavy duty construction. Counter-balancing tension and compression springs are over-engineered. This means they will never fatigue and lose their strength."

I used to think maybe it was freak thing but it sounds like surly someone has told them about this problem because I am not the only one to ever come across it.
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Old 08-28-2011, 10:00 PM   #38
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Re: Pop top scissor bolts snapped & will not rise

Can anyone confirm that the black allen cap bolts are an update, or?
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Old 09-03-2011, 08:59 PM   #39
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Re: Pop top scissor bolts snapped & will not rise

I'm hoping they are these type. It looks like the bolt in the upper left of this site:

http://www.boltmeup.com/m5-x-35-black-h ... 2418-p.asp

Anyone?
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Old 09-03-2011, 09:14 PM   #40
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Re: Pop top scissor bolts snapped & will not rise

Quote:
Originally Posted by 4x4tour
Can anyone confirm that the black allen cap bolts are an update, or?
My '06 has zinc plated (gold) bolts.


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