| Author |
Message |
jim wilke (205.188.192.154)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, March 23, 2001 - 5:15 pm: | |
The steel sections of the 4905 I just bought to convert have holes rusted right through in some places. Since I don't want to fight rust for the next 10-20 years I am planning to remove the steel and reskin with aluminum. Has anyone out there done this before? I am interested in your results.
Jim-Bob |
JJ (205.188.192.53)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 24, 2001 - 1:59 am: | |
Jim, the 4905 is a true monocoque construction, so you can't do that, since the steel is the added strength for the distribution of torsional loads from the suspension, and adds strength along the window area, which is weak due to the large area of glass. You'll have to cut out the rusted areas and weld in new. Alternative would be to scab over the holes, but this is very unsightly. If you had no choice and used aluminum it would probably have to be 3/8 in. thick. An added part of the problem is the expansion coeffecient difference between the two, and the galvanic corrosion problem of the dissimilar metals. GM used special techniques to stop this, that are not available to you and I. HTH Cheers...JJ |
Jim Wilke (152.163.204.197)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 24, 2001 - 6:13 am: | |
I know that GMs are monocoque construction. But 4104s are too and they are 100% aluminum (body). I believe that GM used steel for two reasons. First, it's cheaper than aluminum. Second, and maybe the big reason is that it rusts away. Look at the difference between a 50s GM car and one from the 70s. Rusting away is even more important when you don't change your body style. And, of course, there's always parts sales.
If I can't get rid of the steel, then I won't keep it. I'm not going to repair it and convert it & put $4,000. worth of Imron paint job on it just to see rust pop through elsewhere in a year or two.
By the way, there's no torsion on the front & rear upper caps, but they made them out of steel too. |
Steve Fessenden (63.25.54.190)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, March 25, 2001 - 2:09 pm: | |
When I had a 4905 to convert I looked into this question. I checked with suppliers and with the best local aircraft shop.
Since you are covering many of the window areas, the need for steel for strength should not be as important. If you use Tempered aluminum, T4 or T6, you can get the strength you need and still have a fairly thin panel, about the same as the roof and the other structural aluminum panels on the bus. The word I got from Aircraft Engineering was use T6. It is avalilable in 8', 10' and 12' by 4' sheets. Since you are painting it you can use raw T6, not alclad. I would paint the inside of the panels with zinc chromate before installing them. Don't leave any area of raw alulminum to contact raw steel. And you will want to paint, at least prime, the outside as soon as it is on. Tempered aluminum can begin to corrode quickly. Stainless steel rivets and hardware will cause galvanic corrosion. Use the right aluminum rivet or steel hardware with zinc plating. You can use an aluminum washer as a sacraficial metal under any steel hardware.
I was told that T6 is easier to drill than un tempered aluminum. But it has limited bending tolerance. Enough for the 5 degree angle where it goes under the roof.
I am repeating advice that I researched, but not hands on experience. I believe the advice was excellent, but some real expert will probably answer you soon.
One thing I do remember reading in the 4905 repair manuals. Don't beef up one area or another on your own gut feeling like you could in an MCI. The manual says that it will simply transfer the stress to another place in the monocoque construction.
Steve F |
Jim Wilke (205.188.198.187)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 26, 2001 - 7:21 am: | |
Thanks Steve, for the info. By the way, is it you that sells the cruise controls?
Jim-Bob |
Phil (204.89.170.3)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 26, 2001 - 8:07 am: | |
Beyond the temper ("T" number), you need to be concerned with the alloy. 6061-T6 aluminum does not require alclad as it is quite corrosion resistant and is used in marine applications. 2024-T3 is stronger and is probably not available readily without alclad as it has little corrosion resistance. Both are bendable if adequate bend radius is used. As for strength, there are charts that will show strength in PSI based on thickness and can be compared to steel. Try aircraft catalogs for this information (www.wicks.com).
Phil |
Jake Ranisate (209.240.224.226)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 26, 2001 - 8:44 am: | |
As a former Aircraft Strcutural Mechanic, this is not a procedure I would recommend. I've read the other comments posted here and I agree with a number of them. Steve Fessenden is right on about corrosion. However, unless you use rather thick material, 6061-T6 is too soft to resist the loads that will be imposed on it. If you were to attempt to do this, I would recommend 2024-T3. It would handle the loads much better. But as I stated in the beginning, I wouldn't try this. The 4104 was designed for al skin. The 4905 was designed for steel. I'm sure the rib and brace designs are completely different. There's also the thickness question. You can't just guess at how thick it needs to be. You might get it right, but then again, think of the consequences if you get it wrong. Another factor is the skinning itself. In a monocoque design, the skin holds the shape of the vehicle itself. In order to reskin this thing without worrying about permanently distorting the structure, you would have to strip it down to nothing and build some sort of jig to hold the frame straight. When I say strip to nothing, I mean nothing. Engine, trans, suspension, everything. Again, you could try it a section at a time, but if you get it wrong.... Bottom line is that I wouldn't try it. Take JJ's advice and weld in some patches, or just get a different bus. |
Steve Fessenden (63.27.89.180)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, March 26, 2001 - 10:03 pm: | |
The book calls for removing no more than two panels at a time. More can be removed if the bus is blocked up under each bulkhead on each side, as in a roof raise. There should be a little more wiggle room in doing a bus than an airplane. It was also passed on to me that you will need to buck regular rivets with a rivet gun. This may not be a pop rivet job. Maybe cherry rivets, but I would get a used aircraft rivet gun and buck the rivets. There is really not much strength in the window secion anyway and I suspect that the ease of forming steel sections had a lot to do with the use of steel. The 4905 has steel everyplace that aluminum would have been too much work. Just don't try fiberglass. You should be able to use the same strength aluminum as the galvanized steel that people have replaced the windows with.
Also, there was a post about not drilling the rivets out. Drill or grind the heads off and punch them out so you do not enlarge the hole.
Where are the experts. I'm just passing on second hand information. Believe the aircraft people about the importance of doing monocoque siding right, but you are not building an airplane. You can do what you suggested.
Steve Fessenden |
Jim Wilke (205.188.198.21)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 27, 2001 - 6:36 am: | |
Now, this is getting interesting! Thanks for the advice on grades of aluminum. I was planning to strip the entire interior down to the ribs anyway, so access to the rivets would be no problem. I had never considered any other method than hand bucked real aluminum rivets just like original. I had also planned to block it up carefully at the bulkheads, bumpers & engine, then let the air out of the suspension. There will still be a lot of strength in the structure because the steel is limited to a band about 24" high between the lower edge of the curve of the roof to halfway down to the baggage bays. Thanks for the two panel maximum tip though.
As for welding in patches, that's probably not practical. The rust is coming from or starting at the joints where the aluminum and steel panels are riveted together. The prevailing ocean breezes here in Florida turn that kind of construction into a 40' battery. While it may work in many parts of the country, nobody who lives near the ocean would ever construct something this way. Heck, I live 20 miles inland and I wouldn't use plain steel screws to hold my aluminum mailbox up. Of course if you are building something that you want to fall apart in 10-15 years that's another thing. Remember the quality of the cars coming from Detroit in the late 70s until the imports woke them up?
Jim-Bob |
FAST FRED (209.26.87.70)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 27, 2001 - 12:48 pm: | |
DOING every thing right is of course correct, but remember the conversion place in Arcadia used to cut the coaches apart , and DRIVE them inside there big empty place
WITH THE ENTIRE ROOF OFF!!
They had no trammels or other method to even guess that the chasis was straight , but it seemed to work OK.
I think they went out of business for other reasons.
There is an extroadinary amount of basic streignth in these coaches, if you get it 90% right , you will probably still have a 300% safty margin..
FAST FRED |
Steve Fessenden (63.27.89.157)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 27, 2001 - 8:57 pm: | |
Fred, that conversion place, under the old management, had a 4905 fall down in the middle doing that too. Hartland said it is still there in a junkyard.
Maybe they could get us some pictures for educational purposes.
Jim, you can work on more than two panels at a time if you are blocked up properly. SF |
Peter Broadribb (Madbrit) (216.67.194.243)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, March 27, 2001 - 10:29 pm: | |
Talking about Blocking properly......
Can anyone tell me where to place the blocks on an MCI-8? I am about to raise the roof and need this info. Thanks.
Peter. |
Dave-CA (64.111.114.107)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, March 31, 2001 - 2:35 am: | |
concerning rust and corrosion, take a note from the boatnuts. Salt water is very corrosive and the use of electric fields and sacrificial anodes seem to work. Check with a salt water boat dealer |
Dave (209.40.78.18)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 20, 2001 - 11:43 pm: | |
Jimmy's are tougher than most think. I have A 4107 that didn't have a front cap or any windows that i drove down a 4x4 road and 40 miles to my house. Body just as straight as can be. Fall in half my uknow what. Skinning with aluminum will require .100" instead of .030" sheetmetal. Figured it out with a man that designs vehicles. Or for a smooth finish weld 030 metal on and using adhesive and only a top and bottom row of rivets skin over with fiberglass. Looks damn nice. But then again thats only my opinion and you know what those are like. |
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