Bohman bus conversion

Len Silva · February 13, 2012, 04:34:31 PM

The Eagle is dramatically different from the GM buses. It is not monocoque at all, but has a frame and a bridge like structure. It will stand without any skin at all. A GM in that same condition would buckle and the engine would be on the ground. There is no comparison between the two.

Scott & Heather · February 13, 2012, 07:08:53 PM

Jeremy, seeing those photos of the Eagle naked reminded me of two summers ago when I drove our MCI 9 looking exactly like that.

Good times. Coach was just fine driving around like that...amazing.

Jeremy · February 14, 2012, 02:26:38 AM

Quote from: Len Silva on February 13, 2012, 04:34:31 PM
The Eagle is dramatically different from the GM buses. It is not monocoque at all, but has a frame and a bridge like structure. It will stand without any skin at all. A GM in that same condition would buckle and the engine would be on the ground. There is no comparison between the two.

Ok; in that case I can't really envisage what a GMC looks like at all.

When you say and Eagle has a "frame and a bridge like structure", it is probably technically correct to say that that isn't a monocoque, but I think the industry does universally refer to this arrangement as such - I can't really think of another word which is used to distinguish buses with 'spaceframe' chassis from ones with 'ladderframe' chassis.

The picture below is of the chassis of a Mercedes 'monocoque' bus, as it is delivered to the bodybuilder. Clearly the chassis frame doesn't do much more than hold the front and rear ends together for delivery purposes - it doesn't gain any strength until the bodyshell 'bridge' is built over it. I assume that this is more-or-less how an Eagle is built too, but that, because everything is built in one factory, the bottom-most 'chassis' bit is built into the bodyshell frame from the word go, and the mechanical bits attached as separate elements.

Jeremy

Jeremy · February 14, 2012, 03:50:56 AM

The post a above prompted me to find a picture of the chassis under my bus. The fuel tank is further back and on the other side on mine, but that's the only difference I think.

I used to see these being driven up the motorway to the Plaxton factory just as shown here, with just a temporary windscreen in front of the driver. Obviously it's a full-fat traditional ladder-frame chassis, and yet I doubt the bodyshell of my bus has any less steel in it than shown in photos of the skinless Eagle - which shows the advantage of a monocoque design I suppose. I got quite close to buying a monocoque Bova Futura at one stage, but the dealer selling it actually advised me to look for a traditionally chassis'd bus instead - he spoke of windscreens falling out if the bus was jacked-up in the wrong place.

Jeremy

gus · February 14, 2012, 03:56:48 PM

One main difference in the old GMCs and newer buses is the round top. A round top has far more strength than a flat one. This makes it partly a cylinder and not just a square metal box.

Obviously cylinders are stronger than cubes.

luvrbus · February 14, 2012, 06:44:14 PM

Jeremy,Eagle like Len said are a truss design you can remove all the skin , take the bays and bottom floor out and drive down the road no other bus can you do that with

I saw a guy's cut the floor of the bays from a MCI and a GM it was not a pretty sight I also saw a Prevost XL a shop cut all the floors from the bays it buckled in the middle and was sold for scrap we bought the front clip.

GM's are built well but they scare me with all the weight hanging from the roof

Iceni John · February 15, 2012, 08:06:16 AM

Jeremy,
Is that an upright engine I see in your bus? If so, that's giving me some ideas for potential mid-engine Crown and Gillig repowers . . . How high is your floor off the ground, and how much width do you have between the frame rails?

John

Jeremy · February 15, 2012, 09:07:45 AM

Hi John

Yes the engine (Bedford 500 Turbo) is certainly upright. I'll need a tape measure to answer the other questions...I'll be back...

Jeremy

Jeremy · February 15, 2012, 10:07:34 AM

Ok, I removed the floor panel above the engine and measured there:-

- Height of top surface of floor from ground - 1090mm
(the floor panels are quite thick (lots of sound-proofing as you would expect), and the bottom surface of them is very close to the engine - only 40mm or so from the rocker cover)

- Width between chassis rails at narrowest point (inner edges of top flange) - 860mm
(there's actually more room than this implies with the measurement between the chassis side walls being more like 1000mm. But having said that, the engine sits well within even the 860mm measurement, with lots of space around it).

Hope that helps

Jeremy

Iceni John · February 15, 2012, 12:49:53 PM

Thanks, Jeremy. Us few full-frame folk need to stick together!

John

gus · February 15, 2012, 04:12:40 PM

Yeah, it does make one pause thinking about all the weight in the engine comp hanging from the roof and six bolts!! Actually, it is probably four bolts since the lower firewall bolts don't appear to support much of the total weight.

However, never heard of one falling off but considering ,the ages of these old timers and Al corrosion possibilities, it could happen.

Never had to worry about that with my 4104 because it keep things well oiled!!