Best places to block-up chassis

Geom · October 17, 2014, 08:09:27 AM

OK, so the last few days of chasing air-leaks and crawling around under the bus got me to thinking; where is the best place to block up the chassis (on a 4107)?

One suggestion I've received is to place a block between the bellows in between the two beams. While I'm sure that is a sturdy point, I don't want to crawl that far up in there to place blocks that I would later need to remove.

The book says to block the chassis by placing blocks under the front engine cradle mount. It doesn't exactly identify that spot, but I was able to figure out what they mean (or at least I think I did). So my question there is two-fold

1) I assumed the front engine cradle mounting bracket to be a point that tapers downward from the back of the bus - forward, and comes to a pretty solid looking mount area just behind the lower radius arms. It looks pretty solid and there is a fairly solid looking pair of beams that converge onto that point. Is that the right spot? If it's not, then I really don't see what else it could be.

2) The way I understood these engines were mounted were for them to "hang" from the body in the rear bay. As such, do I want to place that much weight (the chassis) on that spot for extended periods of time? Is that a good spot to do so? Am I doing untold damage keeping it there? Is there a better spot?

For the front, the book says to place blocks ahead of the radius rod, but doesn't specify where. So I put blocks under the sturdy looking mount for the front radius rods. It's the point the radius rods connect to the chassis and I placed the blocks directly underneath those mounts just ahead of the radius rod bushing. Is that a good spot? Again can that much weight be on that spot for long periods of time? Another alternative place I considered was the mounting bracket for the tow-rings in the front. They appear to be attached via a solid looking bracket, although not as sturdy looking at the radius-rod mount.

Thanks again in advance for the info.
George

gus · October 17, 2014, 07:31:32 PM

The only safe place to block is the axles.

The best way to raise the body is run the tires up on blocks. I have a built up area of coarse limestone gravel to do the same thing.

I agree with you, it is too spooky to crawl up underneath to block at the air bags. I did that crawl halfway once and chickened out.

The Al body is so old that hidden corrosion can spell disaster, blocking it is a guessing game but always do it at bulkheads if absolutely necessary.

The engine is not supported by the firewall, it is supported by the rear overhead structure of the body. Strange but true! Look at the two steel poles that support the two engine door brackets.

luvrbus · October 18, 2014, 05:19:38 AM

Where is the front of of a engine on a GM I know were it supposed to be

you have to block the body up to change the air bags the way the GM are designed it looks to me like the bulk head does carries most of engine weight

The roof struts are just more for a balance I could be wrong but it doesn't take much of a jack to move the engine on the back when you remove the bolts in the hangers

Stormcloud · October 18, 2014, 12:37:02 PM

In response to your original question, I would say the "best place" to block up the chassis would be at Luvrbus's place, somewhere near the shop door.

luvrbus · October 18, 2014, 01:06:22 PM

LOL Mark seemed like I worked on so many GM in the past 3 years I am becoming left handed

Purplewillie · October 18, 2014, 03:18:11 PM

Lol

gus · October 18, 2014, 07:17:04 PM

Quote from: luvrbus on October 18, 2014, 05:19:38 AM
Where is the front of of a engine on a GM I know were it supposed to be you have to block the body up to change the air bags the way the GM are designed it looks to me like the bulk head does carries most of engine weight

The roof struts are just more for a balance I could be wrong but it doesn't take much of a jack to move the engine on the back when you remove the bolts in the hangers

You don't have to support the body at all to change bags, just block between axle and steel suspension members and jack the axle. At least that is the way I did it.

I should have said the engine is partly supported by the poles! They support about half the engine weight so it is far more than just balance. That part of the weight is carried by the rear roof cantilever through the poles. Since this cantilever is attached to the top of the firewall bulkhead you could say the bulkhead supports all the engine, but the bottom bulkhead brackets do not.

MightyThor · October 18, 2014, 11:59:20 PM

On the scenic I block in several places. I have measured the air bags at full inflation and cut 4x4 blocks just a little shorter so I can set them next to each air bag and get max lift of the body over the axle. I also use the same blocks on their sides to keep 4 inches of lift when the bags are down. (my rubber bumpers need to be replaced) I can reach these over the tires on the scenic. I also block at the axles when lifting them and at the jacking points on the body. In the rear the jacking pad is outboard of the front engine cradle mounting point, outside of and slightly behind the rear most lower radius rod mounting point. I Also built a set of run up ramps for the front, but intend to build a better set soon. They will be longer and wider and glued as well as screwed. I also will be building a sort of pit by raising the level of the ground on either side of two parallel retaining walls. I will be able to drive up onto the raised area with the front or the back of the bus and then crawl underneath between the two walls.

mung · October 19, 2014, 03:35:56 PM

Just wondering, how hard would it be to design something that could sit on the rail under the air bags all of the time, and had some kind of lever or wire, that would allow you to pull it into place in order to block the bags up? Maybe even just have a loop on it that you could use a hook on the end of a pole to pull into place, then the same pole could be used to drop it when you are done.

Geom · October 19, 2014, 09:05:55 PM

Quote from: gus on October 18, 2014, 07:17:04 PM
You don't have to support the body at all to change bags, just block between axle and steel suspension members and jack the axle. At least that is the way I did it.
...

Gus, so is that done between the bags by crawling up in there or is this a different spot?
I'm sorry, I'm just not visualizing where you're putting the blocks.

I really don't want to crawl up under there to shove blocks in between the bags, but I also don't want to damage the chassis or engine mount or frame... Hmm

Mung, I like your idea in principle, but I don't see how I'd be able to rig something that would stand up to road travel and not deploy on its own, yet still be usable. I'll give it some thought.

For the purposes of what I was doing I put the blocks under what I believe to be the front of the engine mounting bracket. The book says to do that. But based on what you guys are saying and the way I understood the way these engines are mounted, that sounds like a pretty bad idea!

It was mostly "just in case" as the bags were ok holding air. I'd just like to know for the next time I'm under there and the bags are not so ok

It sounds like I do need to make some run-up blocks for these types of adventures, although run-up blocks would not have worked in this situation, since the system would not hold air and the brakes would not have disengaged.

For the front I just put blocks ahead of the radius arm bushings under the radius arm mounts (one on each side). They seem like sturdy spots, but I'm not sure how much weight that spot can actually take. Don't know if the chassis weight can be sitting on them.

gus · October 19, 2014, 09:38:57 PM

For the 4107 I just get it high enough up on the ramps to get under it. I've never changed these bags but I assume blocking is not much different from the 4104. The bags are different but the structure appears to be about the same.

I changed all the 4104 bags by blocking between the structural members that support the bags. However, it is not nearly as low as the 07 and not as spooky crawling under. Removing the wheels makes it a lot simpler and allows blocking without getting underneath. I assume, again, that the 4107 can be done the same way, but , fortunately, I've never had to do those:)

I was able to inflate the 4104 bags to raise the body. If your bags are not inflatable I'm not sure just how to do that without taking a good look.

luvrbus · October 20, 2014, 04:55:54 AM

I don't know the answer but I have saw the GM's 3 ft in the air when changing the 3rd member and air bags at bus shops before, I don't believe the old GM is as fragile as most here say it is JMO

Dave5Cs · October 20, 2014, 07:00:20 AM

I do not know the answer because I have an MCI but on mine I have Bump stops on both sides of the axle and the plate that is at the lower side where it hits. don't the GM's have bump stops. Thats where I stick a 3-1/2" metal block between after I raise the bags up and back it up on my ramps. If the bags ever went it could not drop because of those blocks.

luvrbus · October 20, 2014, 07:08:07 AM

Don't you just love the Eagle crawl around anywhere on one without worrying it's going to fall on you

Dave5Cs · October 20, 2014, 07:29:30 AM

If you can get around all the rust pile on the ground, LOL