'67 Gillig: The Magic School Bus Build

[paddywagon]

Not sure what to do about the sideways pictures. I'll see if I can figure that out.


Anyways, build a door for the toilet room. Took several hours but I wanted the fit and finish to be better than usual. I got it stained, urethaned, and hung but forgot to get some pictures. More to come.

[paddywagon]

Also got the last cabinet in. I added additional reinforcements on all the cabinets for the countertop, which is currently being finished. I'm gonna try and get an update video put together next week.

[musigenesis]

Nice job matching the ceiling curvature with your shiplap! That stuff is challenging but fun. Your build is looking great, not sure why I've never seen it here before.

For pic rotation, open them in an image editor, rotate them if necessary so they're oriented correctly, then save as PNG files before uploading here. The reason this works is that JPEGs contain metadata about the image orientation and this can be misinterpreted by the forum software resulting in improper orientation; PNGs don't have this metadata so they can't be presented improperly.

[Bus'n it]

Beautiful work! I love that bus style

[paddywagon]

Thanks musigenesis for the kind words and advise on picture posting.



Yeah, 5 double-sided walls to make the curved cuts for. Now that it's done, it's much easier to say it was worth the dozens of trips in and out of the bus to cut/sand each piece to fit.

[paddywagon]

Hi all,


Not much of an update here. The engineered hardwood was recently installed and honestly really makes the interior feel almost finished. Unfortunately, I forgot to snap some pictures while I was in Sonora, but for sure next time. Various small projects like final installation and plumbing of the air seat, small water system plumbing projects, and one or two carpenter projects were also buttoned up. The next big project is the electrical system.


However, the elephant in the room for the entire build has been the engine (GM 366 big block, tall deck industrial). The records I have on hand show it as having 40k miles on a rebuild. It's never really run right from day 1 and continues to struggle after a fair bit of work invested in it. A whole host of maintenance items have been addressed, including rebuilding the fuel system (tank flushed, new pump, rebuilt carburetor), re-coring the radiator, installing electronic ignition, new plugs/wires, etc.


It continues to backfire when given throttle and bogs down under load. Mind you, this is just driving around the ranch. It would not make it down the road in its current state. I believe the carburetor is not in correct tune, but that may be the tip of the iceberg. While it has great oil pressure, a compression test revealed results from 105-125psi (manual lists a 150psi rating for this engine), so it's not doing so hot. Fortunately, no cylinders were alarmingly low, but it's either worn out or suffering from it's 26-year slumber (seized rings, valves that aren't seating, etc.).


So I've been evaluating my options recently. I could do a ring and valve job to get the compression back up to par but my concerns are 1) parts availability for this engine, 2) finding a decent machine shop to do a valve job, 3) acknowledging that I could find more issues as I dive into it. My other option that I'm leaning towards is a crate or re-manufactured motor which comes with a hefty price tag but is hopefully offset by not having unknowns and coming with a warranty.

[Ronnie]

Have you checked timing both at idle and at different rpms checking to see if the advance is working properly?

While I favor rebuilding the engine, carb and ignition often get moved to a new engine so sorting them out at least to get a base line is of value, then when put on a new /rebuilt engine do the final tuning.

Another cause can be timing chain has jumped a tooth, or was off a tooth to begin with

[cadillackid]

how bad is the compression? low compression itself wont cause backfiring through the carb... if it has a holley on it then you probably blew the power valve the first time it backfired through the carb.. a rochester doesnt have that issue..



retarded ignition timing will cause the issues you mention.. has anyone truly checked the timing properly? I see so many new-schoolers that dont disconnect the vacuum advance or run the idle speed up too high where mechanical advance kicks in and they retard the base timing too much..

[paddywagon]

Originally Posted by Ronnie

Have you checked timing both at idle and at different rpms checking to see if the advance is working properly?

While I favor rebuilding the engine, carb and ignition often get moved to a new engine so sorting them out at least to get a base line is of value, then when put on a new /rebuilt engine do the final tuning.

Another cause can be timing chain has jumped a tooth, or was off a tooth to begin with

I have checked that the advance is working. To what extent it is working, I don't know, but it seems to advance smoothly with increasing RPM.


I am with you on having good components to transfer over to the new engine. Even with the low-ish compression, this engine should run better than it is, and getting the carb and ignition dialed in is important regardless of whether I replace this motor.

Originally Posted by cadillackid

how bad is the compression? low compression itself wont cause backfiring through the carb... if it has a holley on it then you probably blew the power valve the first time it backfired through the carb.. a rochester doesnt have that issue..

Retarded ignition timing will cause the issues you mention.. has anyone truly checked the timing properly? I see so many new-schoolers that dont disconnect the vacuum advance or run the idle speed up too high where mechanical advance kicks in and they retard the base timing too much..

Compression is a spectrum between 105-125. Nothing alarmingly low, but definitely not healthy. Although the low compression is not the root of the backfiring, it is the main influence as to how much money I dump into this engine vs a new one.



It does have a Holley (4776 double pumper). Can you educate me on the power valve? My distributor is mechanical advance only. Right now it idles around 600-800rpm.

[Jolly Roger bus 223]

the power valve for your carb is behind the block on the side of your carb.
i think your valve is holley part number 125-25 and google holley powervalve replacement and holley will have a video on there websight.
about 13$ for the valve and about 10-minutes to replace and i would have a new gasket for the metering block if you have to pull it to replace thepower valve.
some are easier than others.
like one minute versus pulling the cover to get to it.

[paddywagon]

Originally Posted by Jolly Roger bus 223

the power valve for your carb is behind the block on the side of your carb.
i think your valve is holley part number 125-25 and google holley powervalve replacement and holley will have a video on there websight.
about 13$ for the valve and about 10-minutes to replace and i would have a new gasket for the metering block if you have to pull it to replace thepower valve.
some are easier than others.
like one minute versus pulling the cover to get to it.

Thanks for the info. I vaguely remember replacing that when I rebuilt the carb and it seems like something that would have been in the kit. But it would certainly be a simple, inexpensive fix if that was the problem.

[sportyrick]

The tall deck series of engines are VERY LOW compression so they will live with wide open throttle all day. I would say your compression is right on and I say this having run a truck tall deck 427 for 15 years and running them in my fun street cars for decades. Where did you get your compression recommendations? It sounds like a timing issue but have you changed out that old fuel? Also if the accelerator pump isn't working which is quite likely since it's sat for years it's gonna pop up through the carb every time you stab the throttle. It would probably help to put some miles on it with timing set correctly, a carb rebuild and premium fuel.

[Jolly Roger bus 223]

almost any time you get a backfire it will blow the power valve.
definitely a good starting point.
and check the distributor whether points or upgraded to a newer model HEI

[paddywagon]

Originally Posted by sportyrick

The tall deck series of engines are VERY LOW compression so they will live with wide open throttle all day. I would say your compression is right on and I say this having run a truck tall deck 427 for 15 years and running them in my fun street cars for decades. Where did you get your compression recommendations? It sounds like a timing issue but have you changed out that old fuel? Also if the accelerator pump isn't working which is quite likely since it's sat for years it's gonna pop up through the carb every time you stab the throttle. It would probably help to put some miles on it with timing set correctly, a carb rebuild and premium fuel.

The 1968 Chevrolet chassis manual states a factory 150psi compression rating for this engine.
The first work I did on the bus was have the fuel tank boiled and sealed, then I rebuilt the carburetor. I have been running it on 91. The timing is correct at idle and appears to advance with throttle.

[paddywagon]

Originally Posted by Jolly Roger bus 223

almost any time you get a backfire it will blow the power valve.
definitely a good starting point.
and check the distributor whether points or upgraded to a newer model HEI

It is a points distributor that I upgraded to electronic ignition.

[paddywagon]

Progress has been made on the Gillig. My dad and brother jumped in last weekend to help string over 600ft of wiring. Got a lot further than expected and it finally feels like things are getting somewhere. More pictures to come.



What isn't getting anywhere (physically speaking) is this bus. Just moving it around the yard is a hassle with how poorly it runs. I've replaced the power valve, as suggested, adjusted the floats, double checked the timing and it still runs like I'm feeding it peanut butter. Incessant hesitation, regular backfire, and no idle.

Here is a video to see for yourself: https://youtube.com/shorts/7uI2oSRqr10?feature=share


Leaning towards the crate motor route with HEI and TBI to eliminate mechanical unknowns, for ease of maintenance, and long-term reliability.

[Ronnie]

I have been having too many mechanical issues with my old bus. It just is not holding up to all the miles I put on it, especially high speed highway miles. So a newer bus, rather then an antique makes more sense for me. A new engine with modern electronics might well be the best choice long term for you.

In the mean time, wonder if you are getting some sticking valves?

[Bearmtnmartin]

Your video looks like a couple plug wires backwards, or timing. Did it skip a tooth perhaps? Your compression may improve with some miles so I would suggest nailing down and fixing the backfiring first.

[paddywagon]

Originally Posted by Bearmtnmartin

Your video looks like a couple plug wires backwards, or timing. Did it skip a tooth perhaps? Your compression may improve with some miles so I would suggest nailing down and fixing the backfiring first.

I double-checked the plug wire order last time I had the bus out. The timing was dialed in a few months ago but I will be checking that out again.

[paddywagon]

Originally Posted by Ronnie

I have been having too many mechanical issues with my old bus. It just is not holding up to all the miles I put on it, especially high speed highway miles. So a newer bus, rather then an antique makes more sense for me. A new engine with modern electronics might well be the best choice long term for you.

In the mean time, wonder if you are getting some sticking valves?

I feel the same way. If I were to do it over, I'd get the newest bus I could get my hands on. And that's where I am with vehicles in general. I've always driven old cars; Volkswagens, MGs, Volvos, etc. My current wheels is a '66 Volvo Amazon wagon that I've had for 5 years and put about 30-40,000 miles on. It's performed admirably and taken all over the Western US, but it's one thing after another maintenance-wise and it starts to wear on a person.



As far as the bus goes, that's why I want to drop a crate engine in with TBI. As my less-mechanically-minded brother would say, "turn the key and the magic happens". Maybe (many years) down the road, I'll do a modern diesel swap with auto trans. Not sure what'll fit though.


I also suspect sticking valves. I've spun the engine by hand with the valve covers off and the valve trains seemed to be turning over smoothly, but I should do it again at cranking speed.